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-rw-r--r--third_party/abseil_cpp/absl/types/BUILD.bazel337
-rw-r--r--third_party/abseil_cpp/absl/types/CMakeLists.txt373
-rw-r--r--third_party/abseil_cpp/absl/types/any.h528
-rw-r--r--third_party/abseil_cpp/absl/types/any_exception_safety_test.cc173
-rw-r--r--third_party/abseil_cpp/absl/types/any_test.cc781
-rw-r--r--third_party/abseil_cpp/absl/types/bad_any_cast.cc46
-rw-r--r--third_party/abseil_cpp/absl/types/bad_any_cast.h75
-rw-r--r--third_party/abseil_cpp/absl/types/bad_optional_access.cc48
-rw-r--r--third_party/abseil_cpp/absl/types/bad_optional_access.h78
-rw-r--r--third_party/abseil_cpp/absl/types/bad_variant_access.cc64
-rw-r--r--third_party/abseil_cpp/absl/types/bad_variant_access.h82
-rw-r--r--third_party/abseil_cpp/absl/types/compare.h598
-rw-r--r--third_party/abseil_cpp/absl/types/compare_test.cc389
-rw-r--r--third_party/abseil_cpp/absl/types/internal/conformance_aliases.h447
-rw-r--r--third_party/abseil_cpp/absl/types/internal/conformance_archetype.h978
-rw-r--r--third_party/abseil_cpp/absl/types/internal/conformance_profile.h931
-rw-r--r--third_party/abseil_cpp/absl/types/internal/conformance_testing.h1386
-rw-r--r--third_party/abseil_cpp/absl/types/internal/conformance_testing_helpers.h391
-rw-r--r--third_party/abseil_cpp/absl/types/internal/conformance_testing_test.cc1556
-rw-r--r--third_party/abseil_cpp/absl/types/internal/optional.h396
-rw-r--r--third_party/abseil_cpp/absl/types/internal/parentheses.h34
-rw-r--r--third_party/abseil_cpp/absl/types/internal/span.h128
-rw-r--r--third_party/abseil_cpp/absl/types/internal/transform_args.h246
-rw-r--r--third_party/abseil_cpp/absl/types/internal/variant.h1646
-rw-r--r--third_party/abseil_cpp/absl/types/optional.h776
-rw-r--r--third_party/abseil_cpp/absl/types/optional_exception_safety_test.cc292
-rw-r--r--third_party/abseil_cpp/absl/types/optional_test.cc1659
-rw-r--r--third_party/abseil_cpp/absl/types/span.h727
-rw-r--r--third_party/abseil_cpp/absl/types/span_test.cc846
-rw-r--r--third_party/abseil_cpp/absl/types/variant.h861
-rw-r--r--third_party/abseil_cpp/absl/types/variant_benchmark.cc222
-rw-r--r--third_party/abseil_cpp/absl/types/variant_exception_safety_test.cc532
-rw-r--r--third_party/abseil_cpp/absl/types/variant_test.cc2716
33 files changed, 20342 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/types/BUILD.bazel b/third_party/abseil_cpp/absl/types/BUILD.bazel
new file mode 100644
index 0000000000..de71c7347f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/BUILD.bazel
@@ -0,0 +1,337 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
+load(
+    "//absl:copts/configure_copts.bzl",
+    "ABSL_DEFAULT_COPTS",
+    "ABSL_DEFAULT_LINKOPTS",
+    "ABSL_TEST_COPTS",
+)
+
+package(default_visibility = ["//visibility:public"])
+
+licenses(["notice"])  # Apache 2.0
+
+cc_library(
+    name = "any",
+    hdrs = ["any.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":bad_any_cast",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:fast_type_id",
+        "//absl/meta:type_traits",
+        "//absl/utility",
+    ],
+)
+
+cc_library(
+    name = "bad_any_cast",
+    hdrs = ["bad_any_cast.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":bad_any_cast_impl",
+        "//absl/base:config",
+    ],
+)
+
+cc_library(
+    name = "bad_any_cast_impl",
+    srcs = [
+        "bad_any_cast.cc",
+        "bad_any_cast.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        "//absl/base:config",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_test(
+    name = "any_test",
+    size = "small",
+    srcs = [
+        "any_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":any",
+        "//absl/base:config",
+        "//absl/base:exception_testing",
+        "//absl/base:raw_logging_internal",
+        "//absl/container:test_instance_tracker",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "any_exception_safety_test",
+    srcs = ["any_exception_safety_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":any",
+        "//absl/base:config",
+        "//absl/base:exception_safety_testing",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "span",
+    srcs = [
+        "internal/span.h",
+    ],
+    hdrs = [
+        "span.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/algorithm",
+        "//absl/base:core_headers",
+        "//absl/base:throw_delegate",
+        "//absl/meta:type_traits",
+    ],
+)
+
+cc_test(
+    name = "span_test",
+    size = "small",
+    srcs = ["span_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":span",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:exception_testing",
+        "//absl/container:fixed_array",
+        "//absl/container:inlined_vector",
+        "//absl/hash:hash_testing",
+        "//absl/strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "optional",
+    srcs = ["internal/optional.h"],
+    hdrs = ["optional.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":bad_optional_access",
+        "//absl/base:base_internal",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/memory",
+        "//absl/meta:type_traits",
+        "//absl/utility",
+    ],
+)
+
+cc_library(
+    name = "bad_optional_access",
+    srcs = ["bad_optional_access.cc"],
+    hdrs = ["bad_optional_access.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/base:config",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_library(
+    name = "bad_variant_access",
+    srcs = ["bad_variant_access.cc"],
+    hdrs = ["bad_variant_access.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/base:config",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_test(
+    name = "optional_test",
+    size = "small",
+    srcs = [
+        "optional_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":optional",
+        "//absl/base:config",
+        "//absl/base:raw_logging_internal",
+        "//absl/meta:type_traits",
+        "//absl/strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "optional_exception_safety_test",
+    srcs = [
+        "optional_exception_safety_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":optional",
+        "//absl/base:config",
+        "//absl/base:exception_safety_testing",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "conformance_testing",
+    testonly = 1,
+    hdrs = [
+        "internal/conformance_aliases.h",
+        "internal/conformance_archetype.h",
+        "internal/conformance_profile.h",
+        "internal/conformance_testing.h",
+        "internal/conformance_testing_helpers.h",
+        "internal/parentheses.h",
+        "internal/transform_args.h",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/algorithm:container",
+        "//absl/meta:type_traits",
+        "//absl/strings",
+        "//absl/utility",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_test(
+    name = "conformance_testing_test",
+    size = "small",
+    srcs = [
+        "internal/conformance_testing_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":conformance_testing",
+        "//absl/meta:type_traits",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "variant",
+    srcs = ["internal/variant.h"],
+    hdrs = ["variant.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":bad_variant_access",
+        "//absl/base:base_internal",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/meta:type_traits",
+        "//absl/utility",
+    ],
+)
+
+cc_test(
+    name = "variant_test",
+    size = "small",
+    srcs = ["variant_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":variant",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/memory",
+        "//absl/meta:type_traits",
+        "//absl/strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "variant_benchmark",
+    srcs = [
+        "variant_benchmark.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    tags = ["benchmark"],
+    deps = [
+        ":variant",
+        "//absl/utility",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "variant_exception_safety_test",
+    size = "small",
+    srcs = [
+        "variant_exception_safety_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":variant",
+        "//absl/base:config",
+        "//absl/base:exception_safety_testing",
+        "//absl/memory",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "compare",
+    hdrs = ["compare.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        "//absl/base:core_headers",
+        "//absl/meta:type_traits",
+    ],
+)
+
+cc_test(
+    name = "compare_test",
+    size = "small",
+    srcs = [
+        "compare_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":compare",
+        "//absl/base",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
diff --git a/third_party/abseil_cpp/absl/types/CMakeLists.txt b/third_party/abseil_cpp/absl/types/CMakeLists.txt
new file mode 100644
index 0000000000..0dc0d2c7c9
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/CMakeLists.txt
@@ -0,0 +1,373 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+absl_cc_library(
+  NAME
+    any
+  HDRS
+    "any.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::bad_any_cast
+    absl::config
+    absl::core_headers
+    absl::fast_type_id
+    absl::type_traits
+    absl::utility
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    bad_any_cast
+  HDRS
+   "bad_any_cast.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::bad_any_cast_impl
+    absl::config
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    bad_any_cast_impl
+  SRCS
+   "bad_any_cast.h"
+   "bad_any_cast.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::config
+    absl::raw_logging_internal
+)
+
+absl_cc_test(
+  NAME
+    any_test
+  SRCS
+    "any_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::any
+    absl::config
+    absl::exception_testing
+    absl::raw_logging_internal
+    absl::test_instance_tracker
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    any_test_noexceptions
+  SRCS
+    "any_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::any
+    absl::config
+    absl::exception_testing
+    absl::raw_logging_internal
+    absl::test_instance_tracker
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    any_exception_safety_test
+  SRCS
+    "any_exception_safety_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::any
+    absl::config
+    absl::exception_safety_testing
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    span
+  HDRS
+    "span.h"
+  SRCS
+    "internal/span.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::algorithm
+    absl::core_headers
+    absl::throw_delegate
+    absl::type_traits
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    span_test
+  SRCS
+    "span_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::span
+    absl::base
+    absl::config
+    absl::core_headers
+    absl::exception_testing
+    absl::fixed_array
+    absl::inlined_vector
+    absl::hash_testing
+    absl::strings
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    span_test_noexceptions
+  SRCS
+    "span_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::span
+    absl::base
+    absl::config
+    absl::core_headers
+    absl::exception_testing
+    absl::fixed_array
+    absl::inlined_vector
+    absl::hash_testing
+    absl::strings
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    optional
+  HDRS
+    "optional.h"
+  SRCS
+    "internal/optional.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::bad_optional_access
+    absl::base_internal
+    absl::config
+    absl::core_headers
+    absl::memory
+    absl::type_traits
+    absl::utility
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    bad_optional_access
+  HDRS
+    "bad_optional_access.h"
+  SRCS
+    "bad_optional_access.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::config
+    absl::raw_logging_internal
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    bad_variant_access
+  HDRS
+    "bad_variant_access.h"
+  SRCS
+    "bad_variant_access.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::config
+    absl::raw_logging_internal
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    optional_test
+  SRCS
+    "optional_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::optional
+    absl::config
+    absl::raw_logging_internal
+    absl::strings
+    absl::type_traits
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    optional_exception_safety_test
+  SRCS
+    "optional_exception_safety_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::optional
+    absl::config
+    absl::exception_safety_testing
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    conformance_testing
+  HDRS
+    "internal/conformance_aliases.h"
+    "internal/conformance_archetype.h"
+    "internal/conformance_profile.h"
+    "internal/conformance_testing.h"
+    "internal/conformance_testing_helpers.h"
+    "internal/parentheses.h"
+    "internal/transform_args.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::algorithm
+    absl::debugging
+    absl::type_traits
+    absl::strings
+    absl::utility
+    gmock_main
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    conformance_testing_test
+  SRCS
+    "internal/conformance_testing_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+    ${ABSL_EXCEPTIONS_FLAG}
+  LINKOPTS
+    ${ABSL_EXCEPTIONS_FLAG_LINKOPTS}
+  DEPS
+    absl::conformance_testing
+    absl::type_traits
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    conformance_testing_test_no_exceptions
+  SRCS
+    "internal/conformance_testing_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::conformance_testing
+    absl::type_traits
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    variant
+  HDRS
+    "variant.h"
+  SRCS
+    "internal/variant.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::bad_variant_access
+    absl::base_internal
+    absl::config
+    absl::core_headers
+    absl::type_traits
+    absl::utility
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    variant_test
+  SRCS
+    "variant_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::variant
+    absl::config
+    absl::core_headers
+    absl::memory
+    absl::type_traits
+    absl::strings
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    compare
+  HDRS
+    "compare.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::core_headers
+    absl::type_traits
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    compare_test
+  SRCS
+    "compare_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::base
+    absl::compare
+    gmock_main
+)
+
+# TODO(cohenjon,zhangxy) Figure out why this test is failing on gcc 4.8
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9)
+else()
+absl_cc_test(
+  NAME
+    variant_exception_safety_test
+  SRCS
+    "variant_exception_safety_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::variant
+    absl::config
+    absl::exception_safety_testing
+    absl::memory
+    gmock_main
+)
+endif()
diff --git a/third_party/abseil_cpp/absl/types/any.h b/third_party/abseil_cpp/absl/types/any.h
new file mode 100644
index 0000000000..7eed519791
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/any.h
@@ -0,0 +1,528 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// any.h
+// -----------------------------------------------------------------------------
+//
+// This header file define the `absl::any` type for holding a type-safe value
+// of any type. The 'absl::any` type is useful for providing a way to hold
+// something that is, as yet, unspecified. Such unspecified types
+// traditionally are passed between API boundaries until they are later cast to
+// their "destination" types. To cast to such a destination type, use
+// `absl::any_cast()`. Note that when casting an `absl::any`, you must cast it
+// to an explicit type; implicit conversions will throw.
+//
+// Example:
+//
+//   auto a = absl::any(65);
+//   absl::any_cast<int>(a);         // 65
+//   absl::any_cast<char>(a);        // throws absl::bad_any_cast
+//   absl::any_cast<std::string>(a); // throws absl::bad_any_cast
+//
+// `absl::any` is a C++11 compatible version of the C++17 `std::any` abstraction
+// and is designed to be a drop-in replacement for code compliant with C++17.
+//
+// Traditionally, the behavior of casting to a temporary unspecified type has
+// been accomplished with the `void *` paradigm, where the pointer was to some
+// other unspecified type. `absl::any` provides an "owning" version of `void *`
+// that avoids issues of pointer management.
+//
+// Note: just as in the case of `void *`, use of `absl::any` (and its C++17
+// version `std::any`) is a code smell indicating that your API might not be
+// constructed correctly. We have seen that most uses of `any` are unwarranted,
+// and `absl::any`, like `std::any`, is difficult to use properly. Before using
+// this abstraction, make sure that you should not instead be rewriting your
+// code to be more specific.
+//
+// Abseil expects to release an `absl::variant` type shortly (a C++11 compatible
+// version of the C++17 `std::variant), which is generally preferred for use
+// over `absl::any`.
+#ifndef ABSL_TYPES_ANY_H_
+#define ABSL_TYPES_ANY_H_
+
+#include "absl/base/config.h"
+#include "absl/utility/utility.h"
+
+#ifdef ABSL_USES_STD_ANY
+
+#include <any>  // IWYU pragma: export
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using std::any;
+using std::any_cast;
+using std::bad_any_cast;
+using std::make_any;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_ANY
+
+#include <algorithm>
+#include <cstddef>
+#include <initializer_list>
+#include <memory>
+#include <stdexcept>
+#include <type_traits>
+#include <typeinfo>
+#include <utility>
+
+#include "absl/base/internal/fast_type_id.h"
+#include "absl/base/macros.h"
+#include "absl/meta/type_traits.h"
+#include "absl/types/bad_any_cast.h"
+
+// NOTE: This macro is an implementation detail that is undefined at the bottom
+// of the file. It is not intended for expansion directly from user code.
+#ifdef ABSL_ANY_DETAIL_HAS_RTTI
+#error ABSL_ANY_DETAIL_HAS_RTTI cannot be directly set
+#elif !defined(__GNUC__) || defined(__GXX_RTTI)
+#define ABSL_ANY_DETAIL_HAS_RTTI 1
+#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+class any;
+
+// swap()
+//
+// Swaps two `absl::any` values. Equivalent to `x.swap(y) where `x` and `y` are
+// `absl::any` types.
+void swap(any& x, any& y) noexcept;
+
+// make_any()
+//
+// Constructs an `absl::any` of type `T` with the given arguments.
+template <typename T, typename... Args>
+any make_any(Args&&... args);
+
+// Overload of `absl::make_any()` for constructing an `absl::any` type from an
+// initializer list.
+template <typename T, typename U, typename... Args>
+any make_any(std::initializer_list<U> il, Args&&... args);
+
+// any_cast()
+//
+// Statically casts the value of a `const absl::any` type to the given type.
+// This function will throw `absl::bad_any_cast` if the stored value type of the
+// `absl::any` does not match the cast.
+//
+// `any_cast()` can also be used to get a reference to the internal storage iff
+// a reference type is passed as its `ValueType`:
+//
+// Example:
+//
+//   absl::any my_any = std::vector<int>();
+//   absl::any_cast<std::vector<int>&>(my_any).push_back(42);
+template <typename ValueType>
+ValueType any_cast(const any& operand);
+
+// Overload of `any_cast()` to statically cast the value of a non-const
+// `absl::any` type to the given type. This function will throw
+// `absl::bad_any_cast` if the stored value type of the `absl::any` does not
+// match the cast.
+template <typename ValueType>
+ValueType any_cast(any& operand);  // NOLINT(runtime/references)
+
+// Overload of `any_cast()` to statically cast the rvalue of an `absl::any`
+// type. This function will throw `absl::bad_any_cast` if the stored value type
+// of the `absl::any` does not match the cast.
+template <typename ValueType>
+ValueType any_cast(any&& operand);
+
+// Overload of `any_cast()` to statically cast the value of a const pointer
+// `absl::any` type to the given pointer type, or `nullptr` if the stored value
+// type of the `absl::any` does not match the cast.
+template <typename ValueType>
+const ValueType* any_cast(const any* operand) noexcept;
+
+// Overload of `any_cast()` to statically cast the value of a pointer
+// `absl::any` type to the given pointer type, or `nullptr` if the stored value
+// type of the `absl::any` does not match the cast.
+template <typename ValueType>
+ValueType* any_cast(any* operand) noexcept;
+
+// -----------------------------------------------------------------------------
+// absl::any
+// -----------------------------------------------------------------------------
+//
+// An `absl::any` object provides the facility to either store an instance of a
+// type, known as the "contained object", or no value. An `absl::any` is used to
+// store values of types that are unknown at compile time. The `absl::any`
+// object, when containing a value, must contain a value type; storing a
+// reference type is neither desired nor supported.
+//
+// An `absl::any` can only store a type that is copy-constructible; move-only
+// types are not allowed within an `any` object.
+//
+// Example:
+//
+//   auto a = absl::any(65);                 // Literal, copyable
+//   auto b = absl::any(std::vector<int>()); // Default-initialized, copyable
+//   std::unique_ptr<Foo> my_foo;
+//   auto c = absl::any(std::move(my_foo));  // Error, not copy-constructible
+//
+// Note that `absl::any` makes use of decayed types (`absl::decay_t` in this
+// context) to remove const-volatile qualifiers (known as "cv qualifiers"),
+// decay functions to function pointers, etc. We essentially "decay" a given
+// type into its essential type.
+//
+// `absl::any` makes use of decayed types when determining the basic type `T` of
+// the value to store in the any's contained object. In the documentation below,
+// we explicitly denote this by using the phrase "a decayed type of `T`".
+//
+// Example:
+//
+//   const int a = 4;
+//   absl::any foo(a);  // Decay ensures we store an "int", not a "const int&".
+//
+//   void my_function() {}
+//   absl::any bar(my_function);  // Decay ensures we store a function pointer.
+//
+// `absl::any` is a C++11 compatible version of the C++17 `std::any` abstraction
+// and is designed to be a drop-in replacement for code compliant with C++17.
+class any {
+ private:
+  template <typename T>
+  struct IsInPlaceType;
+
+ public:
+  // Constructors
+
+  // Constructs an empty `absl::any` object (`any::has_value()` will return
+  // `false`).
+  constexpr any() noexcept;
+
+  // Copy constructs an `absl::any` object with a "contained object" of the
+  // passed type of `other` (or an empty `absl::any` if `other.has_value()` is
+  // `false`.
+  any(const any& other)
+      : obj_(other.has_value() ? other.obj_->Clone()
+                               : std::unique_ptr<ObjInterface>()) {}
+
+  // Move constructs an `absl::any` object with a "contained object" of the
+  // passed type of `other` (or an empty `absl::any` if `other.has_value()` is
+  // `false`).
+  any(any&& other) noexcept = default;
+
+  // Constructs an `absl::any` object with a "contained object" of the decayed
+  // type of `T`, which is initialized via `std::forward<T>(value)`.
+  //
+  // This constructor will not participate in overload resolution if the
+  // decayed type of `T` is not copy-constructible.
+  template <
+      typename T, typename VT = absl::decay_t<T>,
+      absl::enable_if_t<!absl::disjunction<
+          std::is_same<any, VT>, IsInPlaceType<VT>,
+          absl::negation<std::is_copy_constructible<VT> > >::value>* = nullptr>
+  any(T&& value) : obj_(new Obj<VT>(in_place, std::forward<T>(value))) {}
+
+  // Constructs an `absl::any` object with a "contained object" of the decayed
+  // type of `T`, which is initialized via `std::forward<T>(value)`.
+  template <typename T, typename... Args, typename VT = absl::decay_t<T>,
+            absl::enable_if_t<absl::conjunction<
+                std::is_copy_constructible<VT>,
+                std::is_constructible<VT, Args...>>::value>* = nullptr>
+  explicit any(in_place_type_t<T> /*tag*/, Args&&... args)
+      : obj_(new Obj<VT>(in_place, std::forward<Args>(args)...)) {}
+
+  // Constructs an `absl::any` object with a "contained object" of the passed
+  // type `VT` as a decayed type of `T`. `VT` is initialized as if
+  // direct-non-list-initializing an object of type `VT` with the arguments
+  // `initializer_list, std::forward<Args>(args)...`.
+  template <
+      typename T, typename U, typename... Args, typename VT = absl::decay_t<T>,
+      absl::enable_if_t<
+          absl::conjunction<std::is_copy_constructible<VT>,
+                            std::is_constructible<VT, std::initializer_list<U>&,
+                                                  Args...>>::value>* = nullptr>
+  explicit any(in_place_type_t<T> /*tag*/, std::initializer_list<U> ilist,
+               Args&&... args)
+      : obj_(new Obj<VT>(in_place, ilist, std::forward<Args>(args)...)) {}
+
+  // Assignment operators
+
+  // Copy assigns an `absl::any` object with a "contained object" of the
+  // passed type.
+  any& operator=(const any& rhs) {
+    any(rhs).swap(*this);
+    return *this;
+  }
+
+  // Move assigns an `absl::any` object with a "contained object" of the
+  // passed type. `rhs` is left in a valid but otherwise unspecified state.
+  any& operator=(any&& rhs) noexcept {
+    any(std::move(rhs)).swap(*this);
+    return *this;
+  }
+
+  // Assigns an `absl::any` object with a "contained object" of the passed type.
+  template <typename T, typename VT = absl::decay_t<T>,
+            absl::enable_if_t<absl::conjunction<
+                absl::negation<std::is_same<VT, any>>,
+                std::is_copy_constructible<VT>>::value>* = nullptr>
+  any& operator=(T&& rhs) {
+    any tmp(in_place_type_t<VT>(), std::forward<T>(rhs));
+    tmp.swap(*this);
+    return *this;
+  }
+
+  // Modifiers
+
+  // any::emplace()
+  //
+  // Emplaces a value within an `absl::any` object by calling `any::reset()`,
+  // initializing the contained value as if direct-non-list-initializing an
+  // object of type `VT` with the arguments `std::forward<Args>(args)...`, and
+  // returning a reference to the new contained value.
+  //
+  // Note: If an exception is thrown during the call to `VT`'s constructor,
+  // `*this` does not contain a value, and any previously contained value has
+  // been destroyed.
+  template <
+      typename T, typename... Args, typename VT = absl::decay_t<T>,
+      absl::enable_if_t<std::is_copy_constructible<VT>::value &&
+                        std::is_constructible<VT, Args...>::value>* = nullptr>
+  VT& emplace(Args&&... args) {
+    reset();  // NOTE: reset() is required here even in the world of exceptions.
+    Obj<VT>* const object_ptr =
+        new Obj<VT>(in_place, std::forward<Args>(args)...);
+    obj_ = std::unique_ptr<ObjInterface>(object_ptr);
+    return object_ptr->value;
+  }
+
+  // Overload of `any::emplace()` to emplace a value within an `absl::any`
+  // object by calling `any::reset()`, initializing the contained value as if
+  // direct-non-list-initializing an object of type `VT` with the arguments
+  // `initializer_list, std::forward<Args>(args)...`, and returning a reference
+  // to the new contained value.
+  //
+  // Note: If an exception is thrown during the call to `VT`'s constructor,
+  // `*this` does not contain a value, and any previously contained value has
+  // been destroyed. The function shall not participate in overload resolution
+  // unless `is_copy_constructible_v<VT>` is `true` and
+  // `is_constructible_v<VT, initializer_list<U>&, Args...>` is `true`.
+  template <
+      typename T, typename U, typename... Args, typename VT = absl::decay_t<T>,
+      absl::enable_if_t<std::is_copy_constructible<VT>::value &&
+                        std::is_constructible<VT, std::initializer_list<U>&,
+                                              Args...>::value>* = nullptr>
+  VT& emplace(std::initializer_list<U> ilist, Args&&... args) {
+    reset();  // NOTE: reset() is required here even in the world of exceptions.
+    Obj<VT>* const object_ptr =
+        new Obj<VT>(in_place, ilist, std::forward<Args>(args)...);
+    obj_ = std::unique_ptr<ObjInterface>(object_ptr);
+    return object_ptr->value;
+  }
+
+  // any::reset()
+  //
+  // Resets the state of the `absl::any` object, destroying the contained object
+  // if present.
+  void reset() noexcept { obj_ = nullptr; }
+
+  // any::swap()
+  //
+  // Swaps the passed value and the value of this `absl::any` object.
+  void swap(any& other) noexcept { obj_.swap(other.obj_); }
+
+  // Observers
+
+  // any::has_value()
+  //
+  // Returns `true` if the `any` object has a contained value, otherwise
+  // returns `false`.
+  bool has_value() const noexcept { return obj_ != nullptr; }
+
+#if ABSL_ANY_DETAIL_HAS_RTTI
+  // Returns: typeid(T) if *this has a contained object of type T, otherwise
+  // typeid(void).
+  const std::type_info& type() const noexcept {
+    if (has_value()) {
+      return obj_->Type();
+    }
+
+    return typeid(void);
+  }
+#endif  // ABSL_ANY_DETAIL_HAS_RTTI
+
+ private:
+  // Tagged type-erased abstraction for holding a cloneable object.
+  class ObjInterface {
+   public:
+    virtual ~ObjInterface() = default;
+    virtual std::unique_ptr<ObjInterface> Clone() const = 0;
+    virtual const void* ObjTypeId() const noexcept = 0;
+#if ABSL_ANY_DETAIL_HAS_RTTI
+    virtual const std::type_info& Type() const noexcept = 0;
+#endif  // ABSL_ANY_DETAIL_HAS_RTTI
+  };
+
+  // Hold a value of some queryable type, with an ability to Clone it.
+  template <typename T>
+  class Obj : public ObjInterface {
+   public:
+    template <typename... Args>
+    explicit Obj(in_place_t /*tag*/, Args&&... args)
+        : value(std::forward<Args>(args)...) {}
+
+    std::unique_ptr<ObjInterface> Clone() const final {
+      return std::unique_ptr<ObjInterface>(new Obj(in_place, value));
+    }
+
+    const void* ObjTypeId() const noexcept final { return IdForType<T>(); }
+
+#if ABSL_ANY_DETAIL_HAS_RTTI
+    const std::type_info& Type() const noexcept final { return typeid(T); }
+#endif  // ABSL_ANY_DETAIL_HAS_RTTI
+
+    T value;
+  };
+
+  std::unique_ptr<ObjInterface> CloneObj() const {
+    if (!obj_) return nullptr;
+    return obj_->Clone();
+  }
+
+  template <typename T>
+  constexpr static const void* IdForType() {
+    // Note: This type dance is to make the behavior consistent with typeid.
+    using NormalizedType =
+        typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+
+    return base_internal::FastTypeId<NormalizedType>();
+  }
+
+  const void* GetObjTypeId() const {
+    return obj_ ? obj_->ObjTypeId() : base_internal::FastTypeId<void>();
+  }
+
+  // `absl::any` nonmember functions //
+
+  // Description at the declaration site (top of file).
+  template <typename ValueType>
+  friend ValueType any_cast(const any& operand);
+
+  // Description at the declaration site (top of file).
+  template <typename ValueType>
+  friend ValueType any_cast(any& operand);  // NOLINT(runtime/references)
+
+  // Description at the declaration site (top of file).
+  template <typename T>
+  friend const T* any_cast(const any* operand) noexcept;
+
+  // Description at the declaration site (top of file).
+  template <typename T>
+  friend T* any_cast(any* operand) noexcept;
+
+  std::unique_ptr<ObjInterface> obj_;
+};
+
+// -----------------------------------------------------------------------------
+// Implementation Details
+// -----------------------------------------------------------------------------
+
+constexpr any::any() noexcept = default;
+
+template <typename T>
+struct any::IsInPlaceType : std::false_type {};
+
+template <typename T>
+struct any::IsInPlaceType<in_place_type_t<T>> : std::true_type {};
+
+inline void swap(any& x, any& y) noexcept { x.swap(y); }
+
+// Description at the declaration site (top of file).
+template <typename T, typename... Args>
+any make_any(Args&&... args) {
+  return any(in_place_type_t<T>(), std::forward<Args>(args)...);
+}
+
+// Description at the declaration site (top of file).
+template <typename T, typename U, typename... Args>
+any make_any(std::initializer_list<U> il, Args&&... args) {
+  return any(in_place_type_t<T>(), il, std::forward<Args>(args)...);
+}
+
+// Description at the declaration site (top of file).
+template <typename ValueType>
+ValueType any_cast(const any& operand) {
+  using U = typename std::remove_cv<
+      typename std::remove_reference<ValueType>::type>::type;
+  static_assert(std::is_constructible<ValueType, const U&>::value,
+                "Invalid ValueType");
+  auto* const result = (any_cast<U>)(&operand);
+  if (result == nullptr) {
+    any_internal::ThrowBadAnyCast();
+  }
+  return static_cast<ValueType>(*result);
+}
+
+// Description at the declaration site (top of file).
+template <typename ValueType>
+ValueType any_cast(any& operand) {  // NOLINT(runtime/references)
+  using U = typename std::remove_cv<
+      typename std::remove_reference<ValueType>::type>::type;
+  static_assert(std::is_constructible<ValueType, U&>::value,
+                "Invalid ValueType");
+  auto* result = (any_cast<U>)(&operand);
+  if (result == nullptr) {
+    any_internal::ThrowBadAnyCast();
+  }
+  return static_cast<ValueType>(*result);
+}
+
+// Description at the declaration site (top of file).
+template <typename ValueType>
+ValueType any_cast(any&& operand) {
+  using U = typename std::remove_cv<
+      typename std::remove_reference<ValueType>::type>::type;
+  static_assert(std::is_constructible<ValueType, U>::value,
+                "Invalid ValueType");
+  return static_cast<ValueType>(std::move((any_cast<U&>)(operand)));
+}
+
+// Description at the declaration site (top of file).
+template <typename T>
+const T* any_cast(const any* operand) noexcept {
+  using U =
+      typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+  return operand && operand->GetObjTypeId() == any::IdForType<U>()
+             ? std::addressof(
+                   static_cast<const any::Obj<U>*>(operand->obj_.get())->value)
+             : nullptr;
+}
+
+// Description at the declaration site (top of file).
+template <typename T>
+T* any_cast(any* operand) noexcept {
+  using U =
+      typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+  return operand && operand->GetObjTypeId() == any::IdForType<U>()
+             ? std::addressof(
+                   static_cast<any::Obj<U>*>(operand->obj_.get())->value)
+             : nullptr;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#undef ABSL_ANY_DETAIL_HAS_RTTI
+
+#endif  // ABSL_USES_STD_ANY
+
+#endif  // ABSL_TYPES_ANY_H_
diff --git a/third_party/abseil_cpp/absl/types/any_exception_safety_test.cc b/third_party/abseil_cpp/absl/types/any_exception_safety_test.cc
new file mode 100644
index 0000000000..31c1140135
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/any_exception_safety_test.cc
@@ -0,0 +1,173 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/any.h"
+
+#include "absl/base/config.h"
+
+// This test is a no-op when absl::any is an alias for std::any and when
+// exceptions are not enabled.
+#if !defined(ABSL_USES_STD_ANY) && defined(ABSL_HAVE_EXCEPTIONS)
+
+#include <typeinfo>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/exception_safety_testing.h"
+
+using Thrower = testing::ThrowingValue<>;
+using NoThrowMoveThrower =
+    testing::ThrowingValue<testing::TypeSpec::kNoThrowMove>;
+using ThrowerList = std::initializer_list<Thrower>;
+using ThrowerVec = std::vector<Thrower>;
+using ThrowingAlloc = testing::ThrowingAllocator<Thrower>;
+using ThrowingThrowerVec = std::vector<Thrower, ThrowingAlloc>;
+
+namespace {
+
+testing::AssertionResult AnyInvariants(absl::any* a) {
+  using testing::AssertionFailure;
+  using testing::AssertionSuccess;
+
+  if (a->has_value()) {
+    if (a->type() == typeid(void)) {
+      return AssertionFailure()
+             << "A non-empty any should not have type `void`";
+    }
+  } else {
+    if (a->type() != typeid(void)) {
+      return AssertionFailure()
+             << "An empty any should have type void, but has type "
+             << a->type().name();
+    }
+  }
+
+  //  Make sure that reset() changes any to a valid state.
+  a->reset();
+  if (a->has_value()) {
+    return AssertionFailure() << "A reset `any` should be valueless";
+  }
+  if (a->type() != typeid(void)) {
+    return AssertionFailure() << "A reset `any` should have type() of `void`, "
+                                 "but instead has type "
+                              << a->type().name();
+  }
+  try {
+    auto unused = absl::any_cast<Thrower>(*a);
+    static_cast<void>(unused);
+    return AssertionFailure()
+           << "A reset `any` should not be able to be any_cast";
+  } catch (const absl::bad_any_cast&) {
+  } catch (...) {
+    return AssertionFailure()
+           << "Unexpected exception thrown from absl::any_cast";
+  }
+  return AssertionSuccess();
+}
+
+testing::AssertionResult AnyIsEmpty(absl::any* a) {
+  if (!a->has_value()) {
+    return testing::AssertionSuccess();
+  }
+  return testing::AssertionFailure()
+         << "a should be empty, but instead has value "
+         << absl::any_cast<Thrower>(*a).Get();
+}
+
+TEST(AnyExceptionSafety, Ctors) {
+  Thrower val(1);
+  testing::TestThrowingCtor<absl::any>(val);
+
+  Thrower copy(val);
+  testing::TestThrowingCtor<absl::any>(copy);
+
+  testing::TestThrowingCtor<absl::any>(absl::in_place_type_t<Thrower>(), 1);
+
+  testing::TestThrowingCtor<absl::any>(absl::in_place_type_t<ThrowerVec>(),
+                                       ThrowerList{val});
+
+  testing::TestThrowingCtor<absl::any,
+                            absl::in_place_type_t<ThrowingThrowerVec>,
+                            ThrowerList, ThrowingAlloc>(
+      absl::in_place_type_t<ThrowingThrowerVec>(), {val}, ThrowingAlloc());
+}
+
+TEST(AnyExceptionSafety, Assignment) {
+  auto original =
+      absl::any(absl::in_place_type_t<Thrower>(), 1, testing::nothrow_ctor);
+  auto any_is_strong = [original](absl::any* ap) {
+    return testing::AssertionResult(ap->has_value() &&
+                                    absl::any_cast<Thrower>(original) ==
+                                        absl::any_cast<Thrower>(*ap));
+  };
+  auto any_strong_tester = testing::MakeExceptionSafetyTester()
+                               .WithInitialValue(original)
+                               .WithContracts(AnyInvariants, any_is_strong);
+
+  Thrower val(2);
+  absl::any any_val(val);
+  NoThrowMoveThrower mv_val(2);
+
+  auto assign_any = [&any_val](absl::any* ap) { *ap = any_val; };
+  auto assign_val = [&val](absl::any* ap) { *ap = val; };
+  auto move = [&val](absl::any* ap) { *ap = std::move(val); };
+  auto move_movable = [&mv_val](absl::any* ap) { *ap = std::move(mv_val); };
+
+  EXPECT_TRUE(any_strong_tester.Test(assign_any));
+  EXPECT_TRUE(any_strong_tester.Test(assign_val));
+  EXPECT_TRUE(any_strong_tester.Test(move));
+  EXPECT_TRUE(any_strong_tester.Test(move_movable));
+
+  auto empty_any_is_strong = [](absl::any* ap) {
+    return testing::AssertionResult{!ap->has_value()};
+  };
+  auto strong_empty_any_tester =
+      testing::MakeExceptionSafetyTester()
+          .WithInitialValue(absl::any{})
+          .WithContracts(AnyInvariants, empty_any_is_strong);
+
+  EXPECT_TRUE(strong_empty_any_tester.Test(assign_any));
+  EXPECT_TRUE(strong_empty_any_tester.Test(assign_val));
+  EXPECT_TRUE(strong_empty_any_tester.Test(move));
+}
+
+TEST(AnyExceptionSafety, Emplace) {
+  auto initial_val =
+      absl::any{absl::in_place_type_t<Thrower>(), 1, testing::nothrow_ctor};
+  auto one_tester = testing::MakeExceptionSafetyTester()
+                        .WithInitialValue(initial_val)
+                        .WithContracts(AnyInvariants, AnyIsEmpty);
+
+  auto emp_thrower = [](absl::any* ap) { ap->emplace<Thrower>(2); };
+  auto emp_throwervec = [](absl::any* ap) {
+    std::initializer_list<Thrower> il{Thrower(2, testing::nothrow_ctor)};
+    ap->emplace<ThrowerVec>(il);
+  };
+  auto emp_movethrower = [](absl::any* ap) {
+    ap->emplace<NoThrowMoveThrower>(2);
+  };
+
+  EXPECT_TRUE(one_tester.Test(emp_thrower));
+  EXPECT_TRUE(one_tester.Test(emp_throwervec));
+  EXPECT_TRUE(one_tester.Test(emp_movethrower));
+
+  auto empty_tester = one_tester.WithInitialValue(absl::any{});
+
+  EXPECT_TRUE(empty_tester.Test(emp_thrower));
+  EXPECT_TRUE(empty_tester.Test(emp_throwervec));
+}
+
+}  // namespace
+
+#endif  // #if !defined(ABSL_USES_STD_ANY) && defined(ABSL_HAVE_EXCEPTIONS)
diff --git a/third_party/abseil_cpp/absl/types/any_test.cc b/third_party/abseil_cpp/absl/types/any_test.cc
new file mode 100644
index 0000000000..70e4ba22b1
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/any_test.cc
@@ -0,0 +1,781 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/any.h"
+
+// This test is a no-op when absl::any is an alias for std::any.
+#if !defined(ABSL_USES_STD_ANY)
+
+#include <initializer_list>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/exception_testing.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/container/internal/test_instance_tracker.h"
+
+namespace {
+using absl::test_internal::CopyableOnlyInstance;
+using absl::test_internal::InstanceTracker;
+
+template <typename T>
+const T& AsConst(const T& t) {
+  return t;
+}
+
+struct MoveOnly {
+  MoveOnly() = default;
+  explicit MoveOnly(int value) : value(value) {}
+  MoveOnly(MoveOnly&&) = default;
+  MoveOnly& operator=(MoveOnly&&) = default;
+
+  int value = 0;
+};
+
+struct CopyOnly {
+  CopyOnly() = default;
+  explicit CopyOnly(int value) : value(value) {}
+  CopyOnly(CopyOnly&&) = delete;
+  CopyOnly& operator=(CopyOnly&&) = delete;
+  CopyOnly(const CopyOnly&) = default;
+  CopyOnly& operator=(const CopyOnly&) = default;
+
+  int value = 0;
+};
+
+struct MoveOnlyWithListConstructor {
+  MoveOnlyWithListConstructor() = default;
+  explicit MoveOnlyWithListConstructor(std::initializer_list<int> /*ilist*/,
+                                       int value)
+      : value(value) {}
+  MoveOnlyWithListConstructor(MoveOnlyWithListConstructor&&) = default;
+  MoveOnlyWithListConstructor& operator=(MoveOnlyWithListConstructor&&) =
+      default;
+
+  int value = 0;
+};
+
+struct IntMoveOnlyCopyOnly {
+  IntMoveOnlyCopyOnly(int value, MoveOnly /*move_only*/, CopyOnly /*copy_only*/)
+      : value(value) {}
+
+  int value;
+};
+
+struct ListMoveOnlyCopyOnly {
+  ListMoveOnlyCopyOnly(std::initializer_list<int> ilist, MoveOnly /*move_only*/,
+                       CopyOnly /*copy_only*/)
+      : values(ilist) {}
+
+  std::vector<int> values;
+};
+
+using FunctionType = void();
+void FunctionToEmplace() {}
+
+using ArrayType = int[2];
+using DecayedArray = absl::decay_t<ArrayType>;
+
+TEST(AnyTest, Noexcept) {
+  static_assert(std::is_nothrow_default_constructible<absl::any>(), "");
+  static_assert(std::is_nothrow_move_constructible<absl::any>(), "");
+  static_assert(std::is_nothrow_move_assignable<absl::any>(), "");
+  static_assert(noexcept(std::declval<absl::any&>().has_value()), "");
+  static_assert(noexcept(std::declval<absl::any&>().type()), "");
+  static_assert(noexcept(absl::any_cast<int>(std::declval<absl::any*>())), "");
+  static_assert(
+      noexcept(std::declval<absl::any&>().swap(std::declval<absl::any&>())),
+      "");
+
+  using std::swap;
+  static_assert(
+      noexcept(swap(std::declval<absl::any&>(), std::declval<absl::any&>())),
+      "");
+}
+
+TEST(AnyTest, HasValue) {
+  absl::any o;
+  EXPECT_FALSE(o.has_value());
+  o.emplace<int>();
+  EXPECT_TRUE(o.has_value());
+  o.reset();
+  EXPECT_FALSE(o.has_value());
+}
+
+TEST(AnyTest, Type) {
+  absl::any o;
+  EXPECT_EQ(typeid(void), o.type());
+  o.emplace<int>(5);
+  EXPECT_EQ(typeid(int), o.type());
+  o.emplace<float>(5.f);
+  EXPECT_EQ(typeid(float), o.type());
+  o.reset();
+  EXPECT_EQ(typeid(void), o.type());
+}
+
+TEST(AnyTest, EmptyPointerCast) {
+  // pointer-to-unqualified overload
+  {
+    absl::any o;
+    EXPECT_EQ(nullptr, absl::any_cast<int>(&o));
+    o.emplace<int>();
+    EXPECT_NE(nullptr, absl::any_cast<int>(&o));
+    o.reset();
+    EXPECT_EQ(nullptr, absl::any_cast<int>(&o));
+  }
+
+  // pointer-to-const overload
+  {
+    absl::any o;
+    EXPECT_EQ(nullptr, absl::any_cast<int>(&AsConst(o)));
+    o.emplace<int>();
+    EXPECT_NE(nullptr, absl::any_cast<int>(&AsConst(o)));
+    o.reset();
+    EXPECT_EQ(nullptr, absl::any_cast<int>(&AsConst(o)));
+  }
+}
+
+TEST(AnyTest, InPlaceConstruction) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type_t<IntMoveOnlyCopyOnly>(), 5, MoveOnly(),
+              copy_only);
+  IntMoveOnlyCopyOnly& v = absl::any_cast<IntMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(5, v.value);
+}
+
+TEST(AnyTest, InPlaceConstructionVariableTemplate) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type<IntMoveOnlyCopyOnly>, 5, MoveOnly(),
+              copy_only);
+  auto& v = absl::any_cast<IntMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(5, v.value);
+}
+
+TEST(AnyTest, InPlaceConstructionWithCV) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type_t<const volatile IntMoveOnlyCopyOnly>(), 5,
+              MoveOnly(), copy_only);
+  IntMoveOnlyCopyOnly& v = absl::any_cast<IntMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(5, v.value);
+}
+
+TEST(AnyTest, InPlaceConstructionWithCVVariableTemplate) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type<const volatile IntMoveOnlyCopyOnly>, 5,
+              MoveOnly(), copy_only);
+  auto& v = absl::any_cast<IntMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(5, v.value);
+}
+
+TEST(AnyTest, InPlaceConstructionWithFunction) {
+  absl::any o(absl::in_place_type_t<FunctionType>(), FunctionToEmplace);
+  FunctionType*& construction_result = absl::any_cast<FunctionType*&>(o);
+  EXPECT_EQ(&FunctionToEmplace, construction_result);
+}
+
+TEST(AnyTest, InPlaceConstructionWithFunctionVariableTemplate) {
+  absl::any o(absl::in_place_type<FunctionType>, FunctionToEmplace);
+  auto& construction_result = absl::any_cast<FunctionType*&>(o);
+  EXPECT_EQ(&FunctionToEmplace, construction_result);
+}
+
+TEST(AnyTest, InPlaceConstructionWithArray) {
+  ArrayType ar = {5, 42};
+  absl::any o(absl::in_place_type_t<ArrayType>(), ar);
+  DecayedArray& construction_result = absl::any_cast<DecayedArray&>(o);
+  EXPECT_EQ(&ar[0], construction_result);
+}
+
+TEST(AnyTest, InPlaceConstructionWithArrayVariableTemplate) {
+  ArrayType ar = {5, 42};
+  absl::any o(absl::in_place_type<ArrayType>, ar);
+  auto& construction_result = absl::any_cast<DecayedArray&>(o);
+  EXPECT_EQ(&ar[0], construction_result);
+}
+
+TEST(AnyTest, InPlaceConstructionIlist) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type_t<ListMoveOnlyCopyOnly>(), {1, 2, 3, 4},
+              MoveOnly(), copy_only);
+  ListMoveOnlyCopyOnly& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  std::vector<int> expected_values = {1, 2, 3, 4};
+  EXPECT_EQ(expected_values, v.values);
+}
+
+TEST(AnyTest, InPlaceConstructionIlistVariableTemplate) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type<ListMoveOnlyCopyOnly>, {1, 2, 3, 4},
+              MoveOnly(), copy_only);
+  auto& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  std::vector<int> expected_values = {1, 2, 3, 4};
+  EXPECT_EQ(expected_values, v.values);
+}
+
+TEST(AnyTest, InPlaceConstructionIlistWithCV) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type_t<const volatile ListMoveOnlyCopyOnly>(),
+              {1, 2, 3, 4}, MoveOnly(), copy_only);
+  ListMoveOnlyCopyOnly& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  std::vector<int> expected_values = {1, 2, 3, 4};
+  EXPECT_EQ(expected_values, v.values);
+}
+
+TEST(AnyTest, InPlaceConstructionIlistWithCVVariableTemplate) {
+  const CopyOnly copy_only{};
+  absl::any o(absl::in_place_type<const volatile ListMoveOnlyCopyOnly>,
+              {1, 2, 3, 4}, MoveOnly(), copy_only);
+  auto& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  std::vector<int> expected_values = {1, 2, 3, 4};
+  EXPECT_EQ(expected_values, v.values);
+}
+
+TEST(AnyTest, InPlaceNoArgs) {
+  absl::any o(absl::in_place_type_t<int>{});
+  EXPECT_EQ(0, absl::any_cast<int&>(o));
+}
+
+TEST(AnyTest, InPlaceNoArgsVariableTemplate) {
+  absl::any o(absl::in_place_type<int>);
+  EXPECT_EQ(0, absl::any_cast<int&>(o));
+}
+
+template <typename Enabler, typename T, typename... Args>
+struct CanEmplaceAnyImpl : std::false_type {};
+
+template <typename T, typename... Args>
+struct CanEmplaceAnyImpl<
+    absl::void_t<decltype(
+        std::declval<absl::any&>().emplace<T>(std::declval<Args>()...))>,
+    T, Args...> : std::true_type {};
+
+template <typename T, typename... Args>
+using CanEmplaceAny = CanEmplaceAnyImpl<void, T, Args...>;
+
+TEST(AnyTest, Emplace) {
+  const CopyOnly copy_only{};
+  absl::any o;
+  EXPECT_TRUE((std::is_same<decltype(o.emplace<IntMoveOnlyCopyOnly>(
+                                5, MoveOnly(), copy_only)),
+                            IntMoveOnlyCopyOnly&>::value));
+  IntMoveOnlyCopyOnly& emplace_result =
+      o.emplace<IntMoveOnlyCopyOnly>(5, MoveOnly(), copy_only);
+  EXPECT_EQ(5, emplace_result.value);
+  IntMoveOnlyCopyOnly& v = absl::any_cast<IntMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(5, v.value);
+  EXPECT_EQ(&emplace_result, &v);
+
+  static_assert(!CanEmplaceAny<int, int, int>::value, "");
+  static_assert(!CanEmplaceAny<MoveOnly, MoveOnly>::value, "");
+}
+
+TEST(AnyTest, EmplaceWithCV) {
+  const CopyOnly copy_only{};
+  absl::any o;
+  EXPECT_TRUE(
+      (std::is_same<decltype(o.emplace<const volatile IntMoveOnlyCopyOnly>(
+                        5, MoveOnly(), copy_only)),
+                    IntMoveOnlyCopyOnly&>::value));
+  IntMoveOnlyCopyOnly& emplace_result =
+      o.emplace<const volatile IntMoveOnlyCopyOnly>(5, MoveOnly(), copy_only);
+  EXPECT_EQ(5, emplace_result.value);
+  IntMoveOnlyCopyOnly& v = absl::any_cast<IntMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(5, v.value);
+  EXPECT_EQ(&emplace_result, &v);
+}
+
+TEST(AnyTest, EmplaceWithFunction) {
+  absl::any o;
+  EXPECT_TRUE(
+      (std::is_same<decltype(o.emplace<FunctionType>(FunctionToEmplace)),
+                    FunctionType*&>::value));
+  FunctionType*& emplace_result = o.emplace<FunctionType>(FunctionToEmplace);
+  EXPECT_EQ(&FunctionToEmplace, emplace_result);
+}
+
+TEST(AnyTest, EmplaceWithArray) {
+  absl::any o;
+  ArrayType ar = {5, 42};
+  EXPECT_TRUE(
+      (std::is_same<decltype(o.emplace<ArrayType>(ar)), DecayedArray&>::value));
+  DecayedArray& emplace_result = o.emplace<ArrayType>(ar);
+  EXPECT_EQ(&ar[0], emplace_result);
+}
+
+TEST(AnyTest, EmplaceIlist) {
+  const CopyOnly copy_only{};
+  absl::any o;
+  EXPECT_TRUE((std::is_same<decltype(o.emplace<ListMoveOnlyCopyOnly>(
+                                {1, 2, 3, 4}, MoveOnly(), copy_only)),
+                            ListMoveOnlyCopyOnly&>::value));
+  ListMoveOnlyCopyOnly& emplace_result =
+      o.emplace<ListMoveOnlyCopyOnly>({1, 2, 3, 4}, MoveOnly(), copy_only);
+  ListMoveOnlyCopyOnly& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(&v, &emplace_result);
+  std::vector<int> expected_values = {1, 2, 3, 4};
+  EXPECT_EQ(expected_values, v.values);
+
+  static_assert(!CanEmplaceAny<int, std::initializer_list<int>>::value, "");
+  static_assert(!CanEmplaceAny<MoveOnlyWithListConstructor,
+                               std::initializer_list<int>, int>::value,
+                "");
+}
+
+TEST(AnyTest, EmplaceIlistWithCV) {
+  const CopyOnly copy_only{};
+  absl::any o;
+  EXPECT_TRUE(
+      (std::is_same<decltype(o.emplace<const volatile ListMoveOnlyCopyOnly>(
+                        {1, 2, 3, 4}, MoveOnly(), copy_only)),
+                    ListMoveOnlyCopyOnly&>::value));
+  ListMoveOnlyCopyOnly& emplace_result =
+      o.emplace<const volatile ListMoveOnlyCopyOnly>({1, 2, 3, 4}, MoveOnly(),
+                                                     copy_only);
+  ListMoveOnlyCopyOnly& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  EXPECT_EQ(&v, &emplace_result);
+  std::vector<int> expected_values = {1, 2, 3, 4};
+  EXPECT_EQ(expected_values, v.values);
+}
+
+TEST(AnyTest, EmplaceNoArgs) {
+  absl::any o;
+  o.emplace<int>();
+  EXPECT_EQ(0, absl::any_cast<int>(o));
+}
+
+TEST(AnyTest, ConversionConstruction) {
+  {
+    absl::any o = 5;
+    EXPECT_EQ(5, absl::any_cast<int>(o));
+  }
+
+  {
+    const CopyOnly copy_only(5);
+    absl::any o = copy_only;
+    EXPECT_EQ(5, absl::any_cast<CopyOnly&>(o).value);
+  }
+
+  static_assert(!std::is_convertible<MoveOnly, absl::any>::value, "");
+}
+
+TEST(AnyTest, ConversionAssignment) {
+  {
+    absl::any o;
+    o = 5;
+    EXPECT_EQ(5, absl::any_cast<int>(o));
+  }
+
+  {
+    const CopyOnly copy_only(5);
+    absl::any o;
+    o = copy_only;
+    EXPECT_EQ(5, absl::any_cast<CopyOnly&>(o).value);
+  }
+
+  static_assert(!std::is_assignable<MoveOnly, absl::any>::value, "");
+}
+
+// Suppress MSVC warnings.
+// 4521: multiple copy constructors specified
+// We wrote multiple of them to test that the correct overloads are selected.
+#ifdef _MSC_VER
+#pragma warning( push )
+#pragma warning( disable : 4521)
+#endif
+
+// Weird type for testing, only used to make sure we "properly" perfect-forward
+// when being placed into an absl::any (use the l-value constructor if given an
+// l-value rather than use the copy constructor).
+struct WeirdConstructor42 {
+  explicit WeirdConstructor42(int value) : value(value) {}
+
+  // Copy-constructor
+  WeirdConstructor42(const WeirdConstructor42& other) : value(other.value) {}
+
+  // L-value "weird" constructor (used when given an l-value)
+  WeirdConstructor42(
+      WeirdConstructor42& /*other*/)  // NOLINT(runtime/references)
+      : value(42) {}
+
+  int value;
+};
+#ifdef _MSC_VER
+#pragma warning( pop )
+#endif
+
+TEST(AnyTest, WeirdConversionConstruction) {
+  {
+    const WeirdConstructor42 source(5);
+    absl::any o = source;  // Actual copy
+    EXPECT_EQ(5, absl::any_cast<WeirdConstructor42&>(o).value);
+  }
+
+  {
+    WeirdConstructor42 source(5);
+    absl::any o = source;  // Weird "conversion"
+    EXPECT_EQ(42, absl::any_cast<WeirdConstructor42&>(o).value);
+  }
+}
+
+TEST(AnyTest, WeirdConversionAssignment) {
+  {
+    const WeirdConstructor42 source(5);
+    absl::any o;
+    o = source;  // Actual copy
+    EXPECT_EQ(5, absl::any_cast<WeirdConstructor42&>(o).value);
+  }
+
+  {
+    WeirdConstructor42 source(5);
+    absl::any o;
+    o = source;  // Weird "conversion"
+    EXPECT_EQ(42, absl::any_cast<WeirdConstructor42&>(o).value);
+  }
+}
+
+struct Value {};
+
+TEST(AnyTest, AnyCastValue) {
+  {
+    absl::any o;
+    o.emplace<int>(5);
+    EXPECT_EQ(5, absl::any_cast<int>(o));
+    EXPECT_EQ(5, absl::any_cast<int>(AsConst(o)));
+    static_assert(
+        std::is_same<decltype(absl::any_cast<Value>(o)), Value>::value, "");
+  }
+
+  {
+    absl::any o;
+    o.emplace<int>(5);
+    EXPECT_EQ(5, absl::any_cast<const int>(o));
+    EXPECT_EQ(5, absl::any_cast<const int>(AsConst(o)));
+    static_assert(std::is_same<decltype(absl::any_cast<const Value>(o)),
+                               const Value>::value,
+                  "");
+  }
+}
+
+TEST(AnyTest, AnyCastReference) {
+  {
+    absl::any o;
+    o.emplace<int>(5);
+    EXPECT_EQ(5, absl::any_cast<int&>(o));
+    EXPECT_EQ(5, absl::any_cast<const int&>(AsConst(o)));
+    static_assert(
+        std::is_same<decltype(absl::any_cast<Value&>(o)), Value&>::value, "");
+  }
+
+  {
+    absl::any o;
+    o.emplace<int>(5);
+    EXPECT_EQ(5, absl::any_cast<const int>(o));
+    EXPECT_EQ(5, absl::any_cast<const int>(AsConst(o)));
+    static_assert(std::is_same<decltype(absl::any_cast<const Value&>(o)),
+                               const Value&>::value,
+                  "");
+  }
+
+  {
+    absl::any o;
+    o.emplace<int>(5);
+    EXPECT_EQ(5, absl::any_cast<int&&>(std::move(o)));
+    static_assert(std::is_same<decltype(absl::any_cast<Value&&>(std::move(o))),
+                               Value&&>::value,
+                  "");
+  }
+
+  {
+    absl::any o;
+    o.emplace<int>(5);
+    EXPECT_EQ(5, absl::any_cast<const int>(std::move(o)));
+    static_assert(
+        std::is_same<decltype(absl::any_cast<const Value&&>(std::move(o))),
+                     const Value&&>::value,
+        "");
+  }
+}
+
+TEST(AnyTest, AnyCastPointer) {
+  {
+    absl::any o;
+    EXPECT_EQ(nullptr, absl::any_cast<char>(&o));
+    o.emplace<int>(5);
+    EXPECT_EQ(nullptr, absl::any_cast<char>(&o));
+    o.emplace<char>('a');
+    EXPECT_EQ('a', *absl::any_cast<char>(&o));
+    static_assert(
+        std::is_same<decltype(absl::any_cast<Value>(&o)), Value*>::value, "");
+  }
+
+  {
+    absl::any o;
+    EXPECT_EQ(nullptr, absl::any_cast<const char>(&o));
+    o.emplace<int>(5);
+    EXPECT_EQ(nullptr, absl::any_cast<const char>(&o));
+    o.emplace<char>('a');
+    EXPECT_EQ('a', *absl::any_cast<const char>(&o));
+    static_assert(std::is_same<decltype(absl::any_cast<const Value>(&o)),
+                               const Value*>::value,
+                  "");
+  }
+}
+
+TEST(AnyTest, MakeAny) {
+  const CopyOnly copy_only{};
+  auto o = absl::make_any<IntMoveOnlyCopyOnly>(5, MoveOnly(), copy_only);
+  static_assert(std::is_same<decltype(o), absl::any>::value, "");
+  EXPECT_EQ(5, absl::any_cast<IntMoveOnlyCopyOnly&>(o).value);
+}
+
+TEST(AnyTest, MakeAnyIList) {
+  const CopyOnly copy_only{};
+  auto o =
+      absl::make_any<ListMoveOnlyCopyOnly>({1, 2, 3}, MoveOnly(), copy_only);
+  static_assert(std::is_same<decltype(o), absl::any>::value, "");
+  ListMoveOnlyCopyOnly& v = absl::any_cast<ListMoveOnlyCopyOnly&>(o);
+  std::vector<int> expected_values = {1, 2, 3};
+  EXPECT_EQ(expected_values, v.values);
+}
+
+// Test the use of copy constructor and operator=
+TEST(AnyTest, Copy) {
+  InstanceTracker tracker_raii;
+
+  {
+    absl::any o(absl::in_place_type<CopyableOnlyInstance>, 123);
+    CopyableOnlyInstance* f1 = absl::any_cast<CopyableOnlyInstance>(&o);
+
+    absl::any o2(o);
+    const CopyableOnlyInstance* f2 = absl::any_cast<CopyableOnlyInstance>(&o2);
+    EXPECT_EQ(123, f2->value());
+    EXPECT_NE(f1, f2);
+
+    absl::any o3;
+    o3 = o2;
+    const CopyableOnlyInstance* f3 = absl::any_cast<CopyableOnlyInstance>(&o3);
+    EXPECT_EQ(123, f3->value());
+    EXPECT_NE(f2, f3);
+
+    const absl::any o4(4);
+    // copy construct from const lvalue ref.
+    absl::any o5 = o4;
+    EXPECT_EQ(4, absl::any_cast<int>(o4));
+    EXPECT_EQ(4, absl::any_cast<int>(o5));
+
+    // Copy construct from const rvalue ref.
+    absl::any o6 = std::move(o4);  // NOLINT
+    EXPECT_EQ(4, absl::any_cast<int>(o4));
+    EXPECT_EQ(4, absl::any_cast<int>(o6));
+  }
+}
+
+TEST(AnyTest, Move) {
+  InstanceTracker tracker_raii;
+
+  absl::any any1;
+  any1.emplace<CopyableOnlyInstance>(5);
+
+  // This is a copy, so copy count increases to 1.
+  absl::any any2 = any1;
+  EXPECT_EQ(5, absl::any_cast<CopyableOnlyInstance&>(any1).value());
+  EXPECT_EQ(5, absl::any_cast<CopyableOnlyInstance&>(any2).value());
+  EXPECT_EQ(1, tracker_raii.copies());
+
+  // This isn't a copy, so copy count doesn't increase.
+  absl::any any3 = std::move(any2);
+  EXPECT_EQ(5, absl::any_cast<CopyableOnlyInstance&>(any3).value());
+  EXPECT_EQ(1, tracker_raii.copies());
+
+  absl::any any4;
+  any4 = std::move(any3);
+  EXPECT_EQ(5, absl::any_cast<CopyableOnlyInstance&>(any4).value());
+  EXPECT_EQ(1, tracker_raii.copies());
+
+  absl::any tmp4(4);
+  absl::any o4(std::move(tmp4));  // move construct
+  EXPECT_EQ(4, absl::any_cast<int>(o4));
+  o4 = *&o4;  // self assign
+  EXPECT_EQ(4, absl::any_cast<int>(o4));
+  EXPECT_TRUE(o4.has_value());
+
+  absl::any o5;
+  absl::any tmp5(5);
+  o5 = std::move(tmp5);  // move assign
+  EXPECT_EQ(5, absl::any_cast<int>(o5));
+}
+
+// Reset the ObjectOwner with an object of a different type
+TEST(AnyTest, Reset) {
+  absl::any o;
+  o.emplace<int>();
+
+  o.reset();
+  EXPECT_FALSE(o.has_value());
+
+  o.emplace<char>();
+  EXPECT_TRUE(o.has_value());
+}
+
+TEST(AnyTest, ConversionConstructionCausesOneCopy) {
+  InstanceTracker tracker_raii;
+  CopyableOnlyInstance counter(5);
+  absl::any o(counter);
+  EXPECT_EQ(5, absl::any_cast<CopyableOnlyInstance&>(o).value());
+  EXPECT_EQ(1, tracker_raii.copies());
+}
+
+//////////////////////////////////
+// Tests for Exception Behavior //
+//////////////////////////////////
+
+#if defined(ABSL_USES_STD_ANY)
+
+// If using a std `any` implementation, we can't check for a specific message.
+#define ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(...)                      \
+  ABSL_BASE_INTERNAL_EXPECT_FAIL((__VA_ARGS__), absl::bad_any_cast, \
+                                 "")
+
+#else
+
+// If using the absl `any` implementation, we can rely on a specific message.
+#define ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(...)                      \
+  ABSL_BASE_INTERNAL_EXPECT_FAIL((__VA_ARGS__), absl::bad_any_cast, \
+                                 "Bad any cast")
+
+#endif  // defined(ABSL_USES_STD_ANY)
+
+TEST(AnyTest, ThrowBadAlloc) {
+  {
+    absl::any a;
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<int&>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const int&>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<int&&>(absl::any{}));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const int&&>(absl::any{}));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<int>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const int>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<int>(absl::any{}));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const int>(absl::any{}));
+
+    // const absl::any operand
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const int&>(AsConst(a)));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<int>(AsConst(a)));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const int>(AsConst(a)));
+  }
+
+  {
+    absl::any a(absl::in_place_type<int>);
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<float&>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const float&>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<float&&>(absl::any{}));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(
+        absl::any_cast<const float&&>(absl::any{}));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<float>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const float>(a));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<float>(absl::any{}));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const float>(absl::any{}));
+
+    // const absl::any operand
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const float&>(AsConst(a)));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<float>(AsConst(a)));
+    ABSL_ANY_TEST_EXPECT_BAD_ANY_CAST(absl::any_cast<const float>(AsConst(a)));
+  }
+}
+
+class BadCopy {};
+
+struct BadCopyable {
+  BadCopyable() = default;
+  BadCopyable(BadCopyable&&) = default;
+  BadCopyable(const BadCopyable&) {
+#ifdef ABSL_HAVE_EXCEPTIONS
+    throw BadCopy();
+#else
+    ABSL_RAW_LOG(FATAL, "Bad copy");
+#endif
+  }
+};
+
+#define ABSL_ANY_TEST_EXPECT_BAD_COPY(...) \
+  ABSL_BASE_INTERNAL_EXPECT_FAIL((__VA_ARGS__), BadCopy, "Bad copy")
+
+// Test the guarantees regarding exceptions in copy/assign.
+TEST(AnyTest, FailedCopy) {
+  {
+    const BadCopyable bad{};
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(absl::any{bad});
+  }
+
+  {
+    absl::any src(absl::in_place_type<BadCopyable>);
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(absl::any{src});
+  }
+
+  {
+    BadCopyable bad;
+    absl::any target;
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(target = bad);
+  }
+
+  {
+    BadCopyable bad;
+    absl::any target(absl::in_place_type<BadCopyable>);
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(target = bad);
+    EXPECT_TRUE(target.has_value());
+  }
+
+  {
+    absl::any src(absl::in_place_type<BadCopyable>);
+    absl::any target;
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(target = src);
+    EXPECT_FALSE(target.has_value());
+  }
+
+  {
+    absl::any src(absl::in_place_type<BadCopyable>);
+    absl::any target(absl::in_place_type<BadCopyable>);
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(target = src);
+    EXPECT_TRUE(target.has_value());
+  }
+}
+
+// Test the guarantees regarding exceptions in emplace.
+TEST(AnyTest, FailedEmplace) {
+  {
+    BadCopyable bad;
+    absl::any target;
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(target.emplace<BadCopyable>(bad));
+  }
+
+  {
+    BadCopyable bad;
+    absl::any target(absl::in_place_type<int>);
+    ABSL_ANY_TEST_EXPECT_BAD_COPY(target.emplace<BadCopyable>(bad));
+#if defined(ABSL_USES_STD_ANY) && defined(__GLIBCXX__)
+    // libstdc++ std::any::emplace() implementation (as of 7.2) has a bug: if an
+    // exception is thrown, *this contains a value.
+#define ABSL_GLIBCXX_ANY_EMPLACE_EXCEPTION_BUG 1
+#endif
+#if defined(ABSL_HAVE_EXCEPTIONS) && \
+    !defined(ABSL_GLIBCXX_ANY_EMPLACE_EXCEPTION_BUG)
+    EXPECT_FALSE(target.has_value());
+#endif
+  }
+}
+
+}  // namespace
+
+#endif  // #if !defined(ABSL_USES_STD_ANY)
diff --git a/third_party/abseil_cpp/absl/types/bad_any_cast.cc b/third_party/abseil_cpp/absl/types/bad_any_cast.cc
new file mode 100644
index 0000000000..b0592cc9bc
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/bad_any_cast.cc
@@ -0,0 +1,46 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/bad_any_cast.h"
+
+#ifndef ABSL_USES_STD_ANY
+
+#include <cstdlib>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+bad_any_cast::~bad_any_cast() = default;
+
+const char* bad_any_cast::what() const noexcept { return "Bad any cast"; }
+
+namespace any_internal {
+
+void ThrowBadAnyCast() {
+#ifdef ABSL_HAVE_EXCEPTIONS
+  throw bad_any_cast();
+#else
+  ABSL_RAW_LOG(FATAL, "Bad any cast");
+  std::abort();
+#endif
+}
+
+}  // namespace any_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USES_STD_ANY
diff --git a/third_party/abseil_cpp/absl/types/bad_any_cast.h b/third_party/abseil_cpp/absl/types/bad_any_cast.h
new file mode 100644
index 0000000000..114cef80cd
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/bad_any_cast.h
@@ -0,0 +1,75 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// bad_any_cast.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines the `absl::bad_any_cast` type.
+
+#ifndef ABSL_TYPES_BAD_ANY_CAST_H_
+#define ABSL_TYPES_BAD_ANY_CAST_H_
+
+#include <typeinfo>
+
+#include "absl/base/config.h"
+
+#ifdef ABSL_USES_STD_ANY
+
+#include <any>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using std::bad_any_cast;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_ANY
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// -----------------------------------------------------------------------------
+// bad_any_cast
+// -----------------------------------------------------------------------------
+//
+// An `absl::bad_any_cast` type is an exception type that is thrown when
+// failing to successfully cast the return value of an `absl::any` object.
+//
+// Example:
+//
+//   auto a = absl::any(65);
+//   absl::any_cast<int>(a);         // 65
+//   try {
+//     absl::any_cast<char>(a);
+//   } catch(const absl::bad_any_cast& e) {
+//     std::cout << "Bad any cast: " << e.what() << '\n';
+//   }
+class bad_any_cast : public std::bad_cast {
+ public:
+  ~bad_any_cast() override;
+  const char* what() const noexcept override;
+};
+
+namespace any_internal {
+
+[[noreturn]] void ThrowBadAnyCast();
+
+}  // namespace any_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USES_STD_ANY
+
+#endif  // ABSL_TYPES_BAD_ANY_CAST_H_
diff --git a/third_party/abseil_cpp/absl/types/bad_optional_access.cc b/third_party/abseil_cpp/absl/types/bad_optional_access.cc
new file mode 100644
index 0000000000..26aca70d9c
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/bad_optional_access.cc
@@ -0,0 +1,48 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/bad_optional_access.h"
+
+#ifndef ABSL_USES_STD_OPTIONAL
+
+#include <cstdlib>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+bad_optional_access::~bad_optional_access() = default;
+
+const char* bad_optional_access::what() const noexcept {
+  return "optional has no value";
+}
+
+namespace optional_internal {
+
+void throw_bad_optional_access() {
+#ifdef ABSL_HAVE_EXCEPTIONS
+  throw bad_optional_access();
+#else
+  ABSL_RAW_LOG(FATAL, "Bad optional access");
+  abort();
+#endif
+}
+
+}  // namespace optional_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USES_STD_OPTIONAL
diff --git a/third_party/abseil_cpp/absl/types/bad_optional_access.h b/third_party/abseil_cpp/absl/types/bad_optional_access.h
new file mode 100644
index 0000000000..a500286adc
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/bad_optional_access.h
@@ -0,0 +1,78 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// bad_optional_access.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines the `absl::bad_optional_access` type.
+
+#ifndef ABSL_TYPES_BAD_OPTIONAL_ACCESS_H_
+#define ABSL_TYPES_BAD_OPTIONAL_ACCESS_H_
+
+#include <stdexcept>
+
+#include "absl/base/config.h"
+
+#ifdef ABSL_USES_STD_OPTIONAL
+
+#include <optional>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using std::bad_optional_access;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_OPTIONAL
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// -----------------------------------------------------------------------------
+// bad_optional_access
+// -----------------------------------------------------------------------------
+//
+// An `absl::bad_optional_access` type is an exception type that is thrown when
+// attempting to access an `absl::optional` object that does not contain a
+// value.
+//
+// Example:
+//
+//   absl::optional<int> o;
+//
+//   try {
+//     int n = o.value();
+//   } catch(const absl::bad_optional_access& e) {
+//     std::cout << "Bad optional access: " << e.what() << '\n';
+//   }
+class bad_optional_access : public std::exception {
+ public:
+  bad_optional_access() = default;
+  ~bad_optional_access() override;
+  const char* what() const noexcept override;
+};
+
+namespace optional_internal {
+
+// throw delegator
+[[noreturn]] void throw_bad_optional_access();
+
+}  // namespace optional_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USES_STD_OPTIONAL
+
+#endif  // ABSL_TYPES_BAD_OPTIONAL_ACCESS_H_
diff --git a/third_party/abseil_cpp/absl/types/bad_variant_access.cc b/third_party/abseil_cpp/absl/types/bad_variant_access.cc
new file mode 100644
index 0000000000..3dc88cc09f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/bad_variant_access.cc
@@ -0,0 +1,64 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/bad_variant_access.h"
+
+#ifndef ABSL_USES_STD_VARIANT
+
+#include <cstdlib>
+#include <stdexcept>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+//////////////////////////
+// [variant.bad.access] //
+//////////////////////////
+
+bad_variant_access::~bad_variant_access() = default;
+
+const char* bad_variant_access::what() const noexcept {
+  return "Bad variant access";
+}
+
+namespace variant_internal {
+
+void ThrowBadVariantAccess() {
+#ifdef ABSL_HAVE_EXCEPTIONS
+  throw bad_variant_access();
+#else
+  ABSL_RAW_LOG(FATAL, "Bad variant access");
+  abort();  // TODO(calabrese) Remove once RAW_LOG FATAL is noreturn.
+#endif
+}
+
+void Rethrow() {
+#ifdef ABSL_HAVE_EXCEPTIONS
+  throw;
+#else
+  ABSL_RAW_LOG(FATAL,
+               "Internal error in absl::variant implementation. Attempted to "
+               "rethrow an exception when building with exceptions disabled.");
+  abort();  // TODO(calabrese) Remove once RAW_LOG FATAL is noreturn.
+#endif
+}
+
+}  // namespace variant_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USES_STD_VARIANT
diff --git a/third_party/abseil_cpp/absl/types/bad_variant_access.h b/third_party/abseil_cpp/absl/types/bad_variant_access.h
new file mode 100644
index 0000000000..095969f91e
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/bad_variant_access.h
@@ -0,0 +1,82 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// bad_variant_access.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines the `absl::bad_variant_access` type.
+
+#ifndef ABSL_TYPES_BAD_VARIANT_ACCESS_H_
+#define ABSL_TYPES_BAD_VARIANT_ACCESS_H_
+
+#include <stdexcept>
+
+#include "absl/base/config.h"
+
+#ifdef ABSL_USES_STD_VARIANT
+
+#include <variant>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using std::bad_variant_access;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_VARIANT
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// -----------------------------------------------------------------------------
+// bad_variant_access
+// -----------------------------------------------------------------------------
+//
+// An `absl::bad_variant_access` type is an exception type that is thrown in
+// the following cases:
+//
+//   * Calling `absl::get(absl::variant) with an index or type that does not
+//     match the currently selected alternative type
+//   * Calling `absl::visit on an `absl::variant` that is in the
+//     `variant::valueless_by_exception` state.
+//
+// Example:
+//
+//   absl::variant<int, std::string> v;
+//   v = 1;
+//   try {
+//     absl::get<std::string>(v);
+//   } catch(const absl::bad_variant_access& e) {
+//     std::cout << "Bad variant access: " << e.what() << '\n';
+//   }
+class bad_variant_access : public std::exception {
+ public:
+  bad_variant_access() noexcept = default;
+  ~bad_variant_access() override;
+  const char* what() const noexcept override;
+};
+
+namespace variant_internal {
+
+[[noreturn]] void ThrowBadVariantAccess();
+[[noreturn]] void Rethrow();
+
+}  // namespace variant_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USES_STD_VARIANT
+
+#endif  // ABSL_TYPES_BAD_VARIANT_ACCESS_H_
diff --git a/third_party/abseil_cpp/absl/types/compare.h b/third_party/abseil_cpp/absl/types/compare.h
new file mode 100644
index 0000000000..62ca70f9a7
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/compare.h
@@ -0,0 +1,598 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// compare.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines the `absl::weak_equality`, `absl::strong_equality`,
+// `absl::partial_ordering`, `absl::weak_ordering`, and `absl::strong_ordering`
+// types for storing the results of three way comparisons.
+//
+// Example:
+//   absl::weak_ordering compare(const std::string& a, const std::string& b);
+//
+// These are C++11 compatible versions of the C++20 corresponding types
+// (`std::weak_equality`, etc.) and are designed to be drop-in replacements
+// for code compliant with C++20.
+
+#ifndef ABSL_TYPES_COMPARE_H_
+#define ABSL_TYPES_COMPARE_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <type_traits>
+
+#include "absl/base/attributes.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace compare_internal {
+
+using value_type = int8_t;
+
+template <typename T>
+struct Fail {
+  static_assert(sizeof(T) < 0, "Only literal `0` is allowed.");
+};
+
+// We need the NullPtrT template to avoid triggering the modernize-use-nullptr
+// ClangTidy warning in user code.
+template <typename NullPtrT = std::nullptr_t>
+struct OnlyLiteralZero {
+  constexpr OnlyLiteralZero(NullPtrT) noexcept {}  // NOLINT
+
+  // Fails compilation when `nullptr` or integral type arguments other than
+  // `int` are passed. This constructor doesn't accept `int` because literal `0`
+  // has type `int`. Literal `0` arguments will be implicitly converted to
+  // `std::nullptr_t` and accepted by the above constructor, while other `int`
+  // arguments will fail to be converted and cause compilation failure.
+  template <
+      typename T,
+      typename = typename std::enable_if<
+          std::is_same<T, std::nullptr_t>::value ||
+          (std::is_integral<T>::value && !std::is_same<T, int>::value)>::type,
+      typename = typename Fail<T>::type>
+  OnlyLiteralZero(T);  // NOLINT
+};
+
+enum class eq : value_type {
+  equal = 0,
+  equivalent = equal,
+  nonequal = 1,
+  nonequivalent = nonequal,
+};
+
+enum class ord : value_type { less = -1, greater = 1 };
+
+enum class ncmp : value_type { unordered = -127 };
+
+// Define macros to allow for creation or emulation of C++17 inline variables
+// based on whether the feature is supported. Note: we can't use
+// ABSL_INTERNAL_INLINE_CONSTEXPR here because the variables here are of
+// incomplete types so they need to be defined after the types are complete.
+#ifdef __cpp_inline_variables
+
+#define ABSL_COMPARE_INLINE_BASECLASS_DECL(name)
+
+#define ABSL_COMPARE_INLINE_SUBCLASS_DECL(type, name) \
+  static const type name
+
+#define ABSL_COMPARE_INLINE_INIT(type, name, init) \
+  inline constexpr type type::name(init)
+
+#else  // __cpp_inline_variables
+
+#define ABSL_COMPARE_INLINE_BASECLASS_DECL(name) \
+  ABSL_CONST_INIT static const T name
+
+#define ABSL_COMPARE_INLINE_SUBCLASS_DECL(type, name)
+
+#define ABSL_COMPARE_INLINE_INIT(type, name, init) \
+  template <typename T>                            \
+  const T compare_internal::type##_base<T>::name(init)
+
+#endif  // __cpp_inline_variables
+
+// These template base classes allow for defining the values of the constants
+// in the header file (for performance) without using inline variables (which
+// aren't available in C++11).
+template <typename T>
+struct weak_equality_base {
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(nonequivalent);
+};
+
+template <typename T>
+struct strong_equality_base {
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equal);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(nonequal);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(nonequivalent);
+};
+
+template <typename T>
+struct partial_ordering_base {
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(less);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(greater);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(unordered);
+};
+
+template <typename T>
+struct weak_ordering_base {
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(less);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(greater);
+};
+
+template <typename T>
+struct strong_ordering_base {
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(less);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equal);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(equivalent);
+  ABSL_COMPARE_INLINE_BASECLASS_DECL(greater);
+};
+
+}  // namespace compare_internal
+
+class weak_equality
+    : public compare_internal::weak_equality_base<weak_equality> {
+  explicit constexpr weak_equality(compare_internal::eq v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  friend struct compare_internal::weak_equality_base<weak_equality>;
+
+ public:
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_equality, equivalent);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_equality, nonequivalent);
+
+  // Comparisons
+  friend constexpr bool operator==(
+      weak_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ == 0;
+  }
+  friend constexpr bool operator!=(
+      weak_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ != 0;
+  }
+  friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+                                   weak_equality v) noexcept {
+    return 0 == v.value_;
+  }
+  friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+                                   weak_equality v) noexcept {
+    return 0 != v.value_;
+  }
+  friend constexpr bool operator==(weak_equality v1,
+                                   weak_equality v2) noexcept {
+    return v1.value_ == v2.value_;
+  }
+  friend constexpr bool operator!=(weak_equality v1,
+                                   weak_equality v2) noexcept {
+    return v1.value_ != v2.value_;
+  }
+
+ private:
+  compare_internal::value_type value_;
+};
+ABSL_COMPARE_INLINE_INIT(weak_equality, equivalent,
+                         compare_internal::eq::equivalent);
+ABSL_COMPARE_INLINE_INIT(weak_equality, nonequivalent,
+                         compare_internal::eq::nonequivalent);
+
+class strong_equality
+    : public compare_internal::strong_equality_base<strong_equality> {
+  explicit constexpr strong_equality(compare_internal::eq v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  friend struct compare_internal::strong_equality_base<strong_equality>;
+
+ public:
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_equality, equal);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_equality, nonequal);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_equality, equivalent);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_equality, nonequivalent);
+
+  // Conversion
+  constexpr operator weak_equality() const noexcept {  // NOLINT
+    return value_ == 0 ? weak_equality::equivalent
+                       : weak_equality::nonequivalent;
+  }
+  // Comparisons
+  friend constexpr bool operator==(
+      strong_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ == 0;
+  }
+  friend constexpr bool operator!=(
+      strong_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ != 0;
+  }
+  friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+                                   strong_equality v) noexcept {
+    return 0 == v.value_;
+  }
+  friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+                                   strong_equality v) noexcept {
+    return 0 != v.value_;
+  }
+  friend constexpr bool operator==(strong_equality v1,
+                                   strong_equality v2) noexcept {
+    return v1.value_ == v2.value_;
+  }
+  friend constexpr bool operator!=(strong_equality v1,
+                                   strong_equality v2) noexcept {
+    return v1.value_ != v2.value_;
+  }
+
+ private:
+  compare_internal::value_type value_;
+};
+ABSL_COMPARE_INLINE_INIT(strong_equality, equal, compare_internal::eq::equal);
+ABSL_COMPARE_INLINE_INIT(strong_equality, nonequal,
+                         compare_internal::eq::nonequal);
+ABSL_COMPARE_INLINE_INIT(strong_equality, equivalent,
+                         compare_internal::eq::equivalent);
+ABSL_COMPARE_INLINE_INIT(strong_equality, nonequivalent,
+                         compare_internal::eq::nonequivalent);
+
+class partial_ordering
+    : public compare_internal::partial_ordering_base<partial_ordering> {
+  explicit constexpr partial_ordering(compare_internal::eq v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  explicit constexpr partial_ordering(compare_internal::ord v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  explicit constexpr partial_ordering(compare_internal::ncmp v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  friend struct compare_internal::partial_ordering_base<partial_ordering>;
+
+  constexpr bool is_ordered() const noexcept {
+    return value_ !=
+           compare_internal::value_type(compare_internal::ncmp::unordered);
+  }
+
+ public:
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, less);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, equivalent);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, greater);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(partial_ordering, unordered);
+
+  // Conversion
+  constexpr operator weak_equality() const noexcept {  // NOLINT
+    return value_ == 0 ? weak_equality::equivalent
+                       : weak_equality::nonequivalent;
+  }
+  // Comparisons
+  friend constexpr bool operator==(
+      partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.is_ordered() && v.value_ == 0;
+  }
+  friend constexpr bool operator!=(
+      partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return !v.is_ordered() || v.value_ != 0;
+  }
+  friend constexpr bool operator<(
+      partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.is_ordered() && v.value_ < 0;
+  }
+  friend constexpr bool operator<=(
+      partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.is_ordered() && v.value_ <= 0;
+  }
+  friend constexpr bool operator>(
+      partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.is_ordered() && v.value_ > 0;
+  }
+  friend constexpr bool operator>=(
+      partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.is_ordered() && v.value_ >= 0;
+  }
+  friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+                                   partial_ordering v) noexcept {
+    return v.is_ordered() && 0 == v.value_;
+  }
+  friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+                                   partial_ordering v) noexcept {
+    return !v.is_ordered() || 0 != v.value_;
+  }
+  friend constexpr bool operator<(compare_internal::OnlyLiteralZero<>,
+                                  partial_ordering v) noexcept {
+    return v.is_ordered() && 0 < v.value_;
+  }
+  friend constexpr bool operator<=(compare_internal::OnlyLiteralZero<>,
+                                   partial_ordering v) noexcept {
+    return v.is_ordered() && 0 <= v.value_;
+  }
+  friend constexpr bool operator>(compare_internal::OnlyLiteralZero<>,
+                                  partial_ordering v) noexcept {
+    return v.is_ordered() && 0 > v.value_;
+  }
+  friend constexpr bool operator>=(compare_internal::OnlyLiteralZero<>,
+                                   partial_ordering v) noexcept {
+    return v.is_ordered() && 0 >= v.value_;
+  }
+  friend constexpr bool operator==(partial_ordering v1,
+                                   partial_ordering v2) noexcept {
+    return v1.value_ == v2.value_;
+  }
+  friend constexpr bool operator!=(partial_ordering v1,
+                                   partial_ordering v2) noexcept {
+    return v1.value_ != v2.value_;
+  }
+
+ private:
+  compare_internal::value_type value_;
+};
+ABSL_COMPARE_INLINE_INIT(partial_ordering, less, compare_internal::ord::less);
+ABSL_COMPARE_INLINE_INIT(partial_ordering, equivalent,
+                         compare_internal::eq::equivalent);
+ABSL_COMPARE_INLINE_INIT(partial_ordering, greater,
+                         compare_internal::ord::greater);
+ABSL_COMPARE_INLINE_INIT(partial_ordering, unordered,
+                         compare_internal::ncmp::unordered);
+
+class weak_ordering
+    : public compare_internal::weak_ordering_base<weak_ordering> {
+  explicit constexpr weak_ordering(compare_internal::eq v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  explicit constexpr weak_ordering(compare_internal::ord v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  friend struct compare_internal::weak_ordering_base<weak_ordering>;
+
+ public:
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_ordering, less);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_ordering, equivalent);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(weak_ordering, greater);
+
+  // Conversions
+  constexpr operator weak_equality() const noexcept {  // NOLINT
+    return value_ == 0 ? weak_equality::equivalent
+                       : weak_equality::nonequivalent;
+  }
+  constexpr operator partial_ordering() const noexcept {  // NOLINT
+    return value_ == 0 ? partial_ordering::equivalent
+                       : (value_ < 0 ? partial_ordering::less
+                                     : partial_ordering::greater);
+  }
+  // Comparisons
+  friend constexpr bool operator==(
+      weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ == 0;
+  }
+  friend constexpr bool operator!=(
+      weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ != 0;
+  }
+  friend constexpr bool operator<(
+      weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ < 0;
+  }
+  friend constexpr bool operator<=(
+      weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ <= 0;
+  }
+  friend constexpr bool operator>(
+      weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ > 0;
+  }
+  friend constexpr bool operator>=(
+      weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ >= 0;
+  }
+  friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+                                   weak_ordering v) noexcept {
+    return 0 == v.value_;
+  }
+  friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+                                   weak_ordering v) noexcept {
+    return 0 != v.value_;
+  }
+  friend constexpr bool operator<(compare_internal::OnlyLiteralZero<>,
+                                  weak_ordering v) noexcept {
+    return 0 < v.value_;
+  }
+  friend constexpr bool operator<=(compare_internal::OnlyLiteralZero<>,
+                                   weak_ordering v) noexcept {
+    return 0 <= v.value_;
+  }
+  friend constexpr bool operator>(compare_internal::OnlyLiteralZero<>,
+                                  weak_ordering v) noexcept {
+    return 0 > v.value_;
+  }
+  friend constexpr bool operator>=(compare_internal::OnlyLiteralZero<>,
+                                   weak_ordering v) noexcept {
+    return 0 >= v.value_;
+  }
+  friend constexpr bool operator==(weak_ordering v1,
+                                   weak_ordering v2) noexcept {
+    return v1.value_ == v2.value_;
+  }
+  friend constexpr bool operator!=(weak_ordering v1,
+                                   weak_ordering v2) noexcept {
+    return v1.value_ != v2.value_;
+  }
+
+ private:
+  compare_internal::value_type value_;
+};
+ABSL_COMPARE_INLINE_INIT(weak_ordering, less, compare_internal::ord::less);
+ABSL_COMPARE_INLINE_INIT(weak_ordering, equivalent,
+                         compare_internal::eq::equivalent);
+ABSL_COMPARE_INLINE_INIT(weak_ordering, greater,
+                         compare_internal::ord::greater);
+
+class strong_ordering
+    : public compare_internal::strong_ordering_base<strong_ordering> {
+  explicit constexpr strong_ordering(compare_internal::eq v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  explicit constexpr strong_ordering(compare_internal::ord v) noexcept
+      : value_(static_cast<compare_internal::value_type>(v)) {}
+  friend struct compare_internal::strong_ordering_base<strong_ordering>;
+
+ public:
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, less);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, equal);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, equivalent);
+  ABSL_COMPARE_INLINE_SUBCLASS_DECL(strong_ordering, greater);
+
+  // Conversions
+  constexpr operator weak_equality() const noexcept {  // NOLINT
+    return value_ == 0 ? weak_equality::equivalent
+                       : weak_equality::nonequivalent;
+  }
+  constexpr operator strong_equality() const noexcept {  // NOLINT
+    return value_ == 0 ? strong_equality::equal : strong_equality::nonequal;
+  }
+  constexpr operator partial_ordering() const noexcept {  // NOLINT
+    return value_ == 0 ? partial_ordering::equivalent
+                       : (value_ < 0 ? partial_ordering::less
+                                     : partial_ordering::greater);
+  }
+  constexpr operator weak_ordering() const noexcept {  // NOLINT
+    return value_ == 0
+               ? weak_ordering::equivalent
+               : (value_ < 0 ? weak_ordering::less : weak_ordering::greater);
+  }
+  // Comparisons
+  friend constexpr bool operator==(
+      strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ == 0;
+  }
+  friend constexpr bool operator!=(
+      strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ != 0;
+  }
+  friend constexpr bool operator<(
+      strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ < 0;
+  }
+  friend constexpr bool operator<=(
+      strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ <= 0;
+  }
+  friend constexpr bool operator>(
+      strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ > 0;
+  }
+  friend constexpr bool operator>=(
+      strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
+    return v.value_ >= 0;
+  }
+  friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
+                                   strong_ordering v) noexcept {
+    return 0 == v.value_;
+  }
+  friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
+                                   strong_ordering v) noexcept {
+    return 0 != v.value_;
+  }
+  friend constexpr bool operator<(compare_internal::OnlyLiteralZero<>,
+                                  strong_ordering v) noexcept {
+    return 0 < v.value_;
+  }
+  friend constexpr bool operator<=(compare_internal::OnlyLiteralZero<>,
+                                   strong_ordering v) noexcept {
+    return 0 <= v.value_;
+  }
+  friend constexpr bool operator>(compare_internal::OnlyLiteralZero<>,
+                                  strong_ordering v) noexcept {
+    return 0 > v.value_;
+  }
+  friend constexpr bool operator>=(compare_internal::OnlyLiteralZero<>,
+                                   strong_ordering v) noexcept {
+    return 0 >= v.value_;
+  }
+  friend constexpr bool operator==(strong_ordering v1,
+                                   strong_ordering v2) noexcept {
+    return v1.value_ == v2.value_;
+  }
+  friend constexpr bool operator!=(strong_ordering v1,
+                                   strong_ordering v2) noexcept {
+    return v1.value_ != v2.value_;
+  }
+
+ private:
+  compare_internal::value_type value_;
+};
+ABSL_COMPARE_INLINE_INIT(strong_ordering, less, compare_internal::ord::less);
+ABSL_COMPARE_INLINE_INIT(strong_ordering, equal, compare_internal::eq::equal);
+ABSL_COMPARE_INLINE_INIT(strong_ordering, equivalent,
+                         compare_internal::eq::equivalent);
+ABSL_COMPARE_INLINE_INIT(strong_ordering, greater,
+                         compare_internal::ord::greater);
+
+#undef ABSL_COMPARE_INLINE_BASECLASS_DECL
+#undef ABSL_COMPARE_INLINE_SUBCLASS_DECL
+#undef ABSL_COMPARE_INLINE_INIT
+
+namespace compare_internal {
+// We also provide these comparator adapter functions for internal absl use.
+
+// Helper functions to do a boolean comparison of two keys given a boolean
+// or three-way comparator.
+// SFINAE prevents implicit conversions to bool (such as from int).
+template <typename Bool,
+          absl::enable_if_t<std::is_same<bool, Bool>::value, int> = 0>
+constexpr bool compare_result_as_less_than(const Bool r) { return r; }
+constexpr bool compare_result_as_less_than(const absl::weak_ordering r) {
+  return r < 0;
+}
+
+template <typename Compare, typename K, typename LK>
+constexpr bool do_less_than_comparison(const Compare &compare, const K &x,
+                                       const LK &y) {
+  return compare_result_as_less_than(compare(x, y));
+}
+
+// Helper functions to do a three-way comparison of two keys given a boolean or
+// three-way comparator.
+// SFINAE prevents implicit conversions to int (such as from bool).
+template <typename Int,
+          absl::enable_if_t<std::is_same<int, Int>::value, int> = 0>
+constexpr absl::weak_ordering compare_result_as_ordering(const Int c) {
+  return c < 0 ? absl::weak_ordering::less
+               : c == 0 ? absl::weak_ordering::equivalent
+                        : absl::weak_ordering::greater;
+}
+constexpr absl::weak_ordering compare_result_as_ordering(
+    const absl::weak_ordering c) {
+  return c;
+}
+
+template <
+    typename Compare, typename K, typename LK,
+    absl::enable_if_t<!std::is_same<bool, absl::result_of_t<Compare(
+                                              const K &, const LK &)>>::value,
+                      int> = 0>
+constexpr absl::weak_ordering do_three_way_comparison(const Compare &compare,
+                                                      const K &x, const LK &y) {
+  return compare_result_as_ordering(compare(x, y));
+}
+template <
+    typename Compare, typename K, typename LK,
+    absl::enable_if_t<std::is_same<bool, absl::result_of_t<Compare(
+                                             const K &, const LK &)>>::value,
+                      int> = 0>
+constexpr absl::weak_ordering do_three_way_comparison(const Compare &compare,
+                                                      const K &x, const LK &y) {
+  return compare(x, y) ? absl::weak_ordering::less
+                       : compare(y, x) ? absl::weak_ordering::greater
+                                       : absl::weak_ordering::equivalent;
+}
+
+}  // namespace compare_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TYPES_COMPARE_H_
diff --git a/third_party/abseil_cpp/absl/types/compare_test.cc b/third_party/abseil_cpp/absl/types/compare_test.cc
new file mode 100644
index 0000000000..8095baf956
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/compare_test.cc
@@ -0,0 +1,389 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/compare.h"
+
+#include "gtest/gtest.h"
+#include "absl/base/casts.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace {
+
+// This is necessary to avoid a bunch of lint warnings suggesting that we use
+// EXPECT_EQ/etc., which doesn't work in this case because they convert the `0`
+// to an int, which can't be converted to the unspecified zero type.
+bool Identity(bool b) { return b; }
+
+TEST(Compare, WeakEquality) {
+  EXPECT_TRUE(Identity(weak_equality::equivalent == 0));
+  EXPECT_TRUE(Identity(0 == weak_equality::equivalent));
+  EXPECT_TRUE(Identity(weak_equality::nonequivalent != 0));
+  EXPECT_TRUE(Identity(0 != weak_equality::nonequivalent));
+  const weak_equality values[] = {weak_equality::equivalent,
+                                  weak_equality::nonequivalent};
+  for (const auto& lhs : values) {
+    for (const auto& rhs : values) {
+      const bool are_equal = &lhs == &rhs;
+      EXPECT_EQ(lhs == rhs, are_equal);
+      EXPECT_EQ(lhs != rhs, !are_equal);
+    }
+  }
+}
+
+TEST(Compare, StrongEquality) {
+  EXPECT_TRUE(Identity(strong_equality::equal == 0));
+  EXPECT_TRUE(Identity(0 == strong_equality::equal));
+  EXPECT_TRUE(Identity(strong_equality::nonequal != 0));
+  EXPECT_TRUE(Identity(0 != strong_equality::nonequal));
+  EXPECT_TRUE(Identity(strong_equality::equivalent == 0));
+  EXPECT_TRUE(Identity(0 == strong_equality::equivalent));
+  EXPECT_TRUE(Identity(strong_equality::nonequivalent != 0));
+  EXPECT_TRUE(Identity(0 != strong_equality::nonequivalent));
+  const strong_equality values[] = {strong_equality::equal,
+                                    strong_equality::nonequal};
+  for (const auto& lhs : values) {
+    for (const auto& rhs : values) {
+      const bool are_equal = &lhs == &rhs;
+      EXPECT_EQ(lhs == rhs, are_equal);
+      EXPECT_EQ(lhs != rhs, !are_equal);
+    }
+  }
+  EXPECT_TRUE(Identity(strong_equality::equivalent == strong_equality::equal));
+  EXPECT_TRUE(
+      Identity(strong_equality::nonequivalent == strong_equality::nonequal));
+}
+
+TEST(Compare, PartialOrdering) {
+  EXPECT_TRUE(Identity(partial_ordering::less < 0));
+  EXPECT_TRUE(Identity(0 > partial_ordering::less));
+  EXPECT_TRUE(Identity(partial_ordering::less <= 0));
+  EXPECT_TRUE(Identity(0 >= partial_ordering::less));
+  EXPECT_TRUE(Identity(partial_ordering::equivalent == 0));
+  EXPECT_TRUE(Identity(0 == partial_ordering::equivalent));
+  EXPECT_TRUE(Identity(partial_ordering::greater > 0));
+  EXPECT_TRUE(Identity(0 < partial_ordering::greater));
+  EXPECT_TRUE(Identity(partial_ordering::greater >= 0));
+  EXPECT_TRUE(Identity(0 <= partial_ordering::greater));
+  EXPECT_TRUE(Identity(partial_ordering::unordered != 0));
+  EXPECT_TRUE(Identity(0 != partial_ordering::unordered));
+  EXPECT_FALSE(Identity(partial_ordering::unordered < 0));
+  EXPECT_FALSE(Identity(0 < partial_ordering::unordered));
+  EXPECT_FALSE(Identity(partial_ordering::unordered <= 0));
+  EXPECT_FALSE(Identity(0 <= partial_ordering::unordered));
+  EXPECT_FALSE(Identity(partial_ordering::unordered > 0));
+  EXPECT_FALSE(Identity(0 > partial_ordering::unordered));
+  EXPECT_FALSE(Identity(partial_ordering::unordered >= 0));
+  EXPECT_FALSE(Identity(0 >= partial_ordering::unordered));
+  const partial_ordering values[] = {
+      partial_ordering::less, partial_ordering::equivalent,
+      partial_ordering::greater, partial_ordering::unordered};
+  for (const auto& lhs : values) {
+    for (const auto& rhs : values) {
+      const bool are_equal = &lhs == &rhs;
+      EXPECT_EQ(lhs == rhs, are_equal);
+      EXPECT_EQ(lhs != rhs, !are_equal);
+    }
+  }
+}
+
+TEST(Compare, WeakOrdering) {
+  EXPECT_TRUE(Identity(weak_ordering::less < 0));
+  EXPECT_TRUE(Identity(0 > weak_ordering::less));
+  EXPECT_TRUE(Identity(weak_ordering::less <= 0));
+  EXPECT_TRUE(Identity(0 >= weak_ordering::less));
+  EXPECT_TRUE(Identity(weak_ordering::equivalent == 0));
+  EXPECT_TRUE(Identity(0 == weak_ordering::equivalent));
+  EXPECT_TRUE(Identity(weak_ordering::greater > 0));
+  EXPECT_TRUE(Identity(0 < weak_ordering::greater));
+  EXPECT_TRUE(Identity(weak_ordering::greater >= 0));
+  EXPECT_TRUE(Identity(0 <= weak_ordering::greater));
+  const weak_ordering values[] = {
+      weak_ordering::less, weak_ordering::equivalent, weak_ordering::greater};
+  for (const auto& lhs : values) {
+    for (const auto& rhs : values) {
+      const bool are_equal = &lhs == &rhs;
+      EXPECT_EQ(lhs == rhs, are_equal);
+      EXPECT_EQ(lhs != rhs, !are_equal);
+    }
+  }
+}
+
+TEST(Compare, StrongOrdering) {
+  EXPECT_TRUE(Identity(strong_ordering::less < 0));
+  EXPECT_TRUE(Identity(0 > strong_ordering::less));
+  EXPECT_TRUE(Identity(strong_ordering::less <= 0));
+  EXPECT_TRUE(Identity(0 >= strong_ordering::less));
+  EXPECT_TRUE(Identity(strong_ordering::equal == 0));
+  EXPECT_TRUE(Identity(0 == strong_ordering::equal));
+  EXPECT_TRUE(Identity(strong_ordering::equivalent == 0));
+  EXPECT_TRUE(Identity(0 == strong_ordering::equivalent));
+  EXPECT_TRUE(Identity(strong_ordering::greater > 0));
+  EXPECT_TRUE(Identity(0 < strong_ordering::greater));
+  EXPECT_TRUE(Identity(strong_ordering::greater >= 0));
+  EXPECT_TRUE(Identity(0 <= strong_ordering::greater));
+  const strong_ordering values[] = {
+      strong_ordering::less, strong_ordering::equal, strong_ordering::greater};
+  for (const auto& lhs : values) {
+    for (const auto& rhs : values) {
+      const bool are_equal = &lhs == &rhs;
+      EXPECT_EQ(lhs == rhs, are_equal);
+      EXPECT_EQ(lhs != rhs, !are_equal);
+    }
+  }
+  EXPECT_TRUE(Identity(strong_ordering::equivalent == strong_ordering::equal));
+}
+
+TEST(Compare, Conversions) {
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_equality::equal) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_equality::nonequal) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_equality::equivalent) == 0));
+  EXPECT_TRUE(Identity(
+      implicit_cast<weak_equality>(strong_equality::nonequivalent) != 0));
+
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(partial_ordering::less) != 0));
+  EXPECT_TRUE(Identity(
+      implicit_cast<weak_equality>(partial_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(partial_ordering::greater) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(partial_ordering::unordered) != 0));
+
+  EXPECT_TRUE(implicit_cast<weak_equality>(weak_ordering::less) != 0);
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(weak_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(weak_ordering::greater) != 0));
+
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(weak_ordering::less) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(weak_ordering::less) < 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(weak_ordering::less) <= 0));
+  EXPECT_TRUE(Identity(
+      implicit_cast<partial_ordering>(weak_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(weak_ordering::greater) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(weak_ordering::greater) > 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(weak_ordering::greater) >= 0));
+
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_ordering::less) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_ordering::equal) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_equality>(strong_ordering::greater) != 0));
+
+  EXPECT_TRUE(
+      Identity(implicit_cast<strong_equality>(strong_ordering::less) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<strong_equality>(strong_ordering::equal) == 0));
+  EXPECT_TRUE(Identity(
+      implicit_cast<strong_equality>(strong_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<strong_equality>(strong_ordering::greater) != 0));
+
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::less) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::less) < 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::less) <= 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::equal) == 0));
+  EXPECT_TRUE(Identity(
+      implicit_cast<partial_ordering>(strong_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::greater) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::greater) > 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<partial_ordering>(strong_ordering::greater) >= 0));
+
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::less) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::less) < 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::less) <= 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::equal) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::equivalent) == 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::greater) != 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::greater) > 0));
+  EXPECT_TRUE(
+      Identity(implicit_cast<weak_ordering>(strong_ordering::greater) >= 0));
+}
+
+struct WeakOrderingLess {
+  template <typename T>
+  absl::weak_ordering operator()(const T& a, const T& b) const {
+    return a < b ? absl::weak_ordering::less
+                 : a == b ? absl::weak_ordering::equivalent
+                          : absl::weak_ordering::greater;
+  }
+};
+
+TEST(CompareResultAsLessThan, SanityTest) {
+  EXPECT_FALSE(absl::compare_internal::compare_result_as_less_than(false));
+  EXPECT_TRUE(absl::compare_internal::compare_result_as_less_than(true));
+
+  EXPECT_TRUE(
+      absl::compare_internal::compare_result_as_less_than(weak_ordering::less));
+  EXPECT_FALSE(absl::compare_internal::compare_result_as_less_than(
+      weak_ordering::equivalent));
+  EXPECT_FALSE(absl::compare_internal::compare_result_as_less_than(
+      weak_ordering::greater));
+}
+
+TEST(DoLessThanComparison, SanityTest) {
+  std::less<int> less;
+  WeakOrderingLess weak;
+
+  EXPECT_TRUE(absl::compare_internal::do_less_than_comparison(less, -1, 0));
+  EXPECT_TRUE(absl::compare_internal::do_less_than_comparison(weak, -1, 0));
+
+  EXPECT_FALSE(absl::compare_internal::do_less_than_comparison(less, 10, 10));
+  EXPECT_FALSE(absl::compare_internal::do_less_than_comparison(weak, 10, 10));
+
+  EXPECT_FALSE(absl::compare_internal::do_less_than_comparison(less, 10, 5));
+  EXPECT_FALSE(absl::compare_internal::do_less_than_comparison(weak, 10, 5));
+}
+
+TEST(CompareResultAsOrdering, SanityTest) {
+  EXPECT_TRUE(
+      Identity(absl::compare_internal::compare_result_as_ordering(-1) < 0));
+  EXPECT_FALSE(
+      Identity(absl::compare_internal::compare_result_as_ordering(-1) == 0));
+  EXPECT_FALSE(
+      Identity(absl::compare_internal::compare_result_as_ordering(-1) > 0));
+  EXPECT_TRUE(Identity(absl::compare_internal::compare_result_as_ordering(
+                           weak_ordering::less) < 0));
+  EXPECT_FALSE(Identity(absl::compare_internal::compare_result_as_ordering(
+                            weak_ordering::less) == 0));
+  EXPECT_FALSE(Identity(absl::compare_internal::compare_result_as_ordering(
+                            weak_ordering::less) > 0));
+
+  EXPECT_FALSE(
+      Identity(absl::compare_internal::compare_result_as_ordering(0) < 0));
+  EXPECT_TRUE(
+      Identity(absl::compare_internal::compare_result_as_ordering(0) == 0));
+  EXPECT_FALSE(
+      Identity(absl::compare_internal::compare_result_as_ordering(0) > 0));
+  EXPECT_FALSE(Identity(absl::compare_internal::compare_result_as_ordering(
+                            weak_ordering::equivalent) < 0));
+  EXPECT_TRUE(Identity(absl::compare_internal::compare_result_as_ordering(
+                           weak_ordering::equivalent) == 0));
+  EXPECT_FALSE(Identity(absl::compare_internal::compare_result_as_ordering(
+                            weak_ordering::equivalent) > 0));
+
+  EXPECT_FALSE(
+      Identity(absl::compare_internal::compare_result_as_ordering(1) < 0));
+  EXPECT_FALSE(
+      Identity(absl::compare_internal::compare_result_as_ordering(1) == 0));
+  EXPECT_TRUE(
+      Identity(absl::compare_internal::compare_result_as_ordering(1) > 0));
+  EXPECT_FALSE(Identity(absl::compare_internal::compare_result_as_ordering(
+                            weak_ordering::greater) < 0));
+  EXPECT_FALSE(Identity(absl::compare_internal::compare_result_as_ordering(
+                            weak_ordering::greater) == 0));
+  EXPECT_TRUE(Identity(absl::compare_internal::compare_result_as_ordering(
+                           weak_ordering::greater) > 0));
+}
+
+TEST(DoThreeWayComparison, SanityTest) {
+  std::less<int> less;
+  WeakOrderingLess weak;
+
+  EXPECT_TRUE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, -1, 0) < 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, -1, 0) == 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, -1, 0) > 0));
+  EXPECT_TRUE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, -1, 0) < 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, -1, 0) == 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, -1, 0) > 0));
+
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, 10, 10) < 0));
+  EXPECT_TRUE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, 10, 10) == 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, 10, 10) > 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, 10, 10) < 0));
+  EXPECT_TRUE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, 10, 10) == 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, 10, 10) > 0));
+
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, 10, 5) < 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, 10, 5) == 0));
+  EXPECT_TRUE(Identity(
+      absl::compare_internal::do_three_way_comparison(less, 10, 5) > 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, 10, 5) < 0));
+  EXPECT_FALSE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, 10, 5) == 0));
+  EXPECT_TRUE(Identity(
+      absl::compare_internal::do_three_way_comparison(weak, 10, 5) > 0));
+}
+
+#ifdef __cpp_inline_variables
+TEST(Compare, StaticAsserts) {
+  static_assert(weak_equality::equivalent == 0, "");
+  static_assert(weak_equality::nonequivalent != 0, "");
+
+  static_assert(strong_equality::equal == 0, "");
+  static_assert(strong_equality::nonequal != 0, "");
+  static_assert(strong_equality::equivalent == 0, "");
+  static_assert(strong_equality::nonequivalent != 0, "");
+
+  static_assert(partial_ordering::less < 0, "");
+  static_assert(partial_ordering::equivalent == 0, "");
+  static_assert(partial_ordering::greater > 0, "");
+  static_assert(partial_ordering::unordered != 0, "");
+
+  static_assert(weak_ordering::less < 0, "");
+  static_assert(weak_ordering::equivalent == 0, "");
+  static_assert(weak_ordering::greater > 0, "");
+
+  static_assert(strong_ordering::less < 0, "");
+  static_assert(strong_ordering::equal == 0, "");
+  static_assert(strong_ordering::equivalent == 0, "");
+  static_assert(strong_ordering::greater > 0, "");
+}
+#endif  // __cpp_inline_variables
+
+}  // namespace
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/types/internal/conformance_aliases.h b/third_party/abseil_cpp/absl/types/internal/conformance_aliases.h
new file mode 100644
index 0000000000..0cc6884e30
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/conformance_aliases.h
@@ -0,0 +1,447 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// regularity_aliases.h
+// -----------------------------------------------------------------------------
+//
+// This file contains type aliases of common ConformanceProfiles and Archetypes
+// so that they can be directly used by name without creating them from scratch.
+
+#ifndef ABSL_TYPES_INTERNAL_CONFORMANCE_ALIASES_H_
+#define ABSL_TYPES_INTERNAL_CONFORMANCE_ALIASES_H_
+
+#include "absl/types/internal/conformance_archetype.h"
+#include "absl/types/internal/conformance_profile.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace types_internal {
+
+// Creates both a Profile and a corresponding Archetype with root name "name".
+#define ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(name, ...)                \
+  struct name##Profile : __VA_ARGS__ {};                                    \
+                                                                            \
+  using name##Archetype = ::absl::types_internal::Archetype<name##Profile>; \
+                                                                            \
+  template <class AbslInternalProfileTag>                                   \
+  using name##Archetype##_ = ::absl::types_internal::Archetype<             \
+      ::absl::types_internal::StrongProfileTypedef<name##Profile,           \
+                                                   AbslInternalProfileTag>>
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasTrivialDefaultConstructor,
+    ConformanceProfile<default_constructible::trivial>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowDefaultConstructor,
+    ConformanceProfile<default_constructible::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasDefaultConstructor, ConformanceProfile<default_constructible::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasTrivialMoveConstructor, ConformanceProfile<default_constructible::maybe,
+                                                  move_constructible::trivial>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowMoveConstructor, ConformanceProfile<default_constructible::maybe,
+                                                  move_constructible::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasMoveConstructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasTrivialCopyConstructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::trivial>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowCopyConstructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasCopyConstructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasTrivialMoveAssign,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::trivial>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowMoveAssign,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasMoveAssign,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasTrivialCopyAssign,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::trivial>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowCopyAssign,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasCopyAssign,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasTrivialDestructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::trivial>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowDestructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasDestructor,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowEquality,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasEquality,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowInequality,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::maybe,
+                       inequality_comparable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasInequality,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::maybe, inequality_comparable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowLessThan,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::maybe, inequality_comparable::maybe,
+                       less_than_comparable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasLessThan,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::maybe, inequality_comparable::maybe,
+                       less_than_comparable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowLessEqual,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::maybe, inequality_comparable::maybe,
+                       less_than_comparable::maybe,
+                       less_equal_comparable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasLessEqual,
+    ConformanceProfile<default_constructible::maybe, move_constructible::maybe,
+                       copy_constructible::maybe, move_assignable::maybe,
+                       copy_assignable::maybe, destructible::maybe,
+                       equality_comparable::maybe, inequality_comparable::maybe,
+                       less_than_comparable::maybe,
+                       less_equal_comparable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowGreaterEqual,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasGreaterEqual,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowGreaterThan,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::maybe,
+        greater_than_comparable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasGreaterThan,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::maybe,
+        greater_than_comparable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasNothrowSwap,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::maybe,
+        greater_than_comparable::maybe, swappable::nothrow>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasSwap,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::maybe,
+        greater_than_comparable::maybe, swappable::yes>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HasStdHashSpecialization,
+    ConformanceProfile<
+        default_constructible::maybe, move_constructible::maybe,
+        copy_constructible::maybe, move_assignable::maybe,
+        copy_assignable::maybe, destructible::maybe, equality_comparable::maybe,
+        inequality_comparable::maybe, less_than_comparable::maybe,
+        less_equal_comparable::maybe, greater_equal_comparable::maybe,
+        greater_than_comparable::maybe, swappable::maybe, hashable::yes>);
+
+////////////////////////////////////////////////////////////////////////////////
+////     The remaining aliases are combinations of the previous aliases.    ////
+////////////////////////////////////////////////////////////////////////////////
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    Equatable, CombineProfiles<HasEqualityProfile, HasInequalityProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    Comparable,
+    CombineProfiles<EquatableProfile, HasLessThanProfile, HasLessEqualProfile,
+                    HasGreaterEqualProfile, HasGreaterThanProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    NothrowEquatable,
+    CombineProfiles<HasNothrowEqualityProfile, HasNothrowInequalityProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    NothrowComparable,
+    CombineProfiles<NothrowEquatableProfile, HasNothrowLessThanProfile,
+                    HasNothrowLessEqualProfile, HasNothrowGreaterEqualProfile,
+                    HasNothrowGreaterThanProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    Value,
+    CombineProfiles<HasNothrowMoveConstructorProfile, HasCopyConstructorProfile,
+                    HasNothrowMoveAssignProfile, HasCopyAssignProfile,
+                    HasNothrowDestructorProfile, HasNothrowSwapProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    EquatableValue, CombineProfiles<EquatableProfile, ValueProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    ComparableValue, CombineProfiles<ComparableProfile, ValueProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    DefaultConstructibleValue,
+    CombineProfiles<HasDefaultConstructorProfile, ValueProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    NothrowMoveConstructible, CombineProfiles<HasNothrowMoveConstructorProfile,
+                                              HasNothrowDestructorProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    EquatableNothrowMoveConstructible,
+    CombineProfiles<EquatableProfile, NothrowMoveConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    ComparableNothrowMoveConstructible,
+    CombineProfiles<ComparableProfile, NothrowMoveConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    DefaultConstructibleNothrowMoveConstructible,
+    CombineProfiles<HasDefaultConstructorProfile,
+                    NothrowMoveConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    CopyConstructible,
+    CombineProfiles<HasNothrowMoveConstructorProfile, HasCopyConstructorProfile,
+                    HasNothrowDestructorProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    EquatableCopyConstructible,
+    CombineProfiles<EquatableProfile, CopyConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    ComparableCopyConstructible,
+    CombineProfiles<ComparableProfile, CopyConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    DefaultConstructibleCopyConstructible,
+    CombineProfiles<HasDefaultConstructorProfile, CopyConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    NothrowMovable,
+    CombineProfiles<HasNothrowMoveConstructorProfile,
+                    HasNothrowMoveAssignProfile, HasNothrowDestructorProfile,
+                    HasNothrowSwapProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    EquatableNothrowMovable,
+    CombineProfiles<EquatableProfile, NothrowMovableProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    ComparableNothrowMovable,
+    CombineProfiles<ComparableProfile, NothrowMovableProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    DefaultConstructibleNothrowMovable,
+    CombineProfiles<HasDefaultConstructorProfile, NothrowMovableProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    TrivialSpecialMemberFunctions,
+    CombineProfiles<HasTrivialDefaultConstructorProfile,
+                    HasTrivialMoveConstructorProfile,
+                    HasTrivialCopyConstructorProfile,
+                    HasTrivialMoveAssignProfile, HasTrivialCopyAssignProfile,
+                    HasTrivialDestructorProfile, HasNothrowSwapProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    TriviallyComplete,
+    CombineProfiles<TrivialSpecialMemberFunctionsProfile, ComparableProfile,
+                    HasStdHashSpecializationProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HashableNothrowMoveConstructible,
+    CombineProfiles<HasStdHashSpecializationProfile,
+                    NothrowMoveConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HashableCopyConstructible,
+    CombineProfiles<HasStdHashSpecializationProfile, CopyConstructibleProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HashableNothrowMovable,
+    CombineProfiles<HasStdHashSpecializationProfile, NothrowMovableProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    HashableValue,
+    CombineProfiles<HasStdHashSpecializationProfile, ValueProfile>);
+
+ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS(
+    ComparableHashableValue,
+    CombineProfiles<HashableValueProfile, ComparableProfile>);
+
+// The "preferred" profiles that we support in Abseil.
+template <template <class...> class Receiver>
+using ExpandBasicProfiles =
+    Receiver<NothrowMoveConstructibleProfile, CopyConstructibleProfile,
+             NothrowMovableProfile, ValueProfile>;
+
+// The basic profiles except that they are also all Equatable.
+template <template <class...> class Receiver>
+using ExpandBasicEquatableProfiles =
+    Receiver<EquatableNothrowMoveConstructibleProfile,
+             EquatableCopyConstructibleProfile, EquatableNothrowMovableProfile,
+             EquatableValueProfile>;
+
+// The basic profiles except that they are also all Comparable.
+template <template <class...> class Receiver>
+using ExpandBasicComparableProfiles =
+    Receiver<ComparableNothrowMoveConstructibleProfile,
+             ComparableCopyConstructibleProfile,
+             ComparableNothrowMovableProfile, ComparableValueProfile>;
+
+// The basic profiles except that they are also all Hashable.
+template <template <class...> class Receiver>
+using ExpandBasicHashableProfiles =
+    Receiver<HashableNothrowMoveConstructibleProfile,
+             HashableCopyConstructibleProfile, HashableNothrowMovableProfile,
+             HashableValueProfile>;
+
+// The basic profiles except that they are also all DefaultConstructible.
+template <template <class...> class Receiver>
+using ExpandBasicDefaultConstructibleProfiles =
+    Receiver<DefaultConstructibleNothrowMoveConstructibleProfile,
+             DefaultConstructibleCopyConstructibleProfile,
+             DefaultConstructibleNothrowMovableProfile,
+             DefaultConstructibleValueProfile>;
+
+// The type profiles that we support in Abseil (all of the previous lists).
+template <template <class...> class Receiver>
+using ExpandSupportedProfiles = Receiver<
+    NothrowMoveConstructibleProfile, CopyConstructibleProfile,
+    NothrowMovableProfile, ValueProfile,
+    EquatableNothrowMoveConstructibleProfile, EquatableCopyConstructibleProfile,
+    EquatableNothrowMovableProfile, EquatableValueProfile,
+    ComparableNothrowMoveConstructibleProfile,
+    ComparableCopyConstructibleProfile, ComparableNothrowMovableProfile,
+    ComparableValueProfile, DefaultConstructibleNothrowMoveConstructibleProfile,
+    DefaultConstructibleCopyConstructibleProfile,
+    DefaultConstructibleNothrowMovableProfile, DefaultConstructibleValueProfile,
+    HashableNothrowMoveConstructibleProfile, HashableCopyConstructibleProfile,
+    HashableNothrowMovableProfile, HashableValueProfile>;
+
+// TODO(calabrese) Include types that have throwing move constructors, since in
+// practice we still need to support them because of standard library types with
+// (potentially) non-noexcept moves.
+
+}  // namespace types_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#undef ABSL_INTERNAL_PROFILE_AND_ARCHETYPE_ALIAS
+
+#endif  // ABSL_TYPES_INTERNAL_CONFORMANCE_ALIASES_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/conformance_archetype.h b/third_party/abseil_cpp/absl/types/internal/conformance_archetype.h
new file mode 100644
index 0000000000..2349e0f726
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/conformance_archetype.h
@@ -0,0 +1,978 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// conformance_archetype.h
+// -----------------------------------------------------------------------------
+//
+// This file contains a facility for generating "archetypes" of out of
+// "Conformance Profiles" (see "conformance_profiles.h" for more information
+// about Conformance Profiles). An archetype is a type that aims to support the
+// bare minimum requirements of a given Conformance Profile. For instance, an
+// archetype that corresponds to an ImmutableProfile has exactly a nothrow
+// move-constructor, a potentially-throwing copy constructor, a nothrow
+// destructor, with all other special-member-functions deleted. These archetypes
+// are useful for testing to make sure that templates are able to work with the
+// kinds of types that they claim to support (i.e. that they do not accidentally
+// under-constrain),
+//
+// The main type template in this file is the Archetype template, which takes
+// a Conformance Profile as a template argument and its instantiations are a
+// minimum-conforming model of that profile.
+
+#ifndef ABSL_TYPES_INTERNAL_CONFORMANCE_ARCHETYPE_H_
+#define ABSL_TYPES_INTERNAL_CONFORMANCE_ARCHETYPE_H_
+
+#include <cstddef>
+#include <functional>
+#include <type_traits>
+#include <utility>
+
+#include "absl/meta/type_traits.h"
+#include "absl/types/internal/conformance_profile.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace types_internal {
+
+// A minimum-conforming implementation of a type with properties specified in
+// `Prof`, where `Prof` is a valid Conformance Profile.
+template <class Prof, class /*Enabler*/ = void>
+class Archetype;
+
+// Given an Archetype, obtain the properties of the profile associated with that
+// archetype.
+template <class Archetype>
+struct PropertiesOfArchetype;
+
+template <class Prof>
+struct PropertiesOfArchetype<Archetype<Prof>> {
+  using type = PropertiesOfT<Prof>;
+};
+
+template <class Archetype>
+using PropertiesOfArchetypeT = typename PropertiesOfArchetype<Archetype>::type;
+
+// A metafunction to determine if a type is an `Archetype`.
+template <class T>
+struct IsArchetype : std::false_type {};
+
+template <class Prof>
+struct IsArchetype<Archetype<Prof>> : std::true_type {};
+
+// A constructor tag type used when creating an Archetype with internal state.
+struct MakeArchetypeState {};
+
+// Data stored within an archetype that is copied/compared/hashed when the
+// corresponding operations are used.
+using ArchetypeState = std::size_t;
+
+////////////////////////////////////////////////////////////////////////////////
+//   This section of the file defines a chain of base classes for Archetype,  //
+//   where each base defines a specific special member function with the      //
+//   appropriate properties (deleted, noexcept(false), noexcept, or trivial). //
+////////////////////////////////////////////////////////////////////////////////
+
+// The bottom-most base, which contains the state and the default constructor.
+template <default_constructible DefaultConstructibleValue>
+struct ArchetypeStateBase {
+  static_assert(DefaultConstructibleValue == default_constructible::yes ||
+                    DefaultConstructibleValue == default_constructible::nothrow,
+                "");
+
+  ArchetypeStateBase() noexcept(
+      DefaultConstructibleValue ==
+      default_constructible::
+          nothrow) /*Vacuous archetype_state initialization*/ {}
+  explicit ArchetypeStateBase(MakeArchetypeState, ArchetypeState state) noexcept
+      : archetype_state(state) {}
+
+  ArchetypeState archetype_state;
+};
+
+template <>
+struct ArchetypeStateBase<default_constructible::maybe> {
+  explicit ArchetypeStateBase() = delete;
+  explicit ArchetypeStateBase(MakeArchetypeState, ArchetypeState state) noexcept
+      : archetype_state(state) {}
+
+  ArchetypeState archetype_state;
+};
+
+template <>
+struct ArchetypeStateBase<default_constructible::trivial> {
+  ArchetypeStateBase() = default;
+  explicit ArchetypeStateBase(MakeArchetypeState, ArchetypeState state) noexcept
+      : archetype_state(state) {}
+
+  ArchetypeState archetype_state;
+};
+
+// The move-constructor base
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue>
+struct ArchetypeMoveConstructor
+    : ArchetypeStateBase<DefaultConstructibleValue> {
+  static_assert(MoveConstructibleValue == move_constructible::yes ||
+                    MoveConstructibleValue == move_constructible::nothrow,
+                "");
+
+  explicit ArchetypeMoveConstructor(MakeArchetypeState,
+                                    ArchetypeState state) noexcept
+      : ArchetypeStateBase<DefaultConstructibleValue>(MakeArchetypeState(),
+                                                      state) {}
+
+  ArchetypeMoveConstructor() = default;
+  ArchetypeMoveConstructor(ArchetypeMoveConstructor&& other) noexcept(
+      MoveConstructibleValue == move_constructible::nothrow)
+      : ArchetypeStateBase<DefaultConstructibleValue>(MakeArchetypeState(),
+                                                      other.archetype_state) {}
+  ArchetypeMoveConstructor(const ArchetypeMoveConstructor&) = default;
+  ArchetypeMoveConstructor& operator=(ArchetypeMoveConstructor&&) = default;
+  ArchetypeMoveConstructor& operator=(const ArchetypeMoveConstructor&) =
+      default;
+};
+
+template <default_constructible DefaultConstructibleValue>
+struct ArchetypeMoveConstructor<DefaultConstructibleValue,
+                                move_constructible::trivial>
+    : ArchetypeStateBase<DefaultConstructibleValue> {
+  explicit ArchetypeMoveConstructor(MakeArchetypeState,
+                                    ArchetypeState state) noexcept
+      : ArchetypeStateBase<DefaultConstructibleValue>(MakeArchetypeState(),
+                                                      state) {}
+
+  ArchetypeMoveConstructor() = default;
+};
+
+// The copy-constructor base
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue>
+struct ArchetypeCopyConstructor
+    : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                               MoveConstructibleValue> {
+  static_assert(CopyConstructibleValue == copy_constructible::yes ||
+                    CopyConstructibleValue == copy_constructible::nothrow,
+                "");
+  explicit ArchetypeCopyConstructor(MakeArchetypeState,
+                                    ArchetypeState state) noexcept
+      : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                                 MoveConstructibleValue>(MakeArchetypeState(),
+                                                         state) {}
+
+  ArchetypeCopyConstructor() = default;
+  ArchetypeCopyConstructor(ArchetypeCopyConstructor&&) = default;
+  ArchetypeCopyConstructor(const ArchetypeCopyConstructor& other) noexcept(
+      CopyConstructibleValue == copy_constructible::nothrow)
+      : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                                 MoveConstructibleValue>(
+            MakeArchetypeState(), other.archetype_state) {}
+  ArchetypeCopyConstructor& operator=(ArchetypeCopyConstructor&&) = default;
+  ArchetypeCopyConstructor& operator=(const ArchetypeCopyConstructor&) =
+      default;
+};
+
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue>
+struct ArchetypeCopyConstructor<DefaultConstructibleValue,
+                                MoveConstructibleValue,
+                                copy_constructible::maybe>
+    : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                               MoveConstructibleValue> {
+  explicit ArchetypeCopyConstructor(MakeArchetypeState,
+                                    ArchetypeState state) noexcept
+      : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                                 MoveConstructibleValue>(MakeArchetypeState(),
+                                                         state) {}
+
+  ArchetypeCopyConstructor() = default;
+  ArchetypeCopyConstructor(ArchetypeCopyConstructor&&) = default;
+  ArchetypeCopyConstructor(const ArchetypeCopyConstructor&) = delete;
+  ArchetypeCopyConstructor& operator=(ArchetypeCopyConstructor&&) = default;
+  ArchetypeCopyConstructor& operator=(const ArchetypeCopyConstructor&) =
+      default;
+};
+
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue>
+struct ArchetypeCopyConstructor<DefaultConstructibleValue,
+                                MoveConstructibleValue,
+                                copy_constructible::trivial>
+    : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                               MoveConstructibleValue> {
+  explicit ArchetypeCopyConstructor(MakeArchetypeState,
+                                    ArchetypeState state) noexcept
+      : ArchetypeMoveConstructor<DefaultConstructibleValue,
+                                 MoveConstructibleValue>(MakeArchetypeState(),
+                                                         state) {}
+
+  ArchetypeCopyConstructor() = default;
+};
+
+// The move-assign base
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue>
+struct ArchetypeMoveAssign
+    : ArchetypeCopyConstructor<DefaultConstructibleValue,
+                               MoveConstructibleValue, CopyConstructibleValue> {
+  static_assert(MoveAssignableValue == move_assignable::yes ||
+                    MoveAssignableValue == move_assignable::nothrow,
+                "");
+  explicit ArchetypeMoveAssign(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeCopyConstructor<DefaultConstructibleValue,
+                                 MoveConstructibleValue,
+                                 CopyConstructibleValue>(MakeArchetypeState(),
+                                                         state) {}
+
+  ArchetypeMoveAssign() = default;
+  ArchetypeMoveAssign(ArchetypeMoveAssign&&) = default;
+  ArchetypeMoveAssign(const ArchetypeMoveAssign&) = default;
+  ArchetypeMoveAssign& operator=(ArchetypeMoveAssign&& other) noexcept(
+      MoveAssignableValue == move_assignable::nothrow) {
+    this->archetype_state = other.archetype_state;
+    return *this;
+  }
+
+  ArchetypeMoveAssign& operator=(const ArchetypeMoveAssign&) = default;
+};
+
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue>
+struct ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                           CopyConstructibleValue, move_assignable::trivial>
+    : ArchetypeCopyConstructor<DefaultConstructibleValue,
+                               MoveConstructibleValue, CopyConstructibleValue> {
+  explicit ArchetypeMoveAssign(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeCopyConstructor<DefaultConstructibleValue,
+                                 MoveConstructibleValue,
+                                 CopyConstructibleValue>(MakeArchetypeState(),
+                                                         state) {}
+
+  ArchetypeMoveAssign() = default;
+};
+
+// The copy-assign base
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue,
+          copy_assignable CopyAssignableValue>
+struct ArchetypeCopyAssign
+    : ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                          CopyConstructibleValue, MoveAssignableValue> {
+  static_assert(CopyAssignableValue == copy_assignable::yes ||
+                    CopyAssignableValue == copy_assignable::nothrow,
+                "");
+  explicit ArchetypeCopyAssign(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                            CopyConstructibleValue, MoveAssignableValue>(
+            MakeArchetypeState(), state) {}
+
+  ArchetypeCopyAssign() = default;
+  ArchetypeCopyAssign(ArchetypeCopyAssign&&) = default;
+  ArchetypeCopyAssign(const ArchetypeCopyAssign&) = default;
+  ArchetypeCopyAssign& operator=(ArchetypeCopyAssign&&) = default;
+
+  ArchetypeCopyAssign& operator=(const ArchetypeCopyAssign& other) noexcept(
+      CopyAssignableValue == copy_assignable::nothrow) {
+    this->archetype_state = other.archetype_state;
+    return *this;
+  }
+};
+
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue>
+struct ArchetypeCopyAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                           CopyConstructibleValue, MoveAssignableValue,
+                           copy_assignable::maybe>
+    : ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                          CopyConstructibleValue, MoveAssignableValue> {
+  explicit ArchetypeCopyAssign(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                            CopyConstructibleValue, MoveAssignableValue>(
+            MakeArchetypeState(), state) {}
+
+  ArchetypeCopyAssign() = default;
+  ArchetypeCopyAssign(ArchetypeCopyAssign&&) = default;
+  ArchetypeCopyAssign(const ArchetypeCopyAssign&) = default;
+  ArchetypeCopyAssign& operator=(ArchetypeCopyAssign&&) = default;
+  ArchetypeCopyAssign& operator=(const ArchetypeCopyAssign&) = delete;
+};
+
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue>
+struct ArchetypeCopyAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                           CopyConstructibleValue, MoveAssignableValue,
+                           copy_assignable::trivial>
+    : ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                          CopyConstructibleValue, MoveAssignableValue> {
+  explicit ArchetypeCopyAssign(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeMoveAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                            CopyConstructibleValue, MoveAssignableValue>(
+            MakeArchetypeState(), state) {}
+
+  ArchetypeCopyAssign() = default;
+};
+
+// The destructor base
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue,
+          copy_assignable CopyAssignableValue, destructible DestructibleValue>
+struct ArchetypeDestructor
+    : ArchetypeCopyAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                          CopyConstructibleValue, MoveAssignableValue,
+                          CopyAssignableValue> {
+  static_assert(DestructibleValue == destructible::yes ||
+                    DestructibleValue == destructible::nothrow,
+                "");
+
+  explicit ArchetypeDestructor(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeCopyAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                            CopyConstructibleValue, MoveAssignableValue,
+                            CopyAssignableValue>(MakeArchetypeState(), state) {}
+
+  ArchetypeDestructor() = default;
+  ArchetypeDestructor(ArchetypeDestructor&&) = default;
+  ArchetypeDestructor(const ArchetypeDestructor&) = default;
+  ArchetypeDestructor& operator=(ArchetypeDestructor&&) = default;
+  ArchetypeDestructor& operator=(const ArchetypeDestructor&) = default;
+  ~ArchetypeDestructor() noexcept(DestructibleValue == destructible::nothrow) {}
+};
+
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue,
+          copy_assignable CopyAssignableValue>
+struct ArchetypeDestructor<DefaultConstructibleValue, MoveConstructibleValue,
+                           CopyConstructibleValue, MoveAssignableValue,
+                           CopyAssignableValue, destructible::trivial>
+    : ArchetypeCopyAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                          CopyConstructibleValue, MoveAssignableValue,
+                          CopyAssignableValue> {
+  explicit ArchetypeDestructor(MakeArchetypeState,
+                               ArchetypeState state) noexcept
+      : ArchetypeCopyAssign<DefaultConstructibleValue, MoveConstructibleValue,
+                            CopyConstructibleValue, MoveAssignableValue,
+                            CopyAssignableValue>(MakeArchetypeState(), state) {}
+
+  ArchetypeDestructor() = default;
+};
+
+// An alias to the top of the chain of bases for special-member functions.
+// NOTE: move_constructible::maybe, move_assignable::maybe, and
+// destructible::maybe are handled in the top-level type by way of SFINAE.
+// Because of this, we never instantiate the base classes with
+// move_constructible::maybe, move_assignable::maybe, or destructible::maybe so
+// that we minimize the number of different possible type-template
+// instantiations.
+template <default_constructible DefaultConstructibleValue,
+          move_constructible MoveConstructibleValue,
+          copy_constructible CopyConstructibleValue,
+          move_assignable MoveAssignableValue,
+          copy_assignable CopyAssignableValue, destructible DestructibleValue>
+using ArchetypeSpecialMembersBase = ArchetypeDestructor<
+    DefaultConstructibleValue,
+    MoveConstructibleValue != move_constructible::maybe
+        ? MoveConstructibleValue
+        : move_constructible::nothrow,
+    CopyConstructibleValue,
+    MoveAssignableValue != move_assignable::maybe ? MoveAssignableValue
+                                                  : move_assignable::nothrow,
+    CopyAssignableValue,
+    DestructibleValue != destructible::maybe ? DestructibleValue
+                                             : destructible::nothrow>;
+
+// A function that is used to create an archetype with some associated state.
+template <class Arch>
+Arch MakeArchetype(ArchetypeState state) noexcept {
+  static_assert(IsArchetype<Arch>::value,
+                "The explicit template argument to MakeArchetype is required "
+                "to be an Archetype.");
+  return Arch(MakeArchetypeState(), state);
+}
+
+// This is used to conditionally delete "copy" and "move" constructors in a way
+// that is consistent with what the ConformanceProfile requires and that also
+// strictly enforces the arguments to the copy/move to not come from implicit
+// conversions when dealing with the Archetype.
+template <class Prof, class T>
+constexpr bool ShouldDeleteConstructor() {
+  return !((PropertiesOfT<Prof>::move_constructible_support !=
+                move_constructible::maybe &&
+            std::is_same<T, Archetype<Prof>>::value) ||
+           (PropertiesOfT<Prof>::copy_constructible_support !=
+                copy_constructible::maybe &&
+            (std::is_same<T, const Archetype<Prof>&>::value ||
+             std::is_same<T, Archetype<Prof>&>::value ||
+             std::is_same<T, const Archetype<Prof>>::value)));
+}
+
+// This is used to conditionally delete "copy" and "move" assigns in a way
+// that is consistent with what the ConformanceProfile requires and that also
+// strictly enforces the arguments to the copy/move to not come from implicit
+// conversions when dealing with the Archetype.
+template <class Prof, class T>
+constexpr bool ShouldDeleteAssign() {
+  return !(
+      (PropertiesOfT<Prof>::move_assignable_support != move_assignable::maybe &&
+       std::is_same<T, Archetype<Prof>>::value) ||
+      (PropertiesOfT<Prof>::copy_assignable_support != copy_assignable::maybe &&
+       (std::is_same<T, const Archetype<Prof>&>::value ||
+        std::is_same<T, Archetype<Prof>&>::value ||
+        std::is_same<T, const Archetype<Prof>>::value)));
+}
+
+// TODO(calabrese) Inherit from a chain of secondary bases to pull in the
+// associated functions of other concepts.
+template <class Prof, class Enabler>
+class Archetype : ArchetypeSpecialMembersBase<
+                      PropertiesOfT<Prof>::default_constructible_support,
+                      PropertiesOfT<Prof>::move_constructible_support,
+                      PropertiesOfT<Prof>::copy_constructible_support,
+                      PropertiesOfT<Prof>::move_assignable_support,
+                      PropertiesOfT<Prof>::copy_assignable_support,
+                      PropertiesOfT<Prof>::destructible_support> {
+  static_assert(std::is_same<Enabler, void>::value,
+                "An explicit type must not be passed as the second template "
+                "argument to 'Archetype`.");
+
+  // The cases mentioned in these static_asserts are expected to be handled in
+  // the partial template specializations of Archetype that follow this
+  // definition.
+  static_assert(PropertiesOfT<Prof>::destructible_support !=
+                    destructible::maybe,
+                "");
+  static_assert(PropertiesOfT<Prof>::move_constructible_support !=
+                        move_constructible::maybe ||
+                    PropertiesOfT<Prof>::copy_constructible_support ==
+                        copy_constructible::maybe,
+                "");
+  static_assert(PropertiesOfT<Prof>::move_assignable_support !=
+                        move_assignable::maybe ||
+                    PropertiesOfT<Prof>::copy_assignable_support ==
+                        copy_assignable::maybe,
+                "");
+
+ public:
+  Archetype() = default;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+template <class Prof>
+class Archetype<Prof, typename std::enable_if<
+                          PropertiesOfT<Prof>::move_constructible_support !=
+                              move_constructible::maybe &&
+                          PropertiesOfT<Prof>::move_assignable_support ==
+                              move_assignable::maybe &&
+                          PropertiesOfT<Prof>::destructible_support !=
+                              destructible::maybe>::type>
+    : ArchetypeSpecialMembersBase<
+          PropertiesOfT<Prof>::default_constructible_support,
+          PropertiesOfT<Prof>::move_constructible_support,
+          PropertiesOfT<Prof>::copy_constructible_support,
+          PropertiesOfT<Prof>::move_assignable_support,
+          PropertiesOfT<Prof>::copy_assignable_support,
+          PropertiesOfT<Prof>::destructible_support> {
+ public:
+  Archetype() = default;
+  Archetype(Archetype&&) = default;
+  Archetype(const Archetype&) = default;
+  Archetype& operator=(Archetype&&) = delete;
+  Archetype& operator=(const Archetype&) = default;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+template <class Prof>
+class Archetype<Prof, typename std::enable_if<
+                          PropertiesOfT<Prof>::move_constructible_support ==
+                              move_constructible::maybe &&
+                          PropertiesOfT<Prof>::move_assignable_support ==
+                              move_assignable::maybe &&
+                          PropertiesOfT<Prof>::destructible_support !=
+                              destructible::maybe>::type>
+    : ArchetypeSpecialMembersBase<
+          PropertiesOfT<Prof>::default_constructible_support,
+          PropertiesOfT<Prof>::move_constructible_support,
+          PropertiesOfT<Prof>::copy_constructible_support,
+          PropertiesOfT<Prof>::move_assignable_support,
+          PropertiesOfT<Prof>::copy_assignable_support,
+          PropertiesOfT<Prof>::destructible_support> {
+ public:
+  Archetype() = default;
+  Archetype(Archetype&&) = delete;
+  Archetype(const Archetype&) = default;
+  Archetype& operator=(Archetype&&) = delete;
+  Archetype& operator=(const Archetype&) = default;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+template <class Prof>
+class Archetype<Prof, typename std::enable_if<
+                          PropertiesOfT<Prof>::move_constructible_support ==
+                              move_constructible::maybe &&
+                          PropertiesOfT<Prof>::move_assignable_support !=
+                              move_assignable::maybe &&
+                          PropertiesOfT<Prof>::destructible_support !=
+                              destructible::maybe>::type>
+    : ArchetypeSpecialMembersBase<
+          PropertiesOfT<Prof>::default_constructible_support,
+          PropertiesOfT<Prof>::move_constructible_support,
+          PropertiesOfT<Prof>::copy_constructible_support,
+          PropertiesOfT<Prof>::move_assignable_support,
+          PropertiesOfT<Prof>::copy_assignable_support,
+          PropertiesOfT<Prof>::destructible_support> {
+ public:
+  Archetype() = default;
+  Archetype(Archetype&&) = delete;
+  Archetype(const Archetype&) = default;
+  Archetype& operator=(Archetype&&) = default;
+  Archetype& operator=(const Archetype&) = default;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+template <class Prof>
+class Archetype<Prof, typename std::enable_if<
+                          PropertiesOfT<Prof>::move_constructible_support !=
+                              move_constructible::maybe &&
+                          PropertiesOfT<Prof>::move_assignable_support ==
+                              move_assignable::maybe &&
+                          PropertiesOfT<Prof>::destructible_support ==
+                              destructible::maybe>::type>
+    : ArchetypeSpecialMembersBase<
+          PropertiesOfT<Prof>::default_constructible_support,
+          PropertiesOfT<Prof>::move_constructible_support,
+          PropertiesOfT<Prof>::copy_constructible_support,
+          PropertiesOfT<Prof>::move_assignable_support,
+          PropertiesOfT<Prof>::copy_assignable_support,
+          PropertiesOfT<Prof>::destructible_support> {
+ public:
+  Archetype() = default;
+  Archetype(Archetype&&) = default;
+  Archetype(const Archetype&) = default;
+  Archetype& operator=(Archetype&&) = delete;
+  Archetype& operator=(const Archetype&) = default;
+  ~Archetype() = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+template <class Prof>
+class Archetype<Prof, typename std::enable_if<
+                          PropertiesOfT<Prof>::move_constructible_support ==
+                              move_constructible::maybe &&
+                          PropertiesOfT<Prof>::move_assignable_support ==
+                              move_assignable::maybe &&
+                          PropertiesOfT<Prof>::destructible_support ==
+                              destructible::maybe>::type>
+    : ArchetypeSpecialMembersBase<
+          PropertiesOfT<Prof>::default_constructible_support,
+          PropertiesOfT<Prof>::move_constructible_support,
+          PropertiesOfT<Prof>::copy_constructible_support,
+          PropertiesOfT<Prof>::move_assignable_support,
+          PropertiesOfT<Prof>::copy_assignable_support,
+          PropertiesOfT<Prof>::destructible_support> {
+ public:
+  Archetype() = default;
+  Archetype(Archetype&&) = delete;
+  Archetype(const Archetype&) = default;
+  Archetype& operator=(Archetype&&) = delete;
+  Archetype& operator=(const Archetype&) = default;
+  ~Archetype() = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+template <class Prof>
+class Archetype<Prof, typename std::enable_if<
+                          PropertiesOfT<Prof>::move_constructible_support ==
+                              move_constructible::maybe &&
+                          PropertiesOfT<Prof>::move_assignable_support !=
+                              move_assignable::maybe &&
+                          PropertiesOfT<Prof>::destructible_support ==
+                              destructible::maybe>::type>
+    : ArchetypeSpecialMembersBase<
+          PropertiesOfT<Prof>::default_constructible_support,
+          PropertiesOfT<Prof>::move_constructible_support,
+          PropertiesOfT<Prof>::copy_constructible_support,
+          PropertiesOfT<Prof>::move_assignable_support,
+          PropertiesOfT<Prof>::copy_assignable_support,
+          PropertiesOfT<Prof>::destructible_support> {
+ public:
+  Archetype() = default;
+  Archetype(Archetype&&) = delete;
+  Archetype(const Archetype&) = default;
+  Archetype& operator=(Archetype&&) = default;
+  Archetype& operator=(const Archetype&) = default;
+  ~Archetype() = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteConstructor<Prof, T>()>::type* = nullptr>
+  Archetype(T&&) = delete;
+
+  // Disallow moves when requested, and disallow implicit conversions.
+  template <class T, typename std::enable_if<
+                         ShouldDeleteAssign<Prof, T>()>::type* = nullptr>
+  Archetype& operator=(T&&) = delete;
+
+  using ArchetypeSpecialMembersBase<
+      PropertiesOfT<Prof>::default_constructible_support,
+      PropertiesOfT<Prof>::move_constructible_support,
+      PropertiesOfT<Prof>::copy_constructible_support,
+      PropertiesOfT<Prof>::move_assignable_support,
+      PropertiesOfT<Prof>::copy_assignable_support,
+      PropertiesOfT<Prof>::destructible_support>::archetype_state;
+
+ private:
+  explicit Archetype(MakeArchetypeState, ArchetypeState state) noexcept
+      : ArchetypeSpecialMembersBase<
+            PropertiesOfT<Prof>::default_constructible_support,
+            PropertiesOfT<Prof>::move_constructible_support,
+            PropertiesOfT<Prof>::copy_constructible_support,
+            PropertiesOfT<Prof>::move_assignable_support,
+            PropertiesOfT<Prof>::copy_assignable_support,
+            PropertiesOfT<Prof>::destructible_support>(MakeArchetypeState(),
+                                                       state) {}
+
+  friend Archetype MakeArchetype<Archetype>(ArchetypeState) noexcept;
+};
+
+// Explicitly deleted swap for Archetype if the profile does not require swap.
+// It is important to delete it rather than simply leave it out so that the
+// "using std::swap;" idiom will result in this deleted overload being picked.
+template <class Prof,
+          absl::enable_if_t<!PropertiesOfT<Prof>::is_swappable, int> = 0>
+void swap(Archetype<Prof>&, Archetype<Prof>&) = delete;  // NOLINT
+
+// A conditionally-noexcept swap implementation for Archetype when the profile
+// supports swap.
+template <class Prof,
+          absl::enable_if_t<PropertiesOfT<Prof>::is_swappable, int> = 0>
+void swap(Archetype<Prof>& lhs, Archetype<Prof>& rhs)  // NOLINT
+    noexcept(PropertiesOfT<Prof>::swappable_support != swappable::yes) {
+  std::swap(lhs.archetype_state, rhs.archetype_state);
+}
+
+// A convertible-to-bool type that is used as the return type of comparison
+// operators since the standard doesn't always require exactly bool.
+struct NothrowBool {
+  explicit NothrowBool() = delete;
+  ~NothrowBool() = default;
+
+  // TODO(calabrese) Delete the copy constructor in C++17 mode since guaranteed
+  // elision makes it not required when returning from a function.
+  // NothrowBool(NothrowBool const&) = delete;
+
+  NothrowBool& operator=(NothrowBool const&) = delete;
+
+  explicit operator bool() const noexcept { return value; }
+
+  static NothrowBool make(bool const value) noexcept {
+    return NothrowBool(value);
+  }
+
+ private:
+  explicit NothrowBool(bool const value) noexcept : value(value) {}
+
+  bool value;
+};
+
+// A convertible-to-bool type that is used as the return type of comparison
+// operators since the standard doesn't always require exactly bool.
+// Note: ExceptionalBool has a conversion operator that is not noexcept, so
+// that even when a comparison operator is noexcept, that operation may still
+// potentially throw when converted to bool.
+struct ExceptionalBool {
+  explicit ExceptionalBool() = delete;
+  ~ExceptionalBool() = default;
+
+  // TODO(calabrese) Delete the copy constructor in C++17 mode since guaranteed
+  // elision makes it not required when returning from a function.
+  // ExceptionalBool(ExceptionalBool const&) = delete;
+
+  ExceptionalBool& operator=(ExceptionalBool const&) = delete;
+
+  explicit operator bool() const { return value; }  // NOLINT
+
+  static ExceptionalBool make(bool const value) noexcept {
+    return ExceptionalBool(value);
+  }
+
+ private:
+  explicit ExceptionalBool(bool const value) noexcept : value(value) {}
+
+  bool value;
+};
+
+// The following macro is only used as a helper in this file to stamp out
+// comparison operator definitions. It is undefined after usage.
+//
+// NOTE: Non-nothrow operators throw via their result's conversion to bool even
+// though the operation itself is noexcept.
+#define ABSL_TYPES_INTERNAL_OP(enum_name, op)                                \
+  template <class Prof>                                                      \
+  absl::enable_if_t<!PropertiesOfT<Prof>::is_##enum_name, bool> operator op( \
+      const Archetype<Prof>&, const Archetype<Prof>&) = delete;              \
+                                                                             \
+  template <class Prof>                                                      \
+  typename absl::enable_if_t<                                                \
+      PropertiesOfT<Prof>::is_##enum_name,                                   \
+      std::conditional<PropertiesOfT<Prof>::enum_name##_support ==           \
+                           enum_name::nothrow,                               \
+                       NothrowBool, ExceptionalBool>>::type                  \
+  operator op(const Archetype<Prof>& lhs,                                    \
+              const Archetype<Prof>& rhs) noexcept {                         \
+    return absl::conditional_t<                                              \
+        PropertiesOfT<Prof>::enum_name##_support == enum_name::nothrow,      \
+        NothrowBool, ExceptionalBool>::make(lhs.archetype_state op           \
+                                                rhs.archetype_state);        \
+  }
+
+ABSL_TYPES_INTERNAL_OP(equality_comparable, ==);
+ABSL_TYPES_INTERNAL_OP(inequality_comparable, !=);
+ABSL_TYPES_INTERNAL_OP(less_than_comparable, <);
+ABSL_TYPES_INTERNAL_OP(less_equal_comparable, <=);
+ABSL_TYPES_INTERNAL_OP(greater_equal_comparable, >=);
+ABSL_TYPES_INTERNAL_OP(greater_than_comparable, >);
+
+#undef ABSL_TYPES_INTERNAL_OP
+
+// Base class for std::hash specializations when an Archetype doesn't support
+// hashing.
+struct PoisonedHash {
+  PoisonedHash() = delete;
+  PoisonedHash(const PoisonedHash&) = delete;
+  PoisonedHash& operator=(const PoisonedHash&) = delete;
+};
+
+// Base class for std::hash specializations when an Archetype supports hashing.
+template <class Prof>
+struct EnabledHash {
+  using argument_type = Archetype<Prof>;
+  using result_type = std::size_t;
+  result_type operator()(const argument_type& arg) const {
+    return std::hash<ArchetypeState>()(arg.archetype_state);
+  }
+};
+
+}  // namespace types_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+namespace std {
+
+template <class Prof>  // NOLINT
+struct hash<::absl::types_internal::Archetype<Prof>>
+    : conditional<::absl::types_internal::PropertiesOfT<Prof>::is_hashable,
+                  ::absl::types_internal::EnabledHash<Prof>,
+                  ::absl::types_internal::PoisonedHash>::type {};
+
+}  // namespace std
+
+#endif  // ABSL_TYPES_INTERNAL_CONFORMANCE_ARCHETYPE_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/conformance_profile.h b/third_party/abseil_cpp/absl/types/internal/conformance_profile.h
new file mode 100644
index 0000000000..cf64ff4fcd
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/conformance_profile.h
@@ -0,0 +1,931 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// conformance_profiles.h
+// -----------------------------------------------------------------------------
+//
+// This file contains templates for representing "Regularity Profiles" and
+// concisely-named versions of commonly used Regularity Profiles.
+//
+// A Regularity Profile is a compile-time description of the types of operations
+// that a given type supports, along with properties of those operations when
+// they do exist. For instance, a Regularity Profile may describe a type that
+// has a move-constructor that is noexcept and a copy constructor that is not
+// noexcept. This description can then be examined and passed around to other
+// templates for the purposes of asserting expectations on user-defined types
+// via a series trait checks, or for determining what kinds of run-time tests
+// are able to be performed.
+//
+// Regularity Profiles are also used when creating "archetypes," which are
+// minimum-conforming types that meet all of the requirements of a given
+// Regularity Profile. For more information regarding archetypes, see
+// "conformance_archetypes.h".
+
+#ifndef ABSL_TYPES_INTERNAL_CONFORMANCE_PROFILE_H_
+#define ABSL_TYPES_INTERNAL_CONFORMANCE_PROFILE_H_
+
+#include <set>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/algorithm/container.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+#include "absl/types/internal/conformance_testing_helpers.h"
+#include "absl/utility/utility.h"
+
+// TODO(calabrese) Add support for extending profiles.
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace types_internal {
+
+// Converts an enum to its underlying integral value.
+template <typename Enum>
+constexpr absl::underlying_type_t<Enum> UnderlyingValue(Enum value) {
+  return static_cast<absl::underlying_type_t<Enum>>(value);
+}
+
+// A tag type used in place of a matcher when checking that an assertion result
+// does not actually contain any errors.
+struct NoError {};
+
+// -----------------------------------------------------------------------------
+// ConformanceErrors
+// -----------------------------------------------------------------------------
+class ConformanceErrors {
+ public:
+  // Setup the error reporting mechanism by seeding it with the name of the type
+  // that is being tested.
+  explicit ConformanceErrors(std::string type_name)
+      : assertion_result_(false), type_name_(std::move(type_name)) {
+    assertion_result_ << "\n\n"
+                         "Assuming the following type alias:\n"
+                         "\n"
+                         "  using _T = "
+                      << type_name_ << ";\n\n";
+    outputDivider();
+  }
+
+  // Adds the test name to the list of successfully run tests iff it was not
+  // previously reported as failing. This behavior is useful for tests that
+  // have multiple parts, where failures and successes are reported individually
+  // with the same test name.
+  void addTestSuccess(absl::string_view test_name) {
+    auto normalized_test_name = absl::AsciiStrToLower(test_name);
+
+    // If the test is already reported as failing, do not add it to the list of
+    // successes.
+    if (test_failures_.find(normalized_test_name) == test_failures_.end()) {
+      test_successes_.insert(std::move(normalized_test_name));
+    }
+  }
+
+  // Streams a single error description into the internal buffer (a visual
+  // divider is automatically inserted after the error so that multiple errors
+  // are visibly distinct).
+  //
+  // This function increases the error count by 1.
+  //
+  // TODO(calabrese) Determine desired behavior when if this function throws.
+  template <class... P>
+  void addTestFailure(absl::string_view test_name, const P&... args) {
+    // Output a message related to the test failure.
+    assertion_result_ << "\n\n"
+                         "Failed test: "
+                      << test_name << "\n\n";
+    addTestFailureImpl(args...);
+    assertion_result_ << "\n\n";
+    outputDivider();
+
+    auto normalized_test_name = absl::AsciiStrToLower(test_name);
+
+    // If previous parts of this test succeeded, remove it from that set.
+    test_successes_.erase(normalized_test_name);
+
+    // Add the test name to the list of failed tests.
+    test_failures_.insert(std::move(normalized_test_name));
+
+    has_error_ = true;
+  }
+
+  // Convert this object into a testing::AssertionResult instance such that it
+  // can be used with gtest.
+  ::testing::AssertionResult assertionResult() const {
+    return has_error_ ? assertion_result_ : ::testing::AssertionSuccess();
+  }
+
+  // Convert this object into a testing::AssertionResult instance such that it
+  // can be used with gtest. This overload expects errors, using the specified
+  // matcher.
+  ::testing::AssertionResult expectFailedTests(
+      const std::set<std::string>& test_names) const {
+    // Since we are expecting nonconformance, output an error message when the
+    // type actually conformed to the specified profile.
+    if (!has_error_) {
+      return ::testing::AssertionFailure()
+             << "Unexpected conformance of type:\n"
+                "    "
+             << type_name_ << "\n\n";
+    }
+
+    // Get a list of all expected failures that did not actually fail
+    // (or that were not run).
+    std::vector<std::string> nonfailing_tests;
+    absl::c_set_difference(test_names, test_failures_,
+                           std::back_inserter(nonfailing_tests));
+
+    // Get a list of all "expected failures" that were never actually run.
+    std::vector<std::string> unrun_tests;
+    absl::c_set_difference(nonfailing_tests, test_successes_,
+                           std::back_inserter(unrun_tests));
+
+    // Report when the user specified tests that were not run.
+    if (!unrun_tests.empty()) {
+      const bool tests_were_run =
+          !(test_failures_.empty() && test_successes_.empty());
+
+      // Prepare an assertion result used in the case that tests pass that were
+      // expected to fail.
+      ::testing::AssertionResult result = ::testing::AssertionFailure();
+      result << "When testing type:\n    " << type_name_
+             << "\n\nThe following tests were expected to fail but were not "
+                "run";
+
+      if (tests_were_run) result << " (was the test name spelled correctly?)";
+
+      result << ":\n\n";
+
+      // List all of the tests that unexpectedly passed.
+      for (const auto& test_name : unrun_tests) {
+        result << "    " << test_name << "\n";
+      }
+
+      if (!tests_were_run) result << "\nNo tests were run.";
+
+      if (!test_failures_.empty()) {
+        // List test failures
+        result << "\nThe tests that were run and failed are:\n\n";
+        for (const auto& test_name : test_failures_) {
+          result << "    " << test_name << "\n";
+        }
+      }
+
+      if (!test_successes_.empty()) {
+        // List test successes
+        result << "\nThe tests that were run and succeeded are:\n\n";
+        for (const auto& test_name : test_successes_) {
+          result << "    " << test_name << "\n";
+        }
+      }
+
+      return result;
+    }
+
+    // If some tests passed when they were expected to fail, alert the caller.
+    if (nonfailing_tests.empty()) return ::testing::AssertionSuccess();
+
+    // Prepare an assertion result used in the case that tests pass that were
+    // expected to fail.
+    ::testing::AssertionResult unexpected_successes =
+        ::testing::AssertionFailure();
+    unexpected_successes << "When testing type:\n    " << type_name_
+                         << "\n\nThe following tests passed when they were "
+                            "expected to fail:\n\n";
+
+    // List all of the tests that unexpectedly passed.
+    for (const auto& test_name : nonfailing_tests) {
+      unexpected_successes << "    " << test_name << "\n";
+    }
+
+    return unexpected_successes;
+  }
+
+ private:
+  void outputDivider() {
+    assertion_result_ << "========================================";
+  }
+
+  void addTestFailureImpl() {}
+
+  template <class H, class... T>
+  void addTestFailureImpl(const H& head, const T&... tail) {
+    assertion_result_ << head;
+    addTestFailureImpl(tail...);
+  }
+
+  ::testing::AssertionResult assertion_result_;
+  std::set<std::string> test_failures_;
+  std::set<std::string> test_successes_;
+  std::string type_name_;
+  bool has_error_ = false;
+};
+
+template <class T, class /*Enabler*/ = void>
+struct PropertiesOfImpl {};
+
+template <class T>
+struct PropertiesOfImpl<T, absl::void_t<typename T::properties>> {
+  using type = typename T::properties;
+};
+
+template <class T>
+struct PropertiesOfImpl<T, absl::void_t<typename T::profile_alias_of>> {
+  using type = typename PropertiesOfImpl<typename T::profile_alias_of>::type;
+};
+
+template <class T>
+struct PropertiesOf : PropertiesOfImpl<T> {};
+
+template <class T>
+using PropertiesOfT = typename PropertiesOf<T>::type;
+
+// NOTE: These enums use this naming convention to be consistent with the
+// standard trait names, which is useful since it allows us to match up each
+// enum name with a corresponding trait name in macro definitions.
+
+// An enum that describes the various expectations on an operations existence.
+enum class function_support { maybe, yes, nothrow, trivial };
+
+constexpr const char* PessimisticPropertyDescription(function_support v) {
+  return v == function_support::maybe
+             ? "no"
+             : v == function_support::yes
+                   ? "yes, potentially throwing"
+                   : v == function_support::nothrow ? "yes, nothrow"
+                                                    : "yes, trivial";
+}
+
+// Return a string that describes the kind of property support that was
+// expected.
+inline std::string ExpectedFunctionKindList(function_support min,
+                                            function_support max) {
+  if (min == max) {
+    std::string result =
+        absl::StrCat("Expected:\n  ",
+                     PessimisticPropertyDescription(
+                         static_cast<function_support>(UnderlyingValue(min))),
+                     "\n");
+    return result;
+  }
+
+  std::string result = "Expected one of:\n";
+  for (auto curr_support = UnderlyingValue(min);
+       curr_support <= UnderlyingValue(max); ++curr_support) {
+    absl::StrAppend(&result, "  ",
+                    PessimisticPropertyDescription(
+                        static_cast<function_support>(curr_support)),
+                    "\n");
+  }
+
+  return result;
+}
+
+template <class Enum>
+void ExpectModelOfImpl(ConformanceErrors* errors, Enum min_support,
+                       Enum max_support, Enum kind) {
+  const auto kind_value = UnderlyingValue(kind);
+  const auto min_support_value = UnderlyingValue(min_support);
+  const auto max_support_value = UnderlyingValue(max_support);
+
+  if (!(kind_value >= min_support_value && kind_value <= max_support_value)) {
+    errors->addTestFailure(
+        PropertyName(kind), "**Failed property expectation**\n\n",
+        ExpectedFunctionKindList(
+            static_cast<function_support>(min_support_value),
+            static_cast<function_support>(max_support_value)),
+        '\n', "Actual:\n  ",
+        PessimisticPropertyDescription(
+            static_cast<function_support>(kind_value)));
+  } else {
+    errors->addTestSuccess(PropertyName(kind));
+  }
+}
+
+#define ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM(description, name) \
+  enum class name { maybe, yes, nothrow, trivial };                   \
+                                                                      \
+  constexpr const char* PropertyName(name v) { return description; }  \
+  static_assert(true, "")  // Force a semicolon when using this macro.
+
+ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM("support for default construction",
+                                           default_constructible);
+ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM("support for move construction",
+                                           move_constructible);
+ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM("support for copy construction",
+                                           copy_constructible);
+ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM("support for move assignment",
+                                           move_assignable);
+ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM("support for copy assignment",
+                                           copy_assignable);
+ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM("support for destruction",
+                                           destructible);
+
+#undef ABSL_INTERNAL_SPECIAL_MEMBER_FUNCTION_ENUM
+
+#define ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM(description, name)     \
+  enum class name { maybe, yes, nothrow };                           \
+                                                                     \
+  constexpr const char* PropertyName(name v) { return description; } \
+  static_assert(true, "")  // Force a semicolon when using this macro.
+
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for ==", equality_comparable);
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for !=", inequality_comparable);
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for <", less_than_comparable);
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for <=", less_equal_comparable);
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for >=",
+                                      greater_equal_comparable);
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for >", greater_than_comparable);
+
+ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM("support for swap", swappable);
+
+#undef ABSL_INTERNAL_INTRINSIC_FUNCTION_ENUM
+
+enum class hashable { maybe, yes };
+
+constexpr const char* PropertyName(hashable v) {
+  return "support for std::hash";
+}
+
+template <class T>
+using AlwaysFalse = std::false_type;
+
+#define ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(name, property)   \
+  template <class T>                                                        \
+  constexpr property property##_support_of() {                              \
+    return std::is_##property<T>::value                                     \
+               ? std::is_nothrow_##property<T>::value                       \
+                     ? absl::is_trivially_##property<T>::value              \
+                           ? property::trivial                              \
+                           : property::nothrow                              \
+                     : property::yes                                        \
+               : property::maybe;                                           \
+  }                                                                         \
+                                                                            \
+  template <class T, class MinProf, class MaxProf>                          \
+  void ExpectModelOf##name(ConformanceErrors* errors) {                     \
+    (ExpectModelOfImpl)(errors, PropertiesOfT<MinProf>::property##_support, \
+                        PropertiesOfT<MaxProf>::property##_support,         \
+                        property##_support_of<T>());                        \
+  }
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(DefaultConstructible,
+                                                  default_constructible);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(MoveConstructible,
+                                                  move_constructible);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(CopyConstructible,
+                                                  copy_constructible);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(MoveAssignable,
+                                                  move_assignable);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(CopyAssignable,
+                                                  copy_assignable);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER(Destructible, destructible);
+
+#undef ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_SPECIAL_MEMBER
+
+void BoolFunction(bool) noexcept;
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction for checking if an operation exists through SFINAE.
+//
+// `T` is the type to test and Op is an alias containing the expression to test.
+template <class T, template <class...> class Op, class = void>
+struct IsOpableImpl : std::false_type {};
+
+template <class T, template <class...> class Op>
+struct IsOpableImpl<T, Op, absl::void_t<Op<T>>> : std::true_type {};
+
+template <template <class...> class Op>
+struct IsOpable {
+  template <class T>
+  using apply = typename IsOpableImpl<T, Op>::type;
+};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction for checking if an operation exists and is also noexcept
+// through SFINAE and the noexcept operator.
+///
+// `T` is the type to test and Op is an alias containing the expression to test.
+template <class T, template <class...> class Op, class = void>
+struct IsNothrowOpableImpl : std::false_type {};
+
+template <class T, template <class...> class Op>
+struct IsNothrowOpableImpl<T, Op, absl::enable_if_t<Op<T>::value>>
+    : std::true_type {};
+
+template <template <class...> class Op>
+struct IsNothrowOpable {
+  template <class T>
+  using apply = typename IsNothrowOpableImpl<T, Op>::type;
+};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A macro that produces the necessary function for reporting what kind of
+// support a specific comparison operation has and a function for reporting an
+// error if a given type's support for that operation does not meet the expected
+// requirements.
+#define ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(name, property, op)      \
+  template <class T,                                                           \
+            class Result = std::integral_constant<                             \
+                bool, noexcept((BoolFunction)(std::declval<const T&>() op      \
+                                                  std::declval<const T&>()))>> \
+  using name = Result;                                                         \
+                                                                               \
+  template <class T>                                                           \
+  constexpr property property##_support_of() {                                 \
+    return IsOpable<name>::apply<T>::value                                     \
+               ? IsNothrowOpable<name>::apply<T>::value ? property::nothrow    \
+                                                        : property::yes        \
+               : property::maybe;                                              \
+  }                                                                            \
+                                                                               \
+  template <class T, class MinProf, class MaxProf>                             \
+  void ExpectModelOf##name(ConformanceErrors* errors) {                        \
+    (ExpectModelOfImpl)(errors, PropertiesOfT<MinProf>::property##_support,    \
+                        PropertiesOfT<MaxProf>::property##_support,            \
+                        property##_support_of<T>());                           \
+  }
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Generate the necessary support-checking and error reporting functions for
+// each of the comparison operators.
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(EqualityComparable,
+                                              equality_comparable, ==);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(InequalityComparable,
+                                              inequality_comparable, !=);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(LessThanComparable,
+                                              less_than_comparable, <);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(LessEqualComparable,
+                                              less_equal_comparable, <=);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(GreaterEqualComparable,
+                                              greater_equal_comparable, >=);
+
+ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON(GreaterThanComparable,
+                                              greater_than_comparable, >);
+
+#undef ABSL_INTERNAL_PESSIMISTIC_MODEL_OF_COMPARISON
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// The necessary support-checking and error-reporting functions for swap.
+template <class T>
+constexpr swappable swappable_support_of() {
+  return type_traits_internal::IsSwappable<T>::value
+             ? type_traits_internal::IsNothrowSwappable<T>::value
+                   ? swappable::nothrow
+                   : swappable::yes
+             : swappable::maybe;
+}
+
+template <class T, class MinProf, class MaxProf>
+void ExpectModelOfSwappable(ConformanceErrors* errors) {
+  (ExpectModelOfImpl)(errors, PropertiesOfT<MinProf>::swappable_support,
+                      PropertiesOfT<MaxProf>::swappable_support,
+                      swappable_support_of<T>());
+}
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// The necessary support-checking and error-reporting functions for std::hash.
+template <class T>
+constexpr hashable hashable_support_of() {
+  return type_traits_internal::IsHashable<T>::value ? hashable::yes
+                                                    : hashable::maybe;
+}
+
+template <class T, class MinProf, class MaxProf>
+void ExpectModelOfHashable(ConformanceErrors* errors) {
+  (ExpectModelOfImpl)(errors, PropertiesOfT<MinProf>::hashable_support,
+                      PropertiesOfT<MaxProf>::hashable_support,
+                      hashable_support_of<T>());
+}
+//
+////////////////////////////////////////////////////////////////////////////////
+
+template <
+    default_constructible DefaultConstructibleValue =
+        default_constructible::maybe,
+    move_constructible MoveConstructibleValue = move_constructible::maybe,
+    copy_constructible CopyConstructibleValue = copy_constructible::maybe,
+    move_assignable MoveAssignableValue = move_assignable::maybe,
+    copy_assignable CopyAssignableValue = copy_assignable::maybe,
+    destructible DestructibleValue = destructible::maybe,
+    equality_comparable EqualityComparableValue = equality_comparable::maybe,
+    inequality_comparable InequalityComparableValue =
+        inequality_comparable::maybe,
+    less_than_comparable LessThanComparableValue = less_than_comparable::maybe,
+    less_equal_comparable LessEqualComparableValue =
+        less_equal_comparable::maybe,
+    greater_equal_comparable GreaterEqualComparableValue =
+        greater_equal_comparable::maybe,
+    greater_than_comparable GreaterThanComparableValue =
+        greater_than_comparable::maybe,
+    swappable SwappableValue = swappable::maybe,
+    hashable HashableValue = hashable::maybe>
+struct ConformanceProfile {
+  using properties = ConformanceProfile;
+
+  static constexpr default_constructible
+      default_constructible_support =  // NOLINT
+      DefaultConstructibleValue;
+
+  static constexpr move_constructible move_constructible_support =  // NOLINT
+      MoveConstructibleValue;
+
+  static constexpr copy_constructible copy_constructible_support =  // NOLINT
+      CopyConstructibleValue;
+
+  static constexpr move_assignable move_assignable_support =  // NOLINT
+      MoveAssignableValue;
+
+  static constexpr copy_assignable copy_assignable_support =  // NOLINT
+      CopyAssignableValue;
+
+  static constexpr destructible destructible_support =  // NOLINT
+      DestructibleValue;
+
+  static constexpr equality_comparable equality_comparable_support =  // NOLINT
+      EqualityComparableValue;
+
+  static constexpr inequality_comparable
+      inequality_comparable_support =  // NOLINT
+      InequalityComparableValue;
+
+  static constexpr less_than_comparable
+      less_than_comparable_support =  // NOLINT
+      LessThanComparableValue;
+
+  static constexpr less_equal_comparable
+      less_equal_comparable_support =  // NOLINT
+      LessEqualComparableValue;
+
+  static constexpr greater_equal_comparable
+      greater_equal_comparable_support =  // NOLINT
+      GreaterEqualComparableValue;
+
+  static constexpr greater_than_comparable
+      greater_than_comparable_support =  // NOLINT
+      GreaterThanComparableValue;
+
+  static constexpr swappable swappable_support = SwappableValue;  // NOLINT
+
+  static constexpr hashable hashable_support = HashableValue;  // NOLINT
+
+  static constexpr bool is_default_constructible =  // NOLINT
+      DefaultConstructibleValue != default_constructible::maybe;
+
+  static constexpr bool is_move_constructible =  // NOLINT
+      MoveConstructibleValue != move_constructible::maybe;
+
+  static constexpr bool is_copy_constructible =  // NOLINT
+      CopyConstructibleValue != copy_constructible::maybe;
+
+  static constexpr bool is_move_assignable =  // NOLINT
+      MoveAssignableValue != move_assignable::maybe;
+
+  static constexpr bool is_copy_assignable =  // NOLINT
+      CopyAssignableValue != copy_assignable::maybe;
+
+  static constexpr bool is_destructible =  // NOLINT
+      DestructibleValue != destructible::maybe;
+
+  static constexpr bool is_equality_comparable =  // NOLINT
+      EqualityComparableValue != equality_comparable::maybe;
+
+  static constexpr bool is_inequality_comparable =  // NOLINT
+      InequalityComparableValue != inequality_comparable::maybe;
+
+  static constexpr bool is_less_than_comparable =  // NOLINT
+      LessThanComparableValue != less_than_comparable::maybe;
+
+  static constexpr bool is_less_equal_comparable =  // NOLINT
+      LessEqualComparableValue != less_equal_comparable::maybe;
+
+  static constexpr bool is_greater_equal_comparable =  // NOLINT
+      GreaterEqualComparableValue != greater_equal_comparable::maybe;
+
+  static constexpr bool is_greater_than_comparable =  // NOLINT
+      GreaterThanComparableValue != greater_than_comparable::maybe;
+
+  static constexpr bool is_swappable =  // NOLINT
+      SwappableValue != swappable::maybe;
+
+  static constexpr bool is_hashable =  // NOLINT
+      HashableValue != hashable::maybe;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Compliant SFINAE-friendliness is not always present on the standard library
+// implementations that we support. This helper-struct (and associated enum) is
+// used as a means to conditionally check the hashability support of a type.
+enum class CheckHashability { no, yes };
+
+template <class T, CheckHashability ShouldCheckHashability>
+struct conservative_hashable_support_of;
+
+template <class T>
+struct conservative_hashable_support_of<T, CheckHashability::no> {
+  static constexpr hashable Invoke() { return hashable::maybe; }
+};
+
+template <class T>
+struct conservative_hashable_support_of<T, CheckHashability::yes> {
+  static constexpr hashable Invoke() { return hashable_support_of<T>(); }
+};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// The ConformanceProfile that is expected based on introspection into the type
+// by way of trait checks.
+template <class T, CheckHashability ShouldCheckHashability>
+struct SyntacticConformanceProfileOf {
+  using properties = ConformanceProfile<
+      default_constructible_support_of<T>(), move_constructible_support_of<T>(),
+      copy_constructible_support_of<T>(), move_assignable_support_of<T>(),
+      copy_assignable_support_of<T>(), destructible_support_of<T>(),
+      equality_comparable_support_of<T>(),
+      inequality_comparable_support_of<T>(),
+      less_than_comparable_support_of<T>(),
+      less_equal_comparable_support_of<T>(),
+      greater_equal_comparable_support_of<T>(),
+      greater_than_comparable_support_of<T>(), swappable_support_of<T>(),
+      conservative_hashable_support_of<T, ShouldCheckHashability>::Invoke()>;
+};
+
+#define ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF_IMPL(type, name)     \
+  template <default_constructible DefaultConstructibleValue,                   \
+            move_constructible MoveConstructibleValue,                         \
+            copy_constructible CopyConstructibleValue,                         \
+            move_assignable MoveAssignableValue,                               \
+            copy_assignable CopyAssignableValue,                               \
+            destructible DestructibleValue,                                    \
+            equality_comparable EqualityComparableValue,                       \
+            inequality_comparable InequalityComparableValue,                   \
+            less_than_comparable LessThanComparableValue,                      \
+            less_equal_comparable LessEqualComparableValue,                    \
+            greater_equal_comparable GreaterEqualComparableValue,              \
+            greater_than_comparable GreaterThanComparableValue,                \
+            swappable SwappableValue, hashable HashableValue>                  \
+  constexpr type ConformanceProfile<                                           \
+      DefaultConstructibleValue, MoveConstructibleValue,                       \
+      CopyConstructibleValue, MoveAssignableValue, CopyAssignableValue,        \
+      DestructibleValue, EqualityComparableValue, InequalityComparableValue,   \
+      LessThanComparableValue, LessEqualComparableValue,                       \
+      GreaterEqualComparableValue, GreaterThanComparableValue, SwappableValue, \
+      HashableValue>::name
+
+#define ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(type)           \
+  ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF_IMPL(type,            \
+                                                         type##_support); \
+  ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF_IMPL(bool, is_##type)
+
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(default_constructible);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(move_constructible);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(copy_constructible);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(move_assignable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(copy_assignable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(destructible);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(equality_comparable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(inequality_comparable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(less_than_comparable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(less_equal_comparable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(greater_equal_comparable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(greater_than_comparable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(swappable);
+ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF(hashable);
+
+#undef ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF
+#undef ABSL_INTERNAL_CONFORMANCE_TESTING_DATA_MEMBER_DEF_IMPL
+
+// Retrieve the enum with the minimum underlying value.
+// Note: std::min is not constexpr in C++11, which is why this is necessary.
+template <class H>
+constexpr H MinEnum(H head) {
+  return head;
+}
+
+template <class H, class N, class... T>
+constexpr H MinEnum(H head, N next, T... tail) {
+  return (UnderlyingValue)(head) < (UnderlyingValue)(next)
+             ? (MinEnum)(head, tail...)
+             : (MinEnum)(next, tail...);
+}
+
+template <class... Profs>
+struct MinimalProfiles {
+  static constexpr default_constructible
+      default_constructible_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::default_constructible_support...);
+
+  static constexpr move_constructible move_constructible_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::move_constructible_support...);
+
+  static constexpr copy_constructible copy_constructible_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::copy_constructible_support...);
+
+  static constexpr move_assignable move_assignable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::move_assignable_support...);
+
+  static constexpr copy_assignable copy_assignable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::copy_assignable_support...);
+
+  static constexpr destructible destructible_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::destructible_support...);
+
+  static constexpr equality_comparable equality_comparable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::equality_comparable_support...);
+
+  static constexpr inequality_comparable
+      inequality_comparable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::inequality_comparable_support...);
+
+  static constexpr less_than_comparable
+      less_than_comparable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::less_than_comparable_support...);
+
+  static constexpr less_equal_comparable
+      less_equal_comparable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::less_equal_comparable_support...);
+
+  static constexpr greater_equal_comparable
+      greater_equal_comparable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::greater_equal_comparable_support...);
+
+  static constexpr greater_than_comparable
+      greater_than_comparable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::greater_than_comparable_support...);
+
+  static constexpr swappable swappable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::swappable_support...);
+
+  static constexpr hashable hashable_support =  // NOLINT
+      (MinEnum)(PropertiesOfT<Profs>::hashable_support...);
+
+  using properties = ConformanceProfile<
+      default_constructible_support, move_constructible_support,
+      copy_constructible_support, move_assignable_support,
+      copy_assignable_support, destructible_support,
+      equality_comparable_support, inequality_comparable_support,
+      less_than_comparable_support, less_equal_comparable_support,
+      greater_equal_comparable_support, greater_than_comparable_support,
+      swappable_support, hashable_support>;
+};
+
+// Retrieve the enum with the greatest underlying value.
+// Note: std::max is not constexpr in C++11, which is why this is necessary.
+template <class H>
+constexpr H MaxEnum(H head) {
+  return head;
+}
+
+template <class H, class N, class... T>
+constexpr H MaxEnum(H head, N next, T... tail) {
+  return (UnderlyingValue)(next) < (UnderlyingValue)(head)
+             ? (MaxEnum)(head, tail...)
+             : (MaxEnum)(next, tail...);
+}
+
+template <class... Profs>
+struct CombineProfilesImpl {
+  static constexpr default_constructible
+      default_constructible_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::default_constructible_support...);
+
+  static constexpr move_constructible move_constructible_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::move_constructible_support...);
+
+  static constexpr copy_constructible copy_constructible_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::copy_constructible_support...);
+
+  static constexpr move_assignable move_assignable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::move_assignable_support...);
+
+  static constexpr copy_assignable copy_assignable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::copy_assignable_support...);
+
+  static constexpr destructible destructible_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::destructible_support...);
+
+  static constexpr equality_comparable equality_comparable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::equality_comparable_support...);
+
+  static constexpr inequality_comparable
+      inequality_comparable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::inequality_comparable_support...);
+
+  static constexpr less_than_comparable
+      less_than_comparable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::less_than_comparable_support...);
+
+  static constexpr less_equal_comparable
+      less_equal_comparable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::less_equal_comparable_support...);
+
+  static constexpr greater_equal_comparable
+      greater_equal_comparable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::greater_equal_comparable_support...);
+
+  static constexpr greater_than_comparable
+      greater_than_comparable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::greater_than_comparable_support...);
+
+  static constexpr swappable swappable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::swappable_support...);
+
+  static constexpr hashable hashable_support =  // NOLINT
+      (MaxEnum)(PropertiesOfT<Profs>::hashable_support...);
+
+  using properties = ConformanceProfile<
+      default_constructible_support, move_constructible_support,
+      copy_constructible_support, move_assignable_support,
+      copy_assignable_support, destructible_support,
+      equality_comparable_support, inequality_comparable_support,
+      less_than_comparable_support, less_equal_comparable_support,
+      greater_equal_comparable_support, greater_than_comparable_support,
+      swappable_support, hashable_support>;
+};
+
+// NOTE: We use this as opposed to a direct alias of CombineProfilesImpl so that
+// when named aliases of CombineProfiles are created (such as in
+// conformance_aliases.h), we only pay for the combination algorithm on the
+// profiles that are actually used.
+template <class... Profs>
+struct CombineProfiles {
+  using profile_alias_of = CombineProfilesImpl<Profs...>;
+};
+
+template <>
+struct CombineProfiles<> {
+  using properties = ConformanceProfile<>;
+};
+
+template <class Profile, class Tag>
+struct StrongProfileTypedef {
+  using properties = PropertiesOfT<Profile>;
+};
+
+template <class T, class /*Enabler*/ = void>
+struct IsProfileImpl : std::false_type {};
+
+template <class T>
+struct IsProfileImpl<T, absl::void_t<PropertiesOfT<T>>> : std::true_type {};
+
+template <class T>
+struct IsProfile : IsProfileImpl<T>::type {};
+
+// A tag that describes which set of properties we will check when the user
+// requires a strict match in conformance (as opposed to a loose match which
+// allows more-refined support of any given operation).
+//
+// Currently only the RegularityDomain exists and it includes all operations
+// that the conformance testing suite knows about. The intent is that if the
+// suite is expanded to support extension, such as for checking conformance of
+// concepts like Iterators or Containers, additional corresponding domains can
+// be created.
+struct RegularityDomain {};
+
+}  // namespace types_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TYPES_INTERNAL_CONFORMANCE_PROFILE_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/conformance_testing.h b/third_party/abseil_cpp/absl/types/internal/conformance_testing.h
new file mode 100644
index 0000000000..487b0f786b
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/conformance_testing.h
@@ -0,0 +1,1386 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// conformance_testing.h
+// -----------------------------------------------------------------------------
+//
+
+#ifndef ABSL_TYPES_INTERNAL_CONFORMANCE_TESTING_H_
+#define ABSL_TYPES_INTERNAL_CONFORMANCE_TESTING_H_
+
+////////////////////////////////////////////////////////////////////////////////
+//                                                                            //
+// Many templates in this file take a `T` and a `Prof` type as explicit       //
+// template arguments. These are a type to be checked and a                   //
+// "Regularity Profile" that describes what operations that type `T` is       //
+// expected to support. See "regularity_profiles.h" for more details          //
+// regarding Regularity Profiles.                                             //
+//                                                                            //
+////////////////////////////////////////////////////////////////////////////////
+
+#include <cstddef>
+#include <set>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+#include "absl/types/internal/conformance_aliases.h"
+#include "absl/types/internal/conformance_archetype.h"
+#include "absl/types/internal/conformance_profile.h"
+#include "absl/types/internal/conformance_testing_helpers.h"
+#include "absl/types/internal/parentheses.h"
+#include "absl/types/internal/transform_args.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace types_internal {
+
+// Returns true if the compiler incorrectly greedily instantiates constexpr
+// templates in any unevaluated context.
+constexpr bool constexpr_instantiation_when_unevaluated() {
+#if defined(__apple_build_version__)  // TODO(calabrese) Make more specific
+  return true;
+#elif defined(__clang__)
+  return __clang_major__ < 4;
+#elif defined(__GNUC__)
+  // TODO(calabrese) Figure out why gcc 7 fails (seems like a different bug)
+  return __GNUC__ < 5 || (__GNUC__ == 5 && __GNUC_MINOR__ < 2) || __GNUC__ >= 7;
+#else
+  return false;
+#endif
+}
+
+// Returns true if the standard library being used incorrectly produces an error
+// when instantiating the definition of a poisoned std::hash specialization.
+constexpr bool poisoned_hash_fails_instantiation() {
+#if defined(_MSC_VER) && !defined(_LIBCPP_VERSION)
+  return _MSC_VER < 1914;
+#else
+  return false;
+#endif
+}
+
+template <class Fun>
+struct GeneratorType {
+  decltype(std::declval<const Fun&>()()) operator()() const
+      noexcept(noexcept(std::declval<const Fun&>()())) {
+    return fun();
+  }
+
+  Fun fun;
+  const char* description;
+};
+
+// A "make" function for the GeneratorType template that deduces the function
+// object type.
+template <class Fun,
+          absl::enable_if_t<IsNullaryCallable<Fun>::value>** = nullptr>
+GeneratorType<Fun> Generator(Fun fun, const char* description) {
+  return GeneratorType<Fun>{absl::move(fun), description};
+}
+
+// A type that contains a set of nullary function objects that each return an
+// instance of the same type and value (though possibly different
+// representations, such as +0 and -0 or two vectors with the same elements but
+// with different capacities).
+template <class... Funs>
+struct EquivalenceClassType {
+  std::tuple<GeneratorType<Funs>...> generators;
+};
+
+// A "make" function for the EquivalenceClassType template that deduces the
+// function object types and is constrained such that a user can only pass in
+// function objects that all have the same return type.
+template <class... Funs, absl::enable_if_t<AreGeneratorsWithTheSameReturnType<
+                             Funs...>::value>** = nullptr>
+EquivalenceClassType<Funs...> EquivalenceClass(GeneratorType<Funs>... funs) {
+  return {std::make_tuple(absl::move(funs)...)};
+}
+
+// A type that contains an ordered series of EquivalenceClassTypes, from
+// smallest value to largest value.
+template <class... EqClasses>
+struct OrderedEquivalenceClasses {
+  std::tuple<EqClasses...> eq_classes;
+};
+
+// An object containing the parts of a given (name, initialization expression),
+// and is capable of generating a string that describes the given.
+struct GivenDeclaration {
+  std::string outputDeclaration(std::size_t width) const {
+    const std::size_t indent_size = 2;
+    std::string result = absl::StrCat("  ", name);
+
+    if (!expression.empty()) {
+      // Indent
+      result.resize(indent_size + width, ' ');
+      absl::StrAppend(&result, " = ", expression, ";\n");
+    } else {
+      absl::StrAppend(&result, ";\n");
+    }
+
+    return result;
+  }
+
+  std::string name;
+  std::string expression;
+};
+
+// Produce a string that contains all of the givens of an error report.
+template <class... Decls>
+std::string PrepareGivenContext(const Decls&... decls) {
+  const std::size_t width = (std::max)({decls.name.size()...});
+  return absl::StrCat("Given:\n", decls.outputDeclaration(width)..., "\n");
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Function objects that perform a check for each comparison operator         //
+////////////////////////////////////////////////////////////////////////////////
+
+#define ABSL_INTERNAL_EXPECT_OP(name, op)                                   \
+  struct Expect##name {                                                     \
+    template <class T>                                                      \
+    void operator()(absl::string_view test_name, absl::string_view context, \
+                    const T& lhs, const T& rhs, absl::string_view lhs_name, \
+                    absl::string_view rhs_name) const {                     \
+      if (!static_cast<bool>(lhs op rhs)) {                                 \
+        errors->addTestFailure(                                             \
+            test_name, absl::StrCat(context,                                \
+                                    "**Unexpected comparison result**\n"    \
+                                    "\n"                                    \
+                                    "Expression:\n"                         \
+                                    "  ",                                   \
+                                    lhs_name, " " #op " ", rhs_name,        \
+                                    "\n"                                    \
+                                    "\n"                                    \
+                                    "Expected: true\n"                      \
+                                    "  Actual: false"));                    \
+      } else {                                                              \
+        errors->addTestSuccess(test_name);                                  \
+      }                                                                     \
+    }                                                                       \
+                                                                            \
+    ConformanceErrors* errors;                                              \
+  };                                                                        \
+                                                                            \
+  struct ExpectNot##name {                                                  \
+    template <class T>                                                      \
+    void operator()(absl::string_view test_name, absl::string_view context, \
+                    const T& lhs, const T& rhs, absl::string_view lhs_name, \
+                    absl::string_view rhs_name) const {                     \
+      if (lhs op rhs) {                                                     \
+        errors->addTestFailure(                                             \
+            test_name, absl::StrCat(context,                                \
+                                    "**Unexpected comparison result**\n"    \
+                                    "\n"                                    \
+                                    "Expression:\n"                         \
+                                    "  ",                                   \
+                                    lhs_name, " " #op " ", rhs_name,        \
+                                    "\n"                                    \
+                                    "\n"                                    \
+                                    "Expected: false\n"                     \
+                                    "  Actual: true"));                     \
+      } else {                                                              \
+        errors->addTestSuccess(test_name);                                  \
+      }                                                                     \
+    }                                                                       \
+                                                                            \
+    ConformanceErrors* errors;                                              \
+  }
+
+ABSL_INTERNAL_EXPECT_OP(Eq, ==);
+ABSL_INTERNAL_EXPECT_OP(Ne, !=);
+ABSL_INTERNAL_EXPECT_OP(Lt, <);
+ABSL_INTERNAL_EXPECT_OP(Le, <=);
+ABSL_INTERNAL_EXPECT_OP(Ge, >=);
+ABSL_INTERNAL_EXPECT_OP(Gt, >);
+
+#undef ABSL_INTERNAL_EXPECT_OP
+
+// A function object that verifies that two objects hash to the same value by
+// way of the std::hash specialization.
+struct ExpectSameHash {
+  template <class T>
+  void operator()(absl::string_view test_name, absl::string_view context,
+                  const T& lhs, const T& rhs, absl::string_view lhs_name,
+                  absl::string_view rhs_name) const {
+    if (std::hash<T>()(lhs) != std::hash<T>()(rhs)) {
+      errors->addTestFailure(
+          test_name, absl::StrCat(context,
+                                  "**Unexpected hash result**\n"
+                                  "\n"
+                                  "Expression:\n"
+                                  "  std::hash<T>()(",
+                                  lhs_name, ") == std::hash<T>()(", rhs_name,
+                                  ")\n"
+                                  "\n"
+                                  "Expected: true\n"
+                                  "  Actual: false"));
+    } else {
+      errors->addTestSuccess(test_name);
+    }
+  }
+
+  ConformanceErrors* errors;
+};
+
+// A function template that takes two objects and verifies that each comparison
+// operator behaves in a way that is consistent with equality. It has "OneWay"
+// in the name because the first argument will always be the left-hand operand
+// of the corresponding comparison operator and the second argument will
+// always be the right-hand operand. It will never switch that order.
+// At a higher level in the test suite, the one-way form is called once for each
+// of the two possible orders whenever lhs and rhs are not the same initializer.
+template <class T, class Prof>
+void ExpectOneWayEquality(ConformanceErrors* errors,
+                          absl::string_view test_name,
+                          absl::string_view context, const T& lhs, const T& rhs,
+                          absl::string_view lhs_name,
+                          absl::string_view rhs_name) {
+  If<PropertiesOfT<Prof>::is_equality_comparable>::Invoke(
+      ExpectEq{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+
+  If<PropertiesOfT<Prof>::is_inequality_comparable>::Invoke(
+      ExpectNotNe{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+
+  If<PropertiesOfT<Prof>::is_less_than_comparable>::Invoke(
+      ExpectNotLt{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+
+  If<PropertiesOfT<Prof>::is_less_equal_comparable>::Invoke(
+      ExpectLe{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+
+  If<PropertiesOfT<Prof>::is_greater_equal_comparable>::Invoke(
+      ExpectGe{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+
+  If<PropertiesOfT<Prof>::is_greater_than_comparable>::Invoke(
+      ExpectNotGt{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+
+  If<PropertiesOfT<Prof>::is_hashable>::Invoke(
+      ExpectSameHash{errors}, test_name, context, lhs, rhs, lhs_name, rhs_name);
+}
+
+// A function template that takes two objects and verifies that each comparison
+// operator behaves in a way that is consistent with equality. This function
+// differs from ExpectOneWayEquality in that this will do checks with argument
+// order reversed in addition to in-order.
+template <class T, class Prof>
+void ExpectEquality(ConformanceErrors* errors, absl::string_view test_name,
+                    absl::string_view context, const T& lhs, const T& rhs,
+                    absl::string_view lhs_name, absl::string_view rhs_name) {
+  (ExpectOneWayEquality<T, Prof>)(errors, test_name, context, lhs, rhs,
+                                  lhs_name, rhs_name);
+  (ExpectOneWayEquality<T, Prof>)(errors, test_name, context, rhs, lhs,
+                                  rhs_name, lhs_name);
+}
+
+// Given a generator, makes sure that a generated value and a moved-from
+// generated value are equal.
+template <class T, class Prof>
+struct ExpectMoveConstructOneGenerator {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T object = generator();
+    const T moved_object = absl::move(generator());  // Force no elision.
+
+    (ExpectEquality<T, Prof>)(errors, "Move construction",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T object",
+                                                   generator.description},
+                                  GivenDeclaration{"const _T moved_object",
+                                                   std::string("std::move(") +
+                                                       generator.description +
+                                                       ")"}),
+                              object, moved_object, "object", "moved_object");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Given a generator, makes sure that a generated value and a copied-from
+// generated value are equal.
+template <class T, class Prof>
+struct ExpectCopyConstructOneGenerator {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T object = generator();
+    const T copied_object = static_cast<const T&>(generator());
+
+    (ExpectEquality<T, Prof>)(errors, "Copy construction",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T object",
+                                                   generator.description},
+                                  GivenDeclaration{
+                                      "const _T copied_object",
+                                      std::string("static_cast<const _T&>(") +
+                                          generator.description + ")"}),
+                              object, copied_object, "object", "copied_object");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Default-construct and do nothing before destruction.
+//
+// This is useful in exercising the codepath of default construction followed by
+// destruction, but does not explicitly test anything. An example of where this
+// might fail is a default destructor that default-initializes a scalar and a
+// destructor reads the value of that member. Sanitizers can catch this as long
+// as our test attempts to execute such a case.
+template <class T>
+struct ExpectDefaultConstructWithDestruct {
+  void operator()() const {
+    // Scoped so that destructor gets called before reporting success.
+    {
+      T object;
+      static_cast<void>(object);
+    }
+
+    errors->addTestSuccess("Default construction");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Check move-assign into a default-constructed object.
+template <class T, class Prof>
+struct ExpectDefaultConstructWithMoveAssign {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T source_of_truth = generator();
+    T object;
+    object = generator();
+
+    (ExpectEquality<T, Prof>)(errors, "Move assignment",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T object",
+                                                   generator.description},
+                                  GivenDeclaration{"_T object", ""},
+                                  GivenDeclaration{"object",
+                                                   generator.description}),
+                              object, source_of_truth, "std::as_const(object)",
+                              "source_of_truth");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Check copy-assign into a default-constructed object.
+template <class T, class Prof>
+struct ExpectDefaultConstructWithCopyAssign {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T source_of_truth = generator();
+    T object;
+    object = static_cast<const T&>(generator());
+
+    (ExpectEquality<T, Prof>)(errors, "Copy assignment",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T source_of_truth",
+                                                   generator.description},
+                                  GivenDeclaration{"_T object", ""},
+                                  GivenDeclaration{
+                                      "object",
+                                      std::string("static_cast<const _T&>(") +
+                                          generator.description + ")"}),
+                              object, source_of_truth, "std::as_const(object)",
+                              "source_of_truth");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Perform a self move-assign.
+template <class T, class Prof>
+struct ExpectSelfMoveAssign {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    T object = generator();
+    object = absl::move(object);
+
+    // NOTE: Self move-assign results in a valid-but-unspecified state.
+
+    (ExpectEquality<T, Prof>)(errors, "Move assignment",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"_T object",
+                                                   generator.description},
+                                  GivenDeclaration{"object",
+                                                   "std::move(object)"}),
+                              object, object, "object", "object");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Perform a self copy-assign.
+template <class T, class Prof>
+struct ExpectSelfCopyAssign {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T source_of_truth = generator();
+    T object = generator();
+    const T& const_object = object;
+    object = const_object;
+
+    (ExpectEquality<T, Prof>)(errors, "Copy assignment",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T source_of_truth",
+                                                   generator.description},
+                                  GivenDeclaration{"_T object",
+                                                   generator.description},
+                                  GivenDeclaration{"object",
+                                                   "std::as_const(object)"}),
+                              const_object, source_of_truth,
+                              "std::as_const(object)", "source_of_truth");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Perform a self-swap.
+template <class T, class Prof>
+struct ExpectSelfSwap {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T source_of_truth = generator();
+    T object = generator();
+
+    type_traits_internal::Swap(object, object);
+
+    std::string preliminary_info = absl::StrCat(
+        PrepareGivenContext(
+            GivenDeclaration{"const _T source_of_truth", generator.description},
+            GivenDeclaration{"_T object", generator.description}),
+        "After performing a self-swap:\n"
+        "  using std::swap;\n"
+        "  swap(object, object);\n"
+        "\n");
+
+    (ExpectEquality<T, Prof>)(errors, "Swap", std::move(preliminary_info),
+                              object, source_of_truth, "std::as_const(object)",
+                              "source_of_truth");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Perform each of the single-generator checks when necessary operations are
+// supported.
+template <class T, class Prof>
+struct ExpectSelfComparison {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    const T object = generator();
+    (ExpectOneWayEquality<T, Prof>)(errors, "Comparison",
+                                    PrepareGivenContext(GivenDeclaration{
+                                        "const _T object",
+                                        generator.description}),
+                                    object, object, "object", "object");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Perform each of the single-generator checks when necessary operations are
+// supported.
+template <class T, class Prof>
+struct ExpectConsistency {
+  template <class Fun>
+  void operator()(const Fun& generator) const {
+    If<PropertiesOfT<Prof>::is_move_constructible>::Invoke(
+        ExpectMoveConstructOneGenerator<T, Prof>{errors}, generator);
+
+    If<PropertiesOfT<Prof>::is_copy_constructible>::Invoke(
+        ExpectCopyConstructOneGenerator<T, Prof>{errors}, generator);
+
+    If<PropertiesOfT<Prof>::is_default_constructible &&
+       PropertiesOfT<Prof>::is_move_assignable>::
+        Invoke(ExpectDefaultConstructWithMoveAssign<T, Prof>{errors},
+               generator);
+
+    If<PropertiesOfT<Prof>::is_default_constructible &&
+       PropertiesOfT<Prof>::is_copy_assignable>::
+        Invoke(ExpectDefaultConstructWithCopyAssign<T, Prof>{errors},
+               generator);
+
+    If<PropertiesOfT<Prof>::is_move_assignable>::Invoke(
+        ExpectSelfMoveAssign<T, Prof>{errors}, generator);
+
+    If<PropertiesOfT<Prof>::is_copy_assignable>::Invoke(
+        ExpectSelfCopyAssign<T, Prof>{errors}, generator);
+
+    If<PropertiesOfT<Prof>::is_swappable>::Invoke(
+        ExpectSelfSwap<T, Prof>{errors}, generator);
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Check move-assign with two different values.
+template <class T, class Prof>
+struct ExpectMoveAssign {
+  template <class Fun0, class Fun1>
+  void operator()(const Fun0& generator0, const Fun1& generator1) const {
+    const T source_of_truth1 = generator1();
+    T object = generator0();
+    object = generator1();
+
+    (ExpectEquality<T, Prof>)(errors, "Move assignment",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T source_of_truth1",
+                                                   generator1.description},
+                                  GivenDeclaration{"_T object",
+                                                   generator0.description},
+                                  GivenDeclaration{"object",
+                                                   generator1.description}),
+                              object, source_of_truth1, "std::as_const(object)",
+                              "source_of_truth1");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Check copy-assign with two different values.
+template <class T, class Prof>
+struct ExpectCopyAssign {
+  template <class Fun0, class Fun1>
+  void operator()(const Fun0& generator0, const Fun1& generator1) const {
+    const T source_of_truth1 = generator1();
+    T object = generator0();
+    object = static_cast<const T&>(generator1());
+
+    (ExpectEquality<T, Prof>)(errors, "Copy assignment",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T source_of_truth1",
+                                                   generator1.description},
+                                  GivenDeclaration{"_T object",
+                                                   generator0.description},
+                                  GivenDeclaration{
+                                      "object",
+                                      std::string("static_cast<const _T&>(") +
+                                          generator1.description + ")"}),
+                              object, source_of_truth1, "std::as_const(object)",
+                              "source_of_truth1");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Check swap with two different values.
+template <class T, class Prof>
+struct ExpectSwap {
+  template <class Fun0, class Fun1>
+  void operator()(const Fun0& generator0, const Fun1& generator1) const {
+    const T source_of_truth0 = generator0();
+    const T source_of_truth1 = generator1();
+    T object0 = generator0();
+    T object1 = generator1();
+
+    type_traits_internal::Swap(object0, object1);
+
+    const std::string context =
+        PrepareGivenContext(
+            GivenDeclaration{"const _T source_of_truth0",
+                             generator0.description},
+            GivenDeclaration{"const _T source_of_truth1",
+                             generator1.description},
+            GivenDeclaration{"_T object0", generator0.description},
+            GivenDeclaration{"_T object1", generator1.description}) +
+        "After performing a swap:\n"
+        "  using std::swap;\n"
+        "  swap(object0, object1);\n"
+        "\n";
+
+    (ExpectEquality<T, Prof>)(errors, "Swap", context, object0,
+                              source_of_truth1, "std::as_const(object0)",
+                              "source_of_truth1");
+    (ExpectEquality<T, Prof>)(errors, "Swap", context, object1,
+                              source_of_truth0, "std::as_const(object1)",
+                              "source_of_truth0");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Validate that `generator0` and `generator1` produce values that are equal.
+template <class T, class Prof>
+struct ExpectEquivalenceClassComparison {
+  template <class Fun0, class Fun1>
+  void operator()(const Fun0& generator0, const Fun1& generator1) const {
+    const T object0 = generator0();
+    const T object1 = generator1();
+
+    (ExpectEquality<T, Prof>)(errors, "Comparison",
+                              PrepareGivenContext(
+                                  GivenDeclaration{"const _T object0",
+                                                   generator0.description},
+                                  GivenDeclaration{"const _T object1",
+                                                   generator1.description}),
+                              object0, object1, "object0", "object1");
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Validate that all objects in the same equivalence-class have the same value.
+template <class T, class Prof>
+struct ExpectEquivalenceClassConsistency {
+  template <class Fun0, class Fun1>
+  void operator()(const Fun0& generator0, const Fun1& generator1) const {
+    If<PropertiesOfT<Prof>::is_move_assignable>::Invoke(
+        ExpectMoveAssign<T, Prof>{errors}, generator0, generator1);
+
+    If<PropertiesOfT<Prof>::is_copy_assignable>::Invoke(
+        ExpectCopyAssign<T, Prof>{errors}, generator0, generator1);
+
+    If<PropertiesOfT<Prof>::is_swappable>::Invoke(ExpectSwap<T, Prof>{errors},
+                                                  generator0, generator1);
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Given a "lesser" object and a "greater" object, perform every combination of
+// comparison operators supported for the type, expecting consistent results.
+template <class T, class Prof>
+void ExpectOrdered(ConformanceErrors* errors, absl::string_view context,
+                   const T& small, const T& big, absl::string_view small_name,
+                   absl::string_view big_name) {
+  const absl::string_view test_name = "Comparison";
+
+  If<PropertiesOfT<Prof>::is_equality_comparable>::Invoke(
+      ExpectNotEq{errors}, test_name, context, small, big, small_name,
+      big_name);
+  If<PropertiesOfT<Prof>::is_equality_comparable>::Invoke(
+      ExpectNotEq{errors}, test_name, context, big, small, big_name,
+      small_name);
+
+  If<PropertiesOfT<Prof>::is_inequality_comparable>::Invoke(
+      ExpectNe{errors}, test_name, context, small, big, small_name, big_name);
+  If<PropertiesOfT<Prof>::is_inequality_comparable>::Invoke(
+      ExpectNe{errors}, test_name, context, big, small, big_name, small_name);
+
+  If<PropertiesOfT<Prof>::is_less_than_comparable>::Invoke(
+      ExpectLt{errors}, test_name, context, small, big, small_name, big_name);
+  If<PropertiesOfT<Prof>::is_less_than_comparable>::Invoke(
+      ExpectNotLt{errors}, test_name, context, big, small, big_name,
+      small_name);
+
+  If<PropertiesOfT<Prof>::is_less_equal_comparable>::Invoke(
+      ExpectLe{errors}, test_name, context, small, big, small_name, big_name);
+  If<PropertiesOfT<Prof>::is_less_equal_comparable>::Invoke(
+      ExpectNotLe{errors}, test_name, context, big, small, big_name,
+      small_name);
+
+  If<PropertiesOfT<Prof>::is_greater_equal_comparable>::Invoke(
+      ExpectNotGe{errors}, test_name, context, small, big, small_name,
+      big_name);
+  If<PropertiesOfT<Prof>::is_greater_equal_comparable>::Invoke(
+      ExpectGe{errors}, test_name, context, big, small, big_name, small_name);
+
+  If<PropertiesOfT<Prof>::is_greater_than_comparable>::Invoke(
+      ExpectNotGt{errors}, test_name, context, small, big, small_name,
+      big_name);
+  If<PropertiesOfT<Prof>::is_greater_than_comparable>::Invoke(
+      ExpectGt{errors}, test_name, context, big, small, big_name, small_name);
+}
+
+// For every two elements of an equivalence class, makes sure that those two
+// elements compare equal, including checks with the same argument passed as
+// both operands.
+template <class T, class Prof>
+struct ExpectEquivalenceClassComparisons {
+  template <class... Funs>
+  void operator()(EquivalenceClassType<Funs...> eq_class) const {
+    (ForEachTupleElement)(ExpectSelfComparison<T, Prof>{errors},
+                          eq_class.generators);
+
+    (ForEveryTwo)(ExpectEquivalenceClassComparison<T, Prof>{errors},
+                  eq_class.generators);
+  }
+
+  ConformanceErrors* errors;
+};
+
+// For every element of an equivalence class, makes sure that the element is
+// self-consistent (in other words, if any of move/copy/swap are defined,
+// perform those operations and make such that results and operands still
+// compare equal to known values whenever it is required for that operation.
+template <class T, class Prof>
+struct ExpectEquivalenceClass {
+  template <class... Funs>
+  void operator()(EquivalenceClassType<Funs...> eq_class) const {
+    (ForEachTupleElement)(ExpectConsistency<T, Prof>{errors},
+                          eq_class.generators);
+
+    (ForEveryTwo)(ExpectEquivalenceClassConsistency<T, Prof>{errors},
+                  eq_class.generators);
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Validate that the passed-in argument is a generator of a greater value than
+// the one produced by the "small_gen" datamember with respect to all of the
+// comparison operators that Prof requires, with both argument orders to test.
+template <class T, class Prof, class SmallGenerator>
+struct ExpectBiggerGeneratorThanComparisons {
+  template <class BigGenerator>
+  void operator()(BigGenerator big_gen) const {
+    const T small = small_gen();
+    const T big = big_gen();
+
+    (ExpectOrdered<T, Prof>)(errors,
+                             PrepareGivenContext(
+                                 GivenDeclaration{"const _T small",
+                                                  small_gen.description},
+                                 GivenDeclaration{"const _T big",
+                                                  big_gen.description}),
+                             small, big, "small", "big");
+  }
+
+  SmallGenerator small_gen;
+  ConformanceErrors* errors;
+};
+
+// Perform all of the move, copy, and swap checks on the value generated by
+// `small_gen` and the value generated by `big_gen`.
+template <class T, class Prof, class SmallGenerator>
+struct ExpectBiggerGeneratorThan {
+  template <class BigGenerator>
+  void operator()(BigGenerator big_gen) const {
+    If<PropertiesOfT<Prof>::is_move_assignable>::Invoke(
+        ExpectMoveAssign<T, Prof>{errors}, small_gen, big_gen);
+    If<PropertiesOfT<Prof>::is_move_assignable>::Invoke(
+        ExpectMoveAssign<T, Prof>{errors}, big_gen, small_gen);
+
+    If<PropertiesOfT<Prof>::is_copy_assignable>::Invoke(
+        ExpectCopyAssign<T, Prof>{errors}, small_gen, big_gen);
+    If<PropertiesOfT<Prof>::is_copy_assignable>::Invoke(
+        ExpectCopyAssign<T, Prof>{errors}, big_gen, small_gen);
+
+    If<PropertiesOfT<Prof>::is_swappable>::Invoke(ExpectSwap<T, Prof>{errors},
+                                                  small_gen, big_gen);
+  }
+
+  SmallGenerator small_gen;
+  ConformanceErrors* errors;
+};
+
+// Validate that the result of a generator is greater than the results of all
+// generators in an equivalence class with respect to comparisons.
+template <class T, class Prof, class SmallGenerator>
+struct ExpectBiggerGeneratorThanEqClassesComparisons {
+  template <class BigEqClass>
+  void operator()(BigEqClass big_eq_class) const {
+    (ForEachTupleElement)(
+        ExpectBiggerGeneratorThanComparisons<T, Prof, SmallGenerator>{small_gen,
+                                                                      errors},
+        big_eq_class.generators);
+  }
+
+  SmallGenerator small_gen;
+  ConformanceErrors* errors;
+};
+
+// Validate that the non-comparison binary operations required by Prof are
+// correct for the result of each generator of big_eq_class and a generator of
+// the logically smaller value returned by small_gen.
+template <class T, class Prof, class SmallGenerator>
+struct ExpectBiggerGeneratorThanEqClasses {
+  template <class BigEqClass>
+  void operator()(BigEqClass big_eq_class) const {
+    (ForEachTupleElement)(
+        ExpectBiggerGeneratorThan<T, Prof, SmallGenerator>{small_gen, errors},
+        big_eq_class.generators);
+  }
+
+  SmallGenerator small_gen;
+  ConformanceErrors* errors;
+};
+
+// Validate that each equivalence class that is passed is logically less than
+// the equivalence classes that comes later on in the argument list.
+template <class T, class Prof>
+struct ExpectOrderedEquivalenceClassesComparisons {
+  template <class... BigEqClasses>
+  struct Impl {
+    // Validate that the value produced by `small_gen` is less than all of the
+    // values generated by those of the logically larger equivalence classes.
+    template <class SmallGenerator>
+    void operator()(SmallGenerator small_gen) const {
+      (ForEachTupleElement)(ExpectBiggerGeneratorThanEqClassesComparisons<
+                                T, Prof, SmallGenerator>{small_gen, errors},
+                            big_eq_classes);
+    }
+
+    std::tuple<BigEqClasses...> big_eq_classes;
+    ConformanceErrors* errors;
+  };
+
+  // When given no equivalence classes, no validation is necessary.
+  void operator()() const {}
+
+  template <class SmallEqClass, class... BigEqClasses>
+  void operator()(SmallEqClass small_eq_class,
+                  BigEqClasses... big_eq_classes) const {
+    // For each generator in the first equivalence class, make sure that it is
+    // less than each of those in the logically greater equivalence classes.
+    (ForEachTupleElement)(
+        Impl<BigEqClasses...>{std::make_tuple(absl::move(big_eq_classes)...),
+                              errors},
+        small_eq_class.generators);
+
+    // Recurse so that all equivalence class combinations are checked.
+    (*this)(absl::move(big_eq_classes)...);
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Validate that the non-comparison binary operations required by Prof are
+// correct for the result of each generator of big_eq_classes and a generator of
+// the logically smaller value returned by small_gen.
+template <class T, class Prof>
+struct ExpectOrderedEquivalenceClasses {
+  template <class... BigEqClasses>
+  struct Impl {
+    template <class SmallGenerator>
+    void operator()(SmallGenerator small_gen) const {
+      (ForEachTupleElement)(
+          ExpectBiggerGeneratorThanEqClasses<T, Prof, SmallGenerator>{small_gen,
+                                                                      errors},
+          big_eq_classes);
+    }
+
+    std::tuple<BigEqClasses...> big_eq_classes;
+    ConformanceErrors* errors;
+  };
+
+  // Check that small_eq_class is logically consistent and also is logically
+  // less than all values in big_eq_classes.
+  template <class SmallEqClass, class... BigEqClasses>
+  void operator()(SmallEqClass small_eq_class,
+                  BigEqClasses... big_eq_classes) const {
+    (ForEachTupleElement)(
+        Impl<BigEqClasses...>{std::make_tuple(absl::move(big_eq_classes)...),
+                              errors},
+        small_eq_class.generators);
+
+    (*this)(absl::move(big_eq_classes)...);
+  }
+
+  // Terminating case of operator().
+  void operator()() const {}
+
+  ConformanceErrors* errors;
+};
+
+// Validate that a type meets the syntactic requirements of std::hash if the
+// range of profiles requires it.
+template <class T, class MinProf, class MaxProf>
+struct ExpectHashable {
+  void operator()() const {
+    ExpectModelOfHashable<T, MinProf, MaxProf>(errors);
+  }
+
+  ConformanceErrors* errors;
+};
+
+// Validate that the type `T` meets all of the requirements associated with
+// `MinProf` and without going beyond the syntactic properties of `MaxProf`.
+template <class T, class MinProf, class MaxProf>
+struct ExpectModels {
+  void operator()(ConformanceErrors* errors) const {
+    ExpectModelOfDefaultConstructible<T, MinProf, MaxProf>(errors);
+    ExpectModelOfMoveConstructible<T, MinProf, MaxProf>(errors);
+    ExpectModelOfCopyConstructible<T, MinProf, MaxProf>(errors);
+    ExpectModelOfMoveAssignable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfCopyAssignable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfDestructible<T, MinProf, MaxProf>(errors);
+    ExpectModelOfEqualityComparable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfInequalityComparable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfLessThanComparable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfLessEqualComparable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfGreaterEqualComparable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfGreaterThanComparable<T, MinProf, MaxProf>(errors);
+    ExpectModelOfSwappable<T, MinProf, MaxProf>(errors);
+
+    // Only check hashability on compilers that have a compliant default-hash.
+    If<!poisoned_hash_fails_instantiation()>::Invoke(
+        ExpectHashable<T, MinProf, MaxProf>{errors});
+  }
+};
+
+// A metafunction that yields a Profile matching the set of properties that are
+// safe to be checked (lack-of-hashability is only checked on standard library
+// implementations that are standards compliant in that they provide a std::hash
+// primary template that is SFINAE-friendly)
+template <class LogicalProf, class T>
+struct MinimalCheckableProfile {
+  using type =
+      MinimalProfiles<PropertiesOfT<LogicalProf>,
+                      PropertiesOfT<SyntacticConformanceProfileOf<
+                          T, !PropertiesOfT<LogicalProf>::is_hashable &&
+                                     poisoned_hash_fails_instantiation()
+                                 ? CheckHashability::no
+                                 : CheckHashability::yes>>>;
+};
+
+// An identity metafunction
+template <class T>
+struct Always {
+  using type = T;
+};
+
+// Validate the T meets all of the necessary requirements of LogicalProf, with
+// syntactic requirements defined by the profile range [MinProf, MaxProf].
+template <class T, class LogicalProf, class MinProf, class MaxProf,
+          class... EqClasses>
+ConformanceErrors ExpectRegularityImpl(
+    OrderedEquivalenceClasses<EqClasses...> vals) {
+  ConformanceErrors errors((NameOf<T>()));
+
+  If<!constexpr_instantiation_when_unevaluated()>::Invoke(
+      ExpectModels<T, MinProf, MaxProf>(), &errors);
+
+  using minimal_profile = typename absl::conditional_t<
+      constexpr_instantiation_when_unevaluated(), Always<LogicalProf>,
+      MinimalCheckableProfile<LogicalProf, T>>::type;
+
+  If<PropertiesOfT<minimal_profile>::is_default_constructible>::Invoke(
+      ExpectDefaultConstructWithDestruct<T>{&errors});
+
+  //////////////////////////////////////////////////////////////////////////////
+  // Perform all comparison checks first, since later checks depend on their
+  // correctness.
+  //
+  // Check all of the comparisons for all values in the same equivalence
+  // class (equal with respect to comparison operators and hash the same).
+  (ForEachTupleElement)(
+      ExpectEquivalenceClassComparisons<T, minimal_profile>{&errors},
+      vals.eq_classes);
+
+  // Check all of the comparisons for each combination of values that are in
+  // different equivalence classes (not equal with respect to comparison
+  // operators).
+  absl::apply(
+      ExpectOrderedEquivalenceClassesComparisons<T, minimal_profile>{&errors},
+      vals.eq_classes);
+  //
+  //////////////////////////////////////////////////////////////////////////////
+
+  // Perform remaining checks, relying on comparisons.
+  // TODO(calabrese) short circuit if any comparisons above failed.
+  (ForEachTupleElement)(ExpectEquivalenceClass<T, minimal_profile>{&errors},
+                        vals.eq_classes);
+
+  absl::apply(ExpectOrderedEquivalenceClasses<T, minimal_profile>{&errors},
+              vals.eq_classes);
+
+  return errors;
+}
+
+// A type that represents a range of profiles that are acceptable to be matched.
+//
+// `MinProf` is the minimum set of syntactic requirements that must be met.
+//
+// `MaxProf` is the maximum set of syntactic requirements that must be met.
+// This maximum is particularly useful for certain "strictness" checking. Some
+// examples for when this is useful:
+//
+// * Making sure that a type is move-only (rather than simply movable)
+//
+// * Making sure that a member function is *not* noexcept in cases where it
+//   cannot be noexcept, such as if a dependent datamember has certain
+//   operations that are not noexcept.
+//
+// * Making sure that a type tightly matches a spec, such as the standard.
+//
+// `LogicalProf` is the Profile for which run-time testing is to take place.
+//
+// Note: The reason for `LogicalProf` is because it is often the case, when
+// dealing with templates, that a declaration of a given operation is specified,
+// but whose body would fail to instantiate. Examples include the
+// copy-constructor of a standard container when the element-type is move-only,
+// or the comparison operators of a standard container when the element-type
+// does not have the necessary comparison operations defined. The `LogicalProf`
+// parameter allows us to capture the intent of what should be tested at
+// run-time, even in the cases where syntactically it might otherwise appear as
+// though the type undergoing testing supports more than it actually does.
+template <class LogicalProf, class MinProf = LogicalProf,
+          class MaxProf = MinProf>
+struct ProfileRange {
+  using logical_profile = LogicalProf;
+  using min_profile = MinProf;
+  using max_profile = MaxProf;
+};
+
+// Similar to ProfileRange except that it creates a profile range that is
+// coupled with a Domain and is used when testing that a type matches exactly
+// the "minimum" requirements of LogicalProf.
+template <class StrictnessDomain, class LogicalProf,
+          class MinProf = LogicalProf, class MaxProf = MinProf>
+struct StrictProfileRange {
+  // We do not yet support extension.
+  static_assert(
+      std::is_same<StrictnessDomain, RegularityDomain>::value,
+      "Currently, the only valid StrictnessDomain is RegularityDomain.");
+  using strictness_domain = StrictnessDomain;
+  using logical_profile = LogicalProf;
+  using min_profile = MinProf;
+  using max_profile = MaxProf;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction that creates a StrictProfileRange from a Domain and either a
+// Profile or ProfileRange.
+template <class StrictnessDomain, class ProfOrRange>
+struct MakeStrictProfileRange;
+
+template <class StrictnessDomain, class LogicalProf>
+struct MakeStrictProfileRange {
+  using type = StrictProfileRange<StrictnessDomain, LogicalProf>;
+};
+
+template <class StrictnessDomain, class LogicalProf, class MinProf,
+          class MaxProf>
+struct MakeStrictProfileRange<StrictnessDomain,
+                              ProfileRange<LogicalProf, MinProf, MaxProf>> {
+  using type =
+      StrictProfileRange<StrictnessDomain, LogicalProf, MinProf, MaxProf>;
+};
+
+template <class StrictnessDomain, class ProfOrRange>
+using MakeStrictProfileRangeT =
+    typename MakeStrictProfileRange<StrictnessDomain, ProfOrRange>::type;
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// A profile in the RegularityDomain with the strongest possible requirements.
+using MostStrictProfile =
+    CombineProfiles<TriviallyCompleteProfile, NothrowComparableProfile>;
+
+// Forms a ProfileRange that treats the Profile as the bare minimum requirements
+// of a type.
+template <class LogicalProf, class MinProf = LogicalProf>
+using LooseProfileRange = StrictProfileRange<RegularityDomain, LogicalProf,
+                                             MinProf, MostStrictProfile>;
+
+template <class Prof>
+using MakeLooseProfileRangeT = Prof;
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// The following classes implement the metafunction ProfileRangeOfT<T> that
+// takes either a Profile or ProfileRange and yields the ProfileRange to be
+// used during testing.
+//
+template <class T, class /*Enabler*/ = void>
+struct ProfileRangeOfImpl;
+
+template <class T>
+struct ProfileRangeOfImpl<T, absl::void_t<PropertiesOfT<T>>> {
+  using type = LooseProfileRange<T>;
+};
+
+template <class T>
+struct ProfileRangeOf : ProfileRangeOfImpl<T> {};
+
+template <class StrictnessDomain, class LogicalProf, class MinProf,
+          class MaxProf>
+struct ProfileRangeOf<
+    StrictProfileRange<StrictnessDomain, LogicalProf, MinProf, MaxProf>> {
+  using type =
+      StrictProfileRange<StrictnessDomain, LogicalProf, MinProf, MaxProf>;
+};
+
+template <class T>
+using ProfileRangeOfT = typename ProfileRangeOf<T>::type;
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// Extract the logical profile of a range (what will be runtime tested).
+template <class T>
+using LogicalProfileOfT = typename ProfileRangeOfT<T>::logical_profile;
+
+// Extract the minimal syntactic profile of a range (error if not at least).
+template <class T>
+using MinProfileOfT = typename ProfileRangeOfT<T>::min_profile;
+
+// Extract the maximum syntactic profile of a range (error if more than).
+template <class T>
+using MaxProfileOfT = typename ProfileRangeOfT<T>::max_profile;
+
+////////////////////////////////////////////////////////////////////////////////
+//
+template <class T>
+struct IsProfileOrProfileRange : IsProfile<T>::type {};
+
+template <class StrictnessDomain, class LogicalProf, class MinProf,
+          class MaxProf>
+struct IsProfileOrProfileRange<
+    StrictProfileRange<StrictnessDomain, LogicalProf, MinProf, MaxProf>>
+    : std::true_type {};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// TODO(calabrese): Consider naming the functions in this class the same as
+// the macros (defined later on) so that auto-complete leads to the correct name
+// and so that a user cannot accidentally call a function rather than the macro
+// form.
+template <bool ExpectSuccess, class T, class... EqClasses>
+struct ExpectConformanceOf {
+  // Add a value to be tested. Subsequent calls to this function on the same
+  // object must specify logically "larger" values with respect to the
+  // comparison operators of the type, if any.
+  //
+  // NOTE: This function should not be called directly. A stateless lambda is
+  // implicitly formed and passed when using the INITIALIZER macro at the bottom
+  // of this file.
+  template <class Fun,
+            absl::enable_if_t<std::is_same<
+                ResultOfGeneratorT<GeneratorType<Fun>>, T>::value>** = nullptr>
+  ABSL_MUST_USE_RESULT ExpectConformanceOf<ExpectSuccess, T, EqClasses...,
+                                           EquivalenceClassType<Fun>>
+  initializer(GeneratorType<Fun> fun) && {
+    return {
+        {std::tuple_cat(absl::move(ordered_vals.eq_classes),
+                        std::make_tuple((EquivalenceClass)(absl::move(fun))))},
+        std::move(expected_failed_tests)};
+  }
+
+  template <class... TestNames,
+            absl::enable_if_t<!ExpectSuccess && sizeof...(EqClasses) == 0 &&
+                              absl::conjunction<std::is_convertible<
+                                  TestNames, absl::string_view>...>::value>** =
+                nullptr>
+  ABSL_MUST_USE_RESULT ExpectConformanceOf<ExpectSuccess, T, EqClasses...>
+  due_to(TestNames&&... test_names) && {
+    (InsertEach)(&expected_failed_tests,
+                 absl::AsciiStrToLower(absl::string_view(test_names))...);
+
+    return {absl::move(ordered_vals), std::move(expected_failed_tests)};
+  }
+
+  template <class... TestNames, int = 0,  // MSVC disambiguator
+            absl::enable_if_t<ExpectSuccess && sizeof...(EqClasses) == 0 &&
+                              absl::conjunction<std::is_convertible<
+                                  TestNames, absl::string_view>...>::value>** =
+                nullptr>
+  ABSL_MUST_USE_RESULT ExpectConformanceOf<ExpectSuccess, T, EqClasses...>
+  due_to(TestNames&&... test_names) && {
+    // TODO(calabrese) Instead have DUE_TO only exist via a CRTP base.
+    // This would produce better errors messages than the static_assert.
+    static_assert(!ExpectSuccess,
+                  "DUE_TO cannot be called when conformance is expected -- did "
+                  "you mean to use ASSERT_NONCONFORMANCE_OF?");
+  }
+
+  // Add a value to be tested. Subsequent calls to this function on the same
+  // object must specify logically "larger" values with respect to the
+  // comparison operators of the type, if any.
+  //
+  // NOTE: This function should not be called directly. A stateful lambda is
+  // implicitly formed and passed when using the INITIALIZER macro at the bottom
+  // of this file.
+  template <class Fun,
+            absl::enable_if_t<std::is_same<
+                ResultOfGeneratorT<GeneratorType<Fun>>, T>::value>** = nullptr>
+  ABSL_MUST_USE_RESULT ExpectConformanceOf<ExpectSuccess, T, EqClasses...,
+                                           EquivalenceClassType<Fun>>
+  dont_class_directly_stateful_initializer(GeneratorType<Fun> fun) && {
+    return {
+        {std::tuple_cat(absl::move(ordered_vals.eq_classes),
+                        std::make_tuple((EquivalenceClass)(absl::move(fun))))},
+        std::move(expected_failed_tests)};
+  }
+
+  // Add a set of value to be tested, where each value is equal with respect to
+  // the comparison operators and std::hash specialization, if defined.
+  template <
+      class... Funs,
+      absl::void_t<absl::enable_if_t<std::is_same<
+          ResultOfGeneratorT<GeneratorType<Funs>>, T>::value>...>** = nullptr>
+  ABSL_MUST_USE_RESULT ExpectConformanceOf<ExpectSuccess, T, EqClasses...,
+                                           EquivalenceClassType<Funs...>>
+  equivalence_class(GeneratorType<Funs>... funs) && {
+    return {{std::tuple_cat(
+                absl::move(ordered_vals.eq_classes),
+                std::make_tuple((EquivalenceClass)(absl::move(funs)...)))},
+            std::move(expected_failed_tests)};
+  }
+
+  // Execute the tests for the captured set of values, strictly matching a range
+  // of expected profiles in a given domain.
+  template <
+      class ProfRange,
+      absl::enable_if_t<IsProfileOrProfileRange<ProfRange>::value>** = nullptr>
+  ABSL_MUST_USE_RESULT ::testing::AssertionResult with_strict_profile(
+      ProfRange /*profile*/) {
+    ConformanceErrors test_result =
+        (ExpectRegularityImpl<
+            T, LogicalProfileOfT<ProfRange>, MinProfileOfT<ProfRange>,
+            MaxProfileOfT<ProfRange>>)(absl::move(ordered_vals));
+
+    return ExpectSuccess ? test_result.assertionResult()
+                         : test_result.expectFailedTests(expected_failed_tests);
+  }
+
+  // Execute the tests for the captured set of values, loosely matching a range
+  // of expected profiles (loose in that an interface is allowed to be more
+  // refined that a profile suggests, such as a type having a noexcept copy
+  // constructor when all that is required is that the copy constructor exists).
+  template <class Prof, absl::enable_if_t<IsProfile<Prof>::value>** = nullptr>
+  ABSL_MUST_USE_RESULT ::testing::AssertionResult with_loose_profile(
+      Prof /*profile*/) {
+    ConformanceErrors test_result =
+        (ExpectRegularityImpl<
+            T, Prof, Prof,
+            CombineProfiles<TriviallyCompleteProfile,
+                            NothrowComparableProfile>>)(absl::
+                                                            move(ordered_vals));
+
+    return ExpectSuccess ? test_result.assertionResult()
+                         : test_result.expectFailedTests(expected_failed_tests);
+  }
+
+  OrderedEquivalenceClasses<EqClasses...> ordered_vals;
+  std::set<std::string> expected_failed_tests;
+};
+
+template <class T>
+using ExpectConformanceOfType = ExpectConformanceOf</*ExpectSuccess=*/true, T>;
+
+template <class T>
+using ExpectNonconformanceOfType =
+    ExpectConformanceOf</*ExpectSuccess=*/false, T>;
+
+struct EquivalenceClassMaker {
+  // TODO(calabrese) Constrain to callable
+  template <class Fun>
+  static GeneratorType<Fun> initializer(GeneratorType<Fun> fun) {
+    return fun;
+  }
+};
+
+// A top-level macro that begins the builder pattern.
+//
+// The argument here takes the datatype to be tested.
+#define ABSL_INTERNAL_ASSERT_CONFORMANCE_OF(...)                            \
+  GTEST_AMBIGUOUS_ELSE_BLOCKER_                                             \
+  if ABSL_INTERNAL_LPAREN                                                   \
+  const ::testing::AssertionResult gtest_ar =                               \
+      ABSL_INTERNAL_LPAREN ::absl::types_internal::ExpectConformanceOfType< \
+          __VA_ARGS__>()
+
+// Akin to ASSERT_CONFORMANCE_OF except that it expects failure and tries to
+// match text.
+#define ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(...)                            \
+  GTEST_AMBIGUOUS_ELSE_BLOCKER_                                                \
+  if ABSL_INTERNAL_LPAREN                                                      \
+  const ::testing::AssertionResult gtest_ar =                                  \
+      ABSL_INTERNAL_LPAREN ::absl::types_internal::ExpectNonconformanceOfType< \
+          __VA_ARGS__>()
+
+////////////////////////////////////////////////////////////////////////////////
+// NOTE: The following macros look like they are recursive, but are not (macros
+// cannot recurse). These actually refer to member functions of the same name.
+// This is done intentionally so that a user cannot accidentally invoke a
+// member function of the conformance-testing suite without going through the
+// macro.
+////////////////////////////////////////////////////////////////////////////////
+
+// Specify expected test failures as comma-separated strings.
+#define DUE_TO(...) due_to(__VA_ARGS__)
+
+// Specify a value to be tested.
+//
+// Note: Internally, this takes an expression and turns it into the return value
+// of lambda that captures no data. The expression is stringized during
+// preprocessing so that it can be used in error reports.
+#define INITIALIZER(...)                         \
+  initializer(::absl::types_internal::Generator( \
+      [] { return __VA_ARGS__; }, ABSL_INTERNAL_STRINGIZE(__VA_ARGS__)))
+
+// Specify a value to be tested.
+//
+// Note: Internally, this takes an expression and turns it into the return value
+// of lambda that captures data by reference. The expression is stringized
+// during preprocessing so that it can be used in error reports.
+#define STATEFUL_INITIALIZER(...)                         \
+  stateful_initializer(::absl::types_internal::Generator( \
+      [&] { return __VA_ARGS__; }, ABSL_INTERNAL_STRINGIZE(__VA_ARGS__)))
+
+// Used in the builder-pattern.
+//
+// Takes a series of INITIALIZER and/or STATEFUL_INITIALIZER invocations and
+// forwards them along to be tested, grouping them such that the testing suite
+// knows that they are supposed to represent the same logical value (the values
+// compare the same, hash the same, etc.).
+#define EQUIVALENCE_CLASS(...)                    \
+  equivalence_class(ABSL_INTERNAL_TRANSFORM_ARGS( \
+      ABSL_INTERNAL_PREPEND_EQ_MAKER, __VA_ARGS__))
+
+// An invocation of this or WITH_STRICT_PROFILE must end the builder-pattern.
+// It takes a Profile as its argument.
+//
+// This executes the tests and allows types that are "more referined" than the
+// profile specifies, but not less. For instance, if the Profile specifies
+// noexcept copy-constructiblity, the test will fail if the copy-constructor is
+// not noexcept, however, it will succeed if the copy constructor is trivial.
+//
+// This is useful for testing that a type meets some minimum set of
+// requirements.
+#define WITH_LOOSE_PROFILE(...)                                      \
+  with_loose_profile(                                                \
+      ::absl::types_internal::MakeLooseProfileRangeT<__VA_ARGS__>()) \
+      ABSL_INTERNAL_RPAREN ABSL_INTERNAL_RPAREN;                     \
+  else GTEST_FATAL_FAILURE_(gtest_ar.failure_message())  // NOLINT
+
+// An invocation of this or WITH_STRICT_PROFILE must end the builder-pattern.
+// It takes a Domain and a Profile as its arguments.
+//
+// This executes the tests and disallows types that differ at all from the
+// properties of the Profile. For instance, if the Profile specifies noexcept
+// copy-constructiblity, the test will fail if the copy constructor is trivial.
+//
+// This is useful for testing that a type does not do anything more than a
+// specification requires, such as to minimize things like Hyrum's Law, or more
+// commonly, to prevent a type from being "accidentally" copy-constructible in
+// a way that may produce incorrect results, simply because the user forget to
+// delete that operation.
+#define WITH_STRICT_PROFILE(...)                                      \
+  with_strict_profile(                                                \
+      ::absl::types_internal::MakeStrictProfileRangeT<__VA_ARGS__>()) \
+      ABSL_INTERNAL_RPAREN ABSL_INTERNAL_RPAREN;                      \
+  else GTEST_FATAL_FAILURE_(gtest_ar.failure_message())  // NOLINT
+
+// Internal macro that is used in the internals of the EDSL when forming
+// equivalence classes.
+#define ABSL_INTERNAL_PREPEND_EQ_MAKER(arg) \
+  ::absl::types_internal::EquivalenceClassMaker().arg
+
+}  // namespace types_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TYPES_INTERNAL_CONFORMANCE_TESTING_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/conformance_testing_helpers.h b/third_party/abseil_cpp/absl/types/internal/conformance_testing_helpers.h
new file mode 100644
index 0000000000..00775f960c
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/conformance_testing_helpers.h
@@ -0,0 +1,391 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_TYPES_INTERNAL_CONFORMANCE_TESTING_HELPERS_H_
+#define ABSL_TYPES_INTERNAL_CONFORMANCE_TESTING_HELPERS_H_
+
+// Checks to determine whether or not we can use abi::__cxa_demangle
+#if (defined(__ANDROID__) || defined(ANDROID)) && !defined(OS_ANDROID)
+#define ABSL_INTERNAL_OS_ANDROID
+#endif
+
+// We support certain compilers only.  See demangle.h for details.
+#if defined(OS_ANDROID) && (defined(__i386__) || defined(__x86_64__))
+#define ABSL_TYPES_INTERNAL_HAS_CXA_DEMANGLE 0
+#elif (__GNUC__ >= 4 || (__GNUC__ >= 3 && __GNUC_MINOR__ >= 4)) && \
+    !defined(__mips__)
+#define ABSL_TYPES_INTERNAL_HAS_CXA_DEMANGLE 1
+#elif defined(__clang__) && !defined(_MSC_VER)
+#define ABSL_TYPES_INTERNAL_HAS_CXA_DEMANGLE 1
+#else
+#define ABSL_TYPES_INTERNAL_HAS_CXA_DEMANGLE 0
+#endif
+
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "absl/meta/type_traits.h"
+#include "absl/strings/string_view.h"
+#include "absl/utility/utility.h"
+
+#if ABSL_TYPES_INTERNAL_HAS_CXA_DEMANGLE
+#include <cxxabi.h>
+
+#include <cstdlib>
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace types_internal {
+
+// Return a readable name for type T.
+template <class T>
+absl::string_view NameOfImpl() {
+// TODO(calabrese) Investigate using debugging:internal_demangle as a fallback.
+#if ABSL_TYPES_INTERNAL_HAS_CXA_DEMANGLE
+  int status = 0;
+  char* demangled_name = nullptr;
+
+  demangled_name =
+      abi::__cxa_demangle(typeid(T).name(), nullptr, nullptr, &status);
+
+  if (status == 0 && demangled_name != nullptr) {
+    return demangled_name;
+  } else {
+    return typeid(T).name();
+  }
+#else
+  return typeid(T).name();
+#endif
+  // NOTE: We intentionally leak demangled_name so that it remains valid
+  // throughout the remainder of the program.
+}
+
+// Given a type, returns as nice of a type name as we can produce (demangled).
+//
+// Note: This currently strips cv-qualifiers and references, but that is okay
+// because we only use this internally with unqualified object types.
+template <class T>
+std::string NameOf() {
+  static const absl::string_view result = NameOfImpl<T>();
+  return std::string(result);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Metafunction to check if a type is callable with no explicit arguments
+template <class Fun, class /*Enabler*/ = void>
+struct IsNullaryCallableImpl : std::false_type {};
+
+template <class Fun>
+struct IsNullaryCallableImpl<
+    Fun, absl::void_t<decltype(std::declval<const Fun&>()())>>
+    : std::true_type {
+  using result_type = decltype(std::declval<const Fun&>()());
+
+  template <class ValueType>
+  using for_type = std::is_same<ValueType, result_type>;
+
+  using void_if_true = void;
+};
+
+template <class Fun>
+struct IsNullaryCallable : IsNullaryCallableImpl<Fun> {};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// A type that contains a function object that returns an instance of a type
+// that is undergoing conformance testing. This function is required to always
+// return the same value upon invocation.
+template <class Fun>
+struct GeneratorType;
+
+// A type that contains a tuple of GeneratorType<Fun> where each Fun has the
+// same return type. The result of each of the different generators should all
+// be equal values, though the underlying object representation may differ (such
+// as if one returns 0.0 and another return -0.0, or if one returns an empty
+// vector and another returns an empty vector with a different capacity.
+template <class... Funs>
+struct EquivalenceClassType;
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction to check if a type is a specialization of EquivalenceClassType
+template <class T>
+struct IsEquivalenceClass : std::false_type {};
+
+template <>
+struct IsEquivalenceClass<EquivalenceClassType<>> : std::true_type {
+  using self = IsEquivalenceClass;
+
+  // A metafunction to check if this EquivalenceClassType is a valid
+  // EquivalenceClassType for a type `ValueType` that is undergoing testing
+  template <class ValueType>
+  using for_type = std::true_type;
+};
+
+template <class Head, class... Tail>
+struct IsEquivalenceClass<EquivalenceClassType<Head, Tail...>>
+    : std::true_type {
+  using self = IsEquivalenceClass;
+
+  // The type undergoing conformance testing that this EquivalenceClass
+  // corresponds to
+  using result_type = typename IsNullaryCallable<Head>::result_type;
+
+  // A metafunction to check if this EquivalenceClassType is a valid
+  // EquivalenceClassType for a type `ValueType` that is undergoing testing
+  template <class ValueType>
+  using for_type = std::is_same<ValueType, result_type>;
+};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// A type that contains an ordered series of EquivalenceClassTypes, where the
+// the function object of each underlying GeneratorType has the same return type
+//
+// These equivalence classes are required to be in a logical ascending order
+// that is consistent with comparison operators that are defined for the return
+// type of each GeneratorType, if any.
+template <class... EqClasses>
+struct OrderedEquivalenceClasses;
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction to determine the return type of the function object contained
+// in a GeneratorType specialization.
+template <class T>
+struct ResultOfGenerator {};
+
+template <class Fun>
+struct ResultOfGenerator<GeneratorType<Fun>> {
+  using type = decltype(std::declval<const Fun&>()());
+};
+
+template <class Fun>
+using ResultOfGeneratorT = typename ResultOfGenerator<GeneratorType<Fun>>::type;
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction that yields true iff each of Funs is a GeneratorType
+// specialization and they all contain functions with the same return type
+template <class /*Enabler*/, class... Funs>
+struct AreGeneratorsWithTheSameReturnTypeImpl : std::false_type {};
+
+template <>
+struct AreGeneratorsWithTheSameReturnTypeImpl<void> : std::true_type {};
+
+template <class Head, class... Tail>
+struct AreGeneratorsWithTheSameReturnTypeImpl<
+    typename std::enable_if<absl::conjunction<std::is_same<
+        ResultOfGeneratorT<Head>, ResultOfGeneratorT<Tail>>...>::value>::type,
+    Head, Tail...> : std::true_type {};
+
+template <class... Funs>
+struct AreGeneratorsWithTheSameReturnType
+    : AreGeneratorsWithTheSameReturnTypeImpl<void, Funs...>::type {};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// A metafunction that yields true iff each of Funs is an EquivalenceClassType
+// specialization and they all contain GeneratorType specializations that have
+// the same return type
+template <class... EqClasses>
+struct AreEquivalenceClassesOfTheSameType {
+  static_assert(sizeof...(EqClasses) != sizeof...(EqClasses), "");
+};
+
+template <>
+struct AreEquivalenceClassesOfTheSameType<> : std::true_type {
+  using self = AreEquivalenceClassesOfTheSameType;
+
+  // Metafunction to check that a type is the same as all of the equivalence
+  // classes, if any.
+  // Note: In this specialization there are no equivalence classes, so the
+  // value type is always compatible.
+  template <class /*ValueType*/>
+  using for_type = std::true_type;
+};
+
+template <class... Funs>
+struct AreEquivalenceClassesOfTheSameType<EquivalenceClassType<Funs...>>
+    : std::true_type {
+  using self = AreEquivalenceClassesOfTheSameType;
+
+  // Metafunction to check that a type is the same as all of the equivalence
+  // classes, if any.
+  template <class ValueType>
+  using for_type = typename IsEquivalenceClass<
+      EquivalenceClassType<Funs...>>::template for_type<ValueType>;
+};
+
+template <class... TailEqClasses>
+struct AreEquivalenceClassesOfTheSameType<
+    EquivalenceClassType<>, EquivalenceClassType<>, TailEqClasses...>
+    : AreEquivalenceClassesOfTheSameType<TailEqClasses...>::self {};
+
+template <class HeadNextFun, class... TailNextFuns, class... TailEqClasses>
+struct AreEquivalenceClassesOfTheSameType<
+    EquivalenceClassType<>, EquivalenceClassType<HeadNextFun, TailNextFuns...>,
+    TailEqClasses...>
+    : AreEquivalenceClassesOfTheSameType<
+          EquivalenceClassType<HeadNextFun, TailNextFuns...>,
+          TailEqClasses...>::self {};
+
+template <class HeadHeadFun, class... TailHeadFuns, class... TailEqClasses>
+struct AreEquivalenceClassesOfTheSameType<
+    EquivalenceClassType<HeadHeadFun, TailHeadFuns...>, EquivalenceClassType<>,
+    TailEqClasses...>
+    : AreEquivalenceClassesOfTheSameType<
+          EquivalenceClassType<HeadHeadFun, TailHeadFuns...>,
+          TailEqClasses...>::self {};
+
+template <class HeadHeadFun, class... TailHeadFuns, class HeadNextFun,
+          class... TailNextFuns, class... TailEqClasses>
+struct AreEquivalenceClassesOfTheSameType<
+    EquivalenceClassType<HeadHeadFun, TailHeadFuns...>,
+    EquivalenceClassType<HeadNextFun, TailNextFuns...>, TailEqClasses...>
+    : absl::conditional_t<
+          IsNullaryCallable<HeadNextFun>::template for_type<
+              typename IsNullaryCallable<HeadHeadFun>::result_type>::value,
+          AreEquivalenceClassesOfTheSameType<
+              EquivalenceClassType<HeadHeadFun, TailHeadFuns...>,
+              TailEqClasses...>,
+          std::false_type> {};
+//
+////////////////////////////////////////////////////////////////////////////////
+
+// Execute a function for each passed-in parameter.
+template <class Fun, class... Cases>
+void ForEachParameter(const Fun& fun, const Cases&... cases) {
+  const std::initializer_list<bool> results = {
+      (static_cast<void>(fun(cases)), true)...};
+
+  (void)results;
+}
+
+// Execute a function on each passed-in parameter (using a bound function).
+template <class Fun>
+struct ForEachParameterFun {
+  template <class... T>
+  void operator()(const T&... cases) const {
+    (ForEachParameter)(fun, cases...);
+  }
+
+  Fun fun;
+};
+
+// Execute a function on each element of a tuple.
+template <class Fun, class Tup>
+void ForEachTupleElement(const Fun& fun, const Tup& tup) {
+  absl::apply(ForEachParameterFun<Fun>{fun}, tup);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Execute a function for each combination of two elements of a tuple, including
+// combinations of an element with itself.
+template <class Fun, class... T>
+struct ForEveryTwoImpl {
+  template <class Lhs>
+  struct WithBoundLhs {
+    template <class Rhs>
+    void operator()(const Rhs& rhs) const {
+      fun(lhs, rhs);
+    }
+
+    Fun fun;
+    Lhs lhs;
+  };
+
+  template <class Lhs>
+  void operator()(const Lhs& lhs) const {
+    (ForEachTupleElement)(WithBoundLhs<Lhs>{fun, lhs}, args);
+  }
+
+  Fun fun;
+  std::tuple<T...> args;
+};
+
+template <class Fun, class... T>
+void ForEveryTwo(const Fun& fun, std::tuple<T...> args) {
+  (ForEachTupleElement)(ForEveryTwoImpl<Fun, T...>{fun, args}, args);
+}
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Insert all values into an associative container
+template<class Container>
+void InsertEach(Container* cont) {
+}
+
+template<class Container, class H, class... T>
+void InsertEach(Container* cont, H&& head, T&&... tail) {
+  cont->insert(head);
+  (InsertEach)(cont, tail...);
+}
+//
+////////////////////////////////////////////////////////////////////////////////
+// A template with a nested "Invoke" static-member-function that executes a
+// passed-in Callable when `Condition` is true, otherwise it ignores the
+// Callable. This is useful for executing a function object with a condition
+// that corresponds to whether or not the Callable can be safely instantiated.
+// It has some overlapping uses with C++17 `if constexpr`.
+template <bool Condition>
+struct If;
+
+template <>
+struct If</*Condition =*/false> {
+  template <class Fun, class... P>
+  static void Invoke(const Fun& /*fun*/, P&&... /*args*/) {}
+};
+
+template <>
+struct If</*Condition =*/true> {
+  template <class Fun, class... P>
+  static void Invoke(const Fun& fun, P&&... args) {
+    // TODO(calabrese) Use std::invoke equivalent instead of function-call.
+    fun(absl::forward<P>(args)...);
+  }
+};
+
+//
+// ABSL_INTERNAL_STRINGIZE(...)
+//
+// This variadic macro transforms its arguments into a c-string literal after
+// expansion.
+//
+// Example:
+//
+//   ABSL_INTERNAL_STRINGIZE(std::array<int, 10>)
+//
+// Results in:
+//
+//   "std::array<int, 10>"
+#define ABSL_INTERNAL_STRINGIZE(...) ABSL_INTERNAL_STRINGIZE_IMPL((__VA_ARGS__))
+#define ABSL_INTERNAL_STRINGIZE_IMPL(arg) ABSL_INTERNAL_STRINGIZE_IMPL2 arg
+#define ABSL_INTERNAL_STRINGIZE_IMPL2(...) #__VA_ARGS__
+
+}  // namespace types_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TYPES_INTERNAL_CONFORMANCE_TESTING_HELPERS_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/conformance_testing_test.cc b/third_party/abseil_cpp/absl/types/internal/conformance_testing_test.cc
new file mode 100644
index 0000000000..cf262fa6c2
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/conformance_testing_test.cc
@@ -0,0 +1,1556 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/internal/conformance_testing.h"
+
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/meta/type_traits.h"
+#include "absl/types/internal/conformance_aliases.h"
+#include "absl/types/internal/conformance_profile.h"
+
+namespace {
+
+namespace ti = absl::types_internal;
+
+template <class T>
+using DefaultConstructibleWithNewImpl = decltype(::new (std::nothrow) T);
+
+template <class T>
+using DefaultConstructibleWithNew =
+    absl::type_traits_internal::is_detected<DefaultConstructibleWithNewImpl, T>;
+
+template <class T>
+using MoveConstructibleWithNewImpl =
+    decltype(::new (std::nothrow) T(std::declval<T>()));
+
+template <class T>
+using MoveConstructibleWithNew =
+    absl::type_traits_internal::is_detected<MoveConstructibleWithNewImpl, T>;
+
+template <class T>
+using CopyConstructibleWithNewImpl =
+    decltype(::new (std::nothrow) T(std::declval<const T&>()));
+
+template <class T>
+using CopyConstructibleWithNew =
+    absl::type_traits_internal::is_detected<CopyConstructibleWithNewImpl, T>;
+
+template <class T,
+          class Result =
+              std::integral_constant<bool, noexcept(::new (std::nothrow) T)>>
+using NothrowDefaultConstructibleWithNewImpl =
+    typename std::enable_if<Result::value>::type;
+
+template <class T>
+using NothrowDefaultConstructibleWithNew =
+    absl::type_traits_internal::is_detected<
+        NothrowDefaultConstructibleWithNewImpl, T>;
+
+template <class T,
+          class Result = std::integral_constant<
+              bool, noexcept(::new (std::nothrow) T(std::declval<T>()))>>
+using NothrowMoveConstructibleWithNewImpl =
+    typename std::enable_if<Result::value>::type;
+
+template <class T>
+using NothrowMoveConstructibleWithNew =
+    absl::type_traits_internal::is_detected<NothrowMoveConstructibleWithNewImpl,
+                                            T>;
+
+template <class T,
+          class Result = std::integral_constant<
+              bool, noexcept(::new (std::nothrow) T(std::declval<const T&>()))>>
+using NothrowCopyConstructibleWithNewImpl =
+    typename std::enable_if<Result::value>::type;
+
+template <class T>
+using NothrowCopyConstructibleWithNew =
+    absl::type_traits_internal::is_detected<NothrowCopyConstructibleWithNewImpl,
+                                            T>;
+
+// NOTE: ?: is used to verify contextually-convertible to bool and not simply
+//       implicit or explicit convertibility.
+#define ABSL_INTERNAL_COMPARISON_OP_EXPR(op) \
+  ((std::declval<const T&>() op std::declval<const T&>()) ? true : true)
+
+#define ABSL_INTERNAL_COMPARISON_OP_TRAIT(name, op)                         \
+  template <class T>                                                        \
+  using name##Impl = decltype(ABSL_INTERNAL_COMPARISON_OP_EXPR(op));        \
+                                                                            \
+  template <class T>                                                        \
+  using name = absl::type_traits_internal::is_detected<name##Impl, T>;      \
+                                                                            \
+  template <class T,                                                        \
+            class Result = std::integral_constant<                          \
+                bool, noexcept(ABSL_INTERNAL_COMPARISON_OP_EXPR(op))>>      \
+  using Nothrow##name##Impl = typename std::enable_if<Result::value>::type; \
+                                                                            \
+  template <class T>                                                        \
+  using Nothrow##name =                                                     \
+      absl::type_traits_internal::is_detected<Nothrow##name##Impl, T>
+
+ABSL_INTERNAL_COMPARISON_OP_TRAIT(EqualityComparable, ==);
+ABSL_INTERNAL_COMPARISON_OP_TRAIT(InequalityComparable, !=);
+ABSL_INTERNAL_COMPARISON_OP_TRAIT(LessThanComparable, <);
+ABSL_INTERNAL_COMPARISON_OP_TRAIT(LessEqualComparable, <=);
+ABSL_INTERNAL_COMPARISON_OP_TRAIT(GreaterEqualComparable, >=);
+ABSL_INTERNAL_COMPARISON_OP_TRAIT(GreaterThanComparable, >);
+
+#undef ABSL_INTERNAL_COMPARISON_OP_TRAIT
+
+template <class T>
+class ProfileTest : public ::testing::Test {};
+
+TYPED_TEST_SUITE_P(ProfileTest);
+
+TYPED_TEST_P(ProfileTest, HasAppropriateConstructionProperties) {
+  using profile = typename TypeParam::profile;
+  using arch = typename TypeParam::arch;
+  using expected_profile = typename TypeParam::expected_profile;
+
+  using props = ti::PropertiesOfT<profile>;
+  using arch_props = ti::PropertiesOfArchetypeT<arch>;
+  using expected_props = ti::PropertiesOfT<expected_profile>;
+
+  // Make sure all of the properties are as expected.
+  // There are seemingly redundant tests here to make it easier to diagnose
+  // the specifics of the failure if something were to go wrong.
+  EXPECT_TRUE((std::is_same<props, arch_props>::value));
+  EXPECT_TRUE((std::is_same<props, expected_props>::value));
+  EXPECT_TRUE((std::is_same<arch_props, expected_props>::value));
+
+  EXPECT_EQ(props::default_constructible_support,
+            expected_props::default_constructible_support);
+
+  EXPECT_EQ(props::move_constructible_support,
+            expected_props::move_constructible_support);
+
+  EXPECT_EQ(props::copy_constructible_support,
+            expected_props::copy_constructible_support);
+
+  EXPECT_EQ(props::destructible_support, expected_props::destructible_support);
+
+  // Avoid additional error message noise when profile and archetype match with
+  // each other but were not what was expected.
+  if (!std::is_same<props, arch_props>::value) {
+    EXPECT_EQ(arch_props::default_constructible_support,
+              expected_props::default_constructible_support);
+
+    EXPECT_EQ(arch_props::move_constructible_support,
+              expected_props::move_constructible_support);
+
+    EXPECT_EQ(arch_props::copy_constructible_support,
+              expected_props::copy_constructible_support);
+
+    EXPECT_EQ(arch_props::destructible_support,
+              expected_props::destructible_support);
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                       Default constructor checks                         //
+  //////////////////////////////////////////////////////////////////////////////
+  EXPECT_EQ(props::default_constructible_support,
+            expected_props::default_constructible_support);
+
+  switch (expected_props::default_constructible_support) {
+    case ti::default_constructible::maybe:
+      EXPECT_FALSE(DefaultConstructibleWithNew<arch>::value);
+      EXPECT_FALSE(NothrowDefaultConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_FALSE(std::is_default_constructible<arch>::value);
+        EXPECT_FALSE(std::is_nothrow_default_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_default_constructible<arch>::value);
+      }
+      break;
+    case ti::default_constructible::yes:
+      EXPECT_TRUE(DefaultConstructibleWithNew<arch>::value);
+      EXPECT_FALSE(NothrowDefaultConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_default_constructible<arch>::value);
+        EXPECT_FALSE(std::is_nothrow_default_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_default_constructible<arch>::value);
+      }
+      break;
+    case ti::default_constructible::nothrow:
+      EXPECT_TRUE(DefaultConstructibleWithNew<arch>::value);
+      EXPECT_TRUE(NothrowDefaultConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_default_constructible<arch>::value);
+        EXPECT_TRUE(std::is_nothrow_default_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_default_constructible<arch>::value);
+
+        // Constructor traits also check the destructor.
+        if (std::is_nothrow_destructible<arch>::value) {
+          EXPECT_TRUE(std::is_nothrow_default_constructible<arch>::value);
+        }
+      }
+      break;
+    case ti::default_constructible::trivial:
+      EXPECT_TRUE(DefaultConstructibleWithNew<arch>::value);
+      EXPECT_TRUE(NothrowDefaultConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_default_constructible<arch>::value);
+        EXPECT_TRUE(std::is_nothrow_default_constructible<arch>::value);
+
+        // Constructor triviality traits require trivially destructible types.
+        if (absl::is_trivially_destructible<arch>::value) {
+          EXPECT_TRUE(absl::is_trivially_default_constructible<arch>::value);
+        }
+      }
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                         Move constructor checks                          //
+  //////////////////////////////////////////////////////////////////////////////
+  EXPECT_EQ(props::move_constructible_support,
+            expected_props::move_constructible_support);
+
+  switch (expected_props::move_constructible_support) {
+    case ti::move_constructible::maybe:
+      EXPECT_FALSE(MoveConstructibleWithNew<arch>::value);
+      EXPECT_FALSE(NothrowMoveConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_FALSE(std::is_move_constructible<arch>::value);
+        EXPECT_FALSE(std::is_nothrow_move_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_move_constructible<arch>::value);
+      }
+      break;
+    case ti::move_constructible::yes:
+      EXPECT_TRUE(MoveConstructibleWithNew<arch>::value);
+      EXPECT_FALSE(NothrowMoveConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_move_constructible<arch>::value);
+        EXPECT_FALSE(std::is_nothrow_move_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_move_constructible<arch>::value);
+      }
+      break;
+    case ti::move_constructible::nothrow:
+      EXPECT_TRUE(MoveConstructibleWithNew<arch>::value);
+      EXPECT_TRUE(NothrowMoveConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_move_constructible<arch>::value);
+        EXPECT_TRUE(std::is_nothrow_move_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_move_constructible<arch>::value);
+
+        // Constructor traits also check the destructor.
+        if (std::is_nothrow_destructible<arch>::value) {
+          EXPECT_TRUE(std::is_nothrow_move_constructible<arch>::value);
+        }
+      }
+      break;
+    case ti::move_constructible::trivial:
+      EXPECT_TRUE(MoveConstructibleWithNew<arch>::value);
+      EXPECT_TRUE(NothrowMoveConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_move_constructible<arch>::value);
+        EXPECT_TRUE(std::is_nothrow_move_constructible<arch>::value);
+
+        // Constructor triviality traits require trivially destructible types.
+        if (absl::is_trivially_destructible<arch>::value) {
+          EXPECT_TRUE(absl::is_trivially_move_constructible<arch>::value);
+        }
+      }
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                         Copy constructor checks                          //
+  //////////////////////////////////////////////////////////////////////////////
+  EXPECT_EQ(props::copy_constructible_support,
+            expected_props::copy_constructible_support);
+
+  switch (expected_props::copy_constructible_support) {
+    case ti::copy_constructible::maybe:
+      EXPECT_FALSE(CopyConstructibleWithNew<arch>::value);
+      EXPECT_FALSE(NothrowCopyConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_FALSE(std::is_copy_constructible<arch>::value);
+        EXPECT_FALSE(std::is_nothrow_copy_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_copy_constructible<arch>::value);
+      }
+      break;
+    case ti::copy_constructible::yes:
+      EXPECT_TRUE(CopyConstructibleWithNew<arch>::value);
+      EXPECT_FALSE(NothrowCopyConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_copy_constructible<arch>::value);
+        EXPECT_FALSE(std::is_nothrow_copy_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_copy_constructible<arch>::value);
+      }
+      break;
+    case ti::copy_constructible::nothrow:
+      EXPECT_TRUE(CopyConstructibleWithNew<arch>::value);
+      EXPECT_TRUE(NothrowCopyConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_copy_constructible<arch>::value);
+        EXPECT_TRUE(std::is_nothrow_copy_constructible<arch>::value);
+        EXPECT_FALSE(absl::is_trivially_copy_constructible<arch>::value);
+
+        // Constructor traits also check the destructor.
+        if (std::is_nothrow_destructible<arch>::value) {
+          EXPECT_TRUE(std::is_nothrow_copy_constructible<arch>::value);
+        }
+      }
+      break;
+    case ti::copy_constructible::trivial:
+      EXPECT_TRUE(CopyConstructibleWithNew<arch>::value);
+      EXPECT_TRUE(NothrowCopyConstructibleWithNew<arch>::value);
+
+      // Standard constructible traits depend on the destructor.
+      if (std::is_destructible<arch>::value) {
+        EXPECT_TRUE(std::is_copy_constructible<arch>::value);
+        EXPECT_TRUE(std::is_nothrow_copy_constructible<arch>::value);
+
+        // Constructor triviality traits require trivially destructible types.
+        if (absl::is_trivially_destructible<arch>::value) {
+          EXPECT_TRUE(absl::is_trivially_copy_constructible<arch>::value);
+        }
+      }
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                           Destructible checks                            //
+  //////////////////////////////////////////////////////////////////////////////
+  EXPECT_EQ(props::destructible_support, expected_props::destructible_support);
+
+  switch (expected_props::destructible_support) {
+    case ti::destructible::maybe:
+      EXPECT_FALSE(std::is_destructible<arch>::value);
+      EXPECT_FALSE(std::is_nothrow_destructible<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_destructible<arch>::value);
+      break;
+    case ti::destructible::yes:
+      EXPECT_TRUE(std::is_destructible<arch>::value);
+      EXPECT_FALSE(std::is_nothrow_destructible<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_destructible<arch>::value);
+      break;
+    case ti::destructible::nothrow:
+      EXPECT_TRUE(std::is_destructible<arch>::value);
+      EXPECT_TRUE(std::is_nothrow_destructible<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_destructible<arch>::value);
+      break;
+    case ti::destructible::trivial:
+      EXPECT_TRUE(std::is_destructible<arch>::value);
+      EXPECT_TRUE(std::is_nothrow_destructible<arch>::value);
+      EXPECT_TRUE(absl::is_trivially_destructible<arch>::value);
+      break;
+  }
+}
+
+TYPED_TEST_P(ProfileTest, HasAppropriateAssignmentProperties) {
+  using profile = typename TypeParam::profile;
+  using arch = typename TypeParam::arch;
+  using expected_profile = typename TypeParam::expected_profile;
+
+  using props = ti::PropertiesOfT<profile>;
+  using arch_props = ti::PropertiesOfArchetypeT<arch>;
+  using expected_props = ti::PropertiesOfT<expected_profile>;
+
+  // Make sure all of the properties are as expected.
+  // There are seemingly redundant tests here to make it easier to diagnose
+  // the specifics of the failure if something were to go wrong.
+  EXPECT_TRUE((std::is_same<props, arch_props>::value));
+  EXPECT_TRUE((std::is_same<props, expected_props>::value));
+  EXPECT_TRUE((std::is_same<arch_props, expected_props>::value));
+
+  EXPECT_EQ(props::move_assignable_support,
+            expected_props::move_assignable_support);
+
+  EXPECT_EQ(props::copy_assignable_support,
+            expected_props::copy_assignable_support);
+
+  // Avoid additional error message noise when profile and archetype match with
+  // each other but were not what was expected.
+  if (!std::is_same<props, arch_props>::value) {
+    EXPECT_EQ(arch_props::move_assignable_support,
+              expected_props::move_assignable_support);
+
+    EXPECT_EQ(arch_props::copy_assignable_support,
+              expected_props::copy_assignable_support);
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                          Move assignment checks                          //
+  //////////////////////////////////////////////////////////////////////////////
+  EXPECT_EQ(props::move_assignable_support,
+            expected_props::move_assignable_support);
+
+  switch (expected_props::move_assignable_support) {
+    case ti::move_assignable::maybe:
+      EXPECT_FALSE(std::is_move_assignable<arch>::value);
+      EXPECT_FALSE(std::is_nothrow_move_assignable<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_move_assignable<arch>::value);
+      break;
+    case ti::move_assignable::yes:
+      EXPECT_TRUE(std::is_move_assignable<arch>::value);
+      EXPECT_FALSE(std::is_nothrow_move_assignable<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_move_assignable<arch>::value);
+      break;
+    case ti::move_assignable::nothrow:
+      EXPECT_TRUE(std::is_move_assignable<arch>::value);
+      EXPECT_TRUE(std::is_nothrow_move_assignable<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_move_assignable<arch>::value);
+      break;
+    case ti::move_assignable::trivial:
+      EXPECT_TRUE(std::is_move_assignable<arch>::value);
+      EXPECT_TRUE(std::is_nothrow_move_assignable<arch>::value);
+      EXPECT_TRUE(absl::is_trivially_move_assignable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                          Copy assignment checks                          //
+  //////////////////////////////////////////////////////////////////////////////
+  EXPECT_EQ(props::copy_assignable_support,
+            expected_props::copy_assignable_support);
+
+  switch (expected_props::copy_assignable_support) {
+    case ti::copy_assignable::maybe:
+      EXPECT_FALSE(std::is_copy_assignable<arch>::value);
+      EXPECT_FALSE(std::is_nothrow_copy_assignable<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_copy_assignable<arch>::value);
+      break;
+    case ti::copy_assignable::yes:
+      EXPECT_TRUE(std::is_copy_assignable<arch>::value);
+      EXPECT_FALSE(std::is_nothrow_copy_assignable<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_copy_assignable<arch>::value);
+      break;
+    case ti::copy_assignable::nothrow:
+      EXPECT_TRUE(std::is_copy_assignable<arch>::value);
+      EXPECT_TRUE(std::is_nothrow_copy_assignable<arch>::value);
+      EXPECT_FALSE(absl::is_trivially_copy_assignable<arch>::value);
+      break;
+    case ti::copy_assignable::trivial:
+      EXPECT_TRUE(std::is_copy_assignable<arch>::value);
+      EXPECT_TRUE(std::is_nothrow_copy_assignable<arch>::value);
+      EXPECT_TRUE(absl::is_trivially_copy_assignable<arch>::value);
+      break;
+  }
+}
+
+TYPED_TEST_P(ProfileTest, HasAppropriateComparisonProperties) {
+  using profile = typename TypeParam::profile;
+  using arch = typename TypeParam::arch;
+  using expected_profile = typename TypeParam::expected_profile;
+
+  using props = ti::PropertiesOfT<profile>;
+  using arch_props = ti::PropertiesOfArchetypeT<arch>;
+  using expected_props = ti::PropertiesOfT<expected_profile>;
+
+  // Make sure all of the properties are as expected.
+  // There are seemingly redundant tests here to make it easier to diagnose
+  // the specifics of the failure if something were to go wrong.
+  EXPECT_TRUE((std::is_same<props, arch_props>::value));
+  EXPECT_TRUE((std::is_same<props, expected_props>::value));
+  EXPECT_TRUE((std::is_same<arch_props, expected_props>::value));
+
+  EXPECT_EQ(props::equality_comparable_support,
+            expected_props::equality_comparable_support);
+
+  EXPECT_EQ(props::inequality_comparable_support,
+            expected_props::inequality_comparable_support);
+
+  EXPECT_EQ(props::less_than_comparable_support,
+            expected_props::less_than_comparable_support);
+
+  EXPECT_EQ(props::less_equal_comparable_support,
+            expected_props::less_equal_comparable_support);
+
+  EXPECT_EQ(props::greater_equal_comparable_support,
+            expected_props::greater_equal_comparable_support);
+
+  EXPECT_EQ(props::greater_than_comparable_support,
+            expected_props::greater_than_comparable_support);
+
+  // Avoid additional error message noise when profile and archetype match with
+  // each other but were not what was expected.
+  if (!std::is_same<props, arch_props>::value) {
+    EXPECT_EQ(arch_props::equality_comparable_support,
+              expected_props::equality_comparable_support);
+
+    EXPECT_EQ(arch_props::inequality_comparable_support,
+              expected_props::inequality_comparable_support);
+
+    EXPECT_EQ(arch_props::less_than_comparable_support,
+              expected_props::less_than_comparable_support);
+
+    EXPECT_EQ(arch_props::less_equal_comparable_support,
+              expected_props::less_equal_comparable_support);
+
+    EXPECT_EQ(arch_props::greater_equal_comparable_support,
+              expected_props::greater_equal_comparable_support);
+
+    EXPECT_EQ(arch_props::greater_than_comparable_support,
+              expected_props::greater_than_comparable_support);
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                        Equality comparable checks                        //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::equality_comparable_support) {
+    case ti::equality_comparable::maybe:
+      EXPECT_FALSE(EqualityComparable<arch>::value);
+      EXPECT_FALSE(NothrowEqualityComparable<arch>::value);
+      break;
+    case ti::equality_comparable::yes:
+      EXPECT_TRUE(EqualityComparable<arch>::value);
+      EXPECT_FALSE(NothrowEqualityComparable<arch>::value);
+      break;
+    case ti::equality_comparable::nothrow:
+      EXPECT_TRUE(EqualityComparable<arch>::value);
+      EXPECT_TRUE(NothrowEqualityComparable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                       Inequality comparable checks                       //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::inequality_comparable_support) {
+    case ti::inequality_comparable::maybe:
+      EXPECT_FALSE(InequalityComparable<arch>::value);
+      EXPECT_FALSE(NothrowInequalityComparable<arch>::value);
+      break;
+    case ti::inequality_comparable::yes:
+      EXPECT_TRUE(InequalityComparable<arch>::value);
+      EXPECT_FALSE(NothrowInequalityComparable<arch>::value);
+      break;
+    case ti::inequality_comparable::nothrow:
+      EXPECT_TRUE(InequalityComparable<arch>::value);
+      EXPECT_TRUE(NothrowInequalityComparable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                       Less than comparable checks                        //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::less_than_comparable_support) {
+    case ti::less_than_comparable::maybe:
+      EXPECT_FALSE(LessThanComparable<arch>::value);
+      EXPECT_FALSE(NothrowLessThanComparable<arch>::value);
+      break;
+    case ti::less_than_comparable::yes:
+      EXPECT_TRUE(LessThanComparable<arch>::value);
+      EXPECT_FALSE(NothrowLessThanComparable<arch>::value);
+      break;
+    case ti::less_than_comparable::nothrow:
+      EXPECT_TRUE(LessThanComparable<arch>::value);
+      EXPECT_TRUE(NothrowLessThanComparable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                      Less equal comparable checks                        //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::less_equal_comparable_support) {
+    case ti::less_equal_comparable::maybe:
+      EXPECT_FALSE(LessEqualComparable<arch>::value);
+      EXPECT_FALSE(NothrowLessEqualComparable<arch>::value);
+      break;
+    case ti::less_equal_comparable::yes:
+      EXPECT_TRUE(LessEqualComparable<arch>::value);
+      EXPECT_FALSE(NothrowLessEqualComparable<arch>::value);
+      break;
+    case ti::less_equal_comparable::nothrow:
+      EXPECT_TRUE(LessEqualComparable<arch>::value);
+      EXPECT_TRUE(NothrowLessEqualComparable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                     Greater equal comparable checks                      //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::greater_equal_comparable_support) {
+    case ti::greater_equal_comparable::maybe:
+      EXPECT_FALSE(GreaterEqualComparable<arch>::value);
+      EXPECT_FALSE(NothrowGreaterEqualComparable<arch>::value);
+      break;
+    case ti::greater_equal_comparable::yes:
+      EXPECT_TRUE(GreaterEqualComparable<arch>::value);
+      EXPECT_FALSE(NothrowGreaterEqualComparable<arch>::value);
+      break;
+    case ti::greater_equal_comparable::nothrow:
+      EXPECT_TRUE(GreaterEqualComparable<arch>::value);
+      EXPECT_TRUE(NothrowGreaterEqualComparable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                     Greater than comparable checks                       //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::greater_than_comparable_support) {
+    case ti::greater_than_comparable::maybe:
+      EXPECT_FALSE(GreaterThanComparable<arch>::value);
+      EXPECT_FALSE(NothrowGreaterThanComparable<arch>::value);
+      break;
+    case ti::greater_than_comparable::yes:
+      EXPECT_TRUE(GreaterThanComparable<arch>::value);
+      EXPECT_FALSE(NothrowGreaterThanComparable<arch>::value);
+      break;
+    case ti::greater_than_comparable::nothrow:
+      EXPECT_TRUE(GreaterThanComparable<arch>::value);
+      EXPECT_TRUE(NothrowGreaterThanComparable<arch>::value);
+      break;
+  }
+}
+
+TYPED_TEST_P(ProfileTest, HasAppropriateAuxilliaryProperties) {
+  using profile = typename TypeParam::profile;
+  using arch = typename TypeParam::arch;
+  using expected_profile = typename TypeParam::expected_profile;
+
+  using props = ti::PropertiesOfT<profile>;
+  using arch_props = ti::PropertiesOfArchetypeT<arch>;
+  using expected_props = ti::PropertiesOfT<expected_profile>;
+
+  // Make sure all of the properties are as expected.
+  // There are seemingly redundant tests here to make it easier to diagnose
+  // the specifics of the failure if something were to go wrong.
+  EXPECT_TRUE((std::is_same<props, arch_props>::value));
+  EXPECT_TRUE((std::is_same<props, expected_props>::value));
+  EXPECT_TRUE((std::is_same<arch_props, expected_props>::value));
+
+  EXPECT_EQ(props::swappable_support, expected_props::swappable_support);
+
+  EXPECT_EQ(props::hashable_support, expected_props::hashable_support);
+
+  // Avoid additional error message noise when profile and archetype match with
+  // each other but were not what was expected.
+  if (!std::is_same<props, arch_props>::value) {
+    EXPECT_EQ(arch_props::swappable_support, expected_props::swappable_support);
+
+    EXPECT_EQ(arch_props::hashable_support, expected_props::hashable_support);
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                            Swappable checks                              //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::swappable_support) {
+    case ti::swappable::maybe:
+      EXPECT_FALSE(absl::type_traits_internal::IsSwappable<arch>::value);
+      EXPECT_FALSE(absl::type_traits_internal::IsNothrowSwappable<arch>::value);
+      break;
+    case ti::swappable::yes:
+      EXPECT_TRUE(absl::type_traits_internal::IsSwappable<arch>::value);
+      EXPECT_FALSE(absl::type_traits_internal::IsNothrowSwappable<arch>::value);
+      break;
+    case ti::swappable::nothrow:
+      EXPECT_TRUE(absl::type_traits_internal::IsSwappable<arch>::value);
+      EXPECT_TRUE(absl::type_traits_internal::IsNothrowSwappable<arch>::value);
+      break;
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  //                             Hashable checks                              //
+  //////////////////////////////////////////////////////////////////////////////
+  switch (expected_props::hashable_support) {
+    case ti::hashable::maybe:
+#if ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_
+      EXPECT_FALSE(absl::type_traits_internal::IsHashable<arch>::value);
+#endif  // ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_
+      break;
+    case ti::hashable::yes:
+      EXPECT_TRUE(absl::type_traits_internal::IsHashable<arch>::value);
+      break;
+  }
+}
+
+REGISTER_TYPED_TEST_SUITE_P(ProfileTest, HasAppropriateConstructionProperties,
+                            HasAppropriateAssignmentProperties,
+                            HasAppropriateComparisonProperties,
+                            HasAppropriateAuxilliaryProperties);
+
+template <class Profile, class Arch, class ExpectedProfile>
+struct ProfileAndExpectation {
+  using profile = Profile;
+  using arch = Arch;
+  using expected_profile = ExpectedProfile;
+};
+
+using CoreProfilesToTest = ::testing::Types<
+    // The terminating case of combine (all properties are "maybe").
+    ProfileAndExpectation<ti::CombineProfiles<>,
+                          ti::Archetype<ti::CombineProfiles<>>,
+                          ti::ConformanceProfile<>>,
+
+    // Core default constructor profiles
+    ProfileAndExpectation<
+        ti::HasDefaultConstructorProfile, ti::HasDefaultConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowDefaultConstructorProfile,
+        ti::HasNothrowDefaultConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::nothrow>>,
+    ProfileAndExpectation<
+        ti::HasTrivialDefaultConstructorProfile,
+        ti::HasTrivialDefaultConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::trivial>>,
+
+    // Core move constructor profiles
+    ProfileAndExpectation<
+        ti::HasMoveConstructorProfile, ti::HasMoveConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::maybe,
+                               ti::move_constructible::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowMoveConstructorProfile,
+        ti::HasNothrowMoveConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::maybe,
+                               ti::move_constructible::nothrow>>,
+    ProfileAndExpectation<
+        ti::HasTrivialMoveConstructorProfile,
+        ti::HasTrivialMoveConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::maybe,
+                               ti::move_constructible::trivial>>,
+
+    // Core copy constructor profiles
+    ProfileAndExpectation<
+        ti::HasCopyConstructorProfile, ti::HasCopyConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::maybe,
+                               ti::move_constructible::maybe,
+                               ti::copy_constructible::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowCopyConstructorProfile,
+        ti::HasNothrowCopyConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::maybe,
+                               ti::move_constructible::maybe,
+                               ti::copy_constructible::nothrow>>,
+    ProfileAndExpectation<
+        ti::HasTrivialCopyConstructorProfile,
+        ti::HasTrivialCopyConstructorArchetype,
+        ti::ConformanceProfile<ti::default_constructible::maybe,
+                               ti::move_constructible::maybe,
+                               ti::copy_constructible::trivial>>,
+
+    // Core move assignment profiles
+    ProfileAndExpectation<
+        ti::HasMoveAssignProfile, ti::HasMoveAssignArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowMoveAssignProfile, ti::HasNothrowMoveAssignArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::nothrow>>,
+    ProfileAndExpectation<
+        ti::HasTrivialMoveAssignProfile, ti::HasTrivialMoveAssignArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::trivial>>,
+
+    // Core copy assignment profiles
+    ProfileAndExpectation<
+        ti::HasCopyAssignProfile, ti::HasCopyAssignArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowCopyAssignProfile, ti::HasNothrowCopyAssignArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::nothrow>>,
+    ProfileAndExpectation<
+        ti::HasTrivialCopyAssignProfile, ti::HasTrivialCopyAssignArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::trivial>>,
+
+    // Core destructor profiles
+    ProfileAndExpectation<
+        ti::HasDestructorProfile, ti::HasDestructorArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowDestructorProfile, ti::HasNothrowDestructorArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow>>,
+    ProfileAndExpectation<
+        ti::HasTrivialDestructorProfile, ti::HasTrivialDestructorArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::trivial>>,
+
+    // Core equality comparable profiles
+    ProfileAndExpectation<
+        ti::HasEqualityProfile, ti::HasEqualityArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowEqualityProfile, ti::HasNothrowEqualityArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::nothrow>>,
+
+    // Core inequality comparable profiles
+    ProfileAndExpectation<
+        ti::HasInequalityProfile, ti::HasInequalityArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowInequalityProfile, ti::HasNothrowInequalityArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe,
+            ti::inequality_comparable::nothrow>>,
+
+    // Core less than comparable profiles
+    ProfileAndExpectation<
+        ti::HasLessThanProfile, ti::HasLessThanArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowLessThanProfile, ti::HasNothrowLessThanArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::nothrow>>,
+
+    // Core less equal comparable profiles
+    ProfileAndExpectation<
+        ti::HasLessEqualProfile, ti::HasLessEqualArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowLessEqualProfile, ti::HasNothrowLessEqualArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe,
+            ti::less_equal_comparable::nothrow>>,
+
+    // Core greater equal comparable profiles
+    ProfileAndExpectation<
+        ti::HasGreaterEqualProfile, ti::HasGreaterEqualArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowGreaterEqualProfile, ti::HasNothrowGreaterEqualArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::nothrow>>,
+
+    // Core greater than comparable profiles
+    ProfileAndExpectation<
+        ti::HasGreaterThanProfile, ti::HasGreaterThanArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowGreaterThanProfile, ti::HasNothrowGreaterThanArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::nothrow>>,
+
+    // Core swappable profiles
+    ProfileAndExpectation<
+        ti::HasSwapProfile, ti::HasSwapArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::yes>>,
+    ProfileAndExpectation<
+        ti::HasNothrowSwapProfile, ti::HasNothrowSwapArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::nothrow>>,
+
+    // Core hashable profiles
+    ProfileAndExpectation<
+        ti::HasStdHashSpecializationProfile,
+        ti::HasStdHashSpecializationArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::maybe,
+            ti::hashable::yes>>>;
+
+using CommonProfilesToTest = ::testing::Types<
+    // NothrowMoveConstructible
+    ProfileAndExpectation<
+        ti::NothrowMoveConstructibleProfile,
+        ti::NothrowMoveConstructibleArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow>>,
+
+    // CopyConstructible
+    ProfileAndExpectation<
+        ti::CopyConstructibleProfile, ti::CopyConstructibleArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::yes, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow>>,
+
+    // NothrowMovable
+    ProfileAndExpectation<
+        ti::NothrowMovableProfile, ti::NothrowMovableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::maybe, ti::move_assignable::nothrow,
+            ti::copy_assignable::maybe, ti::destructible::nothrow,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::nothrow>>,
+
+    // Value
+    ProfileAndExpectation<
+        ti::ValueProfile, ti::ValueArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::yes, ti::move_assignable::nothrow,
+            ti::copy_assignable::yes, ti::destructible::nothrow,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::nothrow>>,
+
+    ////////////////////////////////////////////////////////////////////////////
+    //                  Common but also DefaultConstructible                  //
+    ////////////////////////////////////////////////////////////////////////////
+
+    // DefaultConstructibleNothrowMoveConstructible
+    ProfileAndExpectation<
+        ti::DefaultConstructibleNothrowMoveConstructibleProfile,
+        ti::DefaultConstructibleNothrowMoveConstructibleArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::yes, ti::move_constructible::nothrow,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow>>,
+
+    // DefaultConstructibleCopyConstructible
+    ProfileAndExpectation<
+        ti::DefaultConstructibleCopyConstructibleProfile,
+        ti::DefaultConstructibleCopyConstructibleArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::yes, ti::move_constructible::nothrow,
+            ti::copy_constructible::yes, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow>>,
+
+    // DefaultConstructibleNothrowMovable
+    ProfileAndExpectation<
+        ti::DefaultConstructibleNothrowMovableProfile,
+        ti::DefaultConstructibleNothrowMovableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::yes, ti::move_constructible::nothrow,
+            ti::copy_constructible::maybe, ti::move_assignable::nothrow,
+            ti::copy_assignable::maybe, ti::destructible::nothrow,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::nothrow>>,
+
+    // DefaultConstructibleValue
+    ProfileAndExpectation<
+        ti::DefaultConstructibleValueProfile,
+        ti::DefaultConstructibleValueArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::yes, ti::move_constructible::nothrow,
+            ti::copy_constructible::yes, ti::move_assignable::nothrow,
+            ti::copy_assignable::yes, ti::destructible::nothrow,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::nothrow>>>;
+
+using ComparableHelpersProfilesToTest = ::testing::Types<
+    // Equatable
+    ProfileAndExpectation<
+        ti::EquatableProfile, ti::EquatableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes>>,
+
+    // Comparable
+    ProfileAndExpectation<
+        ti::ComparableProfile, ti::ComparableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes,
+            ti::less_than_comparable::yes, ti::less_equal_comparable::yes,
+            ti::greater_equal_comparable::yes,
+            ti::greater_than_comparable::yes>>,
+
+    // NothrowEquatable
+    ProfileAndExpectation<
+        ti::NothrowEquatableProfile, ti::NothrowEquatableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::nothrow,
+            ti::inequality_comparable::nothrow>>,
+
+    // NothrowComparable
+    ProfileAndExpectation<
+        ti::NothrowComparableProfile, ti::NothrowComparableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::maybe,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::maybe,
+            ti::equality_comparable::nothrow,
+            ti::inequality_comparable::nothrow,
+            ti::less_than_comparable::nothrow,
+            ti::less_equal_comparable::nothrow,
+            ti::greater_equal_comparable::nothrow,
+            ti::greater_than_comparable::nothrow>>>;
+
+using CommonComparableProfilesToTest = ::testing::Types<
+    // ComparableNothrowMoveConstructible
+    ProfileAndExpectation<
+        ti::ComparableNothrowMoveConstructibleProfile,
+        ti::ComparableNothrowMoveConstructibleArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::maybe, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes,
+            ti::less_than_comparable::yes, ti::less_equal_comparable::yes,
+            ti::greater_equal_comparable::yes,
+            ti::greater_than_comparable::yes>>,
+
+    // ComparableCopyConstructible
+    ProfileAndExpectation<
+        ti::ComparableCopyConstructibleProfile,
+        ti::ComparableCopyConstructibleArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::yes, ti::move_assignable::maybe,
+            ti::copy_assignable::maybe, ti::destructible::nothrow,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes,
+            ti::less_than_comparable::yes, ti::less_equal_comparable::yes,
+            ti::greater_equal_comparable::yes,
+            ti::greater_than_comparable::yes>>,
+
+    // ComparableNothrowMovable
+    ProfileAndExpectation<
+        ti::ComparableNothrowMovableProfile,
+        ti::ComparableNothrowMovableArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::maybe, ti::move_assignable::nothrow,
+            ti::copy_assignable::maybe, ti::destructible::nothrow,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes,
+            ti::less_than_comparable::yes, ti::less_equal_comparable::yes,
+            ti::greater_equal_comparable::yes, ti::greater_than_comparable::yes,
+            ti::swappable::nothrow>>,
+
+    // ComparableValue
+    ProfileAndExpectation<
+        ti::ComparableValueProfile, ti::ComparableValueArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::maybe, ti::move_constructible::nothrow,
+            ti::copy_constructible::yes, ti::move_assignable::nothrow,
+            ti::copy_assignable::yes, ti::destructible::nothrow,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes,
+            ti::less_than_comparable::yes, ti::less_equal_comparable::yes,
+            ti::greater_equal_comparable::yes, ti::greater_than_comparable::yes,
+            ti::swappable::nothrow>>>;
+
+using TrivialProfilesToTest = ::testing::Types<
+    ProfileAndExpectation<
+        ti::TrivialSpecialMemberFunctionsProfile,
+        ti::TrivialSpecialMemberFunctionsArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::trivial, ti::move_constructible::trivial,
+            ti::copy_constructible::trivial, ti::move_assignable::trivial,
+            ti::copy_assignable::trivial, ti::destructible::trivial,
+            ti::equality_comparable::maybe, ti::inequality_comparable::maybe,
+            ti::less_than_comparable::maybe, ti::less_equal_comparable::maybe,
+            ti::greater_equal_comparable::maybe,
+            ti::greater_than_comparable::maybe, ti::swappable::nothrow>>,
+
+    ProfileAndExpectation<
+        ti::TriviallyCompleteProfile, ti::TriviallyCompleteArchetype,
+        ti::ConformanceProfile<
+            ti::default_constructible::trivial, ti::move_constructible::trivial,
+            ti::copy_constructible::trivial, ti::move_assignable::trivial,
+            ti::copy_assignable::trivial, ti::destructible::trivial,
+            ti::equality_comparable::yes, ti::inequality_comparable::yes,
+            ti::less_than_comparable::yes, ti::less_equal_comparable::yes,
+            ti::greater_equal_comparable::yes, ti::greater_than_comparable::yes,
+            ti::swappable::nothrow, ti::hashable::yes>>>;
+
+INSTANTIATE_TYPED_TEST_SUITE_P(Core, ProfileTest, CoreProfilesToTest);
+INSTANTIATE_TYPED_TEST_SUITE_P(Common, ProfileTest, CommonProfilesToTest);
+INSTANTIATE_TYPED_TEST_SUITE_P(ComparableHelpers, ProfileTest,
+                               ComparableHelpersProfilesToTest);
+INSTANTIATE_TYPED_TEST_SUITE_P(CommonComparable, ProfileTest,
+                               CommonComparableProfilesToTest);
+INSTANTIATE_TYPED_TEST_SUITE_P(Trivial, ProfileTest, TrivialProfilesToTest);
+
+TEST(ConformanceTestingTest, Basic) {
+  using profile = ti::CombineProfiles<ti::TriviallyCompleteProfile,
+                                      ti::NothrowComparableProfile>;
+
+  using lim = std::numeric_limits<float>;
+
+  ABSL_INTERNAL_ASSERT_CONFORMANCE_OF(float)
+      .INITIALIZER(-lim::infinity())
+      .INITIALIZER(lim::lowest())
+      .INITIALIZER(-1.f)
+      .INITIALIZER(-lim::min())
+      .EQUIVALENCE_CLASS(INITIALIZER(-0.f), INITIALIZER(0.f))
+      .INITIALIZER(lim::min())
+      .INITIALIZER(1.f)
+      .INITIALIZER(lim::max())
+      .INITIALIZER(lim::infinity())
+      .WITH_STRICT_PROFILE(absl::types_internal::RegularityDomain, profile);
+}
+
+struct BadMoveConstruct {
+  BadMoveConstruct() = default;
+  BadMoveConstruct(BadMoveConstruct&& other) noexcept
+      : value(other.value + 1) {}
+  BadMoveConstruct& operator=(BadMoveConstruct&& other) noexcept = default;
+  int value = 0;
+
+  friend bool operator==(BadMoveConstruct const& lhs,
+                         BadMoveConstruct const& rhs) {
+    return lhs.value == rhs.value;
+  }
+  friend bool operator!=(BadMoveConstruct const& lhs,
+                         BadMoveConstruct const& rhs) {
+    return lhs.value != rhs.value;
+  }
+};
+
+struct BadMoveAssign {
+  BadMoveAssign() = default;
+  BadMoveAssign(BadMoveAssign&& other) noexcept = default;
+  BadMoveAssign& operator=(BadMoveAssign&& other) noexcept {
+    int new_value = other.value + 1;
+    value = new_value;
+    return *this;
+  }
+  int value = 0;
+
+  friend bool operator==(BadMoveAssign const& lhs, BadMoveAssign const& rhs) {
+    return lhs.value == rhs.value;
+  }
+  friend bool operator!=(BadMoveAssign const& lhs, BadMoveAssign const& rhs) {
+    return lhs.value != rhs.value;
+  }
+};
+
+enum class WhichCompIsBad { eq, ne, lt, le, ge, gt };
+
+template <WhichCompIsBad Which>
+struct BadCompare {
+  int value;
+
+  friend bool operator==(BadCompare const& lhs, BadCompare const& rhs) {
+    return Which == WhichCompIsBad::eq ? lhs.value != rhs.value
+                                       : lhs.value == rhs.value;
+  }
+
+  friend bool operator!=(BadCompare const& lhs, BadCompare const& rhs) {
+    return Which == WhichCompIsBad::ne ? lhs.value == rhs.value
+                                       : lhs.value != rhs.value;
+  }
+
+  friend bool operator<(BadCompare const& lhs, BadCompare const& rhs) {
+    return Which == WhichCompIsBad::lt ? lhs.value >= rhs.value
+                                       : lhs.value < rhs.value;
+  }
+
+  friend bool operator<=(BadCompare const& lhs, BadCompare const& rhs) {
+    return Which == WhichCompIsBad::le ? lhs.value > rhs.value
+                                       : lhs.value <= rhs.value;
+  }
+
+  friend bool operator>=(BadCompare const& lhs, BadCompare const& rhs) {
+    return Which == WhichCompIsBad::ge ? lhs.value < rhs.value
+                                       : lhs.value >= rhs.value;
+  }
+
+  friend bool operator>(BadCompare const& lhs, BadCompare const& rhs) {
+    return Which == WhichCompIsBad::gt ? lhs.value <= rhs.value
+                                       : lhs.value > rhs.value;
+  }
+};
+
+TEST(ConformanceTestingDeathTest, Failures) {
+  {
+    using profile = ti::CombineProfiles<ti::TriviallyCompleteProfile,
+                                        ti::NothrowComparableProfile>;
+
+    // Note: The initializers are intentionally in the wrong order.
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(float)
+        .INITIALIZER(1.f)
+        .INITIALIZER(0.f)
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using profile =
+        ti::CombineProfiles<ti::NothrowMovableProfile, ti::EquatableProfile>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadMoveConstruct)
+        .DUE_TO("Move construction")
+        .INITIALIZER(BadMoveConstruct())
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using profile =
+        ti::CombineProfiles<ti::NothrowMovableProfile, ti::EquatableProfile>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadMoveAssign)
+        .DUE_TO("Move assignment")
+        .INITIALIZER(BadMoveAssign())
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+TEST(ConformanceTestingDeathTest, CompFailures) {
+  using profile = ti::ComparableProfile;
+
+  {
+    using BadComp = BadCompare<WhichCompIsBad::eq>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadComp)
+        .DUE_TO("Comparison")
+        .INITIALIZER(BadComp{0})
+        .INITIALIZER(BadComp{1})
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using BadComp = BadCompare<WhichCompIsBad::ne>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadComp)
+        .DUE_TO("Comparison")
+        .INITIALIZER(BadComp{0})
+        .INITIALIZER(BadComp{1})
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using BadComp = BadCompare<WhichCompIsBad::lt>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadComp)
+        .DUE_TO("Comparison")
+        .INITIALIZER(BadComp{0})
+        .INITIALIZER(BadComp{1})
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using BadComp = BadCompare<WhichCompIsBad::le>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadComp)
+        .DUE_TO("Comparison")
+        .INITIALIZER(BadComp{0})
+        .INITIALIZER(BadComp{1})
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using BadComp = BadCompare<WhichCompIsBad::ge>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadComp)
+        .DUE_TO("Comparison")
+        .INITIALIZER(BadComp{0})
+        .INITIALIZER(BadComp{1})
+        .WITH_LOOSE_PROFILE(profile);
+  }
+
+  {
+    using BadComp = BadCompare<WhichCompIsBad::gt>;
+
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadComp)
+        .DUE_TO("Comparison")
+        .INITIALIZER(BadComp{0})
+        .INITIALIZER(BadComp{1})
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+struct BadSelfMove {
+  BadSelfMove() = default;
+  BadSelfMove(BadSelfMove&&) = default;
+  BadSelfMove& operator=(BadSelfMove&& other) noexcept {
+    if (this == &other) {
+      broken_state = true;
+    }
+    return *this;
+  }
+
+  friend bool operator==(const BadSelfMove& lhs, const BadSelfMove& rhs) {
+    return !(lhs.broken_state || rhs.broken_state);
+  }
+
+  friend bool operator!=(const BadSelfMove& lhs, const BadSelfMove& rhs) {
+    return lhs.broken_state || rhs.broken_state;
+  }
+
+  bool broken_state = false;
+};
+
+TEST(ConformanceTestingDeathTest, SelfMoveFailure) {
+  using profile = ti::EquatableNothrowMovableProfile;
+
+  {
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadSelfMove)
+        .DUE_TO("Move assignment")
+        .INITIALIZER(BadSelfMove())
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+struct BadSelfCopy {
+  BadSelfCopy() = default;
+  BadSelfCopy(BadSelfCopy&&) = default;
+  BadSelfCopy(const BadSelfCopy&) = default;
+  BadSelfCopy& operator=(BadSelfCopy&&) = default;
+  BadSelfCopy& operator=(BadSelfCopy const& other) {
+    if (this == &other) {
+      broken_state = true;
+    }
+    return *this;
+  }
+
+  friend bool operator==(const BadSelfCopy& lhs, const BadSelfCopy& rhs) {
+    return !(lhs.broken_state || rhs.broken_state);
+  }
+
+  friend bool operator!=(const BadSelfCopy& lhs, const BadSelfCopy& rhs) {
+    return lhs.broken_state || rhs.broken_state;
+  }
+
+  bool broken_state = false;
+};
+
+TEST(ConformanceTestingDeathTest, SelfCopyFailure) {
+  using profile = ti::EquatableValueProfile;
+
+  {
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadSelfCopy)
+        .DUE_TO("Copy assignment")
+        .INITIALIZER(BadSelfCopy())
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+struct BadSelfSwap {
+  friend void swap(BadSelfSwap& lhs, BadSelfSwap& rhs) noexcept {
+    if (&lhs == &rhs) lhs.broken_state = true;
+  }
+
+  friend bool operator==(const BadSelfSwap& lhs, const BadSelfSwap& rhs) {
+    return !(lhs.broken_state || rhs.broken_state);
+  }
+
+  friend bool operator!=(const BadSelfSwap& lhs, const BadSelfSwap& rhs) {
+    return lhs.broken_state || rhs.broken_state;
+  }
+
+  bool broken_state = false;
+};
+
+TEST(ConformanceTestingDeathTest, SelfSwapFailure) {
+  using profile = ti::EquatableNothrowMovableProfile;
+
+  {
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadSelfSwap)
+        .DUE_TO("Swap")
+        .INITIALIZER(BadSelfSwap())
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+struct BadDefaultInitializedMoveAssign {
+  BadDefaultInitializedMoveAssign() : default_initialized(true) {}
+  explicit BadDefaultInitializedMoveAssign(int v) : value(v) {}
+  BadDefaultInitializedMoveAssign(
+      BadDefaultInitializedMoveAssign&& other) noexcept
+      : value(other.value) {}
+  BadDefaultInitializedMoveAssign& operator=(
+      BadDefaultInitializedMoveAssign&& other) noexcept {
+    value = other.value;
+    if (default_initialized) ++value;  // Bad move if lhs is default initialized
+    return *this;
+  }
+
+  friend bool operator==(const BadDefaultInitializedMoveAssign& lhs,
+                         const BadDefaultInitializedMoveAssign& rhs) {
+    return lhs.value == rhs.value;
+  }
+
+  friend bool operator!=(const BadDefaultInitializedMoveAssign& lhs,
+                         const BadDefaultInitializedMoveAssign& rhs) {
+    return lhs.value != rhs.value;
+  }
+
+  bool default_initialized = false;
+  int value = 0;
+};
+
+TEST(ConformanceTestingDeathTest, DefaultInitializedMoveAssignFailure) {
+  using profile =
+      ti::CombineProfiles<ti::DefaultConstructibleNothrowMovableProfile,
+                          ti::EquatableProfile>;
+
+  {
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadDefaultInitializedMoveAssign)
+        .DUE_TO("move assignment")
+        .INITIALIZER(BadDefaultInitializedMoveAssign(0))
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+struct BadDefaultInitializedCopyAssign {
+  BadDefaultInitializedCopyAssign() : default_initialized(true) {}
+  explicit BadDefaultInitializedCopyAssign(int v) : value(v) {}
+  BadDefaultInitializedCopyAssign(
+      BadDefaultInitializedCopyAssign&& other) noexcept
+      : value(other.value) {}
+  BadDefaultInitializedCopyAssign(const BadDefaultInitializedCopyAssign& other)
+      : value(other.value) {}
+
+  BadDefaultInitializedCopyAssign& operator=(
+      BadDefaultInitializedCopyAssign&& other) noexcept {
+    value = other.value;
+    return *this;
+  }
+
+  BadDefaultInitializedCopyAssign& operator=(
+      const BadDefaultInitializedCopyAssign& other) {
+    value = other.value;
+    if (default_initialized) ++value;  // Bad move if lhs is default initialized
+    return *this;
+  }
+
+  friend bool operator==(const BadDefaultInitializedCopyAssign& lhs,
+                         const BadDefaultInitializedCopyAssign& rhs) {
+    return lhs.value == rhs.value;
+  }
+
+  friend bool operator!=(const BadDefaultInitializedCopyAssign& lhs,
+                         const BadDefaultInitializedCopyAssign& rhs) {
+    return lhs.value != rhs.value;
+  }
+
+  bool default_initialized = false;
+  int value = 0;
+};
+
+TEST(ConformanceTestingDeathTest, DefaultInitializedAssignFailure) {
+  using profile = ti::CombineProfiles<ti::DefaultConstructibleValueProfile,
+                                      ti::EquatableProfile>;
+
+  {
+    ABSL_INTERNAL_ASSERT_NONCONFORMANCE_OF(BadDefaultInitializedCopyAssign)
+        .DUE_TO("copy assignment")
+        .INITIALIZER(BadDefaultInitializedCopyAssign(0))
+        .WITH_LOOSE_PROFILE(profile);
+  }
+}
+
+}  // namespace
diff --git a/third_party/abseil_cpp/absl/types/internal/optional.h b/third_party/abseil_cpp/absl/types/internal/optional.h
new file mode 100644
index 0000000000..92932b6001
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/optional.h
@@ -0,0 +1,396 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef ABSL_TYPES_INTERNAL_OPTIONAL_H_
+#define ABSL_TYPES_INTERNAL_OPTIONAL_H_
+
+#include <functional>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/inline_variable.h"
+#include "absl/memory/memory.h"
+#include "absl/meta/type_traits.h"
+#include "absl/utility/utility.h"
+
+// ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+//
+// Inheriting constructors is supported in GCC 4.8+, Clang 3.3+ and MSVC 2015.
+// __cpp_inheriting_constructors is a predefined macro and a recommended way to
+// check for this language feature, but GCC doesn't support it until 5.0 and
+// Clang doesn't support it until 3.6.
+// Also, MSVC 2015 has a bug: it doesn't inherit the constexpr template
+// constructor. For example, the following code won't work on MSVC 2015 Update3:
+// struct Base {
+//   int t;
+//   template <typename T>
+//   constexpr Base(T t_) : t(t_) {}
+// };
+// struct Foo : Base {
+//   using Base::Base;
+// }
+// constexpr Foo foo(0);  // doesn't work on MSVC 2015
+#if defined(__clang__)
+#if __has_feature(cxx_inheriting_constructors)
+#define ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS 1
+#endif
+#elif (defined(__GNUC__) &&                                       \
+       (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ >= 8)) || \
+    (__cpp_inheriting_constructors >= 200802) ||                  \
+    (defined(_MSC_VER) && _MSC_VER >= 1910)
+#define ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS 1
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// Forward declaration
+template <typename T>
+class optional;
+
+namespace optional_internal {
+
+// This tag type is used as a constructor parameter type for `nullopt_t`.
+struct init_t {
+  explicit init_t() = default;
+};
+
+struct empty_struct {};
+
+// This class stores the data in optional<T>.
+// It is specialized based on whether T is trivially destructible.
+// This is the specialization for non trivially destructible type.
+template <typename T, bool unused = std::is_trivially_destructible<T>::value>
+class optional_data_dtor_base {
+  struct dummy_type {
+    static_assert(sizeof(T) % sizeof(empty_struct) == 0, "");
+    // Use an array to avoid GCC 6 placement-new warning.
+    empty_struct data[sizeof(T) / sizeof(empty_struct)];
+  };
+
+ protected:
+  // Whether there is data or not.
+  bool engaged_;
+  // Data storage
+  union {
+    T data_;
+    dummy_type dummy_;
+  };
+
+  void destruct() noexcept {
+    if (engaged_) {
+      data_.~T();
+      engaged_ = false;
+    }
+  }
+
+  // dummy_ must be initialized for constexpr constructor.
+  constexpr optional_data_dtor_base() noexcept : engaged_(false), dummy_{{}} {}
+
+  template <typename... Args>
+  constexpr explicit optional_data_dtor_base(in_place_t, Args&&... args)
+      : engaged_(true), data_(absl::forward<Args>(args)...) {}
+
+  ~optional_data_dtor_base() { destruct(); }
+};
+
+// Specialization for trivially destructible type.
+template <typename T>
+class optional_data_dtor_base<T, true> {
+  struct dummy_type {
+    static_assert(sizeof(T) % sizeof(empty_struct) == 0, "");
+    // Use array to avoid GCC 6 placement-new warning.
+    empty_struct data[sizeof(T) / sizeof(empty_struct)];
+  };
+
+ protected:
+  // Whether there is data or not.
+  bool engaged_;
+  // Data storage
+  union {
+    T data_;
+    dummy_type dummy_;
+  };
+  void destruct() noexcept { engaged_ = false; }
+
+  // dummy_ must be initialized for constexpr constructor.
+  constexpr optional_data_dtor_base() noexcept : engaged_(false), dummy_{{}} {}
+
+  template <typename... Args>
+  constexpr explicit optional_data_dtor_base(in_place_t, Args&&... args)
+      : engaged_(true), data_(absl::forward<Args>(args)...) {}
+};
+
+template <typename T>
+class optional_data_base : public optional_data_dtor_base<T> {
+ protected:
+  using base = optional_data_dtor_base<T>;
+#ifdef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+  using base::base;
+#else
+  optional_data_base() = default;
+
+  template <typename... Args>
+  constexpr explicit optional_data_base(in_place_t t, Args&&... args)
+      : base(t, absl::forward<Args>(args)...) {}
+#endif
+
+  template <typename... Args>
+  void construct(Args&&... args) {
+    // Use dummy_'s address to work around casting cv-qualified T* to void*.
+    ::new (static_cast<void*>(&this->dummy_)) T(std::forward<Args>(args)...);
+    this->engaged_ = true;
+  }
+
+  template <typename U>
+  void assign(U&& u) {
+    if (this->engaged_) {
+      this->data_ = std::forward<U>(u);
+    } else {
+      construct(std::forward<U>(u));
+    }
+  }
+};
+
+// TODO(absl-team): Add another class using
+// std::is_trivially_move_constructible trait when available to match
+// http://cplusplus.github.io/LWG/lwg-defects.html#2900, for types that
+// have trivial move but nontrivial copy.
+// Also, we should be checking is_trivially_copyable here, which is not
+// supported now, so we use is_trivially_* traits instead.
+template <typename T,
+          bool unused = absl::is_trivially_copy_constructible<T>::value&&
+              absl::is_trivially_copy_assignable<typename std::remove_cv<
+                  T>::type>::value&& std::is_trivially_destructible<T>::value>
+class optional_data;
+
+// Trivially copyable types
+template <typename T>
+class optional_data<T, true> : public optional_data_base<T> {
+ protected:
+#ifdef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+  using optional_data_base<T>::optional_data_base;
+#else
+  optional_data() = default;
+
+  template <typename... Args>
+  constexpr explicit optional_data(in_place_t t, Args&&... args)
+      : optional_data_base<T>(t, absl::forward<Args>(args)...) {}
+#endif
+};
+
+template <typename T>
+class optional_data<T, false> : public optional_data_base<T> {
+ protected:
+#ifdef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+  using optional_data_base<T>::optional_data_base;
+#else
+  template <typename... Args>
+  constexpr explicit optional_data(in_place_t t, Args&&... args)
+      : optional_data_base<T>(t, absl::forward<Args>(args)...) {}
+#endif
+
+  optional_data() = default;
+
+  optional_data(const optional_data& rhs) : optional_data_base<T>() {
+    if (rhs.engaged_) {
+      this->construct(rhs.data_);
+    }
+  }
+
+  optional_data(optional_data&& rhs) noexcept(
+      absl::default_allocator_is_nothrow::value ||
+      std::is_nothrow_move_constructible<T>::value)
+      : optional_data_base<T>() {
+    if (rhs.engaged_) {
+      this->construct(std::move(rhs.data_));
+    }
+  }
+
+  optional_data& operator=(const optional_data& rhs) {
+    if (rhs.engaged_) {
+      this->assign(rhs.data_);
+    } else {
+      this->destruct();
+    }
+    return *this;
+  }
+
+  optional_data& operator=(optional_data&& rhs) noexcept(
+      std::is_nothrow_move_assignable<T>::value&&
+          std::is_nothrow_move_constructible<T>::value) {
+    if (rhs.engaged_) {
+      this->assign(std::move(rhs.data_));
+    } else {
+      this->destruct();
+    }
+    return *this;
+  }
+};
+
+// Ordered by level of restriction, from low to high.
+// Copyable implies movable.
+enum class copy_traits { copyable = 0, movable = 1, non_movable = 2 };
+
+// Base class for enabling/disabling copy/move constructor.
+template <copy_traits>
+class optional_ctor_base;
+
+template <>
+class optional_ctor_base<copy_traits::copyable> {
+ public:
+  constexpr optional_ctor_base() = default;
+  optional_ctor_base(const optional_ctor_base&) = default;
+  optional_ctor_base(optional_ctor_base&&) = default;
+  optional_ctor_base& operator=(const optional_ctor_base&) = default;
+  optional_ctor_base& operator=(optional_ctor_base&&) = default;
+};
+
+template <>
+class optional_ctor_base<copy_traits::movable> {
+ public:
+  constexpr optional_ctor_base() = default;
+  optional_ctor_base(const optional_ctor_base&) = delete;
+  optional_ctor_base(optional_ctor_base&&) = default;
+  optional_ctor_base& operator=(const optional_ctor_base&) = default;
+  optional_ctor_base& operator=(optional_ctor_base&&) = default;
+};
+
+template <>
+class optional_ctor_base<copy_traits::non_movable> {
+ public:
+  constexpr optional_ctor_base() = default;
+  optional_ctor_base(const optional_ctor_base&) = delete;
+  optional_ctor_base(optional_ctor_base&&) = delete;
+  optional_ctor_base& operator=(const optional_ctor_base&) = default;
+  optional_ctor_base& operator=(optional_ctor_base&&) = default;
+};
+
+// Base class for enabling/disabling copy/move assignment.
+template <copy_traits>
+class optional_assign_base;
+
+template <>
+class optional_assign_base<copy_traits::copyable> {
+ public:
+  constexpr optional_assign_base() = default;
+  optional_assign_base(const optional_assign_base&) = default;
+  optional_assign_base(optional_assign_base&&) = default;
+  optional_assign_base& operator=(const optional_assign_base&) = default;
+  optional_assign_base& operator=(optional_assign_base&&) = default;
+};
+
+template <>
+class optional_assign_base<copy_traits::movable> {
+ public:
+  constexpr optional_assign_base() = default;
+  optional_assign_base(const optional_assign_base&) = default;
+  optional_assign_base(optional_assign_base&&) = default;
+  optional_assign_base& operator=(const optional_assign_base&) = delete;
+  optional_assign_base& operator=(optional_assign_base&&) = default;
+};
+
+template <>
+class optional_assign_base<copy_traits::non_movable> {
+ public:
+  constexpr optional_assign_base() = default;
+  optional_assign_base(const optional_assign_base&) = default;
+  optional_assign_base(optional_assign_base&&) = default;
+  optional_assign_base& operator=(const optional_assign_base&) = delete;
+  optional_assign_base& operator=(optional_assign_base&&) = delete;
+};
+
+template <typename T>
+struct ctor_copy_traits {
+  static constexpr copy_traits traits =
+      std::is_copy_constructible<T>::value
+          ? copy_traits::copyable
+          : std::is_move_constructible<T>::value ? copy_traits::movable
+                                                 : copy_traits::non_movable;
+};
+
+template <typename T>
+struct assign_copy_traits {
+  static constexpr copy_traits traits =
+      absl::is_copy_assignable<T>::value && std::is_copy_constructible<T>::value
+          ? copy_traits::copyable
+          : absl::is_move_assignable<T>::value &&
+                    std::is_move_constructible<T>::value
+                ? copy_traits::movable
+                : copy_traits::non_movable;
+};
+
+// Whether T is constructible or convertible from optional<U>.
+template <typename T, typename U>
+struct is_constructible_convertible_from_optional
+    : std::integral_constant<
+          bool, std::is_constructible<T, optional<U>&>::value ||
+                    std::is_constructible<T, optional<U>&&>::value ||
+                    std::is_constructible<T, const optional<U>&>::value ||
+                    std::is_constructible<T, const optional<U>&&>::value ||
+                    std::is_convertible<optional<U>&, T>::value ||
+                    std::is_convertible<optional<U>&&, T>::value ||
+                    std::is_convertible<const optional<U>&, T>::value ||
+                    std::is_convertible<const optional<U>&&, T>::value> {};
+
+// Whether T is constructible or convertible or assignable from optional<U>.
+template <typename T, typename U>
+struct is_constructible_convertible_assignable_from_optional
+    : std::integral_constant<
+          bool, is_constructible_convertible_from_optional<T, U>::value ||
+                    std::is_assignable<T&, optional<U>&>::value ||
+                    std::is_assignable<T&, optional<U>&&>::value ||
+                    std::is_assignable<T&, const optional<U>&>::value ||
+                    std::is_assignable<T&, const optional<U>&&>::value> {};
+
+// Helper function used by [optional.relops], [optional.comp_with_t],
+// for checking whether an expression is convertible to bool.
+bool convertible_to_bool(bool);
+
+// Base class for std::hash<absl::optional<T>>:
+// If std::hash<std::remove_const_t<T>> is enabled, it provides operator() to
+// compute the hash; Otherwise, it is disabled.
+// Reference N4659 23.14.15 [unord.hash].
+template <typename T, typename = size_t>
+struct optional_hash_base {
+  optional_hash_base() = delete;
+  optional_hash_base(const optional_hash_base&) = delete;
+  optional_hash_base(optional_hash_base&&) = delete;
+  optional_hash_base& operator=(const optional_hash_base&) = delete;
+  optional_hash_base& operator=(optional_hash_base&&) = delete;
+};
+
+template <typename T>
+struct optional_hash_base<T, decltype(std::hash<absl::remove_const_t<T> >()(
+                                 std::declval<absl::remove_const_t<T> >()))> {
+  using argument_type = absl::optional<T>;
+  using result_type = size_t;
+  size_t operator()(const absl::optional<T>& opt) const {
+    absl::type_traits_internal::AssertHashEnabled<absl::remove_const_t<T>>();
+    if (opt) {
+      return std::hash<absl::remove_const_t<T> >()(*opt);
+    } else {
+      return static_cast<size_t>(0x297814aaad196e6dULL);
+    }
+  }
+};
+
+}  // namespace optional_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#undef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+
+#endif  // ABSL_TYPES_INTERNAL_OPTIONAL_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/parentheses.h b/third_party/abseil_cpp/absl/types/internal/parentheses.h
new file mode 100644
index 0000000000..5aebee8fde
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/parentheses.h
@@ -0,0 +1,34 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// parentheses.h
+// -----------------------------------------------------------------------------
+//
+// This file contains macros that expand to a left parenthesis and a right
+// parenthesis. These are in their own file and are generated from macros
+// because otherwise clang-format gets confused and clang-format off directives
+// do not help.
+//
+// The parentheses macros are used when wanting to require a rescan before
+// expansion of parenthesized text appearing after a function-style macro name.
+
+#ifndef ABSL_TYPES_INTERNAL_PARENTHESES_H_
+#define ABSL_TYPES_INTERNAL_PARENTHESES_H_
+
+#define ABSL_INTERNAL_LPAREN (
+
+#define ABSL_INTERNAL_RPAREN )
+
+#endif  // ABSL_TYPES_INTERNAL_PARENTHESES_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/span.h b/third_party/abseil_cpp/absl/types/internal/span.h
new file mode 100644
index 0000000000..112612f4bd
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/span.h
@@ -0,0 +1,128 @@
+//
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef ABSL_TYPES_INTERNAL_SPAN_H_
+#define ABSL_TYPES_INTERNAL_SPAN_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <string>
+#include <type_traits>
+
+#include "absl/algorithm/algorithm.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace span_internal {
+// A constexpr min function
+constexpr size_t Min(size_t a, size_t b) noexcept { return a < b ? a : b; }
+
+// Wrappers for access to container data pointers.
+template <typename C>
+constexpr auto GetDataImpl(C& c, char) noexcept  // NOLINT(runtime/references)
+    -> decltype(c.data()) {
+  return c.data();
+}
+
+// Before C++17, std::string::data returns a const char* in all cases.
+inline char* GetDataImpl(std::string& s,  // NOLINT(runtime/references)
+                         int) noexcept {
+  return &s[0];
+}
+
+template <typename C>
+constexpr auto GetData(C& c) noexcept  // NOLINT(runtime/references)
+    -> decltype(GetDataImpl(c, 0)) {
+  return GetDataImpl(c, 0);
+}
+
+// Detection idioms for size() and data().
+template <typename C>
+using HasSize =
+    std::is_integral<absl::decay_t<decltype(std::declval<C&>().size())>>;
+
+// We want to enable conversion from vector<T*> to Span<const T* const> but
+// disable conversion from vector<Derived> to Span<Base>. Here we use
+// the fact that U** is convertible to Q* const* if and only if Q is the same
+// type or a more cv-qualified version of U.  We also decay the result type of
+// data() to avoid problems with classes which have a member function data()
+// which returns a reference.
+template <typename T, typename C>
+using HasData =
+    std::is_convertible<absl::decay_t<decltype(GetData(std::declval<C&>()))>*,
+                        T* const*>;
+
+// Extracts value type from a Container
+template <typename C>
+struct ElementType {
+  using type = typename absl::remove_reference_t<C>::value_type;
+};
+
+template <typename T, size_t N>
+struct ElementType<T (&)[N]> {
+  using type = T;
+};
+
+template <typename C>
+using ElementT = typename ElementType<C>::type;
+
+template <typename T>
+using EnableIfMutable =
+    typename std::enable_if<!std::is_const<T>::value, int>::type;
+
+template <template <typename> class SpanT, typename T>
+bool EqualImpl(SpanT<T> a, SpanT<T> b) {
+  static_assert(std::is_const<T>::value, "");
+  return absl::equal(a.begin(), a.end(), b.begin(), b.end());
+}
+
+template <template <typename> class SpanT, typename T>
+bool LessThanImpl(SpanT<T> a, SpanT<T> b) {
+  // We can't use value_type since that is remove_cv_t<T>, so we go the long way
+  // around.
+  static_assert(std::is_const<T>::value, "");
+  return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
+}
+
+// The `IsConvertible` classes here are needed because of the
+// `std::is_convertible` bug in libcxx when compiled with GCC. This build
+// configuration is used by Android NDK toolchain. Reference link:
+// https://bugs.llvm.org/show_bug.cgi?id=27538.
+template <typename From, typename To>
+struct IsConvertibleHelper {
+ private:
+  static std::true_type testval(To);
+  static std::false_type testval(...);
+
+ public:
+  using type = decltype(testval(std::declval<From>()));
+};
+
+template <typename From, typename To>
+struct IsConvertible : IsConvertibleHelper<From, To>::type {};
+
+// TODO(zhangxy): replace `IsConvertible` with `std::is_convertible` once the
+// older version of libcxx is not supported.
+template <typename From, typename To>
+using EnableIfConvertibleTo =
+    typename std::enable_if<IsConvertible<From, To>::value>::type;
+}  // namespace span_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TYPES_INTERNAL_SPAN_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/transform_args.h b/third_party/abseil_cpp/absl/types/internal/transform_args.h
new file mode 100644
index 0000000000..4a0ab42ac4
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/transform_args.h
@@ -0,0 +1,246 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// transform_args.h
+// -----------------------------------------------------------------------------
+//
+// This file contains a higher-order macro that "transforms" each element of a
+// a variadic argument by a provided secondary macro.
+
+#ifndef ABSL_TYPES_INTERNAL_TRANSFORM_ARGS_H_
+#define ABSL_TYPES_INTERNAL_TRANSFORM_ARGS_H_
+
+//
+// ABSL_INTERNAL_CAT(a, b)
+//
+// This macro takes two arguments and concatenates them together via ## after
+// expansion.
+//
+// Example:
+//
+//   ABSL_INTERNAL_CAT(foo_, bar)
+//
+// Results in:
+//
+//   foo_bar
+#define ABSL_INTERNAL_CAT(a, b) ABSL_INTERNAL_CAT_IMPL(a, b)
+#define ABSL_INTERNAL_CAT_IMPL(a, b) a##b
+
+//
+// ABSL_INTERNAL_TRANSFORM_ARGS(m, ...)
+//
+// This macro takes another macro as an argument followed by a trailing series
+// of additional parameters (up to 32 additional arguments). It invokes the
+// passed-in macro once for each of the additional arguments, with the
+// expansions separated by commas.
+//
+// Example:
+//
+//   ABSL_INTERNAL_TRANSFORM_ARGS(MY_MACRO, a, b, c)
+//
+// Results in:
+//
+//   MY_MACRO(a), MY_MACRO(b), MY_MACRO(c)
+//
+// TODO(calabrese) Handle no arguments as a special case.
+#define ABSL_INTERNAL_TRANSFORM_ARGS(m, ...)             \
+  ABSL_INTERNAL_CAT(ABSL_INTERNAL_TRANSFORM_ARGS,        \
+                    ABSL_INTERNAL_NUM_ARGS(__VA_ARGS__)) \
+  (m, __VA_ARGS__)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS1(m, a0) m(a0)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS2(m, a0, a1) m(a0), m(a1)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS3(m, a0, a1, a2) m(a0), m(a1), m(a2)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS4(m, a0, a1, a2, a3) \
+  m(a0), m(a1), m(a2), m(a3)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS5(m, a0, a1, a2, a3, a4) \
+  m(a0), m(a1), m(a2), m(a3), m(a4)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS6(m, a0, a1, a2, a3, a4, a5) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS7(m, a0, a1, a2, a3, a4, a5, a6) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS8(m, a0, a1, a2, a3, a4, a5, a6, a7) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS9(m, a0, a1, a2, a3, a4, a5, a6, a7, a8) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS10(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9)                                    \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS11(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10)                               \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9), m(a10)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS12(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11)                          \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS13(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12)                     \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS14(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13)                \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS15(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14)           \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS16(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15)      \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS17(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS18(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17)                                   \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS19(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17, a18)                              \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS20(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17, a18, a19)                         \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS21(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17, a18, a19, a20)                    \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS22(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17, a18, a19, a20, a21)               \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS23(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17, a18, a19, a20, a21, a22)          \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS24(m, a0, a1, a2, a3, a4, a5, a6, a7, a8, \
+                                       a9, a10, a11, a12, a13, a14, a15, a16, \
+                                       a17, a18, a19, a20, a21, a22, a23)     \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22), m(a23)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS25(m, a0, a1, a2, a3, a4, a5, a6, a7, a8,  \
+                                       a9, a10, a11, a12, a13, a14, a15, a16,  \
+                                       a17, a18, a19, a20, a21, a22, a23, a24) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),        \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18),  \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS26(                                       \
+    m, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15,  \
+    a16, a17, a18, a19, a20, a21, a22, a23, a24, a25)                         \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS27(                                       \
+    m, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15,  \
+    a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26)                    \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25), m(a26)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS28(                                       \
+    m, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15,  \
+    a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27)               \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25), m(a26), m(a27)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS29(                                       \
+    m, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15,  \
+    a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28)          \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25), m(a26), m(a27), \
+      m(a28)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS30(                                       \
+    m, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15,  \
+    a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29)     \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),       \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18), \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25), m(a26), m(a27), \
+      m(a28), m(a29)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS31(                                        \
+    m, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15,   \
+    a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30) \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),        \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18),  \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25), m(a26), m(a27),  \
+      m(a28), m(a29), m(a30)
+
+#define ABSL_INTERNAL_TRANSFORM_ARGS32(m, a0, a1, a2, a3, a4, a5, a6, a7, a8,  \
+                                       a9, a10, a11, a12, a13, a14, a15, a16,  \
+                                       a17, a18, a19, a20, a21, a22, a23, a24, \
+                                       a25, a26, a27, a28, a29, a30, a31)      \
+  m(a0), m(a1), m(a2), m(a3), m(a4), m(a5), m(a6), m(a7), m(a8), m(a9),        \
+      m(a10), m(a11), m(a12), m(a13), m(a14), m(a15), m(a16), m(a17), m(a18),  \
+      m(a19), m(a20), m(a21), m(a22), m(a23), m(a24), m(a25), m(a26), m(a27),  \
+      m(a28), m(a29), m(a30), m(a31)
+
+#define ABSL_INTERNAL_NUM_ARGS_IMPL(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9,    \
+                                    a10, a11, a12, a13, a14, a15, a16, a17,    \
+                                    a18, a19, a20, a21, a22, a23, a24, a25,    \
+                                    a26, a27, a28, a29, a30, a31, result, ...) \
+  result
+
+#define ABSL_INTERNAL_FORCE_EXPANSION(...) __VA_ARGS__
+
+#define ABSL_INTERNAL_NUM_ARGS(...)                                            \
+  ABSL_INTERNAL_FORCE_EXPANSION(ABSL_INTERNAL_NUM_ARGS_IMPL(                   \
+      __VA_ARGS__, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, \
+      17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, ))
+
+#endif  // ABSL_TYPES_INTERNAL_TRANSFORM_ARGS_H_
diff --git a/third_party/abseil_cpp/absl/types/internal/variant.h b/third_party/abseil_cpp/absl/types/internal/variant.h
new file mode 100644
index 0000000000..71bd3adfc6
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/internal/variant.h
@@ -0,0 +1,1646 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Implementation details of absl/types/variant.h, pulled into a
+// separate file to avoid cluttering the top of the API header with
+// implementation details.
+
+#ifndef ABSL_TYPES_variant_internal_H_
+#define ABSL_TYPES_variant_internal_H_
+
+#include <cassert>
+#include <cstddef>
+#include <cstdlib>
+#include <memory>
+#include <stdexcept>
+#include <tuple>
+#include <type_traits>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/identity.h"
+#include "absl/base/internal/inline_variable.h"
+#include "absl/base/internal/invoke.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/meta/type_traits.h"
+#include "absl/types/bad_variant_access.h"
+#include "absl/utility/utility.h"
+
+#if !defined(ABSL_USES_STD_VARIANT)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+template <class... Types>
+class variant;
+
+ABSL_INTERNAL_INLINE_CONSTEXPR(size_t, variant_npos, -1);
+
+template <class T>
+struct variant_size;
+
+template <std::size_t I, class T>
+struct variant_alternative;
+
+namespace variant_internal {
+
+// NOTE: See specializations below for details.
+template <std::size_t I, class T>
+struct VariantAlternativeSfinae {};
+
+// Requires: I < variant_size_v<T>.
+//
+// Value: The Ith type of Types...
+template <std::size_t I, class T0, class... Tn>
+struct VariantAlternativeSfinae<I, variant<T0, Tn...>>
+    : VariantAlternativeSfinae<I - 1, variant<Tn...>> {};
+
+// Value: T0
+template <class T0, class... Ts>
+struct VariantAlternativeSfinae<0, variant<T0, Ts...>> {
+  using type = T0;
+};
+
+template <std::size_t I, class T>
+using VariantAlternativeSfinaeT = typename VariantAlternativeSfinae<I, T>::type;
+
+// NOTE: Requires T to be a reference type.
+template <class T, class U>
+struct GiveQualsTo;
+
+template <class T, class U>
+struct GiveQualsTo<T&, U> {
+  using type = U&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<T&&, U> {
+  using type = U&&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<const T&, U> {
+  using type = const U&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<const T&&, U> {
+  using type = const U&&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<volatile T&, U> {
+  using type = volatile U&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<volatile T&&, U> {
+  using type = volatile U&&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<volatile const T&, U> {
+  using type = volatile const U&;
+};
+
+template <class T, class U>
+struct GiveQualsTo<volatile const T&&, U> {
+  using type = volatile const U&&;
+};
+
+template <class T, class U>
+using GiveQualsToT = typename GiveQualsTo<T, U>::type;
+
+// Convenience alias, since size_t integral_constant is used a lot in this file.
+template <std::size_t I>
+using SizeT = std::integral_constant<std::size_t, I>;
+
+using NPos = SizeT<variant_npos>;
+
+template <class Variant, class T, class = void>
+struct IndexOfConstructedType {};
+
+template <std::size_t I, class Variant>
+struct VariantAccessResultImpl;
+
+template <std::size_t I, template <class...> class Variantemplate, class... T>
+struct VariantAccessResultImpl<I, Variantemplate<T...>&> {
+  using type = typename absl::variant_alternative<I, variant<T...>>::type&;
+};
+
+template <std::size_t I, template <class...> class Variantemplate, class... T>
+struct VariantAccessResultImpl<I, const Variantemplate<T...>&> {
+  using type =
+      const typename absl::variant_alternative<I, variant<T...>>::type&;
+};
+
+template <std::size_t I, template <class...> class Variantemplate, class... T>
+struct VariantAccessResultImpl<I, Variantemplate<T...>&&> {
+  using type = typename absl::variant_alternative<I, variant<T...>>::type&&;
+};
+
+template <std::size_t I, template <class...> class Variantemplate, class... T>
+struct VariantAccessResultImpl<I, const Variantemplate<T...>&&> {
+  using type =
+      const typename absl::variant_alternative<I, variant<T...>>::type&&;
+};
+
+template <std::size_t I, class Variant>
+using VariantAccessResult =
+    typename VariantAccessResultImpl<I, Variant&&>::type;
+
+// NOTE: This is used instead of std::array to reduce instantiation overhead.
+template <class T, std::size_t Size>
+struct SimpleArray {
+  static_assert(Size != 0, "");
+  T value[Size];
+};
+
+template <class T>
+struct AccessedType {
+  using type = T;
+};
+
+template <class T>
+using AccessedTypeT = typename AccessedType<T>::type;
+
+template <class T, std::size_t Size>
+struct AccessedType<SimpleArray<T, Size>> {
+  using type = AccessedTypeT<T>;
+};
+
+template <class T>
+constexpr T AccessSimpleArray(const T& value) {
+  return value;
+}
+
+template <class T, std::size_t Size, class... SizeT>
+constexpr AccessedTypeT<T> AccessSimpleArray(const SimpleArray<T, Size>& table,
+                                             std::size_t head_index,
+                                             SizeT... tail_indices) {
+  return AccessSimpleArray(table.value[head_index], tail_indices...);
+}
+
+// Note: Intentionally is an alias.
+template <class T>
+using AlwaysZero = SizeT<0>;
+
+template <class Op, class... Vs>
+struct VisitIndicesResultImpl {
+  using type = absl::result_of_t<Op(AlwaysZero<Vs>...)>;
+};
+
+template <class Op, class... Vs>
+using VisitIndicesResultT = typename VisitIndicesResultImpl<Op, Vs...>::type;
+
+template <class ReturnType, class FunctionObject, class EndIndices,
+          class BoundIndices>
+struct MakeVisitationMatrix;
+
+template <class ReturnType, class FunctionObject, std::size_t... Indices>
+constexpr ReturnType call_with_indices(FunctionObject&& function) {
+  static_assert(
+      std::is_same<ReturnType, decltype(std::declval<FunctionObject>()(
+                                   SizeT<Indices>()...))>::value,
+      "Not all visitation overloads have the same return type.");
+  return absl::forward<FunctionObject>(function)(SizeT<Indices>()...);
+}
+
+template <class ReturnType, class FunctionObject, std::size_t... BoundIndices>
+struct MakeVisitationMatrix<ReturnType, FunctionObject, index_sequence<>,
+                            index_sequence<BoundIndices...>> {
+  using ResultType = ReturnType (*)(FunctionObject&&);
+  static constexpr ResultType Run() {
+    return &call_with_indices<ReturnType, FunctionObject,
+                              (BoundIndices - 1)...>;
+  }
+};
+
+template <typename Is, std::size_t J>
+struct AppendToIndexSequence;
+
+template <typename Is, std::size_t J>
+using AppendToIndexSequenceT = typename AppendToIndexSequence<Is, J>::type;
+
+template <std::size_t... Is, std::size_t J>
+struct AppendToIndexSequence<index_sequence<Is...>, J> {
+  using type = index_sequence<Is..., J>;
+};
+
+template <class ReturnType, class FunctionObject, class EndIndices,
+          class CurrIndices, class BoundIndices>
+struct MakeVisitationMatrixImpl;
+
+template <class ReturnType, class FunctionObject, class EndIndices,
+          std::size_t... CurrIndices, class BoundIndices>
+struct MakeVisitationMatrixImpl<ReturnType, FunctionObject, EndIndices,
+                                index_sequence<CurrIndices...>, BoundIndices> {
+  using ResultType = SimpleArray<
+      typename MakeVisitationMatrix<ReturnType, FunctionObject, EndIndices,
+                                    index_sequence<>>::ResultType,
+      sizeof...(CurrIndices)>;
+
+  static constexpr ResultType Run() {
+    return {{MakeVisitationMatrix<
+        ReturnType, FunctionObject, EndIndices,
+        AppendToIndexSequenceT<BoundIndices, CurrIndices>>::Run()...}};
+  }
+};
+
+template <class ReturnType, class FunctionObject, std::size_t HeadEndIndex,
+          std::size_t... TailEndIndices, std::size_t... BoundIndices>
+struct MakeVisitationMatrix<ReturnType, FunctionObject,
+                            index_sequence<HeadEndIndex, TailEndIndices...>,
+                            index_sequence<BoundIndices...>>
+    : MakeVisitationMatrixImpl<ReturnType, FunctionObject,
+                               index_sequence<TailEndIndices...>,
+                               absl::make_index_sequence<HeadEndIndex>,
+                               index_sequence<BoundIndices...>> {};
+
+struct UnreachableSwitchCase {
+  template <class Op>
+  [[noreturn]] static VisitIndicesResultT<Op, std::size_t> Run(
+      Op&& /*ignored*/) {
+#if ABSL_HAVE_BUILTIN(__builtin_unreachable) || \
+    (defined(__GNUC__) && !defined(__clang__))
+    __builtin_unreachable();
+#elif defined(_MSC_VER)
+    __assume(false);
+#else
+    // Try to use assert of false being identified as an unreachable intrinsic.
+    // NOTE: We use assert directly to increase chances of exploiting an assume
+    //       intrinsic.
+    assert(false);  // NOLINT
+
+    // Hack to silence potential no return warning -- cause an infinite loop.
+    return Run(absl::forward<Op>(op));
+#endif  // Checks for __builtin_unreachable
+  }
+};
+
+template <class Op, std::size_t I>
+struct ReachableSwitchCase {
+  static VisitIndicesResultT<Op, std::size_t> Run(Op&& op) {
+    return absl::base_internal::Invoke(absl::forward<Op>(op), SizeT<I>());
+  }
+};
+
+// The number 33 is just a guess at a reasonable maximum to our switch. It is
+// not based on any analysis. The reason it is a power of 2 plus 1 instead of a
+// power of 2 is because the number was picked to correspond to a power of 2
+// amount of "normal" alternatives, plus one for the possibility of the user
+// providing "monostate" in addition to the more natural alternatives.
+ABSL_INTERNAL_INLINE_CONSTEXPR(std::size_t, MaxUnrolledVisitCases, 33);
+
+// Note: The default-definition is for unreachable cases.
+template <bool IsReachable>
+struct PickCaseImpl {
+  template <class Op, std::size_t I>
+  using Apply = UnreachableSwitchCase;
+};
+
+template <>
+struct PickCaseImpl</*IsReachable =*/true> {
+  template <class Op, std::size_t I>
+  using Apply = ReachableSwitchCase<Op, I>;
+};
+
+// Note: This form of dance with template aliases is to make sure that we
+//       instantiate a number of templates proportional to the number of variant
+//       alternatives rather than a number of templates proportional to our
+//       maximum unrolled amount of visitation cases (aliases are effectively
+//       "free" whereas other template instantiations are costly).
+template <class Op, std::size_t I, std::size_t EndIndex>
+using PickCase = typename PickCaseImpl<(I < EndIndex)>::template Apply<Op, I>;
+
+template <class ReturnType>
+[[noreturn]] ReturnType TypedThrowBadVariantAccess() {
+  absl::variant_internal::ThrowBadVariantAccess();
+}
+
+// Given N variant sizes, determine the number of cases there would need to be
+// in a single switch-statement that would cover every possibility in the
+// corresponding N-ary visit operation.
+template <std::size_t... NumAlternatives>
+struct NumCasesOfSwitch;
+
+template <std::size_t HeadNumAlternatives, std::size_t... TailNumAlternatives>
+struct NumCasesOfSwitch<HeadNumAlternatives, TailNumAlternatives...> {
+  static constexpr std::size_t value =
+      (HeadNumAlternatives + 1) *
+      NumCasesOfSwitch<TailNumAlternatives...>::value;
+};
+
+template <>
+struct NumCasesOfSwitch<> {
+  static constexpr std::size_t value = 1;
+};
+
+// A switch statement optimizes better than the table of function pointers.
+template <std::size_t EndIndex>
+struct VisitIndicesSwitch {
+  static_assert(EndIndex <= MaxUnrolledVisitCases,
+                "Maximum unrolled switch size exceeded.");
+
+  template <class Op>
+  static VisitIndicesResultT<Op, std::size_t> Run(Op&& op, std::size_t i) {
+    switch (i) {
+      case 0:
+        return PickCase<Op, 0, EndIndex>::Run(absl::forward<Op>(op));
+      case 1:
+        return PickCase<Op, 1, EndIndex>::Run(absl::forward<Op>(op));
+      case 2:
+        return PickCase<Op, 2, EndIndex>::Run(absl::forward<Op>(op));
+      case 3:
+        return PickCase<Op, 3, EndIndex>::Run(absl::forward<Op>(op));
+      case 4:
+        return PickCase<Op, 4, EndIndex>::Run(absl::forward<Op>(op));
+      case 5:
+        return PickCase<Op, 5, EndIndex>::Run(absl::forward<Op>(op));
+      case 6:
+        return PickCase<Op, 6, EndIndex>::Run(absl::forward<Op>(op));
+      case 7:
+        return PickCase<Op, 7, EndIndex>::Run(absl::forward<Op>(op));
+      case 8:
+        return PickCase<Op, 8, EndIndex>::Run(absl::forward<Op>(op));
+      case 9:
+        return PickCase<Op, 9, EndIndex>::Run(absl::forward<Op>(op));
+      case 10:
+        return PickCase<Op, 10, EndIndex>::Run(absl::forward<Op>(op));
+      case 11:
+        return PickCase<Op, 11, EndIndex>::Run(absl::forward<Op>(op));
+      case 12:
+        return PickCase<Op, 12, EndIndex>::Run(absl::forward<Op>(op));
+      case 13:
+        return PickCase<Op, 13, EndIndex>::Run(absl::forward<Op>(op));
+      case 14:
+        return PickCase<Op, 14, EndIndex>::Run(absl::forward<Op>(op));
+      case 15:
+        return PickCase<Op, 15, EndIndex>::Run(absl::forward<Op>(op));
+      case 16:
+        return PickCase<Op, 16, EndIndex>::Run(absl::forward<Op>(op));
+      case 17:
+        return PickCase<Op, 17, EndIndex>::Run(absl::forward<Op>(op));
+      case 18:
+        return PickCase<Op, 18, EndIndex>::Run(absl::forward<Op>(op));
+      case 19:
+        return PickCase<Op, 19, EndIndex>::Run(absl::forward<Op>(op));
+      case 20:
+        return PickCase<Op, 20, EndIndex>::Run(absl::forward<Op>(op));
+      case 21:
+        return PickCase<Op, 21, EndIndex>::Run(absl::forward<Op>(op));
+      case 22:
+        return PickCase<Op, 22, EndIndex>::Run(absl::forward<Op>(op));
+      case 23:
+        return PickCase<Op, 23, EndIndex>::Run(absl::forward<Op>(op));
+      case 24:
+        return PickCase<Op, 24, EndIndex>::Run(absl::forward<Op>(op));
+      case 25:
+        return PickCase<Op, 25, EndIndex>::Run(absl::forward<Op>(op));
+      case 26:
+        return PickCase<Op, 26, EndIndex>::Run(absl::forward<Op>(op));
+      case 27:
+        return PickCase<Op, 27, EndIndex>::Run(absl::forward<Op>(op));
+      case 28:
+        return PickCase<Op, 28, EndIndex>::Run(absl::forward<Op>(op));
+      case 29:
+        return PickCase<Op, 29, EndIndex>::Run(absl::forward<Op>(op));
+      case 30:
+        return PickCase<Op, 30, EndIndex>::Run(absl::forward<Op>(op));
+      case 31:
+        return PickCase<Op, 31, EndIndex>::Run(absl::forward<Op>(op));
+      case 32:
+        return PickCase<Op, 32, EndIndex>::Run(absl::forward<Op>(op));
+      default:
+        ABSL_ASSERT(i == variant_npos);
+        return absl::base_internal::Invoke(absl::forward<Op>(op), NPos());
+    }
+  }
+};
+
+template <std::size_t... EndIndices>
+struct VisitIndicesFallback {
+  template <class Op, class... SizeT>
+  static VisitIndicesResultT<Op, SizeT...> Run(Op&& op, SizeT... indices) {
+    return AccessSimpleArray(
+        MakeVisitationMatrix<VisitIndicesResultT<Op, SizeT...>, Op,
+                             index_sequence<(EndIndices + 1)...>,
+                             index_sequence<>>::Run(),
+        (indices + 1)...)(absl::forward<Op>(op));
+  }
+};
+
+// Take an N-dimensional series of indices and convert them into a single index
+// without loss of information. The purpose of this is to be able to convert an
+// N-ary visit operation into a single switch statement.
+template <std::size_t...>
+struct FlattenIndices;
+
+template <std::size_t HeadSize, std::size_t... TailSize>
+struct FlattenIndices<HeadSize, TailSize...> {
+  template<class... SizeType>
+  static constexpr std::size_t Run(std::size_t head, SizeType... tail) {
+    return head + HeadSize * FlattenIndices<TailSize...>::Run(tail...);
+  }
+};
+
+template <>
+struct FlattenIndices<> {
+  static constexpr std::size_t Run() { return 0; }
+};
+
+// Take a single "flattened" index (flattened by FlattenIndices) and determine
+// the value of the index of one of the logically represented dimensions.
+template <std::size_t I, std::size_t IndexToGet, std::size_t HeadSize,
+          std::size_t... TailSize>
+struct UnflattenIndex {
+  static constexpr std::size_t value =
+      UnflattenIndex<I / HeadSize, IndexToGet - 1, TailSize...>::value;
+};
+
+template <std::size_t I, std::size_t HeadSize, std::size_t... TailSize>
+struct UnflattenIndex<I, 0, HeadSize, TailSize...> {
+  static constexpr std::size_t value = (I % HeadSize);
+};
+
+// The backend for converting an N-ary visit operation into a unary visit.
+template <class IndexSequence, std::size_t... EndIndices>
+struct VisitIndicesVariadicImpl;
+
+template <std::size_t... N, std::size_t... EndIndices>
+struct VisitIndicesVariadicImpl<absl::index_sequence<N...>, EndIndices...> {
+  // A type that can take an N-ary function object and converts it to a unary
+  // function object that takes a single, flattened index, and "unflattens" it
+  // into its individual dimensions when forwarding to the wrapped object.
+  template <class Op>
+  struct FlattenedOp {
+    template <std::size_t I>
+    VisitIndicesResultT<Op, decltype(EndIndices)...> operator()(
+        SizeT<I> /*index*/) && {
+      return base_internal::Invoke(
+          absl::forward<Op>(op),
+          SizeT<UnflattenIndex<I, N, (EndIndices + 1)...>::value -
+                std::size_t{1}>()...);
+    }
+
+    Op&& op;
+  };
+
+  template <class Op, class... SizeType>
+  static VisitIndicesResultT<Op, decltype(EndIndices)...> Run(
+      Op&& op, SizeType... i) {
+    return VisitIndicesSwitch<NumCasesOfSwitch<EndIndices...>::value>::Run(
+        FlattenedOp<Op>{absl::forward<Op>(op)},
+        FlattenIndices<(EndIndices + std::size_t{1})...>::Run(
+            (i + std::size_t{1})...));
+  }
+};
+
+template <std::size_t... EndIndices>
+struct VisitIndicesVariadic
+    : VisitIndicesVariadicImpl<absl::make_index_sequence<sizeof...(EndIndices)>,
+                               EndIndices...> {};
+
+// This implementation will flatten N-ary visit operations into a single switch
+// statement when the number of cases would be less than our maximum specified
+// switch-statement size.
+// TODO(calabrese)
+//   Based on benchmarks, determine whether the function table approach actually
+//   does optimize better than a chain of switch statements and possibly update
+//   the implementation accordingly. Also consider increasing the maximum switch
+//   size.
+template <std::size_t... EndIndices>
+struct VisitIndices
+    : absl::conditional_t<(NumCasesOfSwitch<EndIndices...>::value <=
+                           MaxUnrolledVisitCases),
+                          VisitIndicesVariadic<EndIndices...>,
+                          VisitIndicesFallback<EndIndices...>> {};
+
+template <std::size_t EndIndex>
+struct VisitIndices<EndIndex>
+    : absl::conditional_t<(EndIndex <= MaxUnrolledVisitCases),
+                          VisitIndicesSwitch<EndIndex>,
+                          VisitIndicesFallback<EndIndex>> {};
+
+// Suppress bogus warning on MSVC: MSVC complains that the `reinterpret_cast`
+// below is returning the address of a temporary or local object.
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable : 4172)
+#endif  // _MSC_VER
+
+// TODO(calabrese) std::launder
+// TODO(calabrese) constexpr
+// NOTE: DO NOT REMOVE the `inline` keyword as it is necessary to work around a
+// MSVC bug. See https://github.com/abseil/abseil-cpp/issues/129 for details.
+template <class Self, std::size_t I>
+inline VariantAccessResult<I, Self> AccessUnion(Self&& self, SizeT<I> /*i*/) {
+  return reinterpret_cast<VariantAccessResult<I, Self>>(self);
+}
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif  // _MSC_VER
+
+template <class T>
+void DeducedDestroy(T& self) {  // NOLINT
+  self.~T();
+}
+
+// NOTE: This type exists as a single entity for variant and its bases to
+// befriend. It contains helper functionality that manipulates the state of the
+// variant, such as the implementation of things like assignment and emplace
+// operations.
+struct VariantCoreAccess {
+  template <class VariantType>
+  static typename VariantType::Variant& Derived(VariantType& self) {  // NOLINT
+    return static_cast<typename VariantType::Variant&>(self);
+  }
+
+  template <class VariantType>
+  static const typename VariantType::Variant& Derived(
+      const VariantType& self) {  // NOLINT
+    return static_cast<const typename VariantType::Variant&>(self);
+  }
+
+  template <class VariantType>
+  static void Destroy(VariantType& self) {  // NOLINT
+    Derived(self).destroy();
+    self.index_ = absl::variant_npos;
+  }
+
+  template <class Variant>
+  static void SetIndex(Variant& self, std::size_t i) {  // NOLINT
+    self.index_ = i;
+  }
+
+  template <class Variant>
+  static void InitFrom(Variant& self, Variant&& other) {  // NOLINT
+    VisitIndices<absl::variant_size<Variant>::value>::Run(
+        InitFromVisitor<Variant, Variant&&>{&self,
+                                            std::forward<Variant>(other)},
+        other.index());
+    self.index_ = other.index();
+  }
+
+  // Access a variant alternative, assuming the index is correct.
+  template <std::size_t I, class Variant>
+  static VariantAccessResult<I, Variant> Access(Variant&& self) {
+    // This cast instead of invocation of AccessUnion with an rvalue is a
+    // workaround for msvc. Without this there is a runtime failure when dealing
+    // with rvalues.
+    // TODO(calabrese) Reduce test case and find a simpler workaround.
+    return static_cast<VariantAccessResult<I, Variant>>(
+        variant_internal::AccessUnion(self.state_, SizeT<I>()));
+  }
+
+  // Access a variant alternative, throwing if the index is incorrect.
+  template <std::size_t I, class Variant>
+  static VariantAccessResult<I, Variant> CheckedAccess(Variant&& self) {
+    if (ABSL_PREDICT_FALSE(self.index_ != I)) {
+      TypedThrowBadVariantAccess<VariantAccessResult<I, Variant>>();
+    }
+
+    return Access<I>(absl::forward<Variant>(self));
+  }
+
+  // The implementation of the move-assignment operation for a variant.
+  template <class VType>
+  struct MoveAssignVisitor {
+    using DerivedType = typename VType::Variant;
+    template <std::size_t NewIndex>
+    void operator()(SizeT<NewIndex> /*new_i*/) const {
+      if (left->index_ == NewIndex) {
+        Access<NewIndex>(*left) = std::move(Access<NewIndex>(*right));
+      } else {
+        Derived(*left).template emplace<NewIndex>(
+            std::move(Access<NewIndex>(*right)));
+      }
+    }
+
+    void operator()(SizeT<absl::variant_npos> /*new_i*/) const {
+      Destroy(*left);
+    }
+
+    VType* left;
+    VType* right;
+  };
+
+  template <class VType>
+  static MoveAssignVisitor<VType> MakeMoveAssignVisitor(VType* left,
+                                                        VType* other) {
+    return {left, other};
+  }
+
+  // The implementation of the assignment operation for a variant.
+  template <class VType>
+  struct CopyAssignVisitor {
+    using DerivedType = typename VType::Variant;
+    template <std::size_t NewIndex>
+    void operator()(SizeT<NewIndex> /*new_i*/) const {
+      using New =
+          typename absl::variant_alternative<NewIndex, DerivedType>::type;
+
+      if (left->index_ == NewIndex) {
+        Access<NewIndex>(*left) = Access<NewIndex>(*right);
+      } else if (std::is_nothrow_copy_constructible<New>::value ||
+                 !std::is_nothrow_move_constructible<New>::value) {
+        Derived(*left).template emplace<NewIndex>(Access<NewIndex>(*right));
+      } else {
+        Derived(*left) = DerivedType(Derived(*right));
+      }
+    }
+
+    void operator()(SizeT<absl::variant_npos> /*new_i*/) const {
+      Destroy(*left);
+    }
+
+    VType* left;
+    const VType* right;
+  };
+
+  template <class VType>
+  static CopyAssignVisitor<VType> MakeCopyAssignVisitor(VType* left,
+                                                        const VType& other) {
+    return {left, &other};
+  }
+
+  // The implementation of conversion-assignment operations for variant.
+  template <class Left, class QualifiedNew>
+  struct ConversionAssignVisitor {
+    using NewIndex =
+        variant_internal::IndexOfConstructedType<Left, QualifiedNew>;
+
+    void operator()(SizeT<NewIndex::value> /*old_i*/
+                    ) const {
+      Access<NewIndex::value>(*left) = absl::forward<QualifiedNew>(other);
+    }
+
+    template <std::size_t OldIndex>
+    void operator()(SizeT<OldIndex> /*old_i*/
+                    ) const {
+      using New =
+          typename absl::variant_alternative<NewIndex::value, Left>::type;
+      if (std::is_nothrow_constructible<New, QualifiedNew>::value ||
+          !std::is_nothrow_move_constructible<New>::value) {
+        left->template emplace<NewIndex::value>(
+            absl::forward<QualifiedNew>(other));
+      } else {
+        // the standard says "equivalent to
+        // operator=(variant(std::forward<T>(t)))", but we use `emplace` here
+        // because the variant's move assignment operator could be deleted.
+        left->template emplace<NewIndex::value>(
+            New(absl::forward<QualifiedNew>(other)));
+      }
+    }
+
+    Left* left;
+    QualifiedNew&& other;
+  };
+
+  template <class Left, class QualifiedNew>
+  static ConversionAssignVisitor<Left, QualifiedNew>
+  MakeConversionAssignVisitor(Left* left, QualifiedNew&& qual) {
+    return {left, absl::forward<QualifiedNew>(qual)};
+  }
+
+  // Backend for operations for `emplace()` which destructs `*self` then
+  // construct a new alternative with `Args...`.
+  template <std::size_t NewIndex, class Self, class... Args>
+  static typename absl::variant_alternative<NewIndex, Self>::type& Replace(
+      Self* self, Args&&... args) {
+    Destroy(*self);
+    using New = typename absl::variant_alternative<NewIndex, Self>::type;
+    New* const result = ::new (static_cast<void*>(&self->state_))
+        New(absl::forward<Args>(args)...);
+    self->index_ = NewIndex;
+    return *result;
+  }
+
+  template <class LeftVariant, class QualifiedRightVariant>
+  struct InitFromVisitor {
+    template <std::size_t NewIndex>
+    void operator()(SizeT<NewIndex> /*new_i*/) const {
+      using Alternative =
+          typename variant_alternative<NewIndex, LeftVariant>::type;
+      ::new (static_cast<void*>(&left->state_)) Alternative(
+          Access<NewIndex>(std::forward<QualifiedRightVariant>(right)));
+    }
+
+    void operator()(SizeT<absl::variant_npos> /*new_i*/) const {
+      // This space intentionally left blank.
+    }
+    LeftVariant* left;
+    QualifiedRightVariant&& right;
+  };
+};
+
+template <class Expected, class... T>
+struct IndexOfImpl;
+
+template <class Expected>
+struct IndexOfImpl<Expected> {
+  using IndexFromEnd = SizeT<0>;
+  using MatchedIndexFromEnd = IndexFromEnd;
+  using MultipleMatches = std::false_type;
+};
+
+template <class Expected, class Head, class... Tail>
+struct IndexOfImpl<Expected, Head, Tail...> : IndexOfImpl<Expected, Tail...> {
+  using IndexFromEnd =
+      SizeT<IndexOfImpl<Expected, Tail...>::IndexFromEnd::value + 1>;
+};
+
+template <class Expected, class... Tail>
+struct IndexOfImpl<Expected, Expected, Tail...>
+    : IndexOfImpl<Expected, Tail...> {
+  using IndexFromEnd =
+      SizeT<IndexOfImpl<Expected, Tail...>::IndexFromEnd::value + 1>;
+  using MatchedIndexFromEnd = IndexFromEnd;
+  using MultipleMatches = std::integral_constant<
+      bool, IndexOfImpl<Expected, Tail...>::MatchedIndexFromEnd::value != 0>;
+};
+
+template <class Expected, class... Types>
+struct IndexOfMeta {
+  using Results = IndexOfImpl<Expected, Types...>;
+  static_assert(!Results::MultipleMatches::value,
+                "Attempted to access a variant by specifying a type that "
+                "matches more than one alternative.");
+  static_assert(Results::MatchedIndexFromEnd::value != 0,
+                "Attempted to access a variant by specifying a type that does "
+                "not match any alternative.");
+  using type = SizeT<sizeof...(Types) - Results::MatchedIndexFromEnd::value>;
+};
+
+template <class Expected, class... Types>
+using IndexOf = typename IndexOfMeta<Expected, Types...>::type;
+
+template <class Variant, class T, std::size_t CurrIndex>
+struct UnambiguousIndexOfImpl;
+
+// Terminating case encountered once we've checked all of the alternatives
+template <class T, std::size_t CurrIndex>
+struct UnambiguousIndexOfImpl<variant<>, T, CurrIndex> : SizeT<CurrIndex> {};
+
+// Case where T is not Head
+template <class Head, class... Tail, class T, std::size_t CurrIndex>
+struct UnambiguousIndexOfImpl<variant<Head, Tail...>, T, CurrIndex>
+    : UnambiguousIndexOfImpl<variant<Tail...>, T, CurrIndex + 1>::type {};
+
+// Case where T is Head
+template <class Head, class... Tail, std::size_t CurrIndex>
+struct UnambiguousIndexOfImpl<variant<Head, Tail...>, Head, CurrIndex>
+    : SizeT<UnambiguousIndexOfImpl<variant<Tail...>, Head, 0>::value ==
+                    sizeof...(Tail)
+                ? CurrIndex
+                : CurrIndex + sizeof...(Tail) + 1> {};
+
+template <class Variant, class T>
+struct UnambiguousIndexOf;
+
+struct NoMatch {
+  struct type {};
+};
+
+template <class... Alts, class T>
+struct UnambiguousIndexOf<variant<Alts...>, T>
+    : std::conditional<UnambiguousIndexOfImpl<variant<Alts...>, T, 0>::value !=
+                           sizeof...(Alts),
+                       UnambiguousIndexOfImpl<variant<Alts...>, T, 0>,
+                       NoMatch>::type::type {};
+
+template <class T, std::size_t /*Dummy*/>
+using UnambiguousTypeOfImpl = T;
+
+template <class Variant, class T>
+using UnambiguousTypeOfT =
+    UnambiguousTypeOfImpl<T, UnambiguousIndexOf<Variant, T>::value>;
+
+template <class H, class... T>
+class VariantStateBase;
+
+// This is an implementation of the "imaginary function" that is described in
+// [variant.ctor]
+// It is used in order to determine which alternative to construct during
+// initialization from some type T.
+template <class Variant, std::size_t I = 0>
+struct ImaginaryFun;
+
+template <std::size_t I>
+struct ImaginaryFun<variant<>, I> {
+  static void Run() = delete;
+};
+
+template <class H, class... T, std::size_t I>
+struct ImaginaryFun<variant<H, T...>, I> : ImaginaryFun<variant<T...>, I + 1> {
+  using ImaginaryFun<variant<T...>, I + 1>::Run;
+
+  // NOTE: const& and && are used instead of by-value due to lack of guaranteed
+  // move elision of C++17. This may have other minor differences, but tests
+  // pass.
+  static SizeT<I> Run(const H&, SizeT<I>);
+  static SizeT<I> Run(H&&, SizeT<I>);
+};
+
+// The following metafunctions are used in constructor and assignment
+// constraints.
+template <class Self, class T>
+struct IsNeitherSelfNorInPlace : std::true_type {};
+
+template <class Self>
+struct IsNeitherSelfNorInPlace<Self, Self> : std::false_type {};
+
+template <class Self, class T>
+struct IsNeitherSelfNorInPlace<Self, in_place_type_t<T>> : std::false_type {};
+
+template <class Self, std::size_t I>
+struct IsNeitherSelfNorInPlace<Self, in_place_index_t<I>> : std::false_type {};
+
+template <class Variant, class T, class = void>
+struct ConversionIsPossibleImpl : std::false_type {};
+
+template <class Variant, class T>
+struct ConversionIsPossibleImpl<
+    Variant, T,
+    void_t<decltype(ImaginaryFun<Variant>::Run(std::declval<T>(), {}))>>
+    : std::true_type {};
+
+template <class Variant, class T>
+struct ConversionIsPossible : ConversionIsPossibleImpl<Variant, T>::type {};
+
+template <class Variant, class T>
+struct IndexOfConstructedType<
+    Variant, T,
+    void_t<decltype(ImaginaryFun<Variant>::Run(std::declval<T>(), {}))>>
+    : decltype(ImaginaryFun<Variant>::Run(std::declval<T>(), {})) {};
+
+template <std::size_t... Is>
+struct ContainsVariantNPos
+    : absl::negation<std::is_same<  // NOLINT
+          absl::integer_sequence<bool, 0 <= Is...>,
+          absl::integer_sequence<bool, Is != absl::variant_npos...>>> {};
+
+template <class Op, class... QualifiedVariants>
+using RawVisitResult =
+    absl::result_of_t<Op(VariantAccessResult<0, QualifiedVariants>...)>;
+
+// NOTE: The spec requires that all return-paths yield the same type and is not
+// SFINAE-friendly, so we can deduce the return type by examining the first
+// result. If it's not callable, then we get an error, but are compliant and
+// fast to compile.
+// TODO(calabrese) Possibly rewrite in a way that yields better compile errors
+// at the cost of longer compile-times.
+template <class Op, class... QualifiedVariants>
+struct VisitResultImpl {
+  using type =
+      absl::result_of_t<Op(VariantAccessResult<0, QualifiedVariants>...)>;
+};
+
+// Done in two steps intentionally so that we don't cause substitution to fail.
+template <class Op, class... QualifiedVariants>
+using VisitResult = typename VisitResultImpl<Op, QualifiedVariants...>::type;
+
+template <class Op, class... QualifiedVariants>
+struct PerformVisitation {
+  using ReturnType = VisitResult<Op, QualifiedVariants...>;
+
+  template <std::size_t... Is>
+  constexpr ReturnType operator()(SizeT<Is>... indices) const {
+    return Run(typename ContainsVariantNPos<Is...>::type{},
+               absl::index_sequence_for<QualifiedVariants...>(), indices...);
+  }
+
+  template <std::size_t... TupIs, std::size_t... Is>
+  constexpr ReturnType Run(std::false_type /*has_valueless*/,
+                           index_sequence<TupIs...>, SizeT<Is>...) const {
+    static_assert(
+        std::is_same<ReturnType,
+                     absl::result_of_t<Op(VariantAccessResult<
+                                          Is, QualifiedVariants>...)>>::value,
+        "All visitation overloads must have the same return type.");
+    return absl::base_internal::Invoke(
+        absl::forward<Op>(op),
+        VariantCoreAccess::Access<Is>(
+            absl::forward<QualifiedVariants>(std::get<TupIs>(variant_tup)))...);
+  }
+
+  template <std::size_t... TupIs, std::size_t... Is>
+  [[noreturn]] ReturnType Run(std::true_type /*has_valueless*/,
+                              index_sequence<TupIs...>, SizeT<Is>...) const {
+    absl::variant_internal::ThrowBadVariantAccess();
+  }
+
+  // TODO(calabrese) Avoid using a tuple, which causes lots of instantiations
+  // Attempts using lambda variadic captures fail on current GCC.
+  std::tuple<QualifiedVariants&&...> variant_tup;
+  Op&& op;
+};
+
+template <class... T>
+union Union;
+
+// We want to allow for variant<> to be trivial. For that, we need the default
+// constructor to be trivial, which means we can't define it ourselves.
+// Instead, we use a non-default constructor that takes NoopConstructorTag
+// that doesn't affect the triviality of the types.
+struct NoopConstructorTag {};
+
+template <std::size_t I>
+struct EmplaceTag {};
+
+template <>
+union Union<> {
+  constexpr explicit Union(NoopConstructorTag) noexcept {}
+};
+
+// Suppress bogus warning on MSVC: MSVC complains that Union<T...> has a defined
+// deleted destructor from the `std::is_destructible` check below.
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable : 4624)
+#endif  // _MSC_VER
+
+template <class Head, class... Tail>
+union Union<Head, Tail...> {
+  using TailUnion = Union<Tail...>;
+
+  explicit constexpr Union(NoopConstructorTag /*tag*/) noexcept
+      : tail(NoopConstructorTag()) {}
+
+  template <class... P>
+  explicit constexpr Union(EmplaceTag<0>, P&&... args)
+      : head(absl::forward<P>(args)...) {}
+
+  template <std::size_t I, class... P>
+  explicit constexpr Union(EmplaceTag<I>, P&&... args)
+      : tail(EmplaceTag<I - 1>{}, absl::forward<P>(args)...) {}
+
+  Head head;
+  TailUnion tail;
+};
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif  // _MSC_VER
+
+// TODO(calabrese) Just contain a Union in this union (certain configs fail).
+template <class... T>
+union DestructibleUnionImpl;
+
+template <>
+union DestructibleUnionImpl<> {
+  constexpr explicit DestructibleUnionImpl(NoopConstructorTag) noexcept {}
+};
+
+template <class Head, class... Tail>
+union DestructibleUnionImpl<Head, Tail...> {
+  using TailUnion = DestructibleUnionImpl<Tail...>;
+
+  explicit constexpr DestructibleUnionImpl(NoopConstructorTag /*tag*/) noexcept
+      : tail(NoopConstructorTag()) {}
+
+  template <class... P>
+  explicit constexpr DestructibleUnionImpl(EmplaceTag<0>, P&&... args)
+      : head(absl::forward<P>(args)...) {}
+
+  template <std::size_t I, class... P>
+  explicit constexpr DestructibleUnionImpl(EmplaceTag<I>, P&&... args)
+      : tail(EmplaceTag<I - 1>{}, absl::forward<P>(args)...) {}
+
+  ~DestructibleUnionImpl() {}
+
+  Head head;
+  TailUnion tail;
+};
+
+// This union type is destructible even if one or more T are not trivially
+// destructible. In the case that all T are trivially destructible, then so is
+// this resultant type.
+template <class... T>
+using DestructibleUnion =
+    absl::conditional_t<std::is_destructible<Union<T...>>::value, Union<T...>,
+                        DestructibleUnionImpl<T...>>;
+
+// Deepest base, containing the actual union and the discriminator
+template <class H, class... T>
+class VariantStateBase {
+ protected:
+  using Variant = variant<H, T...>;
+
+  template <class LazyH = H,
+            class ConstructibleH = absl::enable_if_t<
+                std::is_default_constructible<LazyH>::value, LazyH>>
+  constexpr VariantStateBase() noexcept(
+      std::is_nothrow_default_constructible<ConstructibleH>::value)
+      : state_(EmplaceTag<0>()), index_(0) {}
+
+  template <std::size_t I, class... P>
+  explicit constexpr VariantStateBase(EmplaceTag<I> tag, P&&... args)
+      : state_(tag, absl::forward<P>(args)...), index_(I) {}
+
+  explicit constexpr VariantStateBase(NoopConstructorTag)
+      : state_(NoopConstructorTag()), index_(variant_npos) {}
+
+  void destroy() {}  // Does nothing (shadowed in child if non-trivial)
+
+  DestructibleUnion<H, T...> state_;
+  std::size_t index_;
+};
+
+using absl::internal::identity;
+
+// OverloadSet::Overload() is a unary function which is overloaded to
+// take any of the element types of the variant, by reference-to-const.
+// The return type of the overload on T is identity<T>, so that you
+// can statically determine which overload was called.
+//
+// Overload() is not defined, so it can only be called in unevaluated
+// contexts.
+template <typename... Ts>
+struct OverloadSet;
+
+template <typename T, typename... Ts>
+struct OverloadSet<T, Ts...> : OverloadSet<Ts...> {
+  using Base = OverloadSet<Ts...>;
+  static identity<T> Overload(const T&);
+  using Base::Overload;
+};
+
+template <>
+struct OverloadSet<> {
+  // For any case not handled above.
+  static void Overload(...);
+};
+
+template <class T>
+using LessThanResult = decltype(std::declval<T>() < std::declval<T>());
+
+template <class T>
+using GreaterThanResult = decltype(std::declval<T>() > std::declval<T>());
+
+template <class T>
+using LessThanOrEqualResult = decltype(std::declval<T>() <= std::declval<T>());
+
+template <class T>
+using GreaterThanOrEqualResult =
+    decltype(std::declval<T>() >= std::declval<T>());
+
+template <class T>
+using EqualResult = decltype(std::declval<T>() == std::declval<T>());
+
+template <class T>
+using NotEqualResult = decltype(std::declval<T>() != std::declval<T>());
+
+using type_traits_internal::is_detected_convertible;
+
+template <class... T>
+using RequireAllHaveEqualT = absl::enable_if_t<
+    absl::conjunction<is_detected_convertible<bool, EqualResult, T>...>::value,
+    bool>;
+
+template <class... T>
+using RequireAllHaveNotEqualT =
+    absl::enable_if_t<absl::conjunction<is_detected_convertible<
+                          bool, NotEqualResult, T>...>::value,
+                      bool>;
+
+template <class... T>
+using RequireAllHaveLessThanT =
+    absl::enable_if_t<absl::conjunction<is_detected_convertible<
+                          bool, LessThanResult, T>...>::value,
+                      bool>;
+
+template <class... T>
+using RequireAllHaveLessThanOrEqualT =
+    absl::enable_if_t<absl::conjunction<is_detected_convertible<
+                          bool, LessThanOrEqualResult, T>...>::value,
+                      bool>;
+
+template <class... T>
+using RequireAllHaveGreaterThanOrEqualT =
+    absl::enable_if_t<absl::conjunction<is_detected_convertible<
+                          bool, GreaterThanOrEqualResult, T>...>::value,
+                      bool>;
+
+template <class... T>
+using RequireAllHaveGreaterThanT =
+    absl::enable_if_t<absl::conjunction<is_detected_convertible<
+                          bool, GreaterThanResult, T>...>::value,
+                      bool>;
+
+// Helper template containing implementations details of variant that can't go
+// in the private section. For convenience, this takes the variant type as a
+// single template parameter.
+template <typename T>
+struct VariantHelper;
+
+template <typename... Ts>
+struct VariantHelper<variant<Ts...>> {
+  // Type metafunction which returns the element type selected if
+  // OverloadSet::Overload() is well-formed when called with argument type U.
+  template <typename U>
+  using BestMatch = decltype(
+      variant_internal::OverloadSet<Ts...>::Overload(std::declval<U>()));
+
+  // Type metafunction which returns true if OverloadSet::Overload() is
+  // well-formed when called with argument type U.
+  // CanAccept can't be just an alias because there is a MSVC bug on parameter
+  // pack expansion involving decltype.
+  template <typename U>
+  struct CanAccept :
+      std::integral_constant<bool, !std::is_void<BestMatch<U>>::value> {};
+
+  // Type metafunction which returns true if Other is an instantiation of
+  // variant, and variants's converting constructor from Other will be
+  // well-formed. We will use this to remove constructors that would be
+  // ill-formed from the overload set.
+  template <typename Other>
+  struct CanConvertFrom;
+
+  template <typename... Us>
+  struct CanConvertFrom<variant<Us...>>
+      : public absl::conjunction<CanAccept<Us>...> {};
+};
+
+// A type with nontrivial copy ctor and trivial move ctor.
+struct TrivialMoveOnly {
+  TrivialMoveOnly(TrivialMoveOnly&&) = default;
+};
+
+// Trait class to detect whether a type is trivially move constructible.
+// A union's defaulted copy/move constructor is deleted if any variant member's
+// copy/move constructor is nontrivial.
+template <typename T>
+struct IsTriviallyMoveConstructible:
+  std::is_move_constructible<Union<T, TrivialMoveOnly>> {};
+
+// To guarantee triviality of all special-member functions that can be trivial,
+// we use a chain of conditional bases for each one.
+// The order of inheritance of bases from child to base are logically:
+//
+// variant
+// VariantCopyAssignBase
+// VariantMoveAssignBase
+// VariantCopyBase
+// VariantMoveBase
+// VariantStateBaseDestructor
+// VariantStateBase
+//
+// Note that there is a separate branch at each base that is dependent on
+// whether or not that corresponding special-member-function can be trivial in
+// the resultant variant type.
+
+template <class... T>
+class VariantStateBaseDestructorNontrivial;
+
+template <class... T>
+class VariantMoveBaseNontrivial;
+
+template <class... T>
+class VariantCopyBaseNontrivial;
+
+template <class... T>
+class VariantMoveAssignBaseNontrivial;
+
+template <class... T>
+class VariantCopyAssignBaseNontrivial;
+
+// Base that is dependent on whether or not the destructor can be trivial.
+template <class... T>
+using VariantStateBaseDestructor =
+    absl::conditional_t<std::is_destructible<Union<T...>>::value,
+                        VariantStateBase<T...>,
+                        VariantStateBaseDestructorNontrivial<T...>>;
+
+// Base that is dependent on whether or not the move-constructor can be
+// implicitly generated by the compiler (trivial or deleted).
+// Previously we were using `std::is_move_constructible<Union<T...>>` to check
+// whether all Ts have trivial move constructor, but it ran into a GCC bug:
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84866
+// So we have to use a different approach (i.e. `HasTrivialMoveConstructor`) to
+// work around the bug.
+template <class... T>
+using VariantMoveBase = absl::conditional_t<
+    absl::disjunction<
+        absl::negation<absl::conjunction<std::is_move_constructible<T>...>>,
+        absl::conjunction<IsTriviallyMoveConstructible<T>...>>::value,
+    VariantStateBaseDestructor<T...>, VariantMoveBaseNontrivial<T...>>;
+
+// Base that is dependent on whether or not the copy-constructor can be trivial.
+template <class... T>
+using VariantCopyBase = absl::conditional_t<
+    absl::disjunction<
+        absl::negation<absl::conjunction<std::is_copy_constructible<T>...>>,
+        std::is_copy_constructible<Union<T...>>>::value,
+    VariantMoveBase<T...>, VariantCopyBaseNontrivial<T...>>;
+
+// Base that is dependent on whether or not the move-assign can be trivial.
+template <class... T>
+using VariantMoveAssignBase = absl::conditional_t<
+    absl::disjunction<
+        absl::conjunction<absl::is_move_assignable<Union<T...>>,
+                          std::is_move_constructible<Union<T...>>,
+                          std::is_destructible<Union<T...>>>,
+        absl::negation<absl::conjunction<std::is_move_constructible<T>...,
+                                         // Note: We're not qualifying this with
+                                         // absl:: because it doesn't compile
+                                         // under MSVC.
+                                         is_move_assignable<T>...>>>::value,
+    VariantCopyBase<T...>, VariantMoveAssignBaseNontrivial<T...>>;
+
+// Base that is dependent on whether or not the copy-assign can be trivial.
+template <class... T>
+using VariantCopyAssignBase = absl::conditional_t<
+    absl::disjunction<
+        absl::conjunction<absl::is_copy_assignable<Union<T...>>,
+                          std::is_copy_constructible<Union<T...>>,
+                          std::is_destructible<Union<T...>>>,
+        absl::negation<absl::conjunction<std::is_copy_constructible<T>...,
+                                         // Note: We're not qualifying this with
+                                         // absl:: because it doesn't compile
+                                         // under MSVC.
+                                         is_copy_assignable<T>...>>>::value,
+    VariantMoveAssignBase<T...>, VariantCopyAssignBaseNontrivial<T...>>;
+
+template <class... T>
+using VariantBase = VariantCopyAssignBase<T...>;
+
+template <class... T>
+class VariantStateBaseDestructorNontrivial : protected VariantStateBase<T...> {
+ private:
+  using Base = VariantStateBase<T...>;
+
+ protected:
+  using Base::Base;
+
+  VariantStateBaseDestructorNontrivial() = default;
+  VariantStateBaseDestructorNontrivial(VariantStateBaseDestructorNontrivial&&) =
+      default;
+  VariantStateBaseDestructorNontrivial(
+      const VariantStateBaseDestructorNontrivial&) = default;
+  VariantStateBaseDestructorNontrivial& operator=(
+      VariantStateBaseDestructorNontrivial&&) = default;
+  VariantStateBaseDestructorNontrivial& operator=(
+      const VariantStateBaseDestructorNontrivial&) = default;
+
+  struct Destroyer {
+    template <std::size_t I>
+    void operator()(SizeT<I> i) const {
+      using Alternative =
+          typename absl::variant_alternative<I, variant<T...>>::type;
+      variant_internal::AccessUnion(self->state_, i).~Alternative();
+    }
+
+    void operator()(SizeT<absl::variant_npos> /*i*/) const {
+      // This space intentionally left blank
+    }
+
+    VariantStateBaseDestructorNontrivial* self;
+  };
+
+  void destroy() { VisitIndices<sizeof...(T)>::Run(Destroyer{this}, index_); }
+
+  ~VariantStateBaseDestructorNontrivial() { destroy(); }
+
+ protected:
+  using Base::index_;
+  using Base::state_;
+};
+
+template <class... T>
+class VariantMoveBaseNontrivial : protected VariantStateBaseDestructor<T...> {
+ private:
+  using Base = VariantStateBaseDestructor<T...>;
+
+ protected:
+  using Base::Base;
+
+  struct Construct {
+    template <std::size_t I>
+    void operator()(SizeT<I> i) const {
+      using Alternative =
+          typename absl::variant_alternative<I, variant<T...>>::type;
+      ::new (static_cast<void*>(&self->state_)) Alternative(
+          variant_internal::AccessUnion(absl::move(other->state_), i));
+    }
+
+    void operator()(SizeT<absl::variant_npos> /*i*/) const {}
+
+    VariantMoveBaseNontrivial* self;
+    VariantMoveBaseNontrivial* other;
+  };
+
+  VariantMoveBaseNontrivial() = default;
+  VariantMoveBaseNontrivial(VariantMoveBaseNontrivial&& other) noexcept(
+      absl::conjunction<std::is_nothrow_move_constructible<T>...>::value)
+      : Base(NoopConstructorTag()) {
+    VisitIndices<sizeof...(T)>::Run(Construct{this, &other}, other.index_);
+    index_ = other.index_;
+  }
+
+  VariantMoveBaseNontrivial(VariantMoveBaseNontrivial const&) = default;
+
+  VariantMoveBaseNontrivial& operator=(VariantMoveBaseNontrivial&&) = default;
+  VariantMoveBaseNontrivial& operator=(VariantMoveBaseNontrivial const&) =
+      default;
+
+ protected:
+  using Base::index_;
+  using Base::state_;
+};
+
+template <class... T>
+class VariantCopyBaseNontrivial : protected VariantMoveBase<T...> {
+ private:
+  using Base = VariantMoveBase<T...>;
+
+ protected:
+  using Base::Base;
+
+  VariantCopyBaseNontrivial() = default;
+  VariantCopyBaseNontrivial(VariantCopyBaseNontrivial&&) = default;
+
+  struct Construct {
+    template <std::size_t I>
+    void operator()(SizeT<I> i) const {
+      using Alternative =
+          typename absl::variant_alternative<I, variant<T...>>::type;
+      ::new (static_cast<void*>(&self->state_))
+          Alternative(variant_internal::AccessUnion(other->state_, i));
+    }
+
+    void operator()(SizeT<absl::variant_npos> /*i*/) const {}
+
+    VariantCopyBaseNontrivial* self;
+    const VariantCopyBaseNontrivial* other;
+  };
+
+  VariantCopyBaseNontrivial(VariantCopyBaseNontrivial const& other)
+      : Base(NoopConstructorTag()) {
+    VisitIndices<sizeof...(T)>::Run(Construct{this, &other}, other.index_);
+    index_ = other.index_;
+  }
+
+  VariantCopyBaseNontrivial& operator=(VariantCopyBaseNontrivial&&) = default;
+  VariantCopyBaseNontrivial& operator=(VariantCopyBaseNontrivial const&) =
+      default;
+
+ protected:
+  using Base::index_;
+  using Base::state_;
+};
+
+template <class... T>
+class VariantMoveAssignBaseNontrivial : protected VariantCopyBase<T...> {
+  friend struct VariantCoreAccess;
+
+ private:
+  using Base = VariantCopyBase<T...>;
+
+ protected:
+  using Base::Base;
+
+  VariantMoveAssignBaseNontrivial() = default;
+  VariantMoveAssignBaseNontrivial(VariantMoveAssignBaseNontrivial&&) = default;
+  VariantMoveAssignBaseNontrivial(const VariantMoveAssignBaseNontrivial&) =
+      default;
+  VariantMoveAssignBaseNontrivial& operator=(
+      VariantMoveAssignBaseNontrivial const&) = default;
+
+    VariantMoveAssignBaseNontrivial&
+    operator=(VariantMoveAssignBaseNontrivial&& other) noexcept(
+        absl::conjunction<std::is_nothrow_move_constructible<T>...,
+                          std::is_nothrow_move_assignable<T>...>::value) {
+      VisitIndices<sizeof...(T)>::Run(
+          VariantCoreAccess::MakeMoveAssignVisitor(this, &other), other.index_);
+      return *this;
+    }
+
+ protected:
+  using Base::index_;
+  using Base::state_;
+};
+
+template <class... T>
+class VariantCopyAssignBaseNontrivial : protected VariantMoveAssignBase<T...> {
+  friend struct VariantCoreAccess;
+
+ private:
+  using Base = VariantMoveAssignBase<T...>;
+
+ protected:
+  using Base::Base;
+
+  VariantCopyAssignBaseNontrivial() = default;
+  VariantCopyAssignBaseNontrivial(VariantCopyAssignBaseNontrivial&&) = default;
+  VariantCopyAssignBaseNontrivial(const VariantCopyAssignBaseNontrivial&) =
+      default;
+  VariantCopyAssignBaseNontrivial& operator=(
+      VariantCopyAssignBaseNontrivial&&) = default;
+
+    VariantCopyAssignBaseNontrivial& operator=(
+        const VariantCopyAssignBaseNontrivial& other) {
+      VisitIndices<sizeof...(T)>::Run(
+          VariantCoreAccess::MakeCopyAssignVisitor(this, other), other.index_);
+      return *this;
+    }
+
+ protected:
+  using Base::index_;
+  using Base::state_;
+};
+
+////////////////////////////////////////
+// Visitors for Comparison Operations //
+////////////////////////////////////////
+
+template <class... Types>
+struct EqualsOp {
+  const variant<Types...>* v;
+  const variant<Types...>* w;
+
+  constexpr bool operator()(SizeT<absl::variant_npos> /*v_i*/) const {
+    return true;
+  }
+
+  template <std::size_t I>
+  constexpr bool operator()(SizeT<I> /*v_i*/) const {
+    return VariantCoreAccess::Access<I>(*v) == VariantCoreAccess::Access<I>(*w);
+  }
+};
+
+template <class... Types>
+struct NotEqualsOp {
+  const variant<Types...>* v;
+  const variant<Types...>* w;
+
+  constexpr bool operator()(SizeT<absl::variant_npos> /*v_i*/) const {
+    return false;
+  }
+
+  template <std::size_t I>
+  constexpr bool operator()(SizeT<I> /*v_i*/) const {
+    return VariantCoreAccess::Access<I>(*v) != VariantCoreAccess::Access<I>(*w);
+  }
+};
+
+template <class... Types>
+struct LessThanOp {
+  const variant<Types...>* v;
+  const variant<Types...>* w;
+
+  constexpr bool operator()(SizeT<absl::variant_npos> /*v_i*/) const {
+    return false;
+  }
+
+  template <std::size_t I>
+  constexpr bool operator()(SizeT<I> /*v_i*/) const {
+    return VariantCoreAccess::Access<I>(*v) < VariantCoreAccess::Access<I>(*w);
+  }
+};
+
+template <class... Types>
+struct GreaterThanOp {
+  const variant<Types...>* v;
+  const variant<Types...>* w;
+
+  constexpr bool operator()(SizeT<absl::variant_npos> /*v_i*/) const {
+    return false;
+  }
+
+  template <std::size_t I>
+  constexpr bool operator()(SizeT<I> /*v_i*/) const {
+    return VariantCoreAccess::Access<I>(*v) > VariantCoreAccess::Access<I>(*w);
+  }
+};
+
+template <class... Types>
+struct LessThanOrEqualsOp {
+  const variant<Types...>* v;
+  const variant<Types...>* w;
+
+  constexpr bool operator()(SizeT<absl::variant_npos> /*v_i*/) const {
+    return true;
+  }
+
+  template <std::size_t I>
+  constexpr bool operator()(SizeT<I> /*v_i*/) const {
+    return VariantCoreAccess::Access<I>(*v) <= VariantCoreAccess::Access<I>(*w);
+  }
+};
+
+template <class... Types>
+struct GreaterThanOrEqualsOp {
+  const variant<Types...>* v;
+  const variant<Types...>* w;
+
+  constexpr bool operator()(SizeT<absl::variant_npos> /*v_i*/) const {
+    return true;
+  }
+
+  template <std::size_t I>
+  constexpr bool operator()(SizeT<I> /*v_i*/) const {
+    return VariantCoreAccess::Access<I>(*v) >= VariantCoreAccess::Access<I>(*w);
+  }
+};
+
+// Precondition: v.index() == w.index();
+template <class... Types>
+struct SwapSameIndex {
+  variant<Types...>* v;
+  variant<Types...>* w;
+  template <std::size_t I>
+  void operator()(SizeT<I>) const {
+    type_traits_internal::Swap(VariantCoreAccess::Access<I>(*v),
+                               VariantCoreAccess::Access<I>(*w));
+  }
+
+  void operator()(SizeT<variant_npos>) const {}
+};
+
+// TODO(calabrese) do this from a different namespace for proper adl usage
+template <class... Types>
+struct Swap {
+  variant<Types...>* v;
+  variant<Types...>* w;
+
+  void generic_swap() const {
+    variant<Types...> tmp(std::move(*w));
+    VariantCoreAccess::Destroy(*w);
+    VariantCoreAccess::InitFrom(*w, std::move(*v));
+    VariantCoreAccess::Destroy(*v);
+    VariantCoreAccess::InitFrom(*v, std::move(tmp));
+  }
+
+  void operator()(SizeT<absl::variant_npos> /*w_i*/) const {
+    if (!v->valueless_by_exception()) {
+      generic_swap();
+    }
+  }
+
+  template <std::size_t Wi>
+  void operator()(SizeT<Wi> /*w_i*/) {
+    if (v->index() == Wi) {
+      VisitIndices<sizeof...(Types)>::Run(SwapSameIndex<Types...>{v, w}, Wi);
+    } else {
+      generic_swap();
+    }
+  }
+};
+
+template <typename Variant, typename = void, typename... Ts>
+struct VariantHashBase {
+  VariantHashBase() = delete;
+  VariantHashBase(const VariantHashBase&) = delete;
+  VariantHashBase(VariantHashBase&&) = delete;
+  VariantHashBase& operator=(const VariantHashBase&) = delete;
+  VariantHashBase& operator=(VariantHashBase&&) = delete;
+};
+
+struct VariantHashVisitor {
+  template <typename T>
+  size_t operator()(const T& t) {
+    return std::hash<T>{}(t);
+  }
+};
+
+template <typename Variant, typename... Ts>
+struct VariantHashBase<Variant,
+                       absl::enable_if_t<absl::conjunction<
+                           type_traits_internal::IsHashable<Ts>...>::value>,
+                       Ts...> {
+  using argument_type = Variant;
+  using result_type = size_t;
+  size_t operator()(const Variant& var) const {
+    type_traits_internal::AssertHashEnabled<Ts...>();
+    if (var.valueless_by_exception()) {
+      return 239799884;
+    }
+    size_t result = VisitIndices<variant_size<Variant>::value>::Run(
+        PerformVisitation<VariantHashVisitor, const Variant&>{
+            std::forward_as_tuple(var), VariantHashVisitor{}},
+        var.index());
+    // Combine the index and the hash result in order to distinguish
+    // std::variant<int, int> holding the same value as different alternative.
+    return result ^ var.index();
+  }
+};
+
+}  // namespace variant_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // !defined(ABSL_USES_STD_VARIANT)
+#endif  // ABSL_TYPES_variant_internal_H_
diff --git a/third_party/abseil_cpp/absl/types/optional.h b/third_party/abseil_cpp/absl/types/optional.h
new file mode 100644
index 0000000000..61540cfdb2
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/optional.h
@@ -0,0 +1,776 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// optional.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines the `absl::optional` type for holding a value which
+// may or may not be present. This type is useful for providing value semantics
+// for operations that may either wish to return or hold "something-or-nothing".
+//
+// Example:
+//
+//   // A common way to signal operation failure is to provide an output
+//   // parameter and a bool return type:
+//   bool AcquireResource(const Input&, Resource * out);
+//
+//   // Providing an absl::optional return type provides a cleaner API:
+//   absl::optional<Resource> AcquireResource(const Input&);
+//
+// `absl::optional` is a C++11 compatible version of the C++17 `std::optional`
+// abstraction and is designed to be a drop-in replacement for code compliant
+// with C++17.
+#ifndef ABSL_TYPES_OPTIONAL_H_
+#define ABSL_TYPES_OPTIONAL_H_
+
+#include "absl/base/config.h"   // TODO(calabrese) IWYU removal?
+#include "absl/utility/utility.h"
+
+#ifdef ABSL_USES_STD_OPTIONAL
+
+#include <optional>  // IWYU pragma: export
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using std::bad_optional_access;
+using std::optional;
+using std::make_optional;
+using std::nullopt_t;
+using std::nullopt;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_OPTIONAL
+
+#include <cassert>
+#include <functional>
+#include <initializer_list>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/inline_variable.h"
+#include "absl/meta/type_traits.h"
+#include "absl/types/bad_optional_access.h"
+#include "absl/types/internal/optional.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// nullopt_t
+//
+// Class type for `absl::nullopt` used to indicate an `absl::optional<T>` type
+// that does not contain a value.
+struct nullopt_t {
+  // It must not be default-constructible to avoid ambiguity for opt = {}.
+  explicit constexpr nullopt_t(optional_internal::init_t) noexcept {}
+};
+
+// nullopt
+//
+// A tag constant of type `absl::nullopt_t` used to indicate an empty
+// `absl::optional` in certain functions, such as construction or assignment.
+ABSL_INTERNAL_INLINE_CONSTEXPR(nullopt_t, nullopt,
+                               nullopt_t(optional_internal::init_t()));
+
+// -----------------------------------------------------------------------------
+// absl::optional
+// -----------------------------------------------------------------------------
+//
+// A value of type `absl::optional<T>` holds either a value of `T` or an
+// "empty" value.  When it holds a value of `T`, it stores it as a direct
+// sub-object, so `sizeof(optional<T>)` is approximately
+// `sizeof(T) + sizeof(bool)`.
+//
+// This implementation is based on the specification in the latest draft of the
+// C++17 `std::optional` specification as of May 2017, section 20.6.
+//
+// Differences between `absl::optional<T>` and `std::optional<T>` include:
+//
+//    * `constexpr` is not used for non-const member functions.
+//      (dependency on some differences between C++11 and C++14.)
+//    * `absl::nullopt` and `absl::in_place` are not declared `constexpr`. We
+//      need the inline variable support in C++17 for external linkage.
+//    * Throws `absl::bad_optional_access` instead of
+//      `std::bad_optional_access`.
+//    * `make_optional()` cannot be declared `constexpr` due to the absence of
+//      guaranteed copy elision.
+//    * The move constructor's `noexcept` specification is stronger, i.e. if the
+//      default allocator is non-throwing (via setting
+//      `ABSL_ALLOCATOR_NOTHROW`), it evaluates to `noexcept(true)`, because
+//      we assume
+//       a) move constructors should only throw due to allocation failure and
+//       b) if T's move constructor allocates, it uses the same allocation
+//          function as the default allocator.
+//
+template <typename T>
+class optional : private optional_internal::optional_data<T>,
+                 private optional_internal::optional_ctor_base<
+                     optional_internal::ctor_copy_traits<T>::traits>,
+                 private optional_internal::optional_assign_base<
+                     optional_internal::assign_copy_traits<T>::traits> {
+  using data_base = optional_internal::optional_data<T>;
+
+ public:
+  typedef T value_type;
+
+  // Constructors
+
+  // Constructs an `optional` holding an empty value, NOT a default constructed
+  // `T`.
+  constexpr optional() noexcept {}
+
+  // Constructs an `optional` initialized with `nullopt` to hold an empty value.
+  constexpr optional(nullopt_t) noexcept {}  // NOLINT(runtime/explicit)
+
+  // Copy constructor, standard semantics
+  optional(const optional&) = default;
+
+  // Move constructor, standard semantics
+  optional(optional&&) = default;
+
+  // Constructs a non-empty `optional` direct-initialized value of type `T` from
+  // the arguments `std::forward<Args>(args)...`  within the `optional`.
+  // (The `in_place_t` is a tag used to indicate that the contained object
+  // should be constructed in-place.)
+  template <typename InPlaceT, typename... Args,
+            absl::enable_if_t<absl::conjunction<
+                std::is_same<InPlaceT, in_place_t>,
+                std::is_constructible<T, Args&&...> >::value>* = nullptr>
+  constexpr explicit optional(InPlaceT, Args&&... args)
+      : data_base(in_place_t(), absl::forward<Args>(args)...) {}
+
+  // Constructs a non-empty `optional` direct-initialized value of type `T` from
+  // the arguments of an initializer_list and `std::forward<Args>(args)...`.
+  // (The `in_place_t` is a tag used to indicate that the contained object
+  // should be constructed in-place.)
+  template <typename U, typename... Args,
+            typename = typename std::enable_if<std::is_constructible<
+                T, std::initializer_list<U>&, Args&&...>::value>::type>
+  constexpr explicit optional(in_place_t, std::initializer_list<U> il,
+                              Args&&... args)
+      : data_base(in_place_t(), il, absl::forward<Args>(args)...) {
+  }
+
+  // Value constructor (implicit)
+  template <
+      typename U = T,
+      typename std::enable_if<
+          absl::conjunction<absl::negation<std::is_same<
+                                in_place_t, typename std::decay<U>::type> >,
+                            absl::negation<std::is_same<
+                                optional<T>, typename std::decay<U>::type> >,
+                            std::is_convertible<U&&, T>,
+                            std::is_constructible<T, U&&> >::value,
+          bool>::type = false>
+  constexpr optional(U&& v) : data_base(in_place_t(), absl::forward<U>(v)) {}
+
+  // Value constructor (explicit)
+  template <
+      typename U = T,
+      typename std::enable_if<
+          absl::conjunction<absl::negation<std::is_same<
+                                in_place_t, typename std::decay<U>::type>>,
+                            absl::negation<std::is_same<
+                                optional<T>, typename std::decay<U>::type>>,
+                            absl::negation<std::is_convertible<U&&, T>>,
+                            std::is_constructible<T, U&&>>::value,
+          bool>::type = false>
+  explicit constexpr optional(U&& v)
+      : data_base(in_place_t(), absl::forward<U>(v)) {}
+
+  // Converting copy constructor (implicit)
+  template <typename U,
+            typename std::enable_if<
+                absl::conjunction<
+                    absl::negation<std::is_same<T, U> >,
+                    std::is_constructible<T, const U&>,
+                    absl::negation<
+                        optional_internal::
+                            is_constructible_convertible_from_optional<T, U> >,
+                    std::is_convertible<const U&, T> >::value,
+                bool>::type = false>
+  optional(const optional<U>& rhs) {
+    if (rhs) {
+      this->construct(*rhs);
+    }
+  }
+
+  // Converting copy constructor (explicit)
+  template <typename U,
+            typename std::enable_if<
+                absl::conjunction<
+                    absl::negation<std::is_same<T, U>>,
+                    std::is_constructible<T, const U&>,
+                    absl::negation<
+                        optional_internal::
+                            is_constructible_convertible_from_optional<T, U>>,
+                    absl::negation<std::is_convertible<const U&, T>>>::value,
+                bool>::type = false>
+  explicit optional(const optional<U>& rhs) {
+    if (rhs) {
+      this->construct(*rhs);
+    }
+  }
+
+  // Converting move constructor (implicit)
+  template <typename U,
+            typename std::enable_if<
+                absl::conjunction<
+                    absl::negation<std::is_same<T, U> >,
+                    std::is_constructible<T, U&&>,
+                    absl::negation<
+                        optional_internal::
+                            is_constructible_convertible_from_optional<T, U> >,
+                    std::is_convertible<U&&, T> >::value,
+                bool>::type = false>
+  optional(optional<U>&& rhs) {
+    if (rhs) {
+      this->construct(std::move(*rhs));
+    }
+  }
+
+  // Converting move constructor (explicit)
+  template <
+      typename U,
+      typename std::enable_if<
+          absl::conjunction<
+              absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>,
+              absl::negation<
+                  optional_internal::is_constructible_convertible_from_optional<
+                      T, U>>,
+              absl::negation<std::is_convertible<U&&, T>>>::value,
+          bool>::type = false>
+  explicit optional(optional<U>&& rhs) {
+    if (rhs) {
+      this->construct(std::move(*rhs));
+    }
+  }
+
+  // Destructor. Trivial if `T` is trivially destructible.
+  ~optional() = default;
+
+  // Assignment Operators
+
+  // Assignment from `nullopt`
+  //
+  // Example:
+  //
+  //   struct S { int value; };
+  //   optional<S> opt = absl::nullopt;  // Could also use opt = { };
+  optional& operator=(nullopt_t) noexcept {
+    this->destruct();
+    return *this;
+  }
+
+  // Copy assignment operator, standard semantics
+  optional& operator=(const optional& src) = default;
+
+  // Move assignment operator, standard semantics
+  optional& operator=(optional&& src) = default;
+
+  // Value assignment operators
+  template <
+      typename U = T,
+      typename = typename std::enable_if<absl::conjunction<
+          absl::negation<
+              std::is_same<optional<T>, typename std::decay<U>::type>>,
+          absl::negation<
+              absl::conjunction<std::is_scalar<T>,
+                                std::is_same<T, typename std::decay<U>::type>>>,
+          std::is_constructible<T, U>, std::is_assignable<T&, U>>::value>::type>
+  optional& operator=(U&& v) {
+    this->assign(std::forward<U>(v));
+    return *this;
+  }
+
+  template <
+      typename U,
+      typename = typename std::enable_if<absl::conjunction<
+          absl::negation<std::is_same<T, U>>,
+          std::is_constructible<T, const U&>, std::is_assignable<T&, const U&>,
+          absl::negation<
+              optional_internal::
+                  is_constructible_convertible_assignable_from_optional<
+                      T, U>>>::value>::type>
+  optional& operator=(const optional<U>& rhs) {
+    if (rhs) {
+      this->assign(*rhs);
+    } else {
+      this->destruct();
+    }
+    return *this;
+  }
+
+  template <typename U,
+            typename = typename std::enable_if<absl::conjunction<
+                absl::negation<std::is_same<T, U>>, std::is_constructible<T, U>,
+                std::is_assignable<T&, U>,
+                absl::negation<
+                    optional_internal::
+                        is_constructible_convertible_assignable_from_optional<
+                            T, U>>>::value>::type>
+  optional& operator=(optional<U>&& rhs) {
+    if (rhs) {
+      this->assign(std::move(*rhs));
+    } else {
+      this->destruct();
+    }
+    return *this;
+  }
+
+  // Modifiers
+
+  // optional::reset()
+  //
+  // Destroys the inner `T` value of an `absl::optional` if one is present.
+  ABSL_ATTRIBUTE_REINITIALIZES void reset() noexcept { this->destruct(); }
+
+  // optional::emplace()
+  //
+  // (Re)constructs the underlying `T` in-place with the given forwarded
+  // arguments.
+  //
+  // Example:
+  //
+  //   optional<Foo> opt;
+  //   opt.emplace(arg1,arg2,arg3);  // Constructs Foo(arg1,arg2,arg3)
+  //
+  // If the optional is non-empty, and the `args` refer to subobjects of the
+  // current object, then behaviour is undefined, because the current object
+  // will be destructed before the new object is constructed with `args`.
+  template <typename... Args,
+            typename = typename std::enable_if<
+                std::is_constructible<T, Args&&...>::value>::type>
+  T& emplace(Args&&... args) {
+    this->destruct();
+    this->construct(std::forward<Args>(args)...);
+    return reference();
+  }
+
+  // Emplace reconstruction overload for an initializer list and the given
+  // forwarded arguments.
+  //
+  // Example:
+  //
+  //   struct Foo {
+  //     Foo(std::initializer_list<int>);
+  //   };
+  //
+  //   optional<Foo> opt;
+  //   opt.emplace({1,2,3});  // Constructs Foo({1,2,3})
+  template <typename U, typename... Args,
+            typename = typename std::enable_if<std::is_constructible<
+                T, std::initializer_list<U>&, Args&&...>::value>::type>
+  T& emplace(std::initializer_list<U> il, Args&&... args) {
+    this->destruct();
+    this->construct(il, std::forward<Args>(args)...);
+    return reference();
+  }
+
+  // Swaps
+
+  // Swap, standard semantics
+  void swap(optional& rhs) noexcept(
+      std::is_nothrow_move_constructible<T>::value&&
+          type_traits_internal::IsNothrowSwappable<T>::value) {
+    if (*this) {
+      if (rhs) {
+        type_traits_internal::Swap(**this, *rhs);
+      } else {
+        rhs.construct(std::move(**this));
+        this->destruct();
+      }
+    } else {
+      if (rhs) {
+        this->construct(std::move(*rhs));
+        rhs.destruct();
+      } else {
+        // No effect (swap(disengaged, disengaged)).
+      }
+    }
+  }
+
+  // Observers
+
+  // optional::operator->()
+  //
+  // Accesses the underlying `T` value's member `m` of an `optional`. If the
+  // `optional` is empty, behavior is undefined.
+  //
+  // If you need myOpt->foo in constexpr, use (*myOpt).foo instead.
+  const T* operator->() const {
+    ABSL_HARDENING_ASSERT(this->engaged_);
+    return std::addressof(this->data_);
+  }
+  T* operator->() {
+    ABSL_HARDENING_ASSERT(this->engaged_);
+    return std::addressof(this->data_);
+  }
+
+  // optional::operator*()
+  //
+  // Accesses the underlying `T` value of an `optional`. If the `optional` is
+  // empty, behavior is undefined.
+  constexpr const T& operator*() const& {
+    return ABSL_HARDENING_ASSERT(this->engaged_), reference();
+  }
+  T& operator*() & {
+    ABSL_HARDENING_ASSERT(this->engaged_);
+    return reference();
+  }
+  constexpr const T&& operator*() const && {
+    return ABSL_HARDENING_ASSERT(this->engaged_), absl::move(reference());
+  }
+  T&& operator*() && {
+    ABSL_HARDENING_ASSERT(this->engaged_);
+    return std::move(reference());
+  }
+
+  // optional::operator bool()
+  //
+  // Returns false if and only if the `optional` is empty.
+  //
+  //   if (opt) {
+  //     // do something with *opt or opt->;
+  //   } else {
+  //     // opt is empty.
+  //   }
+  //
+  constexpr explicit operator bool() const noexcept { return this->engaged_; }
+
+  // optional::has_value()
+  //
+  // Determines whether the `optional` contains a value. Returns `false` if and
+  // only if `*this` is empty.
+  constexpr bool has_value() const noexcept { return this->engaged_; }
+
+// Suppress bogus warning on MSVC: MSVC complains call to reference() after
+// throw_bad_optional_access() is unreachable.
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable : 4702)
+#endif  // _MSC_VER
+  // optional::value()
+  //
+  // Returns a reference to an `optional`s underlying value. The constness
+  // and lvalue/rvalue-ness of the `optional` is preserved to the view of
+  // the `T` sub-object. Throws `absl::bad_optional_access` when the `optional`
+  // is empty.
+  constexpr const T& value() const & {
+    return static_cast<bool>(*this)
+               ? reference()
+               : (optional_internal::throw_bad_optional_access(), reference());
+  }
+  T& value() & {
+    return static_cast<bool>(*this)
+               ? reference()
+               : (optional_internal::throw_bad_optional_access(), reference());
+  }
+  T&& value() && {  // NOLINT(build/c++11)
+    return std::move(
+        static_cast<bool>(*this)
+            ? reference()
+            : (optional_internal::throw_bad_optional_access(), reference()));
+  }
+  constexpr const T&& value() const && {  // NOLINT(build/c++11)
+    return absl::move(
+        static_cast<bool>(*this)
+            ? reference()
+            : (optional_internal::throw_bad_optional_access(), reference()));
+  }
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif  // _MSC_VER
+
+  // optional::value_or()
+  //
+  // Returns either the value of `T` or a passed default `v` if the `optional`
+  // is empty.
+  template <typename U>
+  constexpr T value_or(U&& v) const& {
+    static_assert(std::is_copy_constructible<value_type>::value,
+                  "optional<T>::value_or: T must be copy constructible");
+    static_assert(std::is_convertible<U&&, value_type>::value,
+                  "optional<T>::value_or: U must be convertible to T");
+    return static_cast<bool>(*this)
+               ? **this
+               : static_cast<T>(absl::forward<U>(v));
+  }
+  template <typename U>
+  T value_or(U&& v) && {  // NOLINT(build/c++11)
+    static_assert(std::is_move_constructible<value_type>::value,
+                  "optional<T>::value_or: T must be move constructible");
+    static_assert(std::is_convertible<U&&, value_type>::value,
+                  "optional<T>::value_or: U must be convertible to T");
+    return static_cast<bool>(*this) ? std::move(**this)
+                                    : static_cast<T>(std::forward<U>(v));
+  }
+
+ private:
+  // Private accessors for internal storage viewed as reference to T.
+  constexpr const T& reference() const { return this->data_; }
+  T& reference() { return this->data_; }
+
+  // T constraint checks.  You can't have an optional of nullopt_t, in_place_t
+  // or a reference.
+  static_assert(
+      !std::is_same<nullopt_t, typename std::remove_cv<T>::type>::value,
+      "optional<nullopt_t> is not allowed.");
+  static_assert(
+      !std::is_same<in_place_t, typename std::remove_cv<T>::type>::value,
+      "optional<in_place_t> is not allowed.");
+  static_assert(!std::is_reference<T>::value,
+                "optional<reference> is not allowed.");
+};
+
+// Non-member functions
+
+// swap()
+//
+// Performs a swap between two `absl::optional` objects, using standard
+// semantics.
+template <typename T, typename std::enable_if<
+                          std::is_move_constructible<T>::value &&
+                              type_traits_internal::IsSwappable<T>::value,
+                          bool>::type = false>
+void swap(optional<T>& a, optional<T>& b) noexcept(noexcept(a.swap(b))) {
+  a.swap(b);
+}
+
+// make_optional()
+//
+// Creates a non-empty `optional<T>` where the type of `T` is deduced. An
+// `absl::optional` can also be explicitly instantiated with
+// `make_optional<T>(v)`.
+//
+// Note: `make_optional()` constructions may be declared `constexpr` for
+// trivially copyable types `T`. Non-trivial types require copy elision
+// support in C++17 for `make_optional` to support `constexpr` on such
+// non-trivial types.
+//
+// Example:
+//
+//   constexpr absl::optional<int> opt = absl::make_optional(1);
+//   static_assert(opt.value() == 1, "");
+template <typename T>
+constexpr optional<typename std::decay<T>::type> make_optional(T&& v) {
+  return optional<typename std::decay<T>::type>(absl::forward<T>(v));
+}
+
+template <typename T, typename... Args>
+constexpr optional<T> make_optional(Args&&... args) {
+  return optional<T>(in_place_t(), absl::forward<Args>(args)...);
+}
+
+template <typename T, typename U, typename... Args>
+constexpr optional<T> make_optional(std::initializer_list<U> il,
+                                    Args&&... args) {
+  return optional<T>(in_place_t(), il,
+                     absl::forward<Args>(args)...);
+}
+
+// Relational operators [optional.relops]
+
+// Empty optionals are considered equal to each other and less than non-empty
+// optionals. Supports relations between optional<T> and optional<U>, between
+// optional<T> and U, and between optional<T> and nullopt.
+//
+// Note: We're careful to support T having non-bool relationals.
+
+// Requires: The expression, e.g. "*x == *y" shall be well-formed and its result
+// shall be convertible to bool.
+// The C++17 (N4606) "Returns:" statements are translated into
+// code in an obvious way here, and the original text retained as function docs.
+// Returns: If bool(x) != bool(y), false; otherwise if bool(x) == false, true;
+// otherwise *x == *y.
+template <typename T, typename U>
+constexpr auto operator==(const optional<T>& x, const optional<U>& y)
+    -> decltype(optional_internal::convertible_to_bool(*x == *y)) {
+  return static_cast<bool>(x) != static_cast<bool>(y)
+             ? false
+             : static_cast<bool>(x) == false ? true
+                                             : static_cast<bool>(*x == *y);
+}
+
+// Returns: If bool(x) != bool(y), true; otherwise, if bool(x) == false, false;
+// otherwise *x != *y.
+template <typename T, typename U>
+constexpr auto operator!=(const optional<T>& x, const optional<U>& y)
+    -> decltype(optional_internal::convertible_to_bool(*x != *y)) {
+  return static_cast<bool>(x) != static_cast<bool>(y)
+             ? true
+             : static_cast<bool>(x) == false ? false
+                                             : static_cast<bool>(*x != *y);
+}
+// Returns: If !y, false; otherwise, if !x, true; otherwise *x < *y.
+template <typename T, typename U>
+constexpr auto operator<(const optional<T>& x, const optional<U>& y)
+    -> decltype(optional_internal::convertible_to_bool(*x < *y)) {
+  return !y ? false : !x ? true : static_cast<bool>(*x < *y);
+}
+// Returns: If !x, false; otherwise, if !y, true; otherwise *x > *y.
+template <typename T, typename U>
+constexpr auto operator>(const optional<T>& x, const optional<U>& y)
+    -> decltype(optional_internal::convertible_to_bool(*x > *y)) {
+  return !x ? false : !y ? true : static_cast<bool>(*x > *y);
+}
+// Returns: If !x, true; otherwise, if !y, false; otherwise *x <= *y.
+template <typename T, typename U>
+constexpr auto operator<=(const optional<T>& x, const optional<U>& y)
+    -> decltype(optional_internal::convertible_to_bool(*x <= *y)) {
+  return !x ? true : !y ? false : static_cast<bool>(*x <= *y);
+}
+// Returns: If !y, true; otherwise, if !x, false; otherwise *x >= *y.
+template <typename T, typename U>
+constexpr auto operator>=(const optional<T>& x, const optional<U>& y)
+    -> decltype(optional_internal::convertible_to_bool(*x >= *y)) {
+  return !y ? true : !x ? false : static_cast<bool>(*x >= *y);
+}
+
+// Comparison with nullopt [optional.nullops]
+// The C++17 (N4606) "Returns:" statements are used directly here.
+template <typename T>
+constexpr bool operator==(const optional<T>& x, nullopt_t) noexcept {
+  return !x;
+}
+template <typename T>
+constexpr bool operator==(nullopt_t, const optional<T>& x) noexcept {
+  return !x;
+}
+template <typename T>
+constexpr bool operator!=(const optional<T>& x, nullopt_t) noexcept {
+  return static_cast<bool>(x);
+}
+template <typename T>
+constexpr bool operator!=(nullopt_t, const optional<T>& x) noexcept {
+  return static_cast<bool>(x);
+}
+template <typename T>
+constexpr bool operator<(const optional<T>&, nullopt_t) noexcept {
+  return false;
+}
+template <typename T>
+constexpr bool operator<(nullopt_t, const optional<T>& x) noexcept {
+  return static_cast<bool>(x);
+}
+template <typename T>
+constexpr bool operator<=(const optional<T>& x, nullopt_t) noexcept {
+  return !x;
+}
+template <typename T>
+constexpr bool operator<=(nullopt_t, const optional<T>&) noexcept {
+  return true;
+}
+template <typename T>
+constexpr bool operator>(const optional<T>& x, nullopt_t) noexcept {
+  return static_cast<bool>(x);
+}
+template <typename T>
+constexpr bool operator>(nullopt_t, const optional<T>&) noexcept {
+  return false;
+}
+template <typename T>
+constexpr bool operator>=(const optional<T>&, nullopt_t) noexcept {
+  return true;
+}
+template <typename T>
+constexpr bool operator>=(nullopt_t, const optional<T>& x) noexcept {
+  return !x;
+}
+
+// Comparison with T [optional.comp_with_t]
+
+// Requires: The expression, e.g. "*x == v" shall be well-formed and its result
+// shall be convertible to bool.
+// The C++17 (N4606) "Equivalent to:" statements are used directly here.
+template <typename T, typename U>
+constexpr auto operator==(const optional<T>& x, const U& v)
+    -> decltype(optional_internal::convertible_to_bool(*x == v)) {
+  return static_cast<bool>(x) ? static_cast<bool>(*x == v) : false;
+}
+template <typename T, typename U>
+constexpr auto operator==(const U& v, const optional<T>& x)
+    -> decltype(optional_internal::convertible_to_bool(v == *x)) {
+  return static_cast<bool>(x) ? static_cast<bool>(v == *x) : false;
+}
+template <typename T, typename U>
+constexpr auto operator!=(const optional<T>& x, const U& v)
+    -> decltype(optional_internal::convertible_to_bool(*x != v)) {
+  return static_cast<bool>(x) ? static_cast<bool>(*x != v) : true;
+}
+template <typename T, typename U>
+constexpr auto operator!=(const U& v, const optional<T>& x)
+    -> decltype(optional_internal::convertible_to_bool(v != *x)) {
+  return static_cast<bool>(x) ? static_cast<bool>(v != *x) : true;
+}
+template <typename T, typename U>
+constexpr auto operator<(const optional<T>& x, const U& v)
+    -> decltype(optional_internal::convertible_to_bool(*x < v)) {
+  return static_cast<bool>(x) ? static_cast<bool>(*x < v) : true;
+}
+template <typename T, typename U>
+constexpr auto operator<(const U& v, const optional<T>& x)
+    -> decltype(optional_internal::convertible_to_bool(v < *x)) {
+  return static_cast<bool>(x) ? static_cast<bool>(v < *x) : false;
+}
+template <typename T, typename U>
+constexpr auto operator<=(const optional<T>& x, const U& v)
+    -> decltype(optional_internal::convertible_to_bool(*x <= v)) {
+  return static_cast<bool>(x) ? static_cast<bool>(*x <= v) : true;
+}
+template <typename T, typename U>
+constexpr auto operator<=(const U& v, const optional<T>& x)
+    -> decltype(optional_internal::convertible_to_bool(v <= *x)) {
+  return static_cast<bool>(x) ? static_cast<bool>(v <= *x) : false;
+}
+template <typename T, typename U>
+constexpr auto operator>(const optional<T>& x, const U& v)
+    -> decltype(optional_internal::convertible_to_bool(*x > v)) {
+  return static_cast<bool>(x) ? static_cast<bool>(*x > v) : false;
+}
+template <typename T, typename U>
+constexpr auto operator>(const U& v, const optional<T>& x)
+    -> decltype(optional_internal::convertible_to_bool(v > *x)) {
+  return static_cast<bool>(x) ? static_cast<bool>(v > *x) : true;
+}
+template <typename T, typename U>
+constexpr auto operator>=(const optional<T>& x, const U& v)
+    -> decltype(optional_internal::convertible_to_bool(*x >= v)) {
+  return static_cast<bool>(x) ? static_cast<bool>(*x >= v) : false;
+}
+template <typename T, typename U>
+constexpr auto operator>=(const U& v, const optional<T>& x)
+    -> decltype(optional_internal::convertible_to_bool(v >= *x)) {
+  return static_cast<bool>(x) ? static_cast<bool>(v >= *x) : true;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+namespace std {
+
+// std::hash specialization for absl::optional.
+template <typename T>
+struct hash<absl::optional<T> >
+    : absl::optional_internal::optional_hash_base<T> {};
+
+}  // namespace std
+
+#undef ABSL_MSVC_CONSTEXPR_BUG_IN_UNION_LIKE_CLASS
+
+#endif  // ABSL_USES_STD_OPTIONAL
+
+#endif  // ABSL_TYPES_OPTIONAL_H_
diff --git a/third_party/abseil_cpp/absl/types/optional_exception_safety_test.cc b/third_party/abseil_cpp/absl/types/optional_exception_safety_test.cc
new file mode 100644
index 0000000000..8e5fe851db
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/optional_exception_safety_test.cc
@@ -0,0 +1,292 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/optional.h"
+
+#include "absl/base/config.h"
+
+// This test is a no-op when absl::optional is an alias for std::optional and
+// when exceptions are not enabled.
+#if !defined(ABSL_USES_STD_OPTIONAL) && defined(ABSL_HAVE_EXCEPTIONS)
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/exception_safety_testing.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace {
+
+using ::testing::AssertionFailure;
+using ::testing::AssertionResult;
+using ::testing::AssertionSuccess;
+using ::testing::MakeExceptionSafetyTester;
+
+using Thrower = testing::ThrowingValue<testing::TypeSpec::kEverythingThrows>;
+using Optional = absl::optional<Thrower>;
+
+using MoveThrower = testing::ThrowingValue<testing::TypeSpec::kNoThrowMove>;
+using MoveOptional = absl::optional<MoveThrower>;
+
+constexpr int kInitialInteger = 5;
+constexpr int kUpdatedInteger = 10;
+
+template <typename OptionalT>
+bool ValueThrowsBadOptionalAccess(const OptionalT& optional) try {
+  return (static_cast<void>(optional.value()), false);
+} catch (const absl::bad_optional_access&) {
+  return true;
+}
+
+template <typename OptionalT>
+AssertionResult OptionalInvariants(OptionalT* optional_ptr) {
+  // Check the current state post-throw for validity
+  auto& optional = *optional_ptr;
+
+  if (optional.has_value() && ValueThrowsBadOptionalAccess(optional)) {
+    return AssertionFailure()
+           << "Optional with value should not throw bad_optional_access when "
+              "accessing the value.";
+  }
+  if (!optional.has_value() && !ValueThrowsBadOptionalAccess(optional)) {
+    return AssertionFailure()
+           << "Optional without a value should throw bad_optional_access when "
+              "accessing the value.";
+  }
+
+  // Reset to a known state
+  optional.reset();
+
+  // Confirm that the known post-reset state is valid
+  if (optional.has_value()) {
+    return AssertionFailure()
+           << "Optional should not contain a value after being reset.";
+  }
+  if (!ValueThrowsBadOptionalAccess(optional)) {
+    return AssertionFailure() << "Optional should throw bad_optional_access "
+                                 "when accessing the value after being reset.";
+  }
+
+  return AssertionSuccess();
+}
+
+template <typename OptionalT>
+AssertionResult CheckDisengaged(OptionalT* optional_ptr) {
+  auto& optional = *optional_ptr;
+
+  if (optional.has_value()) {
+    return AssertionFailure()
+           << "Expected optional to not contain a value but a value was found.";
+  }
+
+  return AssertionSuccess();
+}
+
+template <typename OptionalT>
+AssertionResult CheckEngaged(OptionalT* optional_ptr) {
+  auto& optional = *optional_ptr;
+
+  if (!optional.has_value()) {
+    return AssertionFailure()
+           << "Expected optional to contain a value but no value was found.";
+  }
+
+  return AssertionSuccess();
+}
+
+TEST(OptionalExceptionSafety, ThrowingConstructors) {
+  auto thrower_nonempty = Optional(Thrower(kInitialInteger));
+  testing::TestThrowingCtor<Optional>(thrower_nonempty);
+
+  auto integer_nonempty = absl::optional<int>(kInitialInteger);
+  testing::TestThrowingCtor<Optional>(integer_nonempty);
+  testing::TestThrowingCtor<Optional>(std::move(integer_nonempty));  // NOLINT
+
+  testing::TestThrowingCtor<Optional>(kInitialInteger);
+  using ThrowerVec = std::vector<Thrower, testing::ThrowingAllocator<Thrower>>;
+  testing::TestThrowingCtor<absl::optional<ThrowerVec>>(
+      absl::in_place,
+      std::initializer_list<Thrower>{Thrower(), Thrower(), Thrower()},
+      testing::ThrowingAllocator<Thrower>());
+}
+
+TEST(OptionalExceptionSafety, NothrowConstructors) {
+  // This constructor is marked noexcept. If it throws, the program will
+  // terminate.
+  testing::TestThrowingCtor<MoveOptional>(MoveOptional(kUpdatedInteger));
+}
+
+TEST(OptionalExceptionSafety, Emplace) {
+  // Test the basic guarantee plus test the result of optional::has_value()
+  // is false in all cases
+  auto disengaged_test = MakeExceptionSafetyTester().WithContracts(
+      OptionalInvariants<Optional>, CheckDisengaged<Optional>);
+  auto disengaged_test_empty = disengaged_test.WithInitialValue(Optional());
+  auto disengaged_test_nonempty =
+      disengaged_test.WithInitialValue(Optional(kInitialInteger));
+
+  auto emplace_thrower_directly = [](Optional* optional_ptr) {
+    optional_ptr->emplace(kUpdatedInteger);
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(emplace_thrower_directly));
+  EXPECT_TRUE(disengaged_test_nonempty.Test(emplace_thrower_directly));
+
+  auto emplace_thrower_copy = [](Optional* optional_ptr) {
+    auto thrower = Thrower(kUpdatedInteger, testing::nothrow_ctor);
+    optional_ptr->emplace(thrower);
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(emplace_thrower_copy));
+  EXPECT_TRUE(disengaged_test_nonempty.Test(emplace_thrower_copy));
+}
+
+TEST(OptionalExceptionSafety, EverythingThrowsSwap) {
+  // Test the basic guarantee plus test the result of optional::has_value()
+  // remains the same
+  auto test =
+      MakeExceptionSafetyTester().WithContracts(OptionalInvariants<Optional>);
+  auto disengaged_test_empty = test.WithInitialValue(Optional())
+                                   .WithContracts(CheckDisengaged<Optional>);
+  auto engaged_test_nonempty = test.WithInitialValue(Optional(kInitialInteger))
+                                   .WithContracts(CheckEngaged<Optional>);
+
+  auto swap_empty = [](Optional* optional_ptr) {
+    auto empty = Optional();
+    optional_ptr->swap(empty);
+  };
+  EXPECT_TRUE(engaged_test_nonempty.Test(swap_empty));
+
+  auto swap_nonempty = [](Optional* optional_ptr) {
+    auto nonempty =
+        Optional(absl::in_place, kUpdatedInteger, testing::nothrow_ctor);
+    optional_ptr->swap(nonempty);
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(swap_nonempty));
+  EXPECT_TRUE(engaged_test_nonempty.Test(swap_nonempty));
+}
+
+TEST(OptionalExceptionSafety, NoThrowMoveSwap) {
+  // Tests the nothrow guarantee for optional of T with non-throwing move
+  {
+    auto empty = MoveOptional();
+    auto nonempty = MoveOptional(kInitialInteger);
+    EXPECT_TRUE(testing::TestNothrowOp([&]() { nonempty.swap(empty); }));
+  }
+  {
+    auto nonempty = MoveOptional(kUpdatedInteger);
+    auto empty = MoveOptional();
+    EXPECT_TRUE(testing::TestNothrowOp([&]() { empty.swap(nonempty); }));
+  }
+  {
+    auto nonempty_from = MoveOptional(kUpdatedInteger);
+    auto nonempty_to = MoveOptional(kInitialInteger);
+    EXPECT_TRUE(
+        testing::TestNothrowOp([&]() { nonempty_to.swap(nonempty_from); }));
+  }
+}
+
+TEST(OptionalExceptionSafety, CopyAssign) {
+  // Test the basic guarantee plus test the result of optional::has_value()
+  // remains the same
+  auto test =
+      MakeExceptionSafetyTester().WithContracts(OptionalInvariants<Optional>);
+  auto disengaged_test_empty = test.WithInitialValue(Optional())
+                                   .WithContracts(CheckDisengaged<Optional>);
+  auto engaged_test_nonempty = test.WithInitialValue(Optional(kInitialInteger))
+                                   .WithContracts(CheckEngaged<Optional>);
+
+  auto copyassign_nonempty = [](Optional* optional_ptr) {
+    auto nonempty =
+        Optional(absl::in_place, kUpdatedInteger, testing::nothrow_ctor);
+    *optional_ptr = nonempty;
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(copyassign_nonempty));
+  EXPECT_TRUE(engaged_test_nonempty.Test(copyassign_nonempty));
+
+  auto copyassign_thrower = [](Optional* optional_ptr) {
+    auto thrower = Thrower(kUpdatedInteger, testing::nothrow_ctor);
+    *optional_ptr = thrower;
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(copyassign_thrower));
+  EXPECT_TRUE(engaged_test_nonempty.Test(copyassign_thrower));
+}
+
+TEST(OptionalExceptionSafety, MoveAssign) {
+  // Test the basic guarantee plus test the result of optional::has_value()
+  // remains the same
+  auto test =
+      MakeExceptionSafetyTester().WithContracts(OptionalInvariants<Optional>);
+  auto disengaged_test_empty = test.WithInitialValue(Optional())
+                                   .WithContracts(CheckDisengaged<Optional>);
+  auto engaged_test_nonempty = test.WithInitialValue(Optional(kInitialInteger))
+                                   .WithContracts(CheckEngaged<Optional>);
+
+  auto moveassign_empty = [](Optional* optional_ptr) {
+    auto empty = Optional();
+    *optional_ptr = std::move(empty);
+  };
+  EXPECT_TRUE(engaged_test_nonempty.Test(moveassign_empty));
+
+  auto moveassign_nonempty = [](Optional* optional_ptr) {
+    auto nonempty =
+        Optional(absl::in_place, kUpdatedInteger, testing::nothrow_ctor);
+    *optional_ptr = std::move(nonempty);
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(moveassign_nonempty));
+  EXPECT_TRUE(engaged_test_nonempty.Test(moveassign_nonempty));
+
+  auto moveassign_thrower = [](Optional* optional_ptr) {
+    auto thrower = Thrower(kUpdatedInteger, testing::nothrow_ctor);
+    *optional_ptr = std::move(thrower);
+  };
+  EXPECT_TRUE(disengaged_test_empty.Test(moveassign_thrower));
+  EXPECT_TRUE(engaged_test_nonempty.Test(moveassign_thrower));
+}
+
+TEST(OptionalExceptionSafety, NothrowMoveAssign) {
+  // Tests the nothrow guarantee for optional of T with non-throwing move
+  {
+    auto empty = MoveOptional();
+    auto nonempty = MoveOptional(kInitialInteger);
+    EXPECT_TRUE(testing::TestNothrowOp([&]() { nonempty = std::move(empty); }));
+  }
+  {
+    auto nonempty = MoveOptional(kInitialInteger);
+    auto empty = MoveOptional();
+    EXPECT_TRUE(testing::TestNothrowOp([&]() { empty = std::move(nonempty); }));
+  }
+  {
+    auto nonempty_from = MoveOptional(kUpdatedInteger);
+    auto nonempty_to = MoveOptional(kInitialInteger);
+    EXPECT_TRUE(testing::TestNothrowOp(
+        [&]() { nonempty_to = std::move(nonempty_from); }));
+  }
+  {
+    auto thrower = MoveThrower(kUpdatedInteger);
+    auto empty = MoveOptional();
+    EXPECT_TRUE(testing::TestNothrowOp([&]() { empty = std::move(thrower); }));
+  }
+  {
+    auto thrower = MoveThrower(kUpdatedInteger);
+    auto nonempty = MoveOptional(kInitialInteger);
+    EXPECT_TRUE(
+        testing::TestNothrowOp([&]() { nonempty = std::move(thrower); }));
+  }
+}
+
+}  // namespace
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // #if !defined(ABSL_USES_STD_OPTIONAL) && defined(ABSL_HAVE_EXCEPTIONS)
diff --git a/third_party/abseil_cpp/absl/types/optional_test.cc b/third_party/abseil_cpp/absl/types/optional_test.cc
new file mode 100644
index 0000000000..7ef142cb99
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/optional_test.cc
@@ -0,0 +1,1659 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/optional.h"
+
+// This test is a no-op when absl::optional is an alias for std::optional.
+#if !defined(ABSL_USES_STD_OPTIONAL)
+
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/string_view.h"
+
+struct Hashable {};
+
+namespace std {
+template <>
+struct hash<Hashable> {
+  size_t operator()(const Hashable&) { return 0; }
+};
+}  // namespace std
+
+struct NonHashable {};
+
+namespace {
+
+std::string TypeQuals(std::string&) { return "&"; }
+std::string TypeQuals(std::string&&) { return "&&"; }
+std::string TypeQuals(const std::string&) { return "c&"; }
+std::string TypeQuals(const std::string&&) { return "c&&"; }
+
+struct StructorListener {
+  int construct0 = 0;
+  int construct1 = 0;
+  int construct2 = 0;
+  int listinit = 0;
+  int copy = 0;
+  int move = 0;
+  int copy_assign = 0;
+  int move_assign = 0;
+  int destruct = 0;
+  int volatile_copy = 0;
+  int volatile_move = 0;
+  int volatile_copy_assign = 0;
+  int volatile_move_assign = 0;
+};
+
+// Suppress MSVC warnings.
+// 4521: multiple copy constructors specified
+// 4522: multiple assignment operators specified
+// We wrote multiple of them to test that the correct overloads are selected.
+#ifdef _MSC_VER
+#pragma warning( push )
+#pragma warning( disable : 4521)
+#pragma warning( disable : 4522)
+#endif
+struct Listenable {
+  static StructorListener* listener;
+
+  Listenable() { ++listener->construct0; }
+  explicit Listenable(int /*unused*/) { ++listener->construct1; }
+  Listenable(int /*unused*/, int /*unused*/) { ++listener->construct2; }
+  Listenable(std::initializer_list<int> /*unused*/) { ++listener->listinit; }
+  Listenable(const Listenable& /*unused*/) { ++listener->copy; }
+  Listenable(const volatile Listenable& /*unused*/) {
+    ++listener->volatile_copy;
+  }
+  Listenable(volatile Listenable&& /*unused*/) { ++listener->volatile_move; }
+  Listenable(Listenable&& /*unused*/) { ++listener->move; }
+  Listenable& operator=(const Listenable& /*unused*/) {
+    ++listener->copy_assign;
+    return *this;
+  }
+  Listenable& operator=(Listenable&& /*unused*/) {
+    ++listener->move_assign;
+    return *this;
+  }
+  // use void return type instead of volatile T& to work around GCC warning
+  // when the assignment's returned reference is ignored.
+  void operator=(const volatile Listenable& /*unused*/) volatile {
+    ++listener->volatile_copy_assign;
+  }
+  void operator=(volatile Listenable&& /*unused*/) volatile {
+    ++listener->volatile_move_assign;
+  }
+  ~Listenable() { ++listener->destruct; }
+};
+#ifdef _MSC_VER
+#pragma warning( pop )
+#endif
+
+StructorListener* Listenable::listener = nullptr;
+
+// ABSL_HAVE_NO_CONSTEXPR_INITIALIZER_LIST is defined to 1 when the standard
+// library implementation doesn't marked initializer_list's default constructor
+// constexpr. The C++11 standard doesn't specify constexpr on it, but C++14
+// added it. However, libstdc++ 4.7 marked it constexpr.
+#if defined(_LIBCPP_VERSION) && \
+    (_LIBCPP_STD_VER <= 11 || defined(_LIBCPP_HAS_NO_CXX14_CONSTEXPR))
+#define ABSL_HAVE_NO_CONSTEXPR_INITIALIZER_LIST 1
+#endif
+
+struct ConstexprType {
+  enum CtorTypes {
+    kCtorDefault,
+    kCtorInt,
+    kCtorInitializerList,
+    kCtorConstChar
+  };
+  constexpr ConstexprType() : x(kCtorDefault) {}
+  constexpr explicit ConstexprType(int i) : x(kCtorInt) {}
+#ifndef ABSL_HAVE_NO_CONSTEXPR_INITIALIZER_LIST
+  constexpr ConstexprType(std::initializer_list<int> il)
+      : x(kCtorInitializerList) {}
+#endif
+  constexpr ConstexprType(const char*)  // NOLINT(runtime/explicit)
+      : x(kCtorConstChar) {}
+  int x;
+};
+
+struct Copyable {
+  Copyable() {}
+  Copyable(const Copyable&) {}
+  Copyable& operator=(const Copyable&) { return *this; }
+};
+
+struct MoveableThrow {
+  MoveableThrow() {}
+  MoveableThrow(MoveableThrow&&) {}
+  MoveableThrow& operator=(MoveableThrow&&) { return *this; }
+};
+
+struct MoveableNoThrow {
+  MoveableNoThrow() {}
+  MoveableNoThrow(MoveableNoThrow&&) noexcept {}
+  MoveableNoThrow& operator=(MoveableNoThrow&&) noexcept { return *this; }
+};
+
+struct NonMovable {
+  NonMovable() {}
+  NonMovable(const NonMovable&) = delete;
+  NonMovable& operator=(const NonMovable&) = delete;
+  NonMovable(NonMovable&&) = delete;
+  NonMovable& operator=(NonMovable&&) = delete;
+};
+
+struct NoDefault {
+  NoDefault() = delete;
+  NoDefault(const NoDefault&) {}
+  NoDefault& operator=(const NoDefault&) { return *this; }
+};
+
+struct ConvertsFromInPlaceT {
+  ConvertsFromInPlaceT(absl::in_place_t) {}  // NOLINT
+};
+
+TEST(optionalTest, DefaultConstructor) {
+  absl::optional<int> empty;
+  EXPECT_FALSE(empty);
+  constexpr absl::optional<int> cempty;
+  static_assert(!cempty.has_value(), "");
+  EXPECT_TRUE(
+      std::is_nothrow_default_constructible<absl::optional<int>>::value);
+}
+
+TEST(optionalTest, nulloptConstructor) {
+  absl::optional<int> empty(absl::nullopt);
+  EXPECT_FALSE(empty);
+  constexpr absl::optional<int> cempty{absl::nullopt};
+  static_assert(!cempty.has_value(), "");
+  EXPECT_TRUE((std::is_nothrow_constructible<absl::optional<int>,
+                                             absl::nullopt_t>::value));
+}
+
+TEST(optionalTest, CopyConstructor) {
+  {
+    absl::optional<int> empty, opt42 = 42;
+    absl::optional<int> empty_copy(empty);
+    EXPECT_FALSE(empty_copy);
+    absl::optional<int> opt42_copy(opt42);
+    EXPECT_TRUE(opt42_copy);
+    EXPECT_EQ(42, *opt42_copy);
+  }
+  {
+    absl::optional<const int> empty, opt42 = 42;
+    absl::optional<const int> empty_copy(empty);
+    EXPECT_FALSE(empty_copy);
+    absl::optional<const int> opt42_copy(opt42);
+    EXPECT_TRUE(opt42_copy);
+    EXPECT_EQ(42, *opt42_copy);
+  }
+  {
+    absl::optional<volatile int> empty, opt42 = 42;
+    absl::optional<volatile int> empty_copy(empty);
+    EXPECT_FALSE(empty_copy);
+    absl::optional<volatile int> opt42_copy(opt42);
+    EXPECT_TRUE(opt42_copy);
+    EXPECT_EQ(42, *opt42_copy);
+  }
+  // test copyablility
+  EXPECT_TRUE(std::is_copy_constructible<absl::optional<int>>::value);
+  EXPECT_TRUE(std::is_copy_constructible<absl::optional<Copyable>>::value);
+  EXPECT_FALSE(
+      std::is_copy_constructible<absl::optional<MoveableThrow>>::value);
+  EXPECT_FALSE(
+      std::is_copy_constructible<absl::optional<MoveableNoThrow>>::value);
+  EXPECT_FALSE(std::is_copy_constructible<absl::optional<NonMovable>>::value);
+
+  EXPECT_FALSE(
+      absl::is_trivially_copy_constructible<absl::optional<Copyable>>::value);
+#if defined(ABSL_USES_STD_OPTIONAL) && defined(__GLIBCXX__)
+  // libstdc++ std::optional implementation (as of 7.2) has a bug: when T is
+  // trivially copyable, optional<T> is not trivially copyable (due to one of
+  // its base class is unconditionally nontrivial).
+#define ABSL_GLIBCXX_OPTIONAL_TRIVIALITY_BUG 1
+#endif
+#ifndef ABSL_GLIBCXX_OPTIONAL_TRIVIALITY_BUG
+  EXPECT_TRUE(
+      absl::is_trivially_copy_constructible<absl::optional<int>>::value);
+  EXPECT_TRUE(
+      absl::is_trivially_copy_constructible<absl::optional<const int>>::value);
+#ifndef _MSC_VER
+  // See defect report "Trivial copy/move constructor for class with volatile
+  // member" at
+  // http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2094
+  // A class with non-static data member of volatile-qualified type should still
+  // have a trivial copy constructor if the data member is trivial.
+  // Also a cv-qualified scalar type should be trivially copyable.
+  EXPECT_TRUE(absl::is_trivially_copy_constructible<
+              absl::optional<volatile int>>::value);
+#endif  // _MSC_VER
+#endif  // ABSL_GLIBCXX_OPTIONAL_TRIVIALITY_BUG
+
+  // constexpr copy constructor for trivially copyable types
+  {
+    constexpr absl::optional<int> o1;
+    constexpr absl::optional<int> o2 = o1;
+    static_assert(!o2, "");
+  }
+  {
+    constexpr absl::optional<int> o1 = 42;
+    constexpr absl::optional<int> o2 = o1;
+    static_assert(o2, "");
+    static_assert(*o2 == 42, "");
+  }
+  {
+    struct TrivialCopyable {
+      constexpr TrivialCopyable() : x(0) {}
+      constexpr explicit TrivialCopyable(int i) : x(i) {}
+      int x;
+    };
+    constexpr absl::optional<TrivialCopyable> o1(42);
+    constexpr absl::optional<TrivialCopyable> o2 = o1;
+    static_assert(o2, "");
+    static_assert((*o2).x == 42, "");
+#ifndef ABSL_GLIBCXX_OPTIONAL_TRIVIALITY_BUG
+    EXPECT_TRUE(absl::is_trivially_copy_constructible<
+                absl::optional<TrivialCopyable>>::value);
+    EXPECT_TRUE(absl::is_trivially_copy_constructible<
+                absl::optional<const TrivialCopyable>>::value);
+#endif
+    // When testing with VS 2017 15.3, there seems to be a bug in MSVC
+    // std::optional when T is volatile-qualified. So skipping this test.
+    // Bug report:
+    // https://connect.microsoft.com/VisualStudio/feedback/details/3142534
+#if defined(ABSL_USES_STD_OPTIONAL) && defined(_MSC_VER) && _MSC_VER >= 1911
+#define ABSL_MSVC_OPTIONAL_VOLATILE_COPY_BUG 1
+#endif
+#ifndef ABSL_MSVC_OPTIONAL_VOLATILE_COPY_BUG
+    EXPECT_FALSE(std::is_copy_constructible<
+                 absl::optional<volatile TrivialCopyable>>::value);
+#endif
+  }
+}
+
+TEST(optionalTest, MoveConstructor) {
+  absl::optional<int> empty, opt42 = 42;
+  absl::optional<int> empty_move(std::move(empty));
+  EXPECT_FALSE(empty_move);
+  absl::optional<int> opt42_move(std::move(opt42));
+  EXPECT_TRUE(opt42_move);
+  EXPECT_EQ(42, opt42_move);
+  // test movability
+  EXPECT_TRUE(std::is_move_constructible<absl::optional<int>>::value);
+  EXPECT_TRUE(std::is_move_constructible<absl::optional<Copyable>>::value);
+  EXPECT_TRUE(std::is_move_constructible<absl::optional<MoveableThrow>>::value);
+  EXPECT_TRUE(
+      std::is_move_constructible<absl::optional<MoveableNoThrow>>::value);
+  EXPECT_FALSE(std::is_move_constructible<absl::optional<NonMovable>>::value);
+  // test noexcept
+  EXPECT_TRUE(std::is_nothrow_move_constructible<absl::optional<int>>::value);
+#ifndef ABSL_USES_STD_OPTIONAL
+  EXPECT_EQ(
+      absl::default_allocator_is_nothrow::value,
+      std::is_nothrow_move_constructible<absl::optional<MoveableThrow>>::value);
+#endif
+  EXPECT_TRUE(std::is_nothrow_move_constructible<
+              absl::optional<MoveableNoThrow>>::value);
+}
+
+TEST(optionalTest, Destructor) {
+  struct Trivial {};
+
+  struct NonTrivial {
+    NonTrivial(const NonTrivial&) {}
+    NonTrivial& operator=(const NonTrivial&) { return *this; }
+    ~NonTrivial() {}
+  };
+
+  EXPECT_TRUE(std::is_trivially_destructible<absl::optional<int>>::value);
+  EXPECT_TRUE(std::is_trivially_destructible<absl::optional<Trivial>>::value);
+  EXPECT_FALSE(
+      std::is_trivially_destructible<absl::optional<NonTrivial>>::value);
+}
+
+TEST(optionalTest, InPlaceConstructor) {
+  constexpr absl::optional<ConstexprType> opt0{absl::in_place_t()};
+  static_assert(opt0, "");
+  static_assert((*opt0).x == ConstexprType::kCtorDefault, "");
+  constexpr absl::optional<ConstexprType> opt1{absl::in_place_t(), 1};
+  static_assert(opt1, "");
+  static_assert((*opt1).x == ConstexprType::kCtorInt, "");
+#ifndef ABSL_HAVE_NO_CONSTEXPR_INITIALIZER_LIST
+  constexpr absl::optional<ConstexprType> opt2{absl::in_place_t(), {1, 2}};
+  static_assert(opt2, "");
+  static_assert((*opt2).x == ConstexprType::kCtorInitializerList, "");
+#endif
+
+  EXPECT_FALSE((std::is_constructible<absl::optional<ConvertsFromInPlaceT>,
+                                      absl::in_place_t>::value));
+  EXPECT_FALSE((std::is_constructible<absl::optional<ConvertsFromInPlaceT>,
+                                      const absl::in_place_t&>::value));
+  EXPECT_TRUE(
+      (std::is_constructible<absl::optional<ConvertsFromInPlaceT>,
+                             absl::in_place_t, absl::in_place_t>::value));
+
+  EXPECT_FALSE((std::is_constructible<absl::optional<NoDefault>,
+                                      absl::in_place_t>::value));
+  EXPECT_FALSE((std::is_constructible<absl::optional<NoDefault>,
+                                      absl::in_place_t&&>::value));
+}
+
+// template<U=T> optional(U&&);
+TEST(optionalTest, ValueConstructor) {
+  constexpr absl::optional<int> opt0(0);
+  static_assert(opt0, "");
+  static_assert(*opt0 == 0, "");
+  EXPECT_TRUE((std::is_convertible<int, absl::optional<int>>::value));
+  // Copy initialization ( = "abc") won't work due to optional(optional&&)
+  // is not constexpr. Use list initialization instead. This invokes
+  // absl::optional<ConstexprType>::absl::optional<U>(U&&), with U = const char
+  // (&) [4], which direct-initializes the ConstexprType value held by the
+  // optional via ConstexprType::ConstexprType(const char*).
+  constexpr absl::optional<ConstexprType> opt1 = {"abc"};
+  static_assert(opt1, "");
+  static_assert(ConstexprType::kCtorConstChar == (*opt1).x, "");
+  EXPECT_TRUE(
+      (std::is_convertible<const char*, absl::optional<ConstexprType>>::value));
+  // direct initialization
+  constexpr absl::optional<ConstexprType> opt2{2};
+  static_assert(opt2, "");
+  static_assert(ConstexprType::kCtorInt == (*opt2).x, "");
+  EXPECT_FALSE(
+      (std::is_convertible<int, absl::optional<ConstexprType>>::value));
+
+  // this invokes absl::optional<int>::optional(int&&)
+  // NOTE: this has different behavior than assignment, e.g.
+  // "opt3 = {};" clears the optional rather than setting the value to 0
+  // According to C++17 standard N4659 [over.ics.list] 16.3.3.1.5, (9.2)- "if
+  // the initializer list has no elements, the implicit conversion is the
+  // identity conversion", so `optional(int&&)` should be a better match than
+  // `optional(optional&&)` which is a user-defined conversion.
+  // Note: GCC 7 has a bug with this overload selection when compiled with
+  // `-std=c++17`.
+#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ == 7 && \
+    __cplusplus == 201703L
+#define ABSL_GCC7_OVER_ICS_LIST_BUG 1
+#endif
+#ifndef ABSL_GCC7_OVER_ICS_LIST_BUG
+  constexpr absl::optional<int> opt3({});
+  static_assert(opt3, "");
+  static_assert(*opt3 == 0, "");
+#endif
+
+  // this invokes the move constructor with a default constructed optional
+  // because non-template function is a better match than template function.
+  absl::optional<ConstexprType> opt4({});
+  EXPECT_FALSE(opt4);
+}
+
+struct Implicit {};
+
+struct Explicit {};
+
+struct Convert {
+  Convert(const Implicit&)  // NOLINT(runtime/explicit)
+      : implicit(true), move(false) {}
+  Convert(Implicit&&)  // NOLINT(runtime/explicit)
+      : implicit(true), move(true) {}
+  explicit Convert(const Explicit&) : implicit(false), move(false) {}
+  explicit Convert(Explicit&&) : implicit(false), move(true) {}
+
+  bool implicit;
+  bool move;
+};
+
+struct ConvertFromOptional {
+  ConvertFromOptional(const Implicit&)  // NOLINT(runtime/explicit)
+      : implicit(true), move(false), from_optional(false) {}
+  ConvertFromOptional(Implicit&&)  // NOLINT(runtime/explicit)
+      : implicit(true), move(true), from_optional(false) {}
+  ConvertFromOptional(
+      const absl::optional<Implicit>&)  // NOLINT(runtime/explicit)
+      : implicit(true), move(false), from_optional(true) {}
+  ConvertFromOptional(absl::optional<Implicit>&&)  // NOLINT(runtime/explicit)
+      : implicit(true), move(true), from_optional(true) {}
+  explicit ConvertFromOptional(const Explicit&)
+      : implicit(false), move(false), from_optional(false) {}
+  explicit ConvertFromOptional(Explicit&&)
+      : implicit(false), move(true), from_optional(false) {}
+  explicit ConvertFromOptional(const absl::optional<Explicit>&)
+      : implicit(false), move(false), from_optional(true) {}
+  explicit ConvertFromOptional(absl::optional<Explicit>&&)
+      : implicit(false), move(true), from_optional(true) {}
+
+  bool implicit;
+  bool move;
+  bool from_optional;
+};
+
+TEST(optionalTest, ConvertingConstructor) {
+  absl::optional<Implicit> i_empty;
+  absl::optional<Implicit> i(absl::in_place);
+  absl::optional<Explicit> e_empty;
+  absl::optional<Explicit> e(absl::in_place);
+  {
+    // implicitly constructing absl::optional<Convert> from
+    // absl::optional<Implicit>
+    absl::optional<Convert> empty = i_empty;
+    EXPECT_FALSE(empty);
+    absl::optional<Convert> opt_copy = i;
+    EXPECT_TRUE(opt_copy);
+    EXPECT_TRUE(opt_copy->implicit);
+    EXPECT_FALSE(opt_copy->move);
+    absl::optional<Convert> opt_move = absl::optional<Implicit>(absl::in_place);
+    EXPECT_TRUE(opt_move);
+    EXPECT_TRUE(opt_move->implicit);
+    EXPECT_TRUE(opt_move->move);
+  }
+  {
+    // explicitly constructing absl::optional<Convert> from
+    // absl::optional<Explicit>
+    absl::optional<Convert> empty(e_empty);
+    EXPECT_FALSE(empty);
+    absl::optional<Convert> opt_copy(e);
+    EXPECT_TRUE(opt_copy);
+    EXPECT_FALSE(opt_copy->implicit);
+    EXPECT_FALSE(opt_copy->move);
+    EXPECT_FALSE((std::is_convertible<const absl::optional<Explicit>&,
+                                      absl::optional<Convert>>::value));
+    absl::optional<Convert> opt_move{absl::optional<Explicit>(absl::in_place)};
+    EXPECT_TRUE(opt_move);
+    EXPECT_FALSE(opt_move->implicit);
+    EXPECT_TRUE(opt_move->move);
+    EXPECT_FALSE((std::is_convertible<absl::optional<Explicit>&&,
+                                      absl::optional<Convert>>::value));
+  }
+  {
+    // implicitly constructing absl::optional<ConvertFromOptional> from
+    // absl::optional<Implicit> via
+    // ConvertFromOptional(absl::optional<Implicit>&&) check that
+    // ConvertFromOptional(Implicit&&) is NOT called
+    static_assert(
+        std::is_convertible<absl::optional<Implicit>,
+                            absl::optional<ConvertFromOptional>>::value,
+        "");
+    absl::optional<ConvertFromOptional> opt0 = i_empty;
+    EXPECT_TRUE(opt0);
+    EXPECT_TRUE(opt0->implicit);
+    EXPECT_FALSE(opt0->move);
+    EXPECT_TRUE(opt0->from_optional);
+    absl::optional<ConvertFromOptional> opt1 = absl::optional<Implicit>();
+    EXPECT_TRUE(opt1);
+    EXPECT_TRUE(opt1->implicit);
+    EXPECT_TRUE(opt1->move);
+    EXPECT_TRUE(opt1->from_optional);
+  }
+  {
+    // implicitly constructing absl::optional<ConvertFromOptional> from
+    // absl::optional<Explicit> via
+    // ConvertFromOptional(absl::optional<Explicit>&&) check that
+    // ConvertFromOptional(Explicit&&) is NOT called
+    absl::optional<ConvertFromOptional> opt0(e_empty);
+    EXPECT_TRUE(opt0);
+    EXPECT_FALSE(opt0->implicit);
+    EXPECT_FALSE(opt0->move);
+    EXPECT_TRUE(opt0->from_optional);
+    EXPECT_FALSE(
+        (std::is_convertible<const absl::optional<Explicit>&,
+                             absl::optional<ConvertFromOptional>>::value));
+    absl::optional<ConvertFromOptional> opt1{absl::optional<Explicit>()};
+    EXPECT_TRUE(opt1);
+    EXPECT_FALSE(opt1->implicit);
+    EXPECT_TRUE(opt1->move);
+    EXPECT_TRUE(opt1->from_optional);
+    EXPECT_FALSE(
+        (std::is_convertible<absl::optional<Explicit>&&,
+                             absl::optional<ConvertFromOptional>>::value));
+  }
+}
+
+TEST(optionalTest, StructorBasic) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+  {
+    absl::optional<Listenable> empty;
+    EXPECT_FALSE(empty);
+    absl::optional<Listenable> opt0(absl::in_place);
+    EXPECT_TRUE(opt0);
+    absl::optional<Listenable> opt1(absl::in_place, 1);
+    EXPECT_TRUE(opt1);
+    absl::optional<Listenable> opt2(absl::in_place, 1, 2);
+    EXPECT_TRUE(opt2);
+  }
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(1, listener.construct1);
+  EXPECT_EQ(1, listener.construct2);
+  EXPECT_EQ(3, listener.destruct);
+}
+
+TEST(optionalTest, CopyMoveStructor) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+  absl::optional<Listenable> original(absl::in_place);
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(0, listener.copy);
+  EXPECT_EQ(0, listener.move);
+  absl::optional<Listenable> copy(original);
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(1, listener.copy);
+  EXPECT_EQ(0, listener.move);
+  absl::optional<Listenable> move(std::move(original));
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(1, listener.copy);
+  EXPECT_EQ(1, listener.move);
+}
+
+TEST(optionalTest, ListInit) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+  absl::optional<Listenable> listinit1(absl::in_place, {1});
+  absl::optional<Listenable> listinit2(absl::in_place, {1, 2});
+  EXPECT_EQ(2, listener.listinit);
+}
+
+TEST(optionalTest, AssignFromNullopt) {
+  absl::optional<int> opt(1);
+  opt = absl::nullopt;
+  EXPECT_FALSE(opt);
+
+  StructorListener listener;
+  Listenable::listener = &listener;
+  absl::optional<Listenable> opt1(absl::in_place);
+  opt1 = absl::nullopt;
+  EXPECT_FALSE(opt1);
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(1, listener.destruct);
+
+  EXPECT_TRUE((
+      std::is_nothrow_assignable<absl::optional<int>, absl::nullopt_t>::value));
+  EXPECT_TRUE((std::is_nothrow_assignable<absl::optional<Listenable>,
+                                          absl::nullopt_t>::value));
+}
+
+TEST(optionalTest, CopyAssignment) {
+  const absl::optional<int> empty, opt1 = 1, opt2 = 2;
+  absl::optional<int> empty_to_opt1, opt1_to_opt2, opt2_to_empty;
+
+  EXPECT_FALSE(empty_to_opt1);
+  empty_to_opt1 = empty;
+  EXPECT_FALSE(empty_to_opt1);
+  empty_to_opt1 = opt1;
+  EXPECT_TRUE(empty_to_opt1);
+  EXPECT_EQ(1, empty_to_opt1.value());
+
+  EXPECT_FALSE(opt1_to_opt2);
+  opt1_to_opt2 = opt1;
+  EXPECT_TRUE(opt1_to_opt2);
+  EXPECT_EQ(1, opt1_to_opt2.value());
+  opt1_to_opt2 = opt2;
+  EXPECT_TRUE(opt1_to_opt2);
+  EXPECT_EQ(2, opt1_to_opt2.value());
+
+  EXPECT_FALSE(opt2_to_empty);
+  opt2_to_empty = opt2;
+  EXPECT_TRUE(opt2_to_empty);
+  EXPECT_EQ(2, opt2_to_empty.value());
+  opt2_to_empty = empty;
+  EXPECT_FALSE(opt2_to_empty);
+
+  EXPECT_FALSE(absl::is_copy_assignable<absl::optional<const int>>::value);
+  EXPECT_TRUE(absl::is_copy_assignable<absl::optional<Copyable>>::value);
+  EXPECT_FALSE(absl::is_copy_assignable<absl::optional<MoveableThrow>>::value);
+  EXPECT_FALSE(
+      absl::is_copy_assignable<absl::optional<MoveableNoThrow>>::value);
+  EXPECT_FALSE(absl::is_copy_assignable<absl::optional<NonMovable>>::value);
+
+  EXPECT_TRUE(absl::is_trivially_copy_assignable<int>::value);
+  EXPECT_TRUE(absl::is_trivially_copy_assignable<volatile int>::value);
+
+  struct Trivial {
+    int i;
+  };
+  struct NonTrivial {
+    NonTrivial& operator=(const NonTrivial&) { return *this; }
+    int i;
+  };
+
+  EXPECT_TRUE(absl::is_trivially_copy_assignable<Trivial>::value);
+  EXPECT_FALSE(absl::is_copy_assignable<const Trivial>::value);
+  EXPECT_FALSE(absl::is_copy_assignable<volatile Trivial>::value);
+  EXPECT_TRUE(absl::is_copy_assignable<NonTrivial>::value);
+  EXPECT_FALSE(absl::is_trivially_copy_assignable<NonTrivial>::value);
+
+  // std::optional doesn't support volatile nontrivial types.
+#ifndef ABSL_USES_STD_OPTIONAL
+  {
+    StructorListener listener;
+    Listenable::listener = &listener;
+
+    absl::optional<volatile Listenable> empty, set(absl::in_place);
+    EXPECT_EQ(1, listener.construct0);
+    absl::optional<volatile Listenable> empty_to_empty, empty_to_set,
+        set_to_empty(absl::in_place), set_to_set(absl::in_place);
+    EXPECT_EQ(3, listener.construct0);
+    empty_to_empty = empty;  // no effect
+    empty_to_set = set;      // copy construct
+    set_to_empty = empty;    // destruct
+    set_to_set = set;        // copy assign
+    EXPECT_EQ(1, listener.volatile_copy);
+    EXPECT_EQ(0, listener.volatile_move);
+    EXPECT_EQ(1, listener.destruct);
+    EXPECT_EQ(1, listener.volatile_copy_assign);
+  }
+#endif  // ABSL_USES_STD_OPTIONAL
+}
+
+TEST(optionalTest, MoveAssignment) {
+  {
+    StructorListener listener;
+    Listenable::listener = &listener;
+
+    absl::optional<Listenable> empty1, empty2, set1(absl::in_place),
+        set2(absl::in_place);
+    EXPECT_EQ(2, listener.construct0);
+    absl::optional<Listenable> empty_to_empty, empty_to_set,
+        set_to_empty(absl::in_place), set_to_set(absl::in_place);
+    EXPECT_EQ(4, listener.construct0);
+    empty_to_empty = std::move(empty1);
+    empty_to_set = std::move(set1);
+    set_to_empty = std::move(empty2);
+    set_to_set = std::move(set2);
+    EXPECT_EQ(0, listener.copy);
+    EXPECT_EQ(1, listener.move);
+    EXPECT_EQ(1, listener.destruct);
+    EXPECT_EQ(1, listener.move_assign);
+  }
+  // std::optional doesn't support volatile nontrivial types.
+#ifndef ABSL_USES_STD_OPTIONAL
+  {
+    StructorListener listener;
+    Listenable::listener = &listener;
+
+    absl::optional<volatile Listenable> empty1, empty2, set1(absl::in_place),
+        set2(absl::in_place);
+    EXPECT_EQ(2, listener.construct0);
+    absl::optional<volatile Listenable> empty_to_empty, empty_to_set,
+        set_to_empty(absl::in_place), set_to_set(absl::in_place);
+    EXPECT_EQ(4, listener.construct0);
+    empty_to_empty = std::move(empty1);  // no effect
+    empty_to_set = std::move(set1);      // move construct
+    set_to_empty = std::move(empty2);    // destruct
+    set_to_set = std::move(set2);        // move assign
+    EXPECT_EQ(0, listener.volatile_copy);
+    EXPECT_EQ(1, listener.volatile_move);
+    EXPECT_EQ(1, listener.destruct);
+    EXPECT_EQ(1, listener.volatile_move_assign);
+  }
+#endif  // ABSL_USES_STD_OPTIONAL
+  EXPECT_FALSE(absl::is_move_assignable<absl::optional<const int>>::value);
+  EXPECT_TRUE(absl::is_move_assignable<absl::optional<Copyable>>::value);
+  EXPECT_TRUE(absl::is_move_assignable<absl::optional<MoveableThrow>>::value);
+  EXPECT_TRUE(absl::is_move_assignable<absl::optional<MoveableNoThrow>>::value);
+  EXPECT_FALSE(absl::is_move_assignable<absl::optional<NonMovable>>::value);
+
+  EXPECT_FALSE(
+      std::is_nothrow_move_assignable<absl::optional<MoveableThrow>>::value);
+  EXPECT_TRUE(
+      std::is_nothrow_move_assignable<absl::optional<MoveableNoThrow>>::value);
+}
+
+struct NoConvertToOptional {
+  // disable implicit conversion from const NoConvertToOptional&
+  // to absl::optional<NoConvertToOptional>.
+  NoConvertToOptional(const NoConvertToOptional&) = delete;
+};
+
+struct CopyConvert {
+  CopyConvert(const NoConvertToOptional&);
+  CopyConvert& operator=(const CopyConvert&) = delete;
+  CopyConvert& operator=(const NoConvertToOptional&);
+};
+
+struct CopyConvertFromOptional {
+  CopyConvertFromOptional(const NoConvertToOptional&);
+  CopyConvertFromOptional(const absl::optional<NoConvertToOptional>&);
+  CopyConvertFromOptional& operator=(const CopyConvertFromOptional&) = delete;
+  CopyConvertFromOptional& operator=(const NoConvertToOptional&);
+  CopyConvertFromOptional& operator=(
+      const absl::optional<NoConvertToOptional>&);
+};
+
+struct MoveConvert {
+  MoveConvert(NoConvertToOptional&&);
+  MoveConvert& operator=(const MoveConvert&) = delete;
+  MoveConvert& operator=(NoConvertToOptional&&);
+};
+
+struct MoveConvertFromOptional {
+  MoveConvertFromOptional(NoConvertToOptional&&);
+  MoveConvertFromOptional(absl::optional<NoConvertToOptional>&&);
+  MoveConvertFromOptional& operator=(const MoveConvertFromOptional&) = delete;
+  MoveConvertFromOptional& operator=(NoConvertToOptional&&);
+  MoveConvertFromOptional& operator=(absl::optional<NoConvertToOptional>&&);
+};
+
+// template <typename U = T> absl::optional<T>& operator=(U&& v);
+TEST(optionalTest, ValueAssignment) {
+  absl::optional<int> opt;
+  EXPECT_FALSE(opt);
+  opt = 42;
+  EXPECT_TRUE(opt);
+  EXPECT_EQ(42, opt.value());
+  opt = absl::nullopt;
+  EXPECT_FALSE(opt);
+  opt = 42;
+  EXPECT_TRUE(opt);
+  EXPECT_EQ(42, opt.value());
+  opt = 43;
+  EXPECT_TRUE(opt);
+  EXPECT_EQ(43, opt.value());
+  opt = {};  // this should clear optional
+  EXPECT_FALSE(opt);
+
+  opt = {44};
+  EXPECT_TRUE(opt);
+  EXPECT_EQ(44, opt.value());
+
+  // U = const NoConvertToOptional&
+  EXPECT_TRUE((std::is_assignable<absl::optional<CopyConvert>&,
+                                  const NoConvertToOptional&>::value));
+  // U = const absl::optional<NoConvertToOptional>&
+  EXPECT_TRUE((std::is_assignable<absl::optional<CopyConvertFromOptional>&,
+                                  const NoConvertToOptional&>::value));
+  // U = const NoConvertToOptional& triggers SFINAE because
+  // std::is_constructible_v<MoveConvert, const NoConvertToOptional&> is false
+  EXPECT_FALSE((std::is_assignable<absl::optional<MoveConvert>&,
+                                   const NoConvertToOptional&>::value));
+  // U = NoConvertToOptional
+  EXPECT_TRUE((std::is_assignable<absl::optional<MoveConvert>&,
+                                  NoConvertToOptional&&>::value));
+  // U = const NoConvertToOptional& triggers SFINAE because
+  // std::is_constructible_v<MoveConvertFromOptional, const
+  // NoConvertToOptional&> is false
+  EXPECT_FALSE((std::is_assignable<absl::optional<MoveConvertFromOptional>&,
+                                   const NoConvertToOptional&>::value));
+  // U = NoConvertToOptional
+  EXPECT_TRUE((std::is_assignable<absl::optional<MoveConvertFromOptional>&,
+                                  NoConvertToOptional&&>::value));
+  // U = const absl::optional<NoConvertToOptional>&
+  EXPECT_TRUE(
+      (std::is_assignable<absl::optional<CopyConvertFromOptional>&,
+                          const absl::optional<NoConvertToOptional>&>::value));
+  // U = absl::optional<NoConvertToOptional>
+  EXPECT_TRUE(
+      (std::is_assignable<absl::optional<MoveConvertFromOptional>&,
+                          absl::optional<NoConvertToOptional>&&>::value));
+}
+
+// template <typename U> absl::optional<T>& operator=(const absl::optional<U>&
+// rhs); template <typename U> absl::optional<T>& operator=(absl::optional<U>&&
+// rhs);
+TEST(optionalTest, ConvertingAssignment) {
+  absl::optional<int> opt_i;
+  absl::optional<char> opt_c('c');
+  opt_i = opt_c;
+  EXPECT_TRUE(opt_i);
+  EXPECT_EQ(*opt_c, *opt_i);
+  opt_i = absl::optional<char>();
+  EXPECT_FALSE(opt_i);
+  opt_i = absl::optional<char>('d');
+  EXPECT_TRUE(opt_i);
+  EXPECT_EQ('d', *opt_i);
+
+  absl::optional<std::string> opt_str;
+  absl::optional<const char*> opt_cstr("abc");
+  opt_str = opt_cstr;
+  EXPECT_TRUE(opt_str);
+  EXPECT_EQ(std::string("abc"), *opt_str);
+  opt_str = absl::optional<const char*>();
+  EXPECT_FALSE(opt_str);
+  opt_str = absl::optional<const char*>("def");
+  EXPECT_TRUE(opt_str);
+  EXPECT_EQ(std::string("def"), *opt_str);
+
+  // operator=(const absl::optional<U>&) with U = NoConvertToOptional
+  EXPECT_TRUE(
+      (std::is_assignable<absl::optional<CopyConvert>,
+                          const absl::optional<NoConvertToOptional>&>::value));
+  // operator=(const absl::optional<U>&) with U = NoConvertToOptional
+  // triggers SFINAE because
+  // std::is_constructible_v<MoveConvert, const NoConvertToOptional&> is false
+  EXPECT_FALSE(
+      (std::is_assignable<absl::optional<MoveConvert>&,
+                          const absl::optional<NoConvertToOptional>&>::value));
+  // operator=(absl::optional<U>&&) with U = NoConvertToOptional
+  EXPECT_TRUE(
+      (std::is_assignable<absl::optional<MoveConvert>&,
+                          absl::optional<NoConvertToOptional>&&>::value));
+  // operator=(const absl::optional<U>&) with U = NoConvertToOptional triggers
+  // SFINAE because std::is_constructible_v<MoveConvertFromOptional, const
+  // NoConvertToOptional&> is false. operator=(U&&) with U = const
+  // absl::optional<NoConverToOptional>& triggers SFINAE because
+  // std::is_constructible<MoveConvertFromOptional,
+  // absl::optional<NoConvertToOptional>&&> is true.
+  EXPECT_FALSE(
+      (std::is_assignable<absl::optional<MoveConvertFromOptional>&,
+                          const absl::optional<NoConvertToOptional>&>::value));
+}
+
+TEST(optionalTest, ResetAndHasValue) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+  absl::optional<Listenable> opt;
+  EXPECT_FALSE(opt);
+  EXPECT_FALSE(opt.has_value());
+  opt.emplace();
+  EXPECT_TRUE(opt);
+  EXPECT_TRUE(opt.has_value());
+  opt.reset();
+  EXPECT_FALSE(opt);
+  EXPECT_FALSE(opt.has_value());
+  EXPECT_EQ(1, listener.destruct);
+  opt.reset();
+  EXPECT_FALSE(opt);
+  EXPECT_FALSE(opt.has_value());
+
+  constexpr absl::optional<int> empty;
+  static_assert(!empty.has_value(), "");
+  constexpr absl::optional<int> nonempty(1);
+  static_assert(nonempty.has_value(), "");
+}
+
+TEST(optionalTest, Emplace) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+  absl::optional<Listenable> opt;
+  EXPECT_FALSE(opt);
+  opt.emplace(1);
+  EXPECT_TRUE(opt);
+  opt.emplace(1, 2);
+  EXPECT_EQ(1, listener.construct1);
+  EXPECT_EQ(1, listener.construct2);
+  EXPECT_EQ(1, listener.destruct);
+
+  absl::optional<std::string> o;
+  EXPECT_TRUE((std::is_same<std::string&, decltype(o.emplace("abc"))>::value));
+  std::string& ref = o.emplace("abc");
+  EXPECT_EQ(&ref, &o.value());
+}
+
+TEST(optionalTest, ListEmplace) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+  absl::optional<Listenable> opt;
+  EXPECT_FALSE(opt);
+  opt.emplace({1});
+  EXPECT_TRUE(opt);
+  opt.emplace({1, 2});
+  EXPECT_EQ(2, listener.listinit);
+  EXPECT_EQ(1, listener.destruct);
+
+  absl::optional<Listenable> o;
+  EXPECT_TRUE((std::is_same<Listenable&, decltype(o.emplace({1}))>::value));
+  Listenable& ref = o.emplace({1});
+  EXPECT_EQ(&ref, &o.value());
+}
+
+TEST(optionalTest, Swap) {
+  absl::optional<int> opt_empty, opt1 = 1, opt2 = 2;
+  EXPECT_FALSE(opt_empty);
+  EXPECT_TRUE(opt1);
+  EXPECT_EQ(1, opt1.value());
+  EXPECT_TRUE(opt2);
+  EXPECT_EQ(2, opt2.value());
+  swap(opt_empty, opt1);
+  EXPECT_FALSE(opt1);
+  EXPECT_TRUE(opt_empty);
+  EXPECT_EQ(1, opt_empty.value());
+  EXPECT_TRUE(opt2);
+  EXPECT_EQ(2, opt2.value());
+  swap(opt_empty, opt1);
+  EXPECT_FALSE(opt_empty);
+  EXPECT_TRUE(opt1);
+  EXPECT_EQ(1, opt1.value());
+  EXPECT_TRUE(opt2);
+  EXPECT_EQ(2, opt2.value());
+  swap(opt1, opt2);
+  EXPECT_FALSE(opt_empty);
+  EXPECT_TRUE(opt1);
+  EXPECT_EQ(2, opt1.value());
+  EXPECT_TRUE(opt2);
+  EXPECT_EQ(1, opt2.value());
+
+  EXPECT_TRUE(noexcept(opt1.swap(opt2)));
+  EXPECT_TRUE(noexcept(swap(opt1, opt2)));
+}
+
+template <int v>
+struct DeletedOpAddr {
+  int value = v;
+  constexpr DeletedOpAddr() = default;
+  constexpr const DeletedOpAddr<v>* operator&() const = delete;  // NOLINT
+  DeletedOpAddr<v>* operator&() = delete;                        // NOLINT
+};
+
+// The static_assert featuring a constexpr call to operator->() is commented out
+// to document the fact that the current implementation of absl::optional<T>
+// expects such usecases to be malformed and not compile.
+TEST(optionalTest, OperatorAddr) {
+  constexpr int v = -1;
+  {  // constexpr
+    constexpr absl::optional<DeletedOpAddr<v>> opt(absl::in_place_t{});
+    static_assert(opt.has_value(), "");
+    // static_assert(opt->value == v, "");
+    static_assert((*opt).value == v, "");
+  }
+  {  // non-constexpr
+    const absl::optional<DeletedOpAddr<v>> opt(absl::in_place_t{});
+    EXPECT_TRUE(opt.has_value());
+    EXPECT_TRUE(opt->value == v);
+    EXPECT_TRUE((*opt).value == v);
+  }
+}
+
+TEST(optionalTest, PointerStuff) {
+  absl::optional<std::string> opt(absl::in_place, "foo");
+  EXPECT_EQ("foo", *opt);
+  const auto& opt_const = opt;
+  EXPECT_EQ("foo", *opt_const);
+  EXPECT_EQ(opt->size(), 3);
+  EXPECT_EQ(opt_const->size(), 3);
+
+  constexpr absl::optional<ConstexprType> opt1(1);
+  static_assert((*opt1).x == ConstexprType::kCtorInt, "");
+}
+
+// gcc has a bug pre 4.9.1 where it doesn't do correct overload resolution
+// when overloads are const-qualified and *this is an raluve.
+// Skip that test to make the build green again when using the old compiler.
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59296 is fixed in 4.9.1.
+#if defined(__GNUC__) && !defined(__clang__)
+#define GCC_VERSION (__GNUC__ * 10000 \
+                     + __GNUC_MINOR__ * 100 \
+                     + __GNUC_PATCHLEVEL__)
+#if GCC_VERSION < 40901
+#define ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG
+#endif
+#endif
+
+// MSVC has a bug with "cv-qualifiers in class construction", fixed in 2017. See
+// https://docs.microsoft.com/en-us/cpp/cpp-conformance-improvements-2017#bug-fixes
+// The compiler some incorrectly ingores the cv-qualifier when generating a
+// class object via a constructor call. For example:
+//
+// class optional {
+//   constexpr T&& value() &&;
+//   constexpr const T&& value() const &&;
+// }
+//
+// using COI = const absl::optional<int>;
+// static_assert(2 == COI(2).value(), "");  // const &&
+//
+// This should invoke the "const &&" overload but since it ignores the const
+// qualifier it finds the "&&" overload the best candidate.
+#if defined(_MSC_VER) && _MSC_VER < 1910
+#define ABSL_SKIP_OVERLOAD_TEST_DUE_TO_MSVC_BUG
+#endif
+
+TEST(optionalTest, Value) {
+  using O = absl::optional<std::string>;
+  using CO = const absl::optional<std::string>;
+  using OC = absl::optional<const std::string>;
+  O lvalue(absl::in_place, "lvalue");
+  CO clvalue(absl::in_place, "clvalue");
+  OC lvalue_c(absl::in_place, "lvalue_c");
+  EXPECT_EQ("lvalue", lvalue.value());
+  EXPECT_EQ("clvalue", clvalue.value());
+  EXPECT_EQ("lvalue_c", lvalue_c.value());
+  EXPECT_EQ("xvalue", O(absl::in_place, "xvalue").value());
+  EXPECT_EQ("xvalue_c", OC(absl::in_place, "xvalue_c").value());
+#ifndef ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG
+  EXPECT_EQ("cxvalue", CO(absl::in_place, "cxvalue").value());
+#endif
+  EXPECT_EQ("&", TypeQuals(lvalue.value()));
+  EXPECT_EQ("c&", TypeQuals(clvalue.value()));
+  EXPECT_EQ("c&", TypeQuals(lvalue_c.value()));
+  EXPECT_EQ("&&", TypeQuals(O(absl::in_place, "xvalue").value()));
+#if !defined(ABSL_SKIP_OVERLOAD_TEST_DUE_TO_MSVC_BUG) && \
+    !defined(ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG)
+  EXPECT_EQ("c&&", TypeQuals(CO(absl::in_place, "cxvalue").value()));
+#endif
+  EXPECT_EQ("c&&", TypeQuals(OC(absl::in_place, "xvalue_c").value()));
+
+  // test on volatile type
+  using OV = absl::optional<volatile int>;
+  OV lvalue_v(absl::in_place, 42);
+  EXPECT_EQ(42, lvalue_v.value());
+  EXPECT_EQ(42, OV(42).value());
+  EXPECT_TRUE((std::is_same<volatile int&, decltype(lvalue_v.value())>::value));
+  EXPECT_TRUE((std::is_same<volatile int&&, decltype(OV(42).value())>::value));
+
+  // test exception throw on value()
+  absl::optional<int> empty;
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW((void)empty.value(), absl::bad_optional_access);
+#else
+  EXPECT_DEATH_IF_SUPPORTED((void)empty.value(), "Bad optional access");
+#endif
+
+  // test constexpr value()
+  constexpr absl::optional<int> o1(1);
+  static_assert(1 == o1.value(), "");  // const &
+#if !defined(_MSC_VER) && !defined(ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG)
+  using COI = const absl::optional<int>;
+  static_assert(2 == COI(2).value(), "");  // const &&
+#endif
+}
+
+TEST(optionalTest, DerefOperator) {
+  using O = absl::optional<std::string>;
+  using CO = const absl::optional<std::string>;
+  using OC = absl::optional<const std::string>;
+  O lvalue(absl::in_place, "lvalue");
+  CO clvalue(absl::in_place, "clvalue");
+  OC lvalue_c(absl::in_place, "lvalue_c");
+  EXPECT_EQ("lvalue", *lvalue);
+  EXPECT_EQ("clvalue", *clvalue);
+  EXPECT_EQ("lvalue_c", *lvalue_c);
+  EXPECT_EQ("xvalue", *O(absl::in_place, "xvalue"));
+  EXPECT_EQ("xvalue_c", *OC(absl::in_place, "xvalue_c"));
+#ifndef ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG
+  EXPECT_EQ("cxvalue", *CO(absl::in_place, "cxvalue"));
+#endif
+  EXPECT_EQ("&", TypeQuals(*lvalue));
+  EXPECT_EQ("c&", TypeQuals(*clvalue));
+  EXPECT_EQ("&&", TypeQuals(*O(absl::in_place, "xvalue")));
+#if !defined(ABSL_SKIP_OVERLOAD_TEST_DUE_TO_MSVC_BUG) && \
+    !defined(ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG)
+  EXPECT_EQ("c&&", TypeQuals(*CO(absl::in_place, "cxvalue")));
+#endif
+  EXPECT_EQ("c&&", TypeQuals(*OC(absl::in_place, "xvalue_c")));
+
+  // test on volatile type
+  using OV = absl::optional<volatile int>;
+  OV lvalue_v(absl::in_place, 42);
+  EXPECT_EQ(42, *lvalue_v);
+  EXPECT_EQ(42, *OV(42));
+  EXPECT_TRUE((std::is_same<volatile int&, decltype(*lvalue_v)>::value));
+  EXPECT_TRUE((std::is_same<volatile int&&, decltype(*OV(42))>::value));
+
+  constexpr absl::optional<int> opt1(1);
+  static_assert(*opt1 == 1, "");
+#if !defined(_MSC_VER) && !defined(ABSL_SKIP_OVERLOAD_TEST_DUE_TO_GCC_BUG)
+  using COI = const absl::optional<int>;
+  static_assert(*COI(2) == 2, "");
+#endif
+}
+
+TEST(optionalTest, ValueOr) {
+  absl::optional<double> opt_empty, opt_set = 1.2;
+  EXPECT_EQ(42.0, opt_empty.value_or(42));
+  EXPECT_EQ(1.2, opt_set.value_or(42));
+  EXPECT_EQ(42.0, absl::optional<double>().value_or(42));
+  EXPECT_EQ(1.2, absl::optional<double>(1.2).value_or(42));
+
+  constexpr absl::optional<double> copt_empty, copt_set = {1.2};
+  static_assert(42.0 == copt_empty.value_or(42), "");
+  static_assert(1.2 == copt_set.value_or(42), "");
+#ifndef ABSL_SKIP_OVERLOAD_TEST_DUE_TO_MSVC_BUG
+  using COD = const absl::optional<double>;
+  static_assert(42.0 == COD().value_or(42), "");
+  static_assert(1.2 == COD(1.2).value_or(42), "");
+#endif
+}
+
+// make_optional cannot be constexpr until C++17
+TEST(optionalTest, make_optional) {
+  auto opt_int = absl::make_optional(42);
+  EXPECT_TRUE((std::is_same<decltype(opt_int), absl::optional<int>>::value));
+  EXPECT_EQ(42, opt_int);
+
+  StructorListener listener;
+  Listenable::listener = &listener;
+
+  absl::optional<Listenable> opt0 = absl::make_optional<Listenable>();
+  EXPECT_EQ(1, listener.construct0);
+  absl::optional<Listenable> opt1 = absl::make_optional<Listenable>(1);
+  EXPECT_EQ(1, listener.construct1);
+  absl::optional<Listenable> opt2 = absl::make_optional<Listenable>(1, 2);
+  EXPECT_EQ(1, listener.construct2);
+  absl::optional<Listenable> opt3 = absl::make_optional<Listenable>({1});
+  absl::optional<Listenable> opt4 = absl::make_optional<Listenable>({1, 2});
+  EXPECT_EQ(2, listener.listinit);
+
+  // Constexpr tests on trivially copyable types
+  // optional<T> has trivial copy/move ctors when T is trivially copyable.
+  // For nontrivial types with constexpr constructors, we need copy elision in
+  // C++17 for make_optional to be constexpr.
+  {
+    constexpr absl::optional<int> c_opt = absl::make_optional(42);
+    static_assert(c_opt.value() == 42, "");
+  }
+  {
+    struct TrivialCopyable {
+      constexpr TrivialCopyable() : x(0) {}
+      constexpr explicit TrivialCopyable(int i) : x(i) {}
+      int x;
+    };
+
+    constexpr TrivialCopyable v;
+    constexpr absl::optional<TrivialCopyable> c_opt0 = absl::make_optional(v);
+    static_assert((*c_opt0).x == 0, "");
+    constexpr absl::optional<TrivialCopyable> c_opt1 =
+        absl::make_optional<TrivialCopyable>();
+    static_assert((*c_opt1).x == 0, "");
+    constexpr absl::optional<TrivialCopyable> c_opt2 =
+        absl::make_optional<TrivialCopyable>(42);
+    static_assert((*c_opt2).x == 42, "");
+  }
+}
+
+template <typename T, typename U>
+void optionalTest_Comparisons_EXPECT_LESS(T x, U y) {
+  EXPECT_FALSE(x == y);
+  EXPECT_TRUE(x != y);
+  EXPECT_TRUE(x < y);
+  EXPECT_FALSE(x > y);
+  EXPECT_TRUE(x <= y);
+  EXPECT_FALSE(x >= y);
+}
+
+template <typename T, typename U>
+void optionalTest_Comparisons_EXPECT_SAME(T x, U y) {
+  EXPECT_TRUE(x == y);
+  EXPECT_FALSE(x != y);
+  EXPECT_FALSE(x < y);
+  EXPECT_FALSE(x > y);
+  EXPECT_TRUE(x <= y);
+  EXPECT_TRUE(x >= y);
+}
+
+template <typename T, typename U>
+void optionalTest_Comparisons_EXPECT_GREATER(T x, U y) {
+  EXPECT_FALSE(x == y);
+  EXPECT_TRUE(x != y);
+  EXPECT_FALSE(x < y);
+  EXPECT_TRUE(x > y);
+  EXPECT_FALSE(x <= y);
+  EXPECT_TRUE(x >= y);
+}
+
+
+template <typename T, typename U, typename V>
+void TestComparisons() {
+  absl::optional<T> ae, a2{2}, a4{4};
+  absl::optional<U> be, b2{2}, b4{4};
+  V v3 = 3;
+
+  // LHS: absl::nullopt, ae, a2, v3, a4
+  // RHS: absl::nullopt, be, b2, v3, b4
+
+  // optionalTest_Comparisons_EXPECT_NOT_TO_WORK(absl::nullopt,absl::nullopt);
+  optionalTest_Comparisons_EXPECT_SAME(absl::nullopt, be);
+  optionalTest_Comparisons_EXPECT_LESS(absl::nullopt, b2);
+  // optionalTest_Comparisons_EXPECT_NOT_TO_WORK(absl::nullopt,v3);
+  optionalTest_Comparisons_EXPECT_LESS(absl::nullopt, b4);
+
+  optionalTest_Comparisons_EXPECT_SAME(ae, absl::nullopt);
+  optionalTest_Comparisons_EXPECT_SAME(ae, be);
+  optionalTest_Comparisons_EXPECT_LESS(ae, b2);
+  optionalTest_Comparisons_EXPECT_LESS(ae, v3);
+  optionalTest_Comparisons_EXPECT_LESS(ae, b4);
+
+  optionalTest_Comparisons_EXPECT_GREATER(a2, absl::nullopt);
+  optionalTest_Comparisons_EXPECT_GREATER(a2, be);
+  optionalTest_Comparisons_EXPECT_SAME(a2, b2);
+  optionalTest_Comparisons_EXPECT_LESS(a2, v3);
+  optionalTest_Comparisons_EXPECT_LESS(a2, b4);
+
+  // optionalTest_Comparisons_EXPECT_NOT_TO_WORK(v3,absl::nullopt);
+  optionalTest_Comparisons_EXPECT_GREATER(v3, be);
+  optionalTest_Comparisons_EXPECT_GREATER(v3, b2);
+  optionalTest_Comparisons_EXPECT_SAME(v3, v3);
+  optionalTest_Comparisons_EXPECT_LESS(v3, b4);
+
+  optionalTest_Comparisons_EXPECT_GREATER(a4, absl::nullopt);
+  optionalTest_Comparisons_EXPECT_GREATER(a4, be);
+  optionalTest_Comparisons_EXPECT_GREATER(a4, b2);
+  optionalTest_Comparisons_EXPECT_GREATER(a4, v3);
+  optionalTest_Comparisons_EXPECT_SAME(a4, b4);
+}
+
+struct Int1 {
+  Int1() = default;
+  Int1(int i) : i(i) {}  // NOLINT(runtime/explicit)
+  int i;
+};
+
+struct Int2 {
+  Int2() = default;
+  Int2(int i) : i(i) {}  // NOLINT(runtime/explicit)
+  int i;
+};
+
+// comparison between Int1 and Int2
+constexpr bool operator==(const Int1& lhs, const Int2& rhs) {
+  return lhs.i == rhs.i;
+}
+constexpr bool operator!=(const Int1& lhs, const Int2& rhs) {
+  return !(lhs == rhs);
+}
+constexpr bool operator<(const Int1& lhs, const Int2& rhs) {
+  return lhs.i < rhs.i;
+}
+constexpr bool operator<=(const Int1& lhs, const Int2& rhs) {
+  return lhs < rhs || lhs == rhs;
+}
+constexpr bool operator>(const Int1& lhs, const Int2& rhs) {
+  return !(lhs <= rhs);
+}
+constexpr bool operator>=(const Int1& lhs, const Int2& rhs) {
+  return !(lhs < rhs);
+}
+
+TEST(optionalTest, Comparisons) {
+  TestComparisons<int, int, int>();
+  TestComparisons<const int, int, int>();
+  TestComparisons<Int1, int, int>();
+  TestComparisons<int, Int2, int>();
+  TestComparisons<Int1, Int2, int>();
+
+  // compare absl::optional<std::string> with const char*
+  absl::optional<std::string> opt_str = "abc";
+  const char* cstr = "abc";
+  EXPECT_TRUE(opt_str == cstr);
+  // compare absl::optional<std::string> with absl::optional<const char*>
+  absl::optional<const char*> opt_cstr = cstr;
+  EXPECT_TRUE(opt_str == opt_cstr);
+  // compare absl::optional<std::string> with absl::optional<absl::string_view>
+  absl::optional<absl::string_view> e1;
+  absl::optional<std::string> e2;
+  EXPECT_TRUE(e1 == e2);
+}
+
+
+TEST(optionalTest, SwapRegression) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+
+  {
+    absl::optional<Listenable> a;
+    absl::optional<Listenable> b(absl::in_place);
+    a.swap(b);
+  }
+
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(1, listener.move);
+  EXPECT_EQ(2, listener.destruct);
+
+  {
+    absl::optional<Listenable> a(absl::in_place);
+    absl::optional<Listenable> b;
+    a.swap(b);
+  }
+
+  EXPECT_EQ(2, listener.construct0);
+  EXPECT_EQ(2, listener.move);
+  EXPECT_EQ(4, listener.destruct);
+}
+
+TEST(optionalTest, BigStringLeakCheck) {
+  constexpr size_t n = 1 << 16;
+
+  using OS = absl::optional<std::string>;
+
+  OS a;
+  OS b = absl::nullopt;
+  OS c = std::string(n, 'c');
+  std::string sd(n, 'd');
+  OS d = sd;
+  OS e(absl::in_place, n, 'e');
+  OS f;
+  f.emplace(n, 'f');
+
+  OS ca(a);
+  OS cb(b);
+  OS cc(c);
+  OS cd(d);
+  OS ce(e);
+
+  OS oa;
+  OS ob = absl::nullopt;
+  OS oc = std::string(n, 'c');
+  std::string sod(n, 'd');
+  OS od = sod;
+  OS oe(absl::in_place, n, 'e');
+  OS of;
+  of.emplace(n, 'f');
+
+  OS ma(std::move(oa));
+  OS mb(std::move(ob));
+  OS mc(std::move(oc));
+  OS md(std::move(od));
+  OS me(std::move(oe));
+  OS mf(std::move(of));
+
+  OS aa1;
+  OS ab1 = absl::nullopt;
+  OS ac1 = std::string(n, 'c');
+  std::string sad1(n, 'd');
+  OS ad1 = sad1;
+  OS ae1(absl::in_place, n, 'e');
+  OS af1;
+  af1.emplace(n, 'f');
+
+  OS aa2;
+  OS ab2 = absl::nullopt;
+  OS ac2 = std::string(n, 'c');
+  std::string sad2(n, 'd');
+  OS ad2 = sad2;
+  OS ae2(absl::in_place, n, 'e');
+  OS af2;
+  af2.emplace(n, 'f');
+
+  aa1 = af2;
+  ab1 = ae2;
+  ac1 = ad2;
+  ad1 = ac2;
+  ae1 = ab2;
+  af1 = aa2;
+
+  OS aa3;
+  OS ab3 = absl::nullopt;
+  OS ac3 = std::string(n, 'c');
+  std::string sad3(n, 'd');
+  OS ad3 = sad3;
+  OS ae3(absl::in_place, n, 'e');
+  OS af3;
+  af3.emplace(n, 'f');
+
+  aa3 = absl::nullopt;
+  ab3 = absl::nullopt;
+  ac3 = absl::nullopt;
+  ad3 = absl::nullopt;
+  ae3 = absl::nullopt;
+  af3 = absl::nullopt;
+
+  OS aa4;
+  OS ab4 = absl::nullopt;
+  OS ac4 = std::string(n, 'c');
+  std::string sad4(n, 'd');
+  OS ad4 = sad4;
+  OS ae4(absl::in_place, n, 'e');
+  OS af4;
+  af4.emplace(n, 'f');
+
+  aa4 = OS(absl::in_place, n, 'a');
+  ab4 = OS(absl::in_place, n, 'b');
+  ac4 = OS(absl::in_place, n, 'c');
+  ad4 = OS(absl::in_place, n, 'd');
+  ae4 = OS(absl::in_place, n, 'e');
+  af4 = OS(absl::in_place, n, 'f');
+
+  OS aa5;
+  OS ab5 = absl::nullopt;
+  OS ac5 = std::string(n, 'c');
+  std::string sad5(n, 'd');
+  OS ad5 = sad5;
+  OS ae5(absl::in_place, n, 'e');
+  OS af5;
+  af5.emplace(n, 'f');
+
+  std::string saa5(n, 'a');
+  std::string sab5(n, 'a');
+  std::string sac5(n, 'a');
+  std::string sad52(n, 'a');
+  std::string sae5(n, 'a');
+  std::string saf5(n, 'a');
+
+  aa5 = saa5;
+  ab5 = sab5;
+  ac5 = sac5;
+  ad5 = sad52;
+  ae5 = sae5;
+  af5 = saf5;
+
+  OS aa6;
+  OS ab6 = absl::nullopt;
+  OS ac6 = std::string(n, 'c');
+  std::string sad6(n, 'd');
+  OS ad6 = sad6;
+  OS ae6(absl::in_place, n, 'e');
+  OS af6;
+  af6.emplace(n, 'f');
+
+  aa6 = std::string(n, 'a');
+  ab6 = std::string(n, 'b');
+  ac6 = std::string(n, 'c');
+  ad6 = std::string(n, 'd');
+  ae6 = std::string(n, 'e');
+  af6 = std::string(n, 'f');
+
+  OS aa7;
+  OS ab7 = absl::nullopt;
+  OS ac7 = std::string(n, 'c');
+  std::string sad7(n, 'd');
+  OS ad7 = sad7;
+  OS ae7(absl::in_place, n, 'e');
+  OS af7;
+  af7.emplace(n, 'f');
+
+  aa7.emplace(n, 'A');
+  ab7.emplace(n, 'B');
+  ac7.emplace(n, 'C');
+  ad7.emplace(n, 'D');
+  ae7.emplace(n, 'E');
+  af7.emplace(n, 'F');
+}
+
+TEST(optionalTest, MoveAssignRegression) {
+  StructorListener listener;
+  Listenable::listener = &listener;
+
+  {
+    absl::optional<Listenable> a;
+    Listenable b;
+    a = std::move(b);
+  }
+
+  EXPECT_EQ(1, listener.construct0);
+  EXPECT_EQ(1, listener.move);
+  EXPECT_EQ(2, listener.destruct);
+}
+
+TEST(optionalTest, ValueType) {
+  EXPECT_TRUE((std::is_same<absl::optional<int>::value_type, int>::value));
+  EXPECT_TRUE((std::is_same<absl::optional<std::string>::value_type,
+                            std::string>::value));
+  EXPECT_FALSE(
+      (std::is_same<absl::optional<int>::value_type, absl::nullopt_t>::value));
+}
+
+template <typename T>
+struct is_hash_enabled_for {
+  template <typename U, typename = decltype(std::hash<U>()(std::declval<U>()))>
+  static std::true_type test(int);
+
+  template <typename U>
+  static std::false_type test(...);
+
+  static constexpr bool value = decltype(test<T>(0))::value;
+};
+
+TEST(optionalTest, Hash) {
+  std::hash<absl::optional<int>> hash;
+  std::set<size_t> hashcodes;
+  hashcodes.insert(hash(absl::nullopt));
+  for (int i = 0; i < 100; ++i) {
+    hashcodes.insert(hash(i));
+  }
+  EXPECT_GT(hashcodes.size(), 90);
+
+  static_assert(is_hash_enabled_for<absl::optional<int>>::value, "");
+  static_assert(is_hash_enabled_for<absl::optional<Hashable>>::value, "");
+  static_assert(
+      absl::type_traits_internal::IsHashable<absl::optional<int>>::value, "");
+  static_assert(
+      absl::type_traits_internal::IsHashable<absl::optional<Hashable>>::value,
+      "");
+  absl::type_traits_internal::AssertHashEnabled<absl::optional<int>>();
+  absl::type_traits_internal::AssertHashEnabled<absl::optional<Hashable>>();
+
+#if ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_
+  static_assert(!is_hash_enabled_for<absl::optional<NonHashable>>::value, "");
+  static_assert(!absl::type_traits_internal::IsHashable<
+                    absl::optional<NonHashable>>::value,
+                "");
+#endif
+
+  // libstdc++ std::optional is missing remove_const_t, i.e. it's using
+  // std::hash<T> rather than std::hash<std::remove_const_t<T>>.
+  // Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82262
+#ifndef __GLIBCXX__
+  static_assert(is_hash_enabled_for<absl::optional<const int>>::value, "");
+  static_assert(is_hash_enabled_for<absl::optional<const Hashable>>::value, "");
+  std::hash<absl::optional<const int>> c_hash;
+  for (int i = 0; i < 100; ++i) {
+    EXPECT_EQ(hash(i), c_hash(i));
+  }
+#endif
+}
+
+struct MoveMeNoThrow {
+  MoveMeNoThrow() : x(0) {}
+  [[noreturn]] MoveMeNoThrow(const MoveMeNoThrow& other) : x(other.x) {
+    ABSL_RAW_LOG(FATAL, "Should not be called.");
+    abort();
+  }
+  MoveMeNoThrow(MoveMeNoThrow&& other) noexcept : x(other.x) {}
+  int x;
+};
+
+struct MoveMeThrow {
+  MoveMeThrow() : x(0) {}
+  MoveMeThrow(const MoveMeThrow& other) : x(other.x) {}
+  MoveMeThrow(MoveMeThrow&& other) : x(other.x) {}
+  int x;
+};
+
+TEST(optionalTest, NoExcept) {
+  static_assert(
+      std::is_nothrow_move_constructible<absl::optional<MoveMeNoThrow>>::value,
+      "");
+#ifndef ABSL_USES_STD_OPTIONAL
+  static_assert(absl::default_allocator_is_nothrow::value ==
+                    std::is_nothrow_move_constructible<
+                        absl::optional<MoveMeThrow>>::value,
+                "");
+#endif
+  std::vector<absl::optional<MoveMeNoThrow>> v;
+  for (int i = 0; i < 10; ++i) v.emplace_back();
+}
+
+struct AnyLike {
+  AnyLike(AnyLike&&) = default;
+  AnyLike(const AnyLike&) = default;
+
+  template <typename ValueType,
+            typename T = typename std::decay<ValueType>::type,
+            typename std::enable_if<
+                !absl::disjunction<
+                    std::is_same<AnyLike, T>,
+                    absl::negation<std::is_copy_constructible<T>>>::value,
+                int>::type = 0>
+  AnyLike(ValueType&&) {}  // NOLINT(runtime/explicit)
+
+  AnyLike& operator=(AnyLike&&) = default;
+  AnyLike& operator=(const AnyLike&) = default;
+
+  template <typename ValueType,
+            typename T = typename std::decay<ValueType>::type>
+  typename std::enable_if<
+      absl::conjunction<absl::negation<std::is_same<AnyLike, T>>,
+                        std::is_copy_constructible<T>>::value,
+      AnyLike&>::type
+  operator=(ValueType&& /* rhs */) {
+    return *this;
+  }
+};
+
+TEST(optionalTest, ConstructionConstraints) {
+  EXPECT_TRUE((std::is_constructible<AnyLike, absl::optional<AnyLike>>::value));
+
+  EXPECT_TRUE(
+      (std::is_constructible<AnyLike, const absl::optional<AnyLike>&>::value));
+
+  EXPECT_TRUE((std::is_constructible<absl::optional<AnyLike>, AnyLike>::value));
+  EXPECT_TRUE(
+      (std::is_constructible<absl::optional<AnyLike>, const AnyLike&>::value));
+
+  EXPECT_TRUE((std::is_convertible<absl::optional<AnyLike>, AnyLike>::value));
+
+  EXPECT_TRUE(
+      (std::is_convertible<const absl::optional<AnyLike>&, AnyLike>::value));
+
+  EXPECT_TRUE((std::is_convertible<AnyLike, absl::optional<AnyLike>>::value));
+  EXPECT_TRUE(
+      (std::is_convertible<const AnyLike&, absl::optional<AnyLike>>::value));
+
+  EXPECT_TRUE(std::is_move_constructible<absl::optional<AnyLike>>::value);
+  EXPECT_TRUE(std::is_copy_constructible<absl::optional<AnyLike>>::value);
+}
+
+TEST(optionalTest, AssignmentConstraints) {
+  EXPECT_TRUE((std::is_assignable<AnyLike&, absl::optional<AnyLike>>::value));
+  EXPECT_TRUE(
+      (std::is_assignable<AnyLike&, const absl::optional<AnyLike>&>::value));
+  EXPECT_TRUE((std::is_assignable<absl::optional<AnyLike>&, AnyLike>::value));
+  EXPECT_TRUE(
+      (std::is_assignable<absl::optional<AnyLike>&, const AnyLike&>::value));
+  EXPECT_TRUE(std::is_move_assignable<absl::optional<AnyLike>>::value);
+  EXPECT_TRUE(absl::is_copy_assignable<absl::optional<AnyLike>>::value);
+}
+
+#if !defined(__EMSCRIPTEN__)
+struct NestedClassBug {
+  struct Inner {
+    bool dummy = false;
+  };
+  absl::optional<Inner> value;
+};
+
+TEST(optionalTest, InPlaceTSFINAEBug) {
+  NestedClassBug b;
+  ((void)b);
+  using Inner = NestedClassBug::Inner;
+
+  EXPECT_TRUE((std::is_default_constructible<Inner>::value));
+  EXPECT_TRUE((std::is_constructible<Inner>::value));
+  EXPECT_TRUE(
+      (std::is_constructible<absl::optional<Inner>, absl::in_place_t>::value));
+
+  absl::optional<Inner> o(absl::in_place);
+  EXPECT_TRUE(o.has_value());
+  o.emplace();
+  EXPECT_TRUE(o.has_value());
+}
+#endif  // !defined(__EMSCRIPTEN__)
+
+}  // namespace
+
+#endif  // #if !defined(ABSL_USES_STD_OPTIONAL)
diff --git a/third_party/abseil_cpp/absl/types/span.h b/third_party/abseil_cpp/absl/types/span.h
new file mode 100644
index 0000000000..734db695e3
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/span.h
@@ -0,0 +1,727 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// span.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines a `Span<T>` type for holding a view of an existing
+// array of data. The `Span` object, much like the `absl::string_view` object,
+// does not own such data itself. A span provides a lightweight way to pass
+// around view of such data.
+//
+// Additionally, this header file defines `MakeSpan()` and `MakeConstSpan()`
+// factory functions, for clearly creating spans of type `Span<T>` or read-only
+// `Span<const T>` when such types may be difficult to identify due to issues
+// with implicit conversion.
+//
+// The C++ standards committee currently has a proposal for a `std::span` type,
+// (http://wg21.link/p0122), which is not yet part of the standard (though may
+// become part of C++20). As of August 2017, the differences between
+// `absl::Span` and this proposal are:
+//    * `absl::Span` uses `size_t` for `size_type`
+//    * `absl::Span` has no `operator()`
+//    * `absl::Span` has no constructors for `std::unique_ptr` or
+//      `std::shared_ptr`
+//    * `absl::Span` has the factory functions `MakeSpan()` and
+//      `MakeConstSpan()`
+//    * `absl::Span` has `front()` and `back()` methods
+//    * bounds-checked access to `absl::Span` is accomplished with `at()`
+//    * `absl::Span` has compiler-provided move and copy constructors and
+//      assignment. This is due to them being specified as `constexpr`, but that
+//      implies const in C++11.
+//    * `absl::Span` has no `element_type` or `index_type` typedefs
+//    * A read-only `absl::Span<const T>` can be implicitly constructed from an
+//      initializer list.
+//    * `absl::Span` has no `bytes()`, `size_bytes()`, `as_bytes()`, or
+//      `as_mutable_bytes()` methods
+//    * `absl::Span` has no static extent template parameter, nor constructors
+//      which exist only because of the static extent parameter.
+//    * `absl::Span` has an explicit mutable-reference constructor
+//
+// For more information, see the class comments below.
+#ifndef ABSL_TYPES_SPAN_H_
+#define ABSL_TYPES_SPAN_H_
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <initializer_list>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"    // TODO(strel): remove this include
+#include "absl/meta/type_traits.h"
+#include "absl/types/internal/span.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+//------------------------------------------------------------------------------
+// Span
+//------------------------------------------------------------------------------
+//
+// A `Span` is an "array view" type for holding a view of a contiguous data
+// array; the `Span` object does not and cannot own such data itself. A span
+// provides an easy way to provide overloads for anything operating on
+// contiguous sequences without needing to manage pointers and array lengths
+// manually.
+
+// A span is conceptually a pointer (ptr) and a length (size) into an already
+// existing array of contiguous memory; the array it represents references the
+// elements "ptr[0] .. ptr[size-1]". Passing a properly-constructed `Span`
+// instead of raw pointers avoids many issues related to index out of bounds
+// errors.
+//
+// Spans may also be constructed from containers holding contiguous sequences.
+// Such containers must supply `data()` and `size() const` methods (e.g
+// `std::vector<T>`, `absl::InlinedVector<T, N>`). All implicit conversions to
+// `absl::Span` from such containers will create spans of type `const T`;
+// spans which can mutate their values (of type `T`) must use explicit
+// constructors.
+//
+// A `Span<T>` is somewhat analogous to an `absl::string_view`, but for an array
+// of elements of type `T`. A user of `Span` must ensure that the data being
+// pointed to outlives the `Span` itself.
+//
+// You can construct a `Span<T>` in several ways:
+//
+//   * Explicitly from a reference to a container type
+//   * Explicitly from a pointer and size
+//   * Implicitly from a container type (but only for spans of type `const T`)
+//   * Using the `MakeSpan()` or `MakeConstSpan()` factory functions.
+//
+// Examples:
+//
+//   // Construct a Span explicitly from a container:
+//   std::vector<int> v = {1, 2, 3, 4, 5};
+//   auto span = absl::Span<const int>(v);
+//
+//   // Construct a Span explicitly from a C-style array:
+//   int a[5] =  {1, 2, 3, 4, 5};
+//   auto span = absl::Span<const int>(a);
+//
+//   // Construct a Span implicitly from a container
+//   void MyRoutine(absl::Span<const int> a) {
+//     ...
+//   }
+//   std::vector v = {1,2,3,4,5};
+//   MyRoutine(v)                     // convert to Span<const T>
+//
+// Note that `Span` objects, in addition to requiring that the memory they
+// point to remains alive, must also ensure that such memory does not get
+// reallocated. Therefore, to avoid undefined behavior, containers with
+// associated span views should not invoke operations that may reallocate memory
+// (such as resizing) or invalidate iterators into the container.
+//
+// One common use for a `Span` is when passing arguments to a routine that can
+// accept a variety of array types (e.g. a `std::vector`, `absl::InlinedVector`,
+// a C-style array, etc.). Instead of creating overloads for each case, you
+// can simply specify a `Span` as the argument to such a routine.
+//
+// Example:
+//
+//   void MyRoutine(absl::Span<const int> a) {
+//     ...
+//   }
+//
+//   std::vector v = {1,2,3,4,5};
+//   MyRoutine(v);
+//
+//   absl::InlinedVector<int, 4> my_inline_vector;
+//   MyRoutine(my_inline_vector);
+//
+//   // Explicit constructor from pointer,size
+//   int* my_array = new int[10];
+//   MyRoutine(absl::Span<const int>(my_array, 10));
+template <typename T>
+class Span {
+ private:
+  // Used to determine whether a Span can be constructed from a container of
+  // type C.
+  template <typename C>
+  using EnableIfConvertibleFrom =
+      typename std::enable_if<span_internal::HasData<T, C>::value &&
+                              span_internal::HasSize<C>::value>::type;
+
+  // Used to SFINAE-enable a function when the slice elements are const.
+  template <typename U>
+  using EnableIfConstView =
+      typename std::enable_if<std::is_const<T>::value, U>::type;
+
+  // Used to SFINAE-enable a function when the slice elements are mutable.
+  template <typename U>
+  using EnableIfMutableView =
+      typename std::enable_if<!std::is_const<T>::value, U>::type;
+
+ public:
+  using value_type = absl::remove_cv_t<T>;
+  using pointer = T*;
+  using const_pointer = const T*;
+  using reference = T&;
+  using const_reference = const T&;
+  using iterator = pointer;
+  using const_iterator = const_pointer;
+  using reverse_iterator = std::reverse_iterator<iterator>;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+  using size_type = size_t;
+  using difference_type = ptrdiff_t;
+
+  static const size_type npos = ~(size_type(0));
+
+  constexpr Span() noexcept : Span(nullptr, 0) {}
+  constexpr Span(pointer array, size_type length) noexcept
+      : ptr_(array), len_(length) {}
+
+  // Implicit conversion constructors
+  template <size_t N>
+  constexpr Span(T (&a)[N]) noexcept  // NOLINT(runtime/explicit)
+      : Span(a, N) {}
+
+  // Explicit reference constructor for a mutable `Span<T>` type. Can be
+  // replaced with MakeSpan() to infer the type parameter.
+  template <typename V, typename = EnableIfConvertibleFrom<V>,
+            typename = EnableIfMutableView<V>>
+  explicit Span(V& v) noexcept  // NOLINT(runtime/references)
+      : Span(span_internal::GetData(v), v.size()) {}
+
+  // Implicit reference constructor for a read-only `Span<const T>` type
+  template <typename V, typename = EnableIfConvertibleFrom<V>,
+            typename = EnableIfConstView<V>>
+  constexpr Span(const V& v) noexcept  // NOLINT(runtime/explicit)
+      : Span(span_internal::GetData(v), v.size()) {}
+
+  // Implicit constructor from an initializer list, making it possible to pass a
+  // brace-enclosed initializer list to a function expecting a `Span`. Such
+  // spans constructed from an initializer list must be of type `Span<const T>`.
+  //
+  //   void Process(absl::Span<const int> x);
+  //   Process({1, 2, 3});
+  //
+  // Note that as always the array referenced by the span must outlive the span.
+  // Since an initializer list constructor acts as if it is fed a temporary
+  // array (cf. C++ standard [dcl.init.list]/5), it's safe to use this
+  // constructor only when the `std::initializer_list` itself outlives the span.
+  // In order to meet this requirement it's sufficient to ensure that neither
+  // the span nor a copy of it is used outside of the expression in which it's
+  // created:
+  //
+  //   // Assume that this function uses the array directly, not retaining any
+  //   // copy of the span or pointer to any of its elements.
+  //   void Process(absl::Span<const int> ints);
+  //
+  //   // Okay: the std::initializer_list<int> will reference a temporary array
+  //   // that isn't destroyed until after the call to Process returns.
+  //   Process({ 17, 19 });
+  //
+  //   // Not okay: the storage used by the std::initializer_list<int> is not
+  //   // allowed to be referenced after the first line.
+  //   absl::Span<const int> ints = { 17, 19 };
+  //   Process(ints);
+  //
+  //   // Not okay for the same reason as above: even when the elements of the
+  //   // initializer list expression are not temporaries the underlying array
+  //   // is, so the initializer list must still outlive the span.
+  //   const int foo = 17;
+  //   absl::Span<const int> ints = { foo };
+  //   Process(ints);
+  //
+  template <typename LazyT = T,
+            typename = EnableIfConstView<LazyT>>
+  Span(
+      std::initializer_list<value_type> v) noexcept  // NOLINT(runtime/explicit)
+      : Span(v.begin(), v.size()) {}
+
+  // Accessors
+
+  // Span::data()
+  //
+  // Returns a pointer to the span's underlying array of data (which is held
+  // outside the span).
+  constexpr pointer data() const noexcept { return ptr_; }
+
+  // Span::size()
+  //
+  // Returns the size of this span.
+  constexpr size_type size() const noexcept { return len_; }
+
+  // Span::length()
+  //
+  // Returns the length (size) of this span.
+  constexpr size_type length() const noexcept { return size(); }
+
+  // Span::empty()
+  //
+  // Returns a boolean indicating whether or not this span is considered empty.
+  constexpr bool empty() const noexcept { return size() == 0; }
+
+  // Span::operator[]
+  //
+  // Returns a reference to the i'th element of this span.
+  constexpr reference operator[](size_type i) const noexcept {
+    // MSVC 2015 accepts this as constexpr, but not ptr_[i]
+    return ABSL_HARDENING_ASSERT(i < size()), *(data() + i);
+  }
+
+  // Span::at()
+  //
+  // Returns a reference to the i'th element of this span.
+  constexpr reference at(size_type i) const {
+    return ABSL_PREDICT_TRUE(i < size())  //
+               ? *(data() + i)
+               : (base_internal::ThrowStdOutOfRange(
+                      "Span::at failed bounds check"),
+                  *(data() + i));
+  }
+
+  // Span::front()
+  //
+  // Returns a reference to the first element of this span. The span must not
+  // be empty.
+  constexpr reference front() const noexcept {
+    return ABSL_HARDENING_ASSERT(size() > 0), *data();
+  }
+
+  // Span::back()
+  //
+  // Returns a reference to the last element of this span. The span must not
+  // be empty.
+  constexpr reference back() const noexcept {
+    return ABSL_HARDENING_ASSERT(size() > 0), *(data() + size() - 1);
+  }
+
+  // Span::begin()
+  //
+  // Returns an iterator pointing to the first element of this span, or `end()`
+  // if the span is empty.
+  constexpr iterator begin() const noexcept { return data(); }
+
+  // Span::cbegin()
+  //
+  // Returns a const iterator pointing to the first element of this span, or
+  // `end()` if the span is empty.
+  constexpr const_iterator cbegin() const noexcept { return begin(); }
+
+  // Span::end()
+  //
+  // Returns an iterator pointing just beyond the last element at the
+  // end of this span. This iterator acts as a placeholder; attempting to
+  // access it results in undefined behavior.
+  constexpr iterator end() const noexcept { return data() + size(); }
+
+  // Span::cend()
+  //
+  // Returns a const iterator pointing just beyond the last element at the
+  // end of this span. This iterator acts as a placeholder; attempting to
+  // access it results in undefined behavior.
+  constexpr const_iterator cend() const noexcept { return end(); }
+
+  // Span::rbegin()
+  //
+  // Returns a reverse iterator pointing to the last element at the end of this
+  // span, or `rend()` if the span is empty.
+  constexpr reverse_iterator rbegin() const noexcept {
+    return reverse_iterator(end());
+  }
+
+  // Span::crbegin()
+  //
+  // Returns a const reverse iterator pointing to the last element at the end of
+  // this span, or `crend()` if the span is empty.
+  constexpr const_reverse_iterator crbegin() const noexcept { return rbegin(); }
+
+  // Span::rend()
+  //
+  // Returns a reverse iterator pointing just before the first element
+  // at the beginning of this span. This pointer acts as a placeholder;
+  // attempting to access its element results in undefined behavior.
+  constexpr reverse_iterator rend() const noexcept {
+    return reverse_iterator(begin());
+  }
+
+  // Span::crend()
+  //
+  // Returns a reverse const iterator pointing just before the first element
+  // at the beginning of this span. This pointer acts as a placeholder;
+  // attempting to access its element results in undefined behavior.
+  constexpr const_reverse_iterator crend() const noexcept { return rend(); }
+
+  // Span mutations
+
+  // Span::remove_prefix()
+  //
+  // Removes the first `n` elements from the span.
+  void remove_prefix(size_type n) noexcept {
+    ABSL_HARDENING_ASSERT(size() >= n);
+    ptr_ += n;
+    len_ -= n;
+  }
+
+  // Span::remove_suffix()
+  //
+  // Removes the last `n` elements from the span.
+  void remove_suffix(size_type n) noexcept {
+    ABSL_HARDENING_ASSERT(size() >= n);
+    len_ -= n;
+  }
+
+  // Span::subspan()
+  //
+  // Returns a `Span` starting at element `pos` and of length `len`. Both `pos`
+  // and `len` are of type `size_type` and thus non-negative. Parameter `pos`
+  // must be <= size(). Any `len` value that points past the end of the span
+  // will be trimmed to at most size() - `pos`. A default `len` value of `npos`
+  // ensures the returned subspan continues until the end of the span.
+  //
+  // Examples:
+  //
+  //   std::vector<int> vec = {10, 11, 12, 13};
+  //   absl::MakeSpan(vec).subspan(1, 2);  // {11, 12}
+  //   absl::MakeSpan(vec).subspan(2, 8);  // {12, 13}
+  //   absl::MakeSpan(vec).subspan(1);     // {11, 12, 13}
+  //   absl::MakeSpan(vec).subspan(4);     // {}
+  //   absl::MakeSpan(vec).subspan(5);     // throws std::out_of_range
+  constexpr Span subspan(size_type pos = 0, size_type len = npos) const {
+    return (pos <= size())
+               ? Span(data() + pos, span_internal::Min(size() - pos, len))
+               : (base_internal::ThrowStdOutOfRange("pos > size()"), Span());
+  }
+
+  // Span::first()
+  //
+  // Returns a `Span` containing first `len` elements. Parameter `len` is of
+  // type `size_type` and thus non-negative. `len` value must be <= size().
+  //
+  // Examples:
+  //
+  //   std::vector<int> vec = {10, 11, 12, 13};
+  //   absl::MakeSpan(vec).first(1);  // {10}
+  //   absl::MakeSpan(vec).first(3);  // {10, 11, 12}
+  //   absl::MakeSpan(vec).first(5);  // throws std::out_of_range
+  constexpr Span first(size_type len) const {
+    return (len <= size())
+               ? Span(data(), len)
+               : (base_internal::ThrowStdOutOfRange("len > size()"), Span());
+  }
+
+  // Span::last()
+  //
+  // Returns a `Span` containing last `len` elements. Parameter `len` is of
+  // type `size_type` and thus non-negative. `len` value must be <= size().
+  //
+  // Examples:
+  //
+  //   std::vector<int> vec = {10, 11, 12, 13};
+  //   absl::MakeSpan(vec).last(1);  // {13}
+  //   absl::MakeSpan(vec).last(3);  // {11, 12, 13}
+  //   absl::MakeSpan(vec).last(5);  // throws std::out_of_range
+  constexpr Span last(size_type len) const {
+    return (len <= size())
+               ? Span(size() - len + data(), len)
+               : (base_internal::ThrowStdOutOfRange("len > size()"), Span());
+  }
+
+  // Support for absl::Hash.
+  template <typename H>
+  friend H AbslHashValue(H h, Span v) {
+    return H::combine(H::combine_contiguous(std::move(h), v.data(), v.size()),
+                      v.size());
+  }
+
+ private:
+  pointer ptr_;
+  size_type len_;
+};
+
+template <typename T>
+const typename Span<T>::size_type Span<T>::npos;
+
+// Span relationals
+
+// Equality is compared element-by-element, while ordering is lexicographical.
+// We provide three overloads for each operator to cover any combination on the
+// left or right hand side of mutable Span<T>, read-only Span<const T>, and
+// convertible-to-read-only Span<T>.
+// TODO(zhangxy): Due to MSVC overload resolution bug with partial ordering
+// template functions, 5 overloads per operator is needed as a workaround. We
+// should update them to 3 overloads per operator using non-deduced context like
+// string_view, i.e.
+// - (Span<T>, Span<T>)
+// - (Span<T>, non_deduced<Span<const T>>)
+// - (non_deduced<Span<const T>>, Span<T>)
+
+// operator==
+template <typename T>
+bool operator==(Span<T> a, Span<T> b) {
+  return span_internal::EqualImpl<Span, const T>(a, b);
+}
+template <typename T>
+bool operator==(Span<const T> a, Span<T> b) {
+  return span_internal::EqualImpl<Span, const T>(a, b);
+}
+template <typename T>
+bool operator==(Span<T> a, Span<const T> b) {
+  return span_internal::EqualImpl<Span, const T>(a, b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator==(const U& a, Span<T> b) {
+  return span_internal::EqualImpl<Span, const T>(a, b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator==(Span<T> a, const U& b) {
+  return span_internal::EqualImpl<Span, const T>(a, b);
+}
+
+// operator!=
+template <typename T>
+bool operator!=(Span<T> a, Span<T> b) {
+  return !(a == b);
+}
+template <typename T>
+bool operator!=(Span<const T> a, Span<T> b) {
+  return !(a == b);
+}
+template <typename T>
+bool operator!=(Span<T> a, Span<const T> b) {
+  return !(a == b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator!=(const U& a, Span<T> b) {
+  return !(a == b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator!=(Span<T> a, const U& b) {
+  return !(a == b);
+}
+
+// operator<
+template <typename T>
+bool operator<(Span<T> a, Span<T> b) {
+  return span_internal::LessThanImpl<Span, const T>(a, b);
+}
+template <typename T>
+bool operator<(Span<const T> a, Span<T> b) {
+  return span_internal::LessThanImpl<Span, const T>(a, b);
+}
+template <typename T>
+bool operator<(Span<T> a, Span<const T> b) {
+  return span_internal::LessThanImpl<Span, const T>(a, b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator<(const U& a, Span<T> b) {
+  return span_internal::LessThanImpl<Span, const T>(a, b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator<(Span<T> a, const U& b) {
+  return span_internal::LessThanImpl<Span, const T>(a, b);
+}
+
+// operator>
+template <typename T>
+bool operator>(Span<T> a, Span<T> b) {
+  return b < a;
+}
+template <typename T>
+bool operator>(Span<const T> a, Span<T> b) {
+  return b < a;
+}
+template <typename T>
+bool operator>(Span<T> a, Span<const T> b) {
+  return b < a;
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator>(const U& a, Span<T> b) {
+  return b < a;
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator>(Span<T> a, const U& b) {
+  return b < a;
+}
+
+// operator<=
+template <typename T>
+bool operator<=(Span<T> a, Span<T> b) {
+  return !(b < a);
+}
+template <typename T>
+bool operator<=(Span<const T> a, Span<T> b) {
+  return !(b < a);
+}
+template <typename T>
+bool operator<=(Span<T> a, Span<const T> b) {
+  return !(b < a);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator<=(const U& a, Span<T> b) {
+  return !(b < a);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator<=(Span<T> a, const U& b) {
+  return !(b < a);
+}
+
+// operator>=
+template <typename T>
+bool operator>=(Span<T> a, Span<T> b) {
+  return !(a < b);
+}
+template <typename T>
+bool operator>=(Span<const T> a, Span<T> b) {
+  return !(a < b);
+}
+template <typename T>
+bool operator>=(Span<T> a, Span<const T> b) {
+  return !(a < b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator>=(const U& a, Span<T> b) {
+  return !(a < b);
+}
+template <
+    typename T, typename U,
+    typename = span_internal::EnableIfConvertibleTo<U, absl::Span<const T>>>
+bool operator>=(Span<T> a, const U& b) {
+  return !(a < b);
+}
+
+// MakeSpan()
+//
+// Constructs a mutable `Span<T>`, deducing `T` automatically from either a
+// container or pointer+size.
+//
+// Because a read-only `Span<const T>` is implicitly constructed from container
+// types regardless of whether the container itself is a const container,
+// constructing mutable spans of type `Span<T>` from containers requires
+// explicit constructors. The container-accepting version of `MakeSpan()`
+// deduces the type of `T` by the constness of the pointer received from the
+// container's `data()` member. Similarly, the pointer-accepting version returns
+// a `Span<const T>` if `T` is `const`, and a `Span<T>` otherwise.
+//
+// Examples:
+//
+//   void MyRoutine(absl::Span<MyComplicatedType> a) {
+//     ...
+//   };
+//   // my_vector is a container of non-const types
+//   std::vector<MyComplicatedType> my_vector;
+//
+//   // Constructing a Span implicitly attempts to create a Span of type
+//   // `Span<const T>`
+//   MyRoutine(my_vector);                // error, type mismatch
+//
+//   // Explicitly constructing the Span is verbose
+//   MyRoutine(absl::Span<MyComplicatedType>(my_vector));
+//
+//   // Use MakeSpan() to make an absl::Span<T>
+//   MyRoutine(absl::MakeSpan(my_vector));
+//
+//   // Construct a span from an array ptr+size
+//   absl::Span<T> my_span() {
+//     return absl::MakeSpan(&array[0], num_elements_);
+//   }
+//
+template <int&... ExplicitArgumentBarrier, typename T>
+constexpr Span<T> MakeSpan(T* ptr, size_t size) noexcept {
+  return Span<T>(ptr, size);
+}
+
+template <int&... ExplicitArgumentBarrier, typename T>
+Span<T> MakeSpan(T* begin, T* end) noexcept {
+  return ABSL_HARDENING_ASSERT(begin <= end), Span<T>(begin, end - begin);
+}
+
+template <int&... ExplicitArgumentBarrier, typename C>
+constexpr auto MakeSpan(C& c) noexcept  // NOLINT(runtime/references)
+    -> decltype(absl::MakeSpan(span_internal::GetData(c), c.size())) {
+  return MakeSpan(span_internal::GetData(c), c.size());
+}
+
+template <int&... ExplicitArgumentBarrier, typename T, size_t N>
+constexpr Span<T> MakeSpan(T (&array)[N]) noexcept {
+  return Span<T>(array, N);
+}
+
+// MakeConstSpan()
+//
+// Constructs a `Span<const T>` as with `MakeSpan`, deducing `T` automatically,
+// but always returning a `Span<const T>`.
+//
+// Examples:
+//
+//   void ProcessInts(absl::Span<const int> some_ints);
+//
+//   // Call with a pointer and size.
+//   int array[3] = { 0, 0, 0 };
+//   ProcessInts(absl::MakeConstSpan(&array[0], 3));
+//
+//   // Call with a [begin, end) pair.
+//   ProcessInts(absl::MakeConstSpan(&array[0], &array[3]));
+//
+//   // Call directly with an array.
+//   ProcessInts(absl::MakeConstSpan(array));
+//
+//   // Call with a contiguous container.
+//   std::vector<int> some_ints = ...;
+//   ProcessInts(absl::MakeConstSpan(some_ints));
+//   ProcessInts(absl::MakeConstSpan(std::vector<int>{ 0, 0, 0 }));
+//
+template <int&... ExplicitArgumentBarrier, typename T>
+constexpr Span<const T> MakeConstSpan(T* ptr, size_t size) noexcept {
+  return Span<const T>(ptr, size);
+}
+
+template <int&... ExplicitArgumentBarrier, typename T>
+Span<const T> MakeConstSpan(T* begin, T* end) noexcept {
+  return ABSL_HARDENING_ASSERT(begin <= end), Span<const T>(begin, end - begin);
+}
+
+template <int&... ExplicitArgumentBarrier, typename C>
+constexpr auto MakeConstSpan(const C& c) noexcept -> decltype(MakeSpan(c)) {
+  return MakeSpan(c);
+}
+
+template <int&... ExplicitArgumentBarrier, typename T, size_t N>
+constexpr Span<const T> MakeConstSpan(const T (&array)[N]) noexcept {
+  return Span<const T>(array, N);
+}
+ABSL_NAMESPACE_END
+}  // namespace absl
+#endif  // ABSL_TYPES_SPAN_H_
diff --git a/third_party/abseil_cpp/absl/types/span_test.cc b/third_party/abseil_cpp/absl/types/span_test.cc
new file mode 100644
index 0000000000..2584339bd3
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/span_test.cc
@@ -0,0 +1,846 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/span.h"
+
+#include <array>
+#include <initializer_list>
+#include <numeric>
+#include <stdexcept>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/exception_testing.h"
+#include "absl/base/options.h"
+#include "absl/container/fixed_array.h"
+#include "absl/container/inlined_vector.h"
+#include "absl/hash/hash_testing.h"
+#include "absl/strings/str_cat.h"
+
+namespace {
+
+MATCHER_P(DataIs, data,
+          absl::StrCat("data() ", negation ? "isn't " : "is ",
+                       testing::PrintToString(data))) {
+  return arg.data() == data;
+}
+
+template <typename T>
+auto SpanIs(T data, size_t size)
+    -> decltype(testing::AllOf(DataIs(data), testing::SizeIs(size))) {
+  return testing::AllOf(DataIs(data), testing::SizeIs(size));
+}
+
+template <typename Container>
+auto SpanIs(const Container& c) -> decltype(SpanIs(c.data(), c.size())) {
+  return SpanIs(c.data(), c.size());
+}
+
+std::vector<int> MakeRamp(int len, int offset = 0) {
+  std::vector<int> v(len);
+  std::iota(v.begin(), v.end(), offset);
+  return v;
+}
+
+TEST(IntSpan, EmptyCtors) {
+  absl::Span<int> s;
+  EXPECT_THAT(s, SpanIs(nullptr, 0));
+}
+
+TEST(IntSpan, PtrLenCtor) {
+  int a[] = {1, 2, 3};
+  absl::Span<int> s(&a[0], 2);
+  EXPECT_THAT(s, SpanIs(a, 2));
+}
+
+TEST(IntSpan, ArrayCtor) {
+  int a[] = {1, 2, 3};
+  absl::Span<int> s(a);
+  EXPECT_THAT(s, SpanIs(a, 3));
+
+  EXPECT_TRUE((std::is_constructible<absl::Span<const int>, int[3]>::value));
+  EXPECT_TRUE(
+      (std::is_constructible<absl::Span<const int>, const int[3]>::value));
+  EXPECT_FALSE((std::is_constructible<absl::Span<int>, const int[3]>::value));
+  EXPECT_TRUE((std::is_convertible<int[3], absl::Span<const int>>::value));
+  EXPECT_TRUE(
+      (std::is_convertible<const int[3], absl::Span<const int>>::value));
+}
+
+template <typename T>
+void TakesGenericSpan(absl::Span<T>) {}
+
+TEST(IntSpan, ContainerCtor) {
+  std::vector<int> empty;
+  absl::Span<int> s_empty(empty);
+  EXPECT_THAT(s_empty, SpanIs(empty));
+
+  std::vector<int> filled{1, 2, 3};
+  absl::Span<int> s_filled(filled);
+  EXPECT_THAT(s_filled, SpanIs(filled));
+
+  absl::Span<int> s_from_span(filled);
+  EXPECT_THAT(s_from_span, SpanIs(s_filled));
+
+  absl::Span<const int> const_filled = filled;
+  EXPECT_THAT(const_filled, SpanIs(filled));
+
+  absl::Span<const int> const_from_span = s_filled;
+  EXPECT_THAT(const_from_span, SpanIs(s_filled));
+
+  EXPECT_TRUE(
+      (std::is_convertible<std::vector<int>&, absl::Span<const int>>::value));
+  EXPECT_TRUE(
+      (std::is_convertible<absl::Span<int>&, absl::Span<const int>>::value));
+
+  TakesGenericSpan(absl::Span<int>(filled));
+}
+
+// A struct supplying shallow data() const.
+struct ContainerWithShallowConstData {
+  std::vector<int> storage;
+  int* data() const { return const_cast<int*>(storage.data()); }
+  int size() const { return storage.size(); }
+};
+
+TEST(IntSpan, ShallowConstness) {
+  const ContainerWithShallowConstData c{MakeRamp(20)};
+  absl::Span<int> s(
+      c);  // We should be able to do this even though data() is const.
+  s[0] = -1;
+  EXPECT_EQ(c.storage[0], -1);
+}
+
+TEST(CharSpan, StringCtor) {
+  std::string empty = "";
+  absl::Span<char> s_empty(empty);
+  EXPECT_THAT(s_empty, SpanIs(empty));
+
+  std::string abc = "abc";
+  absl::Span<char> s_abc(abc);
+  EXPECT_THAT(s_abc, SpanIs(abc));
+
+  absl::Span<const char> s_const_abc = abc;
+  EXPECT_THAT(s_const_abc, SpanIs(abc));
+
+  EXPECT_FALSE((std::is_constructible<absl::Span<int>, std::string>::value));
+  EXPECT_FALSE(
+      (std::is_constructible<absl::Span<const int>, std::string>::value));
+  EXPECT_TRUE(
+      (std::is_convertible<std::string, absl::Span<const char>>::value));
+}
+
+TEST(IntSpan, FromConstPointer) {
+  EXPECT_TRUE((std::is_constructible<absl::Span<const int* const>,
+                                     std::vector<int*>>::value));
+  EXPECT_TRUE((std::is_constructible<absl::Span<const int* const>,
+                                     std::vector<const int*>>::value));
+  EXPECT_FALSE((
+      std::is_constructible<absl::Span<const int*>, std::vector<int*>>::value));
+  EXPECT_FALSE((
+      std::is_constructible<absl::Span<int*>, std::vector<const int*>>::value));
+}
+
+struct TypeWithMisleadingData {
+  int& data() { return i; }
+  int size() { return 1; }
+  int i;
+};
+
+struct TypeWithMisleadingSize {
+  int* data() { return &i; }
+  const char* size() { return "1"; }
+  int i;
+};
+
+TEST(IntSpan, EvilTypes) {
+  EXPECT_FALSE(
+      (std::is_constructible<absl::Span<int>, TypeWithMisleadingData&>::value));
+  EXPECT_FALSE(
+      (std::is_constructible<absl::Span<int>, TypeWithMisleadingSize&>::value));
+}
+
+struct Base {
+  int* data() { return &i; }
+  int size() { return 1; }
+  int i;
+};
+struct Derived : Base {};
+
+TEST(IntSpan, SpanOfDerived) {
+  EXPECT_TRUE((std::is_constructible<absl::Span<int>, Base&>::value));
+  EXPECT_TRUE((std::is_constructible<absl::Span<int>, Derived&>::value));
+  EXPECT_FALSE(
+      (std::is_constructible<absl::Span<Base>, std::vector<Derived>>::value));
+}
+
+void TestInitializerList(absl::Span<const int> s, const std::vector<int>& v) {
+  EXPECT_TRUE(absl::equal(s.begin(), s.end(), v.begin(), v.end()));
+}
+
+TEST(ConstIntSpan, InitializerListConversion) {
+  TestInitializerList({}, {});
+  TestInitializerList({1}, {1});
+  TestInitializerList({1, 2, 3}, {1, 2, 3});
+
+  EXPECT_FALSE((std::is_constructible<absl::Span<int>,
+                                      std::initializer_list<int>>::value));
+  EXPECT_FALSE((
+      std::is_convertible<absl::Span<int>, std::initializer_list<int>>::value));
+}
+
+TEST(IntSpan, Data) {
+  int i;
+  absl::Span<int> s(&i, 1);
+  EXPECT_EQ(&i, s.data());
+}
+
+TEST(IntSpan, SizeLengthEmpty) {
+  absl::Span<int> empty;
+  EXPECT_EQ(empty.size(), 0);
+  EXPECT_TRUE(empty.empty());
+  EXPECT_EQ(empty.size(), empty.length());
+
+  auto v = MakeRamp(10);
+  absl::Span<int> s(v);
+  EXPECT_EQ(s.size(), 10);
+  EXPECT_FALSE(s.empty());
+  EXPECT_EQ(s.size(), s.length());
+}
+
+TEST(IntSpan, ElementAccess) {
+  auto v = MakeRamp(10);
+  absl::Span<int> s(v);
+  for (int i = 0; i < s.size(); ++i) {
+    EXPECT_EQ(s[i], s.at(i));
+  }
+
+  EXPECT_EQ(s.front(), s[0]);
+  EXPECT_EQ(s.back(), s[9]);
+
+#if !defined(NDEBUG) || ABSL_OPTION_HARDENED
+  EXPECT_DEATH_IF_SUPPORTED(s[-1], "");
+  EXPECT_DEATH_IF_SUPPORTED(s[10], "");
+#endif
+}
+
+TEST(IntSpan, AtThrows) {
+  auto v = MakeRamp(10);
+  absl::Span<int> s(v);
+
+  EXPECT_EQ(s.at(9), 9);
+  ABSL_BASE_INTERNAL_EXPECT_FAIL(s.at(10), std::out_of_range,
+                                 "failed bounds check");
+}
+
+TEST(IntSpan, RemovePrefixAndSuffix) {
+  auto v = MakeRamp(20, 1);
+  absl::Span<int> s(v);
+  EXPECT_EQ(s.size(), 20);
+
+  s.remove_suffix(0);
+  s.remove_prefix(0);
+  EXPECT_EQ(s.size(), 20);
+
+  s.remove_prefix(1);
+  EXPECT_EQ(s.size(), 19);
+  EXPECT_EQ(s[0], 2);
+
+  s.remove_suffix(1);
+  EXPECT_EQ(s.size(), 18);
+  EXPECT_EQ(s.back(), 19);
+
+  s.remove_prefix(7);
+  EXPECT_EQ(s.size(), 11);
+  EXPECT_EQ(s[0], 9);
+
+  s.remove_suffix(11);
+  EXPECT_EQ(s.size(), 0);
+
+  EXPECT_EQ(v, MakeRamp(20, 1));
+
+#if !defined(NDEBUG) || ABSL_OPTION_HARDENED
+  absl::Span<int> prefix_death(v);
+  EXPECT_DEATH_IF_SUPPORTED(prefix_death.remove_prefix(21), "");
+  absl::Span<int> suffix_death(v);
+  EXPECT_DEATH_IF_SUPPORTED(suffix_death.remove_suffix(21), "");
+#endif
+}
+
+TEST(IntSpan, Subspan) {
+  std::vector<int> empty;
+  EXPECT_EQ(absl::MakeSpan(empty).subspan(), empty);
+  EXPECT_THAT(absl::MakeSpan(empty).subspan(0, 0), SpanIs(empty));
+  EXPECT_THAT(absl::MakeSpan(empty).subspan(0, absl::Span<const int>::npos),
+              SpanIs(empty));
+
+  auto ramp = MakeRamp(10);
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(), SpanIs(ramp));
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(0, 10), SpanIs(ramp));
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(0, absl::Span<const int>::npos),
+              SpanIs(ramp));
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(0, 3), SpanIs(ramp.data(), 3));
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(5, absl::Span<const int>::npos),
+              SpanIs(ramp.data() + 5, 5));
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(3, 3), SpanIs(ramp.data() + 3, 3));
+  EXPECT_THAT(absl::MakeSpan(ramp).subspan(10, 5), SpanIs(ramp.data() + 10, 0));
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW(absl::MakeSpan(ramp).subspan(11, 5), std::out_of_range);
+#else
+  EXPECT_DEATH_IF_SUPPORTED(absl::MakeSpan(ramp).subspan(11, 5), "");
+#endif
+}
+
+TEST(IntSpan, First) {
+  std::vector<int> empty;
+  EXPECT_THAT(absl::MakeSpan(empty).first(0), SpanIs(empty));
+
+  auto ramp = MakeRamp(10);
+  EXPECT_THAT(absl::MakeSpan(ramp).first(0), SpanIs(ramp.data(), 0));
+  EXPECT_THAT(absl::MakeSpan(ramp).first(10), SpanIs(ramp));
+  EXPECT_THAT(absl::MakeSpan(ramp).first(3), SpanIs(ramp.data(), 3));
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW(absl::MakeSpan(ramp).first(11), std::out_of_range);
+#else
+  EXPECT_DEATH_IF_SUPPORTED(absl::MakeSpan(ramp).first(11), "");
+#endif
+}
+
+TEST(IntSpan, Last) {
+  std::vector<int> empty;
+  EXPECT_THAT(absl::MakeSpan(empty).last(0), SpanIs(empty));
+
+  auto ramp = MakeRamp(10);
+  EXPECT_THAT(absl::MakeSpan(ramp).last(0), SpanIs(ramp.data() + 10, 0));
+  EXPECT_THAT(absl::MakeSpan(ramp).last(10), SpanIs(ramp));
+  EXPECT_THAT(absl::MakeSpan(ramp).last(3), SpanIs(ramp.data() + 7, 3));
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW(absl::MakeSpan(ramp).last(11), std::out_of_range);
+#else
+  EXPECT_DEATH_IF_SUPPORTED(absl::MakeSpan(ramp).last(11), "");
+#endif
+}
+
+TEST(IntSpan, MakeSpanPtrLength) {
+  std::vector<int> empty;
+  auto s_empty = absl::MakeSpan(empty.data(), empty.size());
+  EXPECT_THAT(s_empty, SpanIs(empty));
+
+  std::array<int, 3> a{{1, 2, 3}};
+  auto s = absl::MakeSpan(a.data(), a.size());
+  EXPECT_THAT(s, SpanIs(a));
+
+  EXPECT_THAT(absl::MakeConstSpan(empty.data(), empty.size()), SpanIs(s_empty));
+  EXPECT_THAT(absl::MakeConstSpan(a.data(), a.size()), SpanIs(s));
+}
+
+TEST(IntSpan, MakeSpanTwoPtrs) {
+  std::vector<int> empty;
+  auto s_empty = absl::MakeSpan(empty.data(), empty.data());
+  EXPECT_THAT(s_empty, SpanIs(empty));
+
+  std::vector<int> v{1, 2, 3};
+  auto s = absl::MakeSpan(v.data(), v.data() + 1);
+  EXPECT_THAT(s, SpanIs(v.data(), 1));
+
+  EXPECT_THAT(absl::MakeConstSpan(empty.data(), empty.data()), SpanIs(s_empty));
+  EXPECT_THAT(absl::MakeConstSpan(v.data(), v.data() + 1), SpanIs(s));
+}
+
+TEST(IntSpan, MakeSpanContainer) {
+  std::vector<int> empty;
+  auto s_empty = absl::MakeSpan(empty);
+  EXPECT_THAT(s_empty, SpanIs(empty));
+
+  std::vector<int> v{1, 2, 3};
+  auto s = absl::MakeSpan(v);
+  EXPECT_THAT(s, SpanIs(v));
+
+  EXPECT_THAT(absl::MakeConstSpan(empty), SpanIs(s_empty));
+  EXPECT_THAT(absl::MakeConstSpan(v), SpanIs(s));
+
+  EXPECT_THAT(absl::MakeSpan(s), SpanIs(s));
+  EXPECT_THAT(absl::MakeConstSpan(s), SpanIs(s));
+}
+
+TEST(CharSpan, MakeSpanString) {
+  std::string empty = "";
+  auto s_empty = absl::MakeSpan(empty);
+  EXPECT_THAT(s_empty, SpanIs(empty));
+
+  std::string str = "abc";
+  auto s_str = absl::MakeSpan(str);
+  EXPECT_THAT(s_str, SpanIs(str));
+
+  EXPECT_THAT(absl::MakeConstSpan(empty), SpanIs(s_empty));
+  EXPECT_THAT(absl::MakeConstSpan(str), SpanIs(s_str));
+}
+
+TEST(IntSpan, MakeSpanArray) {
+  int a[] = {1, 2, 3};
+  auto s = absl::MakeSpan(a);
+  EXPECT_THAT(s, SpanIs(a, 3));
+
+  const int ca[] = {1, 2, 3};
+  auto s_ca = absl::MakeSpan(ca);
+  EXPECT_THAT(s_ca, SpanIs(ca, 3));
+
+  EXPECT_THAT(absl::MakeConstSpan(a), SpanIs(s));
+  EXPECT_THAT(absl::MakeConstSpan(ca), SpanIs(s_ca));
+}
+
+// Compile-asserts that the argument has the expected decayed type.
+template <typename Expected, typename T>
+void CheckType(const T& /* value */) {
+  testing::StaticAssertTypeEq<Expected, T>();
+}
+
+TEST(IntSpan, MakeSpanTypes) {
+  std::vector<int> vec;
+  const std::vector<int> cvec;
+  int a[1];
+  const int ca[] = {1};
+  int* ip = a;
+  const int* cip = ca;
+  std::string s = "";
+  const std::string cs = "";
+  CheckType<absl::Span<int>>(absl::MakeSpan(vec));
+  CheckType<absl::Span<const int>>(absl::MakeSpan(cvec));
+  CheckType<absl::Span<int>>(absl::MakeSpan(ip, ip + 1));
+  CheckType<absl::Span<int>>(absl::MakeSpan(ip, 1));
+  CheckType<absl::Span<const int>>(absl::MakeSpan(cip, cip + 1));
+  CheckType<absl::Span<const int>>(absl::MakeSpan(cip, 1));
+  CheckType<absl::Span<int>>(absl::MakeSpan(a));
+  CheckType<absl::Span<int>>(absl::MakeSpan(a, a + 1));
+  CheckType<absl::Span<int>>(absl::MakeSpan(a, 1));
+  CheckType<absl::Span<const int>>(absl::MakeSpan(ca));
+  CheckType<absl::Span<const int>>(absl::MakeSpan(ca, ca + 1));
+  CheckType<absl::Span<const int>>(absl::MakeSpan(ca, 1));
+  CheckType<absl::Span<char>>(absl::MakeSpan(s));
+  CheckType<absl::Span<const char>>(absl::MakeSpan(cs));
+}
+
+TEST(ConstIntSpan, MakeConstSpanTypes) {
+  std::vector<int> vec;
+  const std::vector<int> cvec;
+  int array[1];
+  const int carray[] = {0};
+  int* ptr = array;
+  const int* cptr = carray;
+  std::string s = "";
+  std::string cs = "";
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(vec));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(cvec));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(ptr, ptr + 1));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(ptr, 1));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(cptr, cptr + 1));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(cptr, 1));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(array));
+  CheckType<absl::Span<const int>>(absl::MakeConstSpan(carray));
+  CheckType<absl::Span<const char>>(absl::MakeConstSpan(s));
+  CheckType<absl::Span<const char>>(absl::MakeConstSpan(cs));
+}
+
+TEST(IntSpan, Equality) {
+  const int arr1[] = {1, 2, 3, 4, 5};
+  int arr2[] = {1, 2, 3, 4, 5};
+  std::vector<int> vec1(std::begin(arr1), std::end(arr1));
+  std::vector<int> vec2 = vec1;
+  std::vector<int> other_vec = {2, 4, 6, 8, 10};
+  // These two slices are from different vectors, but have the same size and
+  // have the same elements (right now).  They should compare equal. Test both
+  // == and !=.
+  const absl::Span<const int> from1 = vec1;
+  const absl::Span<const int> from2 = vec2;
+  EXPECT_EQ(from1, from1);
+  EXPECT_FALSE(from1 != from1);
+  EXPECT_EQ(from1, from2);
+  EXPECT_FALSE(from1 != from2);
+
+  // These two slices have different underlying vector values. They should be
+  // considered not equal. Test both == and !=.
+  const absl::Span<const int> from_other = other_vec;
+  EXPECT_NE(from1, from_other);
+  EXPECT_FALSE(from1 == from_other);
+
+  // Comparison between a vector and its slice should be equal. And vice-versa.
+  // This ensures implicit conversion to Span works on both sides of ==.
+  EXPECT_EQ(vec1, from1);
+  EXPECT_FALSE(vec1 != from1);
+  EXPECT_EQ(from1, vec1);
+  EXPECT_FALSE(from1 != vec1);
+
+  // This verifies that absl::Span<T> can be compared freely with
+  // absl::Span<const T>.
+  const absl::Span<int> mutable_from1(vec1);
+  const absl::Span<int> mutable_from2(vec2);
+  EXPECT_EQ(from1, mutable_from1);
+  EXPECT_EQ(mutable_from1, from1);
+  EXPECT_EQ(mutable_from1, mutable_from2);
+  EXPECT_EQ(mutable_from2, mutable_from1);
+
+  // Comparison between a vector and its slice should be equal for mutable
+  // Spans as well.
+  EXPECT_EQ(vec1, mutable_from1);
+  EXPECT_FALSE(vec1 != mutable_from1);
+  EXPECT_EQ(mutable_from1, vec1);
+  EXPECT_FALSE(mutable_from1 != vec1);
+
+  // Comparison between convertible-to-Span-of-const and Span-of-mutable. Arrays
+  // are used because they're the only value type which converts to a
+  // Span-of-mutable. EXPECT_TRUE is used instead of EXPECT_EQ to avoid
+  // array-to-pointer decay.
+  EXPECT_TRUE(arr1 == mutable_from1);
+  EXPECT_FALSE(arr1 != mutable_from1);
+  EXPECT_TRUE(mutable_from1 == arr1);
+  EXPECT_FALSE(mutable_from1 != arr1);
+
+  // Comparison between convertible-to-Span-of-mutable and Span-of-const
+  EXPECT_TRUE(arr2 == from1);
+  EXPECT_FALSE(arr2 != from1);
+  EXPECT_TRUE(from1 == arr2);
+  EXPECT_FALSE(from1 != arr2);
+
+  // With a different size, the array slices should not be equal.
+  EXPECT_NE(from1, absl::Span<const int>(from1).subspan(0, from1.size() - 1));
+
+  // With different contents, the array slices should not be equal.
+  ++vec2.back();
+  EXPECT_NE(from1, from2);
+}
+
+class IntSpanOrderComparisonTest : public testing::Test {
+ public:
+  IntSpanOrderComparisonTest()
+      : arr_before_{1, 2, 3},
+        arr_after_{1, 2, 4},
+        carr_after_{1, 2, 4},
+        vec_before_(std::begin(arr_before_), std::end(arr_before_)),
+        vec_after_(std::begin(arr_after_), std::end(arr_after_)),
+        before_(vec_before_),
+        after_(vec_after_),
+        cbefore_(vec_before_),
+        cafter_(vec_after_) {}
+
+ protected:
+  int arr_before_[3], arr_after_[3];
+  const int carr_after_[3];
+  std::vector<int> vec_before_, vec_after_;
+  absl::Span<int> before_, after_;
+  absl::Span<const int> cbefore_, cafter_;
+};
+
+TEST_F(IntSpanOrderComparisonTest, CompareSpans) {
+  EXPECT_TRUE(cbefore_ < cafter_);
+  EXPECT_TRUE(cbefore_ <= cafter_);
+  EXPECT_TRUE(cafter_ > cbefore_);
+  EXPECT_TRUE(cafter_ >= cbefore_);
+
+  EXPECT_FALSE(cbefore_ > cafter_);
+  EXPECT_FALSE(cafter_ < cbefore_);
+
+  EXPECT_TRUE(before_ < after_);
+  EXPECT_TRUE(before_ <= after_);
+  EXPECT_TRUE(after_ > before_);
+  EXPECT_TRUE(after_ >= before_);
+
+  EXPECT_FALSE(before_ > after_);
+  EXPECT_FALSE(after_ < before_);
+
+  EXPECT_TRUE(cbefore_ < after_);
+  EXPECT_TRUE(cbefore_ <= after_);
+  EXPECT_TRUE(after_ > cbefore_);
+  EXPECT_TRUE(after_ >= cbefore_);
+
+  EXPECT_FALSE(cbefore_ > after_);
+  EXPECT_FALSE(after_ < cbefore_);
+}
+
+TEST_F(IntSpanOrderComparisonTest, SpanOfConstAndContainer) {
+  EXPECT_TRUE(cbefore_ < vec_after_);
+  EXPECT_TRUE(cbefore_ <= vec_after_);
+  EXPECT_TRUE(vec_after_ > cbefore_);
+  EXPECT_TRUE(vec_after_ >= cbefore_);
+
+  EXPECT_FALSE(cbefore_ > vec_after_);
+  EXPECT_FALSE(vec_after_ < cbefore_);
+
+  EXPECT_TRUE(arr_before_ < cafter_);
+  EXPECT_TRUE(arr_before_ <= cafter_);
+  EXPECT_TRUE(cafter_ > arr_before_);
+  EXPECT_TRUE(cafter_ >= arr_before_);
+
+  EXPECT_FALSE(arr_before_ > cafter_);
+  EXPECT_FALSE(cafter_ < arr_before_);
+}
+
+TEST_F(IntSpanOrderComparisonTest, SpanOfMutableAndContainer) {
+  EXPECT_TRUE(vec_before_ < after_);
+  EXPECT_TRUE(vec_before_ <= after_);
+  EXPECT_TRUE(after_ > vec_before_);
+  EXPECT_TRUE(after_ >= vec_before_);
+
+  EXPECT_FALSE(vec_before_ > after_);
+  EXPECT_FALSE(after_ < vec_before_);
+
+  EXPECT_TRUE(before_ < carr_after_);
+  EXPECT_TRUE(before_ <= carr_after_);
+  EXPECT_TRUE(carr_after_ > before_);
+  EXPECT_TRUE(carr_after_ >= before_);
+
+  EXPECT_FALSE(before_ > carr_after_);
+  EXPECT_FALSE(carr_after_ < before_);
+}
+
+TEST_F(IntSpanOrderComparisonTest, EqualSpans) {
+  EXPECT_FALSE(before_ < before_);
+  EXPECT_TRUE(before_ <= before_);
+  EXPECT_FALSE(before_ > before_);
+  EXPECT_TRUE(before_ >= before_);
+}
+
+TEST_F(IntSpanOrderComparisonTest, Subspans) {
+  auto subspan = before_.subspan(0, 1);
+  EXPECT_TRUE(subspan < before_);
+  EXPECT_TRUE(subspan <= before_);
+  EXPECT_TRUE(before_ > subspan);
+  EXPECT_TRUE(before_ >= subspan);
+
+  EXPECT_FALSE(subspan > before_);
+  EXPECT_FALSE(before_ < subspan);
+}
+
+TEST_F(IntSpanOrderComparisonTest, EmptySpans) {
+  absl::Span<int> empty;
+  EXPECT_FALSE(empty < empty);
+  EXPECT_TRUE(empty <= empty);
+  EXPECT_FALSE(empty > empty);
+  EXPECT_TRUE(empty >= empty);
+
+  EXPECT_TRUE(empty < before_);
+  EXPECT_TRUE(empty <= before_);
+  EXPECT_TRUE(before_ > empty);
+  EXPECT_TRUE(before_ >= empty);
+
+  EXPECT_FALSE(empty > before_);
+  EXPECT_FALSE(before_ < empty);
+}
+
+TEST(IntSpan, ExposesContainerTypesAndConsts) {
+  absl::Span<int> slice;
+  CheckType<absl::Span<int>::iterator>(slice.begin());
+  EXPECT_TRUE((std::is_convertible<decltype(slice.begin()),
+                                   absl::Span<int>::const_iterator>::value));
+  CheckType<absl::Span<int>::const_iterator>(slice.cbegin());
+  EXPECT_TRUE((std::is_convertible<decltype(slice.end()),
+                                   absl::Span<int>::const_iterator>::value));
+  CheckType<absl::Span<int>::const_iterator>(slice.cend());
+  CheckType<absl::Span<int>::reverse_iterator>(slice.rend());
+  EXPECT_TRUE(
+      (std::is_convertible<decltype(slice.rend()),
+                           absl::Span<int>::const_reverse_iterator>::value));
+  CheckType<absl::Span<int>::const_reverse_iterator>(slice.crend());
+  testing::StaticAssertTypeEq<int, absl::Span<int>::value_type>();
+  testing::StaticAssertTypeEq<int, absl::Span<const int>::value_type>();
+  testing::StaticAssertTypeEq<int*, absl::Span<int>::pointer>();
+  testing::StaticAssertTypeEq<const int*, absl::Span<const int>::pointer>();
+  testing::StaticAssertTypeEq<int&, absl::Span<int>::reference>();
+  testing::StaticAssertTypeEq<const int&, absl::Span<const int>::reference>();
+  testing::StaticAssertTypeEq<const int&, absl::Span<int>::const_reference>();
+  testing::StaticAssertTypeEq<const int&,
+                              absl::Span<const int>::const_reference>();
+  EXPECT_EQ(static_cast<absl::Span<int>::size_type>(-1), absl::Span<int>::npos);
+}
+
+TEST(IntSpan, IteratorsAndReferences) {
+  auto accept_pointer = [](int*) {};
+  auto accept_reference = [](int&) {};
+  auto accept_iterator = [](absl::Span<int>::iterator) {};
+  auto accept_const_iterator = [](absl::Span<int>::const_iterator) {};
+  auto accept_reverse_iterator = [](absl::Span<int>::reverse_iterator) {};
+  auto accept_const_reverse_iterator =
+      [](absl::Span<int>::const_reverse_iterator) {};
+
+  int a[1];
+  absl::Span<int> s = a;
+
+  accept_pointer(s.data());
+  accept_iterator(s.begin());
+  accept_const_iterator(s.begin());
+  accept_const_iterator(s.cbegin());
+  accept_iterator(s.end());
+  accept_const_iterator(s.end());
+  accept_const_iterator(s.cend());
+  accept_reverse_iterator(s.rbegin());
+  accept_const_reverse_iterator(s.rbegin());
+  accept_const_reverse_iterator(s.crbegin());
+  accept_reverse_iterator(s.rend());
+  accept_const_reverse_iterator(s.rend());
+  accept_const_reverse_iterator(s.crend());
+
+  accept_reference(s[0]);
+  accept_reference(s.at(0));
+  accept_reference(s.front());
+  accept_reference(s.back());
+}
+
+TEST(IntSpan, IteratorsAndReferences_Const) {
+  auto accept_pointer = [](int*) {};
+  auto accept_reference = [](int&) {};
+  auto accept_iterator = [](absl::Span<int>::iterator) {};
+  auto accept_const_iterator = [](absl::Span<int>::const_iterator) {};
+  auto accept_reverse_iterator = [](absl::Span<int>::reverse_iterator) {};
+  auto accept_const_reverse_iterator =
+      [](absl::Span<int>::const_reverse_iterator) {};
+
+  int a[1];
+  const absl::Span<int> s = a;
+
+  accept_pointer(s.data());
+  accept_iterator(s.begin());
+  accept_const_iterator(s.begin());
+  accept_const_iterator(s.cbegin());
+  accept_iterator(s.end());
+  accept_const_iterator(s.end());
+  accept_const_iterator(s.cend());
+  accept_reverse_iterator(s.rbegin());
+  accept_const_reverse_iterator(s.rbegin());
+  accept_const_reverse_iterator(s.crbegin());
+  accept_reverse_iterator(s.rend());
+  accept_const_reverse_iterator(s.rend());
+  accept_const_reverse_iterator(s.crend());
+
+  accept_reference(s[0]);
+  accept_reference(s.at(0));
+  accept_reference(s.front());
+  accept_reference(s.back());
+}
+
+TEST(IntSpan, NoexceptTest) {
+  int a[] = {1, 2, 3};
+  std::vector<int> v;
+  EXPECT_TRUE(noexcept(absl::Span<const int>()));
+  EXPECT_TRUE(noexcept(absl::Span<const int>(a, 2)));
+  EXPECT_TRUE(noexcept(absl::Span<const int>(a)));
+  EXPECT_TRUE(noexcept(absl::Span<const int>(v)));
+  EXPECT_TRUE(noexcept(absl::Span<int>(v)));
+  EXPECT_TRUE(noexcept(absl::Span<const int>({1, 2, 3})));
+  EXPECT_TRUE(noexcept(absl::MakeSpan(v)));
+  EXPECT_TRUE(noexcept(absl::MakeSpan(a)));
+  EXPECT_TRUE(noexcept(absl::MakeSpan(a, 2)));
+  EXPECT_TRUE(noexcept(absl::MakeSpan(a, a + 1)));
+  EXPECT_TRUE(noexcept(absl::MakeConstSpan(v)));
+  EXPECT_TRUE(noexcept(absl::MakeConstSpan(a)));
+  EXPECT_TRUE(noexcept(absl::MakeConstSpan(a, 2)));
+  EXPECT_TRUE(noexcept(absl::MakeConstSpan(a, a + 1)));
+
+  absl::Span<int> s(v);
+  EXPECT_TRUE(noexcept(s.data()));
+  EXPECT_TRUE(noexcept(s.size()));
+  EXPECT_TRUE(noexcept(s.length()));
+  EXPECT_TRUE(noexcept(s.empty()));
+  EXPECT_TRUE(noexcept(s[0]));
+  EXPECT_TRUE(noexcept(s.front()));
+  EXPECT_TRUE(noexcept(s.back()));
+  EXPECT_TRUE(noexcept(s.begin()));
+  EXPECT_TRUE(noexcept(s.cbegin()));
+  EXPECT_TRUE(noexcept(s.end()));
+  EXPECT_TRUE(noexcept(s.cend()));
+  EXPECT_TRUE(noexcept(s.rbegin()));
+  EXPECT_TRUE(noexcept(s.crbegin()));
+  EXPECT_TRUE(noexcept(s.rend()));
+  EXPECT_TRUE(noexcept(s.crend()));
+  EXPECT_TRUE(noexcept(s.remove_prefix(0)));
+  EXPECT_TRUE(noexcept(s.remove_suffix(0)));
+}
+
+// ConstexprTester exercises expressions in a constexpr context. Simply placing
+// the expression in a constexpr function is not enough, as some compilers will
+// simply compile the constexpr function as runtime code. Using template
+// parameters forces compile-time execution.
+template <int i>
+struct ConstexprTester {};
+
+#define ABSL_TEST_CONSTEXPR(expr)                       \
+  do {                                                  \
+    ABSL_ATTRIBUTE_UNUSED ConstexprTester<(expr, 1)> t; \
+  } while (0)
+
+struct ContainerWithConstexprMethods {
+  constexpr int size() const { return 1; }
+  constexpr const int* data() const { return &i; }
+  const int i;
+};
+
+TEST(ConstIntSpan, ConstexprTest) {
+  static constexpr int a[] = {1, 2, 3};
+  static constexpr int sized_arr[2] = {1, 2};
+  static constexpr ContainerWithConstexprMethods c{1};
+  ABSL_TEST_CONSTEXPR(absl::Span<const int>());
+  ABSL_TEST_CONSTEXPR(absl::Span<const int>(a, 2));
+  ABSL_TEST_CONSTEXPR(absl::Span<const int>(sized_arr));
+  ABSL_TEST_CONSTEXPR(absl::Span<const int>(c));
+  ABSL_TEST_CONSTEXPR(absl::MakeSpan(&a[0], 1));
+  ABSL_TEST_CONSTEXPR(absl::MakeSpan(c));
+  ABSL_TEST_CONSTEXPR(absl::MakeSpan(a));
+  ABSL_TEST_CONSTEXPR(absl::MakeConstSpan(&a[0], 1));
+  ABSL_TEST_CONSTEXPR(absl::MakeConstSpan(c));
+  ABSL_TEST_CONSTEXPR(absl::MakeConstSpan(a));
+
+  constexpr absl::Span<const int> span = c;
+  ABSL_TEST_CONSTEXPR(span.data());
+  ABSL_TEST_CONSTEXPR(span.size());
+  ABSL_TEST_CONSTEXPR(span.length());
+  ABSL_TEST_CONSTEXPR(span.empty());
+  ABSL_TEST_CONSTEXPR(span.begin());
+  ABSL_TEST_CONSTEXPR(span.cbegin());
+  ABSL_TEST_CONSTEXPR(span.subspan(0, 0));
+  ABSL_TEST_CONSTEXPR(span.first(1));
+  ABSL_TEST_CONSTEXPR(span.last(1));
+  ABSL_TEST_CONSTEXPR(span[0]);
+}
+
+struct BigStruct {
+  char bytes[10000];
+};
+
+TEST(Span, SpanSize) {
+  EXPECT_LE(sizeof(absl::Span<int>), 2 * sizeof(void*));
+  EXPECT_LE(sizeof(absl::Span<BigStruct>), 2 * sizeof(void*));
+}
+
+TEST(Span, Hash) {
+  int array[] = {1, 2, 3, 4};
+  int array2[] = {1, 2, 3};
+  using T = absl::Span<const int>;
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
+      {// Empties
+       T(), T(nullptr, 0), T(array, 0), T(array2, 0),
+       // Different array with same value
+       T(array, 3), T(array2), T({1, 2, 3}),
+       // Same array, but different length
+       T(array, 1), T(array, 2),
+       // Same length, but different array
+       T(array + 1, 2), T(array + 2, 2)}));
+}
+
+}  // namespace
diff --git a/third_party/abseil_cpp/absl/types/variant.h b/third_party/abseil_cpp/absl/types/variant.h
new file mode 100644
index 0000000000..776d19a1c5
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/variant.h
@@ -0,0 +1,861 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// variant.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines an `absl::variant` type for holding a type-safe
+// value of some prescribed set of types (noted as alternative types), and
+// associated functions for managing variants.
+//
+// The `absl::variant` type is a form of type-safe union. An `absl::variant`
+// should always hold a value of one of its alternative types (except in the
+// "valueless by exception state" -- see below). A default-constructed
+// `absl::variant` will hold the value of its first alternative type, provided
+// it is default-constructible.
+//
+// In exceptional cases due to error, an `absl::variant` can hold no
+// value (known as a "valueless by exception" state), though this is not the
+// norm.
+//
+// As with `absl::optional`, an `absl::variant` -- when it holds a value --
+// allocates a value of that type directly within the `variant` itself; it
+// cannot hold a reference, array, or the type `void`; it can, however, hold a
+// pointer to externally managed memory.
+//
+// `absl::variant` is a C++11 compatible version of the C++17 `std::variant`
+// abstraction and is designed to be a drop-in replacement for code compliant
+// with C++17.
+
+#ifndef ABSL_TYPES_VARIANT_H_
+#define ABSL_TYPES_VARIANT_H_
+
+#include "absl/base/config.h"
+#include "absl/utility/utility.h"
+
+#ifdef ABSL_USES_STD_VARIANT
+
+#include <variant>  // IWYU pragma: export
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using std::bad_variant_access;
+using std::get;
+using std::get_if;
+using std::holds_alternative;
+using std::monostate;
+using std::variant;
+using std::variant_alternative;
+using std::variant_alternative_t;
+using std::variant_npos;
+using std::variant_size;
+using std::variant_size_v;
+using std::visit;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_VARIANT
+
+#include <functional>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/meta/type_traits.h"
+#include "absl/types/internal/variant.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// -----------------------------------------------------------------------------
+// absl::variant
+// -----------------------------------------------------------------------------
+//
+// An `absl::variant` type is a form of type-safe union. An `absl::variant` --
+// except in exceptional cases -- always holds a value of one of its alternative
+// types.
+//
+// Example:
+//
+//   // Construct a variant that holds either an integer or a std::string and
+//   // assign it to a std::string.
+//   absl::variant<int, std::string> v = std::string("abc");
+//
+//   // A default-constructed variant will hold a value-initialized value of
+//   // the first alternative type.
+//   auto a = absl::variant<int, std::string>();   // Holds an int of value '0'.
+//
+//   // variants are assignable.
+//
+//   // copy assignment
+//   auto v1 = absl::variant<int, std::string>("abc");
+//   auto v2 = absl::variant<int, std::string>(10);
+//   v2 = v1;  // copy assign
+//
+//   // move assignment
+//   auto v1 = absl::variant<int, std::string>("abc");
+//   v1 = absl::variant<int, std::string>(10);
+//
+//   // assignment through type conversion
+//   a = 128;         // variant contains int
+//   a = "128";       // variant contains std::string
+//
+// An `absl::variant` holding a value of one of its alternative types `T` holds
+// an allocation of `T` directly within the variant itself. An `absl::variant`
+// is not allowed to allocate additional storage, such as dynamic memory, to
+// allocate the contained value. The contained value shall be allocated in a
+// region of the variant storage suitably aligned for all alternative types.
+template <typename... Ts>
+class variant;
+
+// swap()
+//
+// Swaps two `absl::variant` values. This function is equivalent to `v.swap(w)`
+// where `v` and `w` are `absl::variant` types.
+//
+// Note that this function requires all alternative types to be both swappable
+// and move-constructible, because any two variants may refer to either the same
+// type (in which case, they will be swapped) or to two different types (in
+// which case the values will need to be moved).
+//
+template <
+    typename... Ts,
+    absl::enable_if_t<
+        absl::conjunction<std::is_move_constructible<Ts>...,
+                          type_traits_internal::IsSwappable<Ts>...>::value,
+        int> = 0>
+void swap(variant<Ts...>& v, variant<Ts...>& w) noexcept(noexcept(v.swap(w))) {
+  v.swap(w);
+}
+
+// variant_size
+//
+// Returns the number of alternative types available for a given `absl::variant`
+// type as a compile-time constant expression. As this is a class template, it
+// is not generally useful for accessing the number of alternative types of
+// any given `absl::variant` instance.
+//
+// Example:
+//
+//   auto a = absl::variant<int, std::string>;
+//   constexpr int num_types =
+//       absl::variant_size<absl::variant<int, std::string>>();
+//
+//   // You can also use the member constant `value`.
+//   constexpr int num_types =
+//       absl::variant_size<absl::variant<int, std::string>>::value;
+//
+//   // `absl::variant_size` is more valuable for use in generic code:
+//   template <typename Variant>
+//   constexpr bool IsVariantMultivalue() {
+//       return absl::variant_size<Variant>() > 1;
+//   }
+//
+// Note that the set of cv-qualified specializations of `variant_size` are
+// provided to ensure that those specializations compile (especially when passed
+// within template logic).
+template <class T>
+struct variant_size;
+
+template <class... Ts>
+struct variant_size<variant<Ts...>>
+    : std::integral_constant<std::size_t, sizeof...(Ts)> {};
+
+// Specialization of `variant_size` for const qualified variants.
+template <class T>
+struct variant_size<const T> : variant_size<T>::type {};
+
+// Specialization of `variant_size` for volatile qualified variants.
+template <class T>
+struct variant_size<volatile T> : variant_size<T>::type {};
+
+// Specialization of `variant_size` for const volatile qualified variants.
+template <class T>
+struct variant_size<const volatile T> : variant_size<T>::type {};
+
+// variant_alternative
+//
+// Returns the alternative type for a given `absl::variant` at the passed
+// index value as a compile-time constant expression. As this is a class
+// template resulting in a type, it is not useful for access of the run-time
+// value of any given `absl::variant` variable.
+//
+// Example:
+//
+//   // The type of the 0th alternative is "int".
+//   using alternative_type_0
+//     = absl::variant_alternative<0, absl::variant<int, std::string>>::type;
+//
+//   static_assert(std::is_same<alternative_type_0, int>::value, "");
+//
+//   // `absl::variant_alternative` is more valuable for use in generic code:
+//   template <typename Variant>
+//   constexpr bool IsFirstElementTrivial() {
+//       return std::is_trivial_v<variant_alternative<0, Variant>::type>;
+//   }
+//
+// Note that the set of cv-qualified specializations of `variant_alternative`
+// are provided to ensure that those specializations compile (especially when
+// passed within template logic).
+template <std::size_t I, class T>
+struct variant_alternative;
+
+template <std::size_t I, class... Types>
+struct variant_alternative<I, variant<Types...>> {
+  using type =
+      variant_internal::VariantAlternativeSfinaeT<I, variant<Types...>>;
+};
+
+// Specialization of `variant_alternative` for const qualified variants.
+template <std::size_t I, class T>
+struct variant_alternative<I, const T> {
+  using type = const typename variant_alternative<I, T>::type;
+};
+
+// Specialization of `variant_alternative` for volatile qualified variants.
+template <std::size_t I, class T>
+struct variant_alternative<I, volatile T> {
+  using type = volatile typename variant_alternative<I, T>::type;
+};
+
+// Specialization of `variant_alternative` for const volatile qualified
+// variants.
+template <std::size_t I, class T>
+struct variant_alternative<I, const volatile T> {
+  using type = const volatile typename variant_alternative<I, T>::type;
+};
+
+// Template type alias for variant_alternative<I, T>::type.
+//
+// Example:
+//
+//   using alternative_type_0
+//     = absl::variant_alternative_t<0, absl::variant<int, std::string>>;
+//   static_assert(std::is_same<alternative_type_0, int>::value, "");
+template <std::size_t I, class T>
+using variant_alternative_t = typename variant_alternative<I, T>::type;
+
+// holds_alternative()
+//
+// Checks whether the given variant currently holds a given alternative type,
+// returning `true` if so.
+//
+// Example:
+//
+//   absl::variant<int, std::string> foo = 42;
+//   if (absl::holds_alternative<int>(foo)) {
+//       std::cout << "The variant holds an integer";
+//   }
+template <class T, class... Types>
+constexpr bool holds_alternative(const variant<Types...>& v) noexcept {
+  static_assert(
+      variant_internal::UnambiguousIndexOfImpl<variant<Types...>, T,
+                                               0>::value != sizeof...(Types),
+      "The type T must occur exactly once in Types...");
+  return v.index() ==
+         variant_internal::UnambiguousIndexOf<variant<Types...>, T>::value;
+}
+
+// get()
+//
+// Returns a reference to the value currently within a given variant, using
+// either a unique alternative type amongst the variant's set of alternative
+// types, or the variant's index value. Attempting to get a variant's value
+// using a type that is not unique within the variant's set of alternative types
+// is a compile-time error. If the index of the alternative being specified is
+// different from the index of the alternative that is currently stored, throws
+// `absl::bad_variant_access`.
+//
+// Example:
+//
+//   auto a = absl::variant<int, std::string>;
+//
+//   // Get the value by type (if unique).
+//   int i = absl::get<int>(a);
+//
+//   auto b = absl::variant<int, int>;
+//
+//   // Getting the value by a type that is not unique is ill-formed.
+//   int j = absl::get<int>(b);     // Compile Error!
+//
+//   // Getting value by index not ambiguous and allowed.
+//   int k = absl::get<1>(b);
+
+// Overload for getting a variant's lvalue by type.
+template <class T, class... Types>
+constexpr T& get(variant<Types...>& v) {  // NOLINT
+  return variant_internal::VariantCoreAccess::CheckedAccess<
+      variant_internal::IndexOf<T, Types...>::value>(v);
+}
+
+// Overload for getting a variant's rvalue by type.
+// Note: `absl::move()` is required to allow use of constexpr in C++11.
+template <class T, class... Types>
+constexpr T&& get(variant<Types...>&& v) {
+  return variant_internal::VariantCoreAccess::CheckedAccess<
+      variant_internal::IndexOf<T, Types...>::value>(absl::move(v));
+}
+
+// Overload for getting a variant's const lvalue by type.
+template <class T, class... Types>
+constexpr const T& get(const variant<Types...>& v) {
+  return variant_internal::VariantCoreAccess::CheckedAccess<
+      variant_internal::IndexOf<T, Types...>::value>(v);
+}
+
+// Overload for getting a variant's const rvalue by type.
+// Note: `absl::move()` is required to allow use of constexpr in C++11.
+template <class T, class... Types>
+constexpr const T&& get(const variant<Types...>&& v) {
+  return variant_internal::VariantCoreAccess::CheckedAccess<
+      variant_internal::IndexOf<T, Types...>::value>(absl::move(v));
+}
+
+// Overload for getting a variant's lvalue by index.
+template <std::size_t I, class... Types>
+constexpr variant_alternative_t<I, variant<Types...>>& get(
+    variant<Types...>& v) {  // NOLINT
+  return variant_internal::VariantCoreAccess::CheckedAccess<I>(v);
+}
+
+// Overload for getting a variant's rvalue by index.
+// Note: `absl::move()` is required to allow use of constexpr in C++11.
+template <std::size_t I, class... Types>
+constexpr variant_alternative_t<I, variant<Types...>>&& get(
+    variant<Types...>&& v) {
+  return variant_internal::VariantCoreAccess::CheckedAccess<I>(absl::move(v));
+}
+
+// Overload for getting a variant's const lvalue by index.
+template <std::size_t I, class... Types>
+constexpr const variant_alternative_t<I, variant<Types...>>& get(
+    const variant<Types...>& v) {
+  return variant_internal::VariantCoreAccess::CheckedAccess<I>(v);
+}
+
+// Overload for getting a variant's const rvalue by index.
+// Note: `absl::move()` is required to allow use of constexpr in C++11.
+template <std::size_t I, class... Types>
+constexpr const variant_alternative_t<I, variant<Types...>>&& get(
+    const variant<Types...>&& v) {
+  return variant_internal::VariantCoreAccess::CheckedAccess<I>(absl::move(v));
+}
+
+// get_if()
+//
+// Returns a pointer to the value currently stored within a given variant, if
+// present, using either a unique alternative type amongst the variant's set of
+// alternative types, or the variant's index value. If such a value does not
+// exist, returns `nullptr`.
+//
+// As with `get`, attempting to get a variant's value using a type that is not
+// unique within the variant's set of alternative types is a compile-time error.
+
+// Overload for getting a pointer to the value stored in the given variant by
+// index.
+template <std::size_t I, class... Types>
+constexpr absl::add_pointer_t<variant_alternative_t<I, variant<Types...>>>
+get_if(variant<Types...>* v) noexcept {
+  return (v != nullptr && v->index() == I)
+             ? std::addressof(
+                   variant_internal::VariantCoreAccess::Access<I>(*v))
+             : nullptr;
+}
+
+// Overload for getting a pointer to the const value stored in the given
+// variant by index.
+template <std::size_t I, class... Types>
+constexpr absl::add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
+get_if(const variant<Types...>* v) noexcept {
+  return (v != nullptr && v->index() == I)
+             ? std::addressof(
+                   variant_internal::VariantCoreAccess::Access<I>(*v))
+             : nullptr;
+}
+
+// Overload for getting a pointer to the value stored in the given variant by
+// type.
+template <class T, class... Types>
+constexpr absl::add_pointer_t<T> get_if(variant<Types...>* v) noexcept {
+  return absl::get_if<variant_internal::IndexOf<T, Types...>::value>(v);
+}
+
+// Overload for getting a pointer to the const value stored in the given variant
+// by type.
+template <class T, class... Types>
+constexpr absl::add_pointer_t<const T> get_if(
+    const variant<Types...>* v) noexcept {
+  return absl::get_if<variant_internal::IndexOf<T, Types...>::value>(v);
+}
+
+// visit()
+//
+// Calls a provided functor on a given set of variants. `absl::visit()` is
+// commonly used to conditionally inspect the state of a given variant (or set
+// of variants).
+//
+// The functor must return the same type when called with any of the variants'
+// alternatives.
+//
+// Example:
+//
+//   // Define a visitor functor
+//   struct GetVariant {
+//       template<typename T>
+//       void operator()(const T& i) const {
+//         std::cout << "The variant's value is: " << i;
+//       }
+//   };
+//
+//   // Declare our variant, and call `absl::visit()` on it.
+//   // Note that `GetVariant()` returns void in either case.
+//   absl::variant<int, std::string> foo = std::string("foo");
+//   GetVariant visitor;
+//   absl::visit(visitor, foo);  // Prints `The variant's value is: foo'
+template <typename Visitor, typename... Variants>
+variant_internal::VisitResult<Visitor, Variants...> visit(Visitor&& vis,
+                                                          Variants&&... vars) {
+  return variant_internal::
+      VisitIndices<variant_size<absl::decay_t<Variants> >::value...>::Run(
+          variant_internal::PerformVisitation<Visitor, Variants...>{
+              std::forward_as_tuple(absl::forward<Variants>(vars)...),
+              absl::forward<Visitor>(vis)},
+          vars.index()...);
+}
+
+// monostate
+//
+// The monostate class serves as a first alternative type for a variant for
+// which the first variant type is otherwise not default-constructible.
+struct monostate {};
+
+// `absl::monostate` Relational Operators
+
+constexpr bool operator<(monostate, monostate) noexcept { return false; }
+constexpr bool operator>(monostate, monostate) noexcept { return false; }
+constexpr bool operator<=(monostate, monostate) noexcept { return true; }
+constexpr bool operator>=(monostate, monostate) noexcept { return true; }
+constexpr bool operator==(monostate, monostate) noexcept { return true; }
+constexpr bool operator!=(monostate, monostate) noexcept { return false; }
+
+
+//------------------------------------------------------------------------------
+// `absl::variant` Template Definition
+//------------------------------------------------------------------------------
+template <typename T0, typename... Tn>
+class variant<T0, Tn...> : private variant_internal::VariantBase<T0, Tn...> {
+  static_assert(absl::conjunction<std::is_object<T0>,
+                                  std::is_object<Tn>...>::value,
+                "Attempted to instantiate a variant containing a non-object "
+                "type.");
+  // Intentionally not qualifying `negation` with `absl::` to work around a bug
+  // in MSVC 2015 with inline namespace and variadic template.
+  static_assert(absl::conjunction<negation<std::is_array<T0> >,
+                                  negation<std::is_array<Tn> >...>::value,
+                "Attempted to instantiate a variant containing an array type.");
+  static_assert(absl::conjunction<std::is_nothrow_destructible<T0>,
+                                  std::is_nothrow_destructible<Tn>...>::value,
+                "Attempted to instantiate a variant containing a non-nothrow "
+                "destructible type.");
+
+  friend struct variant_internal::VariantCoreAccess;
+
+ private:
+  using Base = variant_internal::VariantBase<T0, Tn...>;
+
+ public:
+  // Constructors
+
+  // Constructs a variant holding a default-initialized value of the first
+  // alternative type.
+  constexpr variant() /*noexcept(see 111above)*/ = default;
+
+  // Copy constructor, standard semantics
+  variant(const variant& other) = default;
+
+  // Move constructor, standard semantics
+  variant(variant&& other) /*noexcept(see above)*/ = default;
+
+  // Constructs a variant of an alternative type specified by overload
+  // resolution of the provided forwarding arguments through
+  // direct-initialization.
+  //
+  // Note: If the selected constructor is a constexpr constructor, this
+  // constructor shall be a constexpr constructor.
+  //
+  // NOTE: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0608r1.html
+  // has been voted passed the design phase in the C++ standard meeting in Mar
+  // 2018. It will be implemented and integrated into `absl::variant`.
+  template <
+      class T,
+      std::size_t I = std::enable_if<
+          variant_internal::IsNeitherSelfNorInPlace<variant,
+                                                    absl::decay_t<T>>::value,
+          variant_internal::IndexOfConstructedType<variant, T>>::type::value,
+      class Tj = absl::variant_alternative_t<I, variant>,
+      absl::enable_if_t<std::is_constructible<Tj, T>::value>* =
+          nullptr>
+  constexpr variant(T&& t) noexcept(std::is_nothrow_constructible<Tj, T>::value)
+      : Base(variant_internal::EmplaceTag<I>(), absl::forward<T>(t)) {}
+
+  // Constructs a variant of an alternative type from the arguments through
+  // direct-initialization.
+  //
+  // Note: If the selected constructor is a constexpr constructor, this
+  // constructor shall be a constexpr constructor.
+  template <class T, class... Args,
+            typename std::enable_if<std::is_constructible<
+                variant_internal::UnambiguousTypeOfT<variant, T>,
+                Args...>::value>::type* = nullptr>
+  constexpr explicit variant(in_place_type_t<T>, Args&&... args)
+      : Base(variant_internal::EmplaceTag<
+                 variant_internal::UnambiguousIndexOf<variant, T>::value>(),
+             absl::forward<Args>(args)...) {}
+
+  // Constructs a variant of an alternative type from an initializer list
+  // and other arguments through direct-initialization.
+  //
+  // Note: If the selected constructor is a constexpr constructor, this
+  // constructor shall be a constexpr constructor.
+  template <class T, class U, class... Args,
+            typename std::enable_if<std::is_constructible<
+                variant_internal::UnambiguousTypeOfT<variant, T>,
+                std::initializer_list<U>&, Args...>::value>::type* = nullptr>
+  constexpr explicit variant(in_place_type_t<T>, std::initializer_list<U> il,
+                             Args&&... args)
+      : Base(variant_internal::EmplaceTag<
+                 variant_internal::UnambiguousIndexOf<variant, T>::value>(),
+             il, absl::forward<Args>(args)...) {}
+
+  // Constructs a variant of an alternative type from a provided index,
+  // through value-initialization using the provided forwarded arguments.
+  template <std::size_t I, class... Args,
+            typename std::enable_if<std::is_constructible<
+                variant_internal::VariantAlternativeSfinaeT<I, variant>,
+                Args...>::value>::type* = nullptr>
+  constexpr explicit variant(in_place_index_t<I>, Args&&... args)
+      : Base(variant_internal::EmplaceTag<I>(), absl::forward<Args>(args)...) {}
+
+  // Constructs a variant of an alternative type from a provided index,
+  // through value-initialization of an initializer list and the provided
+  // forwarded arguments.
+  template <std::size_t I, class U, class... Args,
+            typename std::enable_if<std::is_constructible<
+                variant_internal::VariantAlternativeSfinaeT<I, variant>,
+                std::initializer_list<U>&, Args...>::value>::type* = nullptr>
+  constexpr explicit variant(in_place_index_t<I>, std::initializer_list<U> il,
+                             Args&&... args)
+      : Base(variant_internal::EmplaceTag<I>(), il,
+             absl::forward<Args>(args)...) {}
+
+  // Destructors
+
+  // Destroys the variant's currently contained value, provided that
+  // `absl::valueless_by_exception()` is false.
+  ~variant() = default;
+
+  // Assignment Operators
+
+  // Copy assignment operator
+  variant& operator=(const variant& other) = default;
+
+  // Move assignment operator
+  variant& operator=(variant&& other) /*noexcept(see above)*/ = default;
+
+  // Converting assignment operator
+  //
+  // NOTE: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0608r1.html
+  // has been voted passed the design phase in the C++ standard meeting in Mar
+  // 2018. It will be implemented and integrated into `absl::variant`.
+  template <
+      class T,
+      std::size_t I = std::enable_if<
+          !std::is_same<absl::decay_t<T>, variant>::value,
+          variant_internal::IndexOfConstructedType<variant, T>>::type::value,
+      class Tj = absl::variant_alternative_t<I, variant>,
+      typename std::enable_if<std::is_assignable<Tj&, T>::value &&
+                              std::is_constructible<Tj, T>::value>::type* =
+          nullptr>
+  variant& operator=(T&& t) noexcept(
+      std::is_nothrow_assignable<Tj&, T>::value&&
+          std::is_nothrow_constructible<Tj, T>::value) {
+    variant_internal::VisitIndices<sizeof...(Tn) + 1>::Run(
+        variant_internal::VariantCoreAccess::MakeConversionAssignVisitor(
+            this, absl::forward<T>(t)),
+        index());
+
+    return *this;
+  }
+
+
+  // emplace() Functions
+
+  // Constructs a value of the given alternative type T within the variant.
+  //
+  // Example:
+  //
+  //   absl::variant<std::vector<int>, int, std::string> v;
+  //   v.emplace<int>(99);
+  //   v.emplace<std::string>("abc");
+  template <
+      class T, class... Args,
+      typename std::enable_if<std::is_constructible<
+          absl::variant_alternative_t<
+              variant_internal::UnambiguousIndexOf<variant, T>::value, variant>,
+          Args...>::value>::type* = nullptr>
+  T& emplace(Args&&... args) {
+    return variant_internal::VariantCoreAccess::Replace<
+        variant_internal::UnambiguousIndexOf<variant, T>::value>(
+        this, absl::forward<Args>(args)...);
+  }
+
+  // Constructs a value of the given alternative type T within the variant using
+  // an initializer list.
+  //
+  // Example:
+  //
+  //   absl::variant<std::vector<int>, int, std::string> v;
+  //   v.emplace<std::vector<int>>({0, 1, 2});
+  template <
+      class T, class U, class... Args,
+      typename std::enable_if<std::is_constructible<
+          absl::variant_alternative_t<
+              variant_internal::UnambiguousIndexOf<variant, T>::value, variant>,
+          std::initializer_list<U>&, Args...>::value>::type* = nullptr>
+  T& emplace(std::initializer_list<U> il, Args&&... args) {
+    return variant_internal::VariantCoreAccess::Replace<
+        variant_internal::UnambiguousIndexOf<variant, T>::value>(
+        this, il, absl::forward<Args>(args)...);
+  }
+
+  // Destroys the current value of the variant (provided that
+  // `absl::valueless_by_exception()` is false, and constructs a new value at
+  // the given index.
+  //
+  // Example:
+  //
+  //   absl::variant<std::vector<int>, int, int> v;
+  //   v.emplace<1>(99);
+  //   v.emplace<2>(98);
+  //   v.emplace<int>(99);  // Won't compile. 'int' isn't a unique type.
+  template <std::size_t I, class... Args,
+            typename std::enable_if<
+                std::is_constructible<absl::variant_alternative_t<I, variant>,
+                                      Args...>::value>::type* = nullptr>
+  absl::variant_alternative_t<I, variant>& emplace(Args&&... args) {
+    return variant_internal::VariantCoreAccess::Replace<I>(
+        this, absl::forward<Args>(args)...);
+  }
+
+  // Destroys the current value of the variant (provided that
+  // `absl::valueless_by_exception()` is false, and constructs a new value at
+  // the given index using an initializer list and the provided arguments.
+  //
+  // Example:
+  //
+  //   absl::variant<std::vector<int>, int, int> v;
+  //   v.emplace<0>({0, 1, 2});
+  template <std::size_t I, class U, class... Args,
+            typename std::enable_if<std::is_constructible<
+                absl::variant_alternative_t<I, variant>,
+                std::initializer_list<U>&, Args...>::value>::type* = nullptr>
+  absl::variant_alternative_t<I, variant>& emplace(std::initializer_list<U> il,
+                                                   Args&&... args) {
+    return variant_internal::VariantCoreAccess::Replace<I>(
+        this, il, absl::forward<Args>(args)...);
+  }
+
+  // variant::valueless_by_exception()
+  //
+  // Returns false if and only if the variant currently holds a valid value.
+  constexpr bool valueless_by_exception() const noexcept {
+    return this->index_ == absl::variant_npos;
+  }
+
+  // variant::index()
+  //
+  // Returns the index value of the variant's currently selected alternative
+  // type.
+  constexpr std::size_t index() const noexcept { return this->index_; }
+
+  // variant::swap()
+  //
+  // Swaps the values of two variant objects.
+  //
+  void swap(variant& rhs) noexcept(
+      absl::conjunction<
+          std::is_nothrow_move_constructible<T0>,
+          std::is_nothrow_move_constructible<Tn>...,
+          type_traits_internal::IsNothrowSwappable<T0>,
+          type_traits_internal::IsNothrowSwappable<Tn>...>::value) {
+    return variant_internal::VisitIndices<sizeof...(Tn) + 1>::Run(
+        variant_internal::Swap<T0, Tn...>{this, &rhs}, rhs.index());
+  }
+};
+
+// We need a valid declaration of variant<> for SFINAE and overload resolution
+// to work properly above, but we don't need a full declaration since this type
+// will never be constructed. This declaration, though incomplete, suffices.
+template <>
+class variant<>;
+
+//------------------------------------------------------------------------------
+// Relational Operators
+//------------------------------------------------------------------------------
+//
+// If neither operand is in the `variant::valueless_by_exception` state:
+//
+//   * If the index of both variants is the same, the relational operator
+//     returns the result of the corresponding relational operator for the
+//     corresponding alternative type.
+//   * If the index of both variants is not the same, the relational operator
+//     returns the result of that operation applied to the value of the left
+//     operand's index and the value of the right operand's index.
+//   * If at least one operand is in the valueless_by_exception state:
+//     - A variant in the valueless_by_exception state is only considered equal
+//       to another variant in the valueless_by_exception state.
+//     - If exactly one operand is in the valueless_by_exception state, the
+//       variant in the valueless_by_exception state is less than the variant
+//       that is not in the valueless_by_exception state.
+//
+// Note: The value 1 is added to each index in the relational comparisons such
+// that the index corresponding to the valueless_by_exception state wraps around
+// to 0 (the lowest value for the index type), and the remaining indices stay in
+// the same relative order.
+
+// Equal-to operator
+template <typename... Types>
+constexpr variant_internal::RequireAllHaveEqualT<Types...> operator==(
+    const variant<Types...>& a, const variant<Types...>& b) {
+  return (a.index() == b.index()) &&
+         variant_internal::VisitIndices<sizeof...(Types)>::Run(
+             variant_internal::EqualsOp<Types...>{&a, &b}, a.index());
+}
+
+// Not equal operator
+template <typename... Types>
+constexpr variant_internal::RequireAllHaveNotEqualT<Types...> operator!=(
+    const variant<Types...>& a, const variant<Types...>& b) {
+  return (a.index() != b.index()) ||
+         variant_internal::VisitIndices<sizeof...(Types)>::Run(
+             variant_internal::NotEqualsOp<Types...>{&a, &b}, a.index());
+}
+
+// Less-than operator
+template <typename... Types>
+constexpr variant_internal::RequireAllHaveLessThanT<Types...> operator<(
+    const variant<Types...>& a, const variant<Types...>& b) {
+  return (a.index() != b.index())
+             ? (a.index() + 1) < (b.index() + 1)
+             : variant_internal::VisitIndices<sizeof...(Types)>::Run(
+                   variant_internal::LessThanOp<Types...>{&a, &b}, a.index());
+}
+
+// Greater-than operator
+template <typename... Types>
+constexpr variant_internal::RequireAllHaveGreaterThanT<Types...> operator>(
+    const variant<Types...>& a, const variant<Types...>& b) {
+  return (a.index() != b.index())
+             ? (a.index() + 1) > (b.index() + 1)
+             : variant_internal::VisitIndices<sizeof...(Types)>::Run(
+                   variant_internal::GreaterThanOp<Types...>{&a, &b},
+                   a.index());
+}
+
+// Less-than or equal-to operator
+template <typename... Types>
+constexpr variant_internal::RequireAllHaveLessThanOrEqualT<Types...> operator<=(
+    const variant<Types...>& a, const variant<Types...>& b) {
+  return (a.index() != b.index())
+             ? (a.index() + 1) < (b.index() + 1)
+             : variant_internal::VisitIndices<sizeof...(Types)>::Run(
+                   variant_internal::LessThanOrEqualsOp<Types...>{&a, &b},
+                   a.index());
+}
+
+// Greater-than or equal-to operator
+template <typename... Types>
+constexpr variant_internal::RequireAllHaveGreaterThanOrEqualT<Types...>
+operator>=(const variant<Types...>& a, const variant<Types...>& b) {
+  return (a.index() != b.index())
+             ? (a.index() + 1) > (b.index() + 1)
+             : variant_internal::VisitIndices<sizeof...(Types)>::Run(
+                   variant_internal::GreaterThanOrEqualsOp<Types...>{&a, &b},
+                   a.index());
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+namespace std {
+
+// hash()
+template <>  // NOLINT
+struct hash<absl::monostate> {
+  std::size_t operator()(absl::monostate) const { return 0; }
+};
+
+template <class... T>  // NOLINT
+struct hash<absl::variant<T...>>
+    : absl::variant_internal::VariantHashBase<absl::variant<T...>, void,
+                                              absl::remove_const_t<T>...> {};
+
+}  // namespace std
+
+#endif  // ABSL_USES_STD_VARIANT
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace variant_internal {
+
+// Helper visitor for converting a variant<Ts...>` into another type (mostly
+// variant) that can be constructed from any type.
+template <typename To>
+struct ConversionVisitor {
+  template <typename T>
+  To operator()(T&& v) const {
+    return To(std::forward<T>(v));
+  }
+};
+
+}  // namespace variant_internal
+
+// ConvertVariantTo()
+//
+// Helper functions to convert an `absl::variant` to a variant of another set of
+// types, provided that the alternative type of the new variant type can be
+// converted from any type in the source variant.
+//
+// Example:
+//
+//   absl::variant<name1, name2, float> InternalReq(const Req&);
+//
+//   // name1 and name2 are convertible to name
+//   absl::variant<name, float> ExternalReq(const Req& req) {
+//     return absl::ConvertVariantTo<absl::variant<name, float>>(
+//              InternalReq(req));
+//   }
+template <typename To, typename Variant>
+To ConvertVariantTo(Variant&& variant) {
+  return absl::visit(variant_internal::ConversionVisitor<To>{},
+                     std::forward<Variant>(variant));
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TYPES_VARIANT_H_
diff --git a/third_party/abseil_cpp/absl/types/variant_benchmark.cc b/third_party/abseil_cpp/absl/types/variant_benchmark.cc
new file mode 100644
index 0000000000..350b175364
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/variant_benchmark.cc
@@ -0,0 +1,222 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Unit tests for the variant template. The 'is' and 'IsEmpty' methods
+// of variant are not explicitly tested because they are used repeatedly
+// in building other tests. All other public variant methods should have
+// explicit tests.
+
+#include "absl/types/variant.h"
+
+#include <cstddef>
+#include <cstdlib>
+#include <string>
+#include <tuple>
+
+#include "benchmark/benchmark.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace {
+
+template <std::size_t I>
+struct VariantAlternative {
+  char member;
+};
+
+template <class Indices>
+struct VariantOfAlternativesImpl;
+
+template <std::size_t... Indices>
+struct VariantOfAlternativesImpl<absl::index_sequence<Indices...>> {
+  using type = absl::variant<VariantAlternative<Indices>...>;
+};
+
+template <std::size_t NumAlternatives>
+using VariantOfAlternatives = typename VariantOfAlternativesImpl<
+    absl::make_index_sequence<NumAlternatives>>::type;
+
+struct Empty {};
+
+template <class... T>
+void Ignore(T...) noexcept {}
+
+template <class T>
+Empty DoNotOptimizeAndReturnEmpty(T&& arg) noexcept {
+  benchmark::DoNotOptimize(arg);
+  return {};
+}
+
+struct VisitorApplier {
+  struct Visitor {
+    template <class... T>
+    void operator()(T&&... args) const noexcept {
+      Ignore(DoNotOptimizeAndReturnEmpty(args)...);
+    }
+  };
+
+  template <class... Vars>
+  void operator()(const Vars&... vars) const noexcept {
+    absl::visit(Visitor(), vars...);
+  }
+};
+
+template <std::size_t NumIndices, std::size_t CurrIndex = NumIndices - 1>
+struct MakeWithIndex {
+  using Variant = VariantOfAlternatives<NumIndices>;
+
+  static Variant Run(std::size_t index) {
+    return index == CurrIndex
+               ? Variant(absl::in_place_index_t<CurrIndex>())
+               : MakeWithIndex<NumIndices, CurrIndex - 1>::Run(index);
+  }
+};
+
+template <std::size_t NumIndices>
+struct MakeWithIndex<NumIndices, 0> {
+  using Variant = VariantOfAlternatives<NumIndices>;
+
+  static Variant Run(std::size_t /*index*/) { return Variant(); }
+};
+
+template <std::size_t NumIndices, class Dimensions>
+struct MakeVariantTuple;
+
+template <class T, std::size_t /*I*/>
+using always_t = T;
+
+template <std::size_t NumIndices>
+VariantOfAlternatives<NumIndices> MakeVariant(std::size_t dimension,
+                                              std::size_t index) {
+  return dimension == 0
+             ? MakeWithIndex<NumIndices>::Run(index % NumIndices)
+             : MakeVariant<NumIndices>(dimension - 1, index / NumIndices);
+}
+
+template <std::size_t NumIndices, std::size_t... Dimensions>
+struct MakeVariantTuple<NumIndices, absl::index_sequence<Dimensions...>> {
+  using VariantTuple =
+      std::tuple<always_t<VariantOfAlternatives<NumIndices>, Dimensions>...>;
+
+  static VariantTuple Run(int index) {
+    return std::make_tuple(MakeVariant<NumIndices>(Dimensions, index)...);
+  }
+};
+
+constexpr std::size_t integral_pow(std::size_t base, std::size_t power) {
+  return power == 0 ? 1 : base * integral_pow(base, power - 1);
+}
+
+template <std::size_t End, std::size_t I = 0>
+struct VisitTestBody {
+  template <class Vars, class State>
+  static bool Run(Vars& vars, State& state) {
+    if (state.KeepRunning()) {
+      absl::apply(VisitorApplier(), vars[I]);
+      return VisitTestBody<End, I + 1>::Run(vars, state);
+    }
+    return false;
+  }
+};
+
+template <std::size_t End>
+struct VisitTestBody<End, End> {
+  template <class Vars, class State>
+  static bool Run(Vars& /*vars*/, State& /*state*/) {
+    return true;
+  }
+};
+
+// Visit operations where branch prediction is likely to give a boost.
+template <std::size_t NumIndices, std::size_t NumDimensions = 1>
+void BM_RedundantVisit(benchmark::State& state) {
+  auto vars =
+      MakeVariantTuple<NumIndices, absl::make_index_sequence<NumDimensions>>::
+          Run(static_cast<std::size_t>(state.range(0)));
+
+  for (auto _ : state) {  // NOLINT
+    benchmark::DoNotOptimize(vars);
+    absl::apply(VisitorApplier(), vars);
+  }
+}
+
+// Visit operations where branch prediction is unlikely to give a boost.
+template <std::size_t NumIndices, std::size_t NumDimensions = 1>
+void BM_Visit(benchmark::State& state) {
+  constexpr std::size_t num_possibilities =
+      integral_pow(NumIndices, NumDimensions);
+
+  using VariantTupleMaker =
+      MakeVariantTuple<NumIndices, absl::make_index_sequence<NumDimensions>>;
+  using Tuple = typename VariantTupleMaker::VariantTuple;
+
+  Tuple vars[num_possibilities];
+  for (std::size_t i = 0; i < num_possibilities; ++i)
+    vars[i] = VariantTupleMaker::Run(i);
+
+  while (VisitTestBody<num_possibilities>::Run(vars, state)) {
+  }
+}
+
+// Visitation
+//   Each visit is on a different variant with a different active alternative)
+
+// Unary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1);
+BENCHMARK_TEMPLATE(BM_Visit, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 3);
+BENCHMARK_TEMPLATE(BM_Visit, 4);
+BENCHMARK_TEMPLATE(BM_Visit, 5);
+BENCHMARK_TEMPLATE(BM_Visit, 6);
+BENCHMARK_TEMPLATE(BM_Visit, 7);
+BENCHMARK_TEMPLATE(BM_Visit, 8);
+BENCHMARK_TEMPLATE(BM_Visit, 16);
+BENCHMARK_TEMPLATE(BM_Visit, 32);
+BENCHMARK_TEMPLATE(BM_Visit, 64);
+
+// Binary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 2, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 3, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 4, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 5, 2);
+
+// Ternary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1, 3);
+BENCHMARK_TEMPLATE(BM_Visit, 2, 3);
+BENCHMARK_TEMPLATE(BM_Visit, 3, 3);
+
+// Quaternary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1, 4);
+BENCHMARK_TEMPLATE(BM_Visit, 2, 4);
+
+// Redundant Visitation
+//   Each visit consistently has the same alternative active
+
+// Unary visit
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 1)->Arg(0);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 2)->DenseRange(0, 1);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 8)->DenseRange(0, 7);
+
+// Binary visit
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 1, 2)->Arg(0);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 2, 2)
+    ->DenseRange(0, integral_pow(2, 2) - 1);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 4, 2)
+    ->DenseRange(0, integral_pow(4, 2) - 1);
+
+}  // namespace
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/types/variant_exception_safety_test.cc b/third_party/abseil_cpp/absl/types/variant_exception_safety_test.cc
new file mode 100644
index 0000000000..439c6e1df3
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/variant_exception_safety_test.cc
@@ -0,0 +1,532 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/types/variant.h"
+
+#include "absl/base/config.h"
+
+// This test is a no-op when absl::variant is an alias for std::variant and when
+// exceptions are not enabled.
+#if !defined(ABSL_USES_STD_VARIANT) && defined(ABSL_HAVE_EXCEPTIONS)
+
+#include <iostream>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/internal/exception_safety_testing.h"
+#include "absl/memory/memory.h"
+
+// See comment in absl/base/config.h
+#if !defined(ABSL_INTERNAL_MSVC_2017_DBG_MODE)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace {
+
+using ::testing::MakeExceptionSafetyTester;
+using ::testing::strong_guarantee;
+using ::testing::TestNothrowOp;
+using ::testing::TestThrowingCtor;
+
+using Thrower = testing::ThrowingValue<>;
+using CopyNothrow = testing::ThrowingValue<testing::TypeSpec::kNoThrowCopy>;
+using MoveNothrow = testing::ThrowingValue<testing::TypeSpec::kNoThrowMove>;
+using ThrowingAlloc = testing::ThrowingAllocator<Thrower>;
+using ThrowerVec = std::vector<Thrower, ThrowingAlloc>;
+using ThrowingVariant =
+    absl::variant<Thrower, CopyNothrow, MoveNothrow, ThrowerVec>;
+
+struct ConversionException {};
+
+template <class T>
+struct ExceptionOnConversion {
+  operator T() const {  // NOLINT
+    throw ConversionException();
+  }
+};
+
+// Forces a variant into the valueless by exception state.
+void ToValuelessByException(ThrowingVariant& v) {  // NOLINT
+  try {
+    v.emplace<Thrower>();
+    v.emplace<Thrower>(ExceptionOnConversion<Thrower>());
+  } catch (const ConversionException&) {
+    // This space intentionally left blank.
+  }
+}
+
+// Check that variant is still in a usable state after an exception is thrown.
+testing::AssertionResult VariantInvariants(ThrowingVariant* v) {
+  using testing::AssertionFailure;
+  using testing::AssertionSuccess;
+
+  // Try using the active alternative
+  if (absl::holds_alternative<Thrower>(*v)) {
+    auto& t = absl::get<Thrower>(*v);
+    t = Thrower{-100};
+    if (t.Get() != -100) {
+      return AssertionFailure() << "Thrower should be assigned -100";
+    }
+  } else if (absl::holds_alternative<ThrowerVec>(*v)) {
+    auto& tv = absl::get<ThrowerVec>(*v);
+    tv.clear();
+    tv.emplace_back(-100);
+    if (tv.size() != 1 || tv[0].Get() != -100) {
+      return AssertionFailure() << "ThrowerVec should be {Thrower{-100}}";
+    }
+  } else if (absl::holds_alternative<CopyNothrow>(*v)) {
+    auto& t = absl::get<CopyNothrow>(*v);
+    t = CopyNothrow{-100};
+    if (t.Get() != -100) {
+      return AssertionFailure() << "CopyNothrow should be assigned -100";
+    }
+  } else if (absl::holds_alternative<MoveNothrow>(*v)) {
+    auto& t = absl::get<MoveNothrow>(*v);
+    t = MoveNothrow{-100};
+    if (t.Get() != -100) {
+      return AssertionFailure() << "MoveNothrow should be assigned -100";
+    }
+  }
+
+  // Try making variant valueless_by_exception
+  if (!v->valueless_by_exception()) ToValuelessByException(*v);
+  if (!v->valueless_by_exception()) {
+    return AssertionFailure() << "Variant should be valueless_by_exception";
+  }
+  try {
+    auto unused = absl::get<Thrower>(*v);
+    static_cast<void>(unused);
+    return AssertionFailure() << "Variant should not contain Thrower";
+  } catch (const absl::bad_variant_access&) {
+  } catch (...) {
+    return AssertionFailure() << "Unexpected exception throw from absl::get";
+  }
+
+  // Try using the variant
+  v->emplace<Thrower>(100);
+  if (!absl::holds_alternative<Thrower>(*v) ||
+      absl::get<Thrower>(*v) != Thrower(100)) {
+    return AssertionFailure() << "Variant should contain Thrower(100)";
+  }
+  v->emplace<ThrowerVec>({Thrower(100)});
+  if (!absl::holds_alternative<ThrowerVec>(*v) ||
+      absl::get<ThrowerVec>(*v)[0] != Thrower(100)) {
+    return AssertionFailure()
+           << "Variant should contain ThrowerVec{Thrower(100)}";
+  }
+  return AssertionSuccess();
+}
+
+template <typename... Args>
+Thrower ExpectedThrower(Args&&... args) {
+  return Thrower(42, args...);
+}
+
+ThrowerVec ExpectedThrowerVec() { return {Thrower(100), Thrower(200)}; }
+ThrowingVariant ValuelessByException() {
+  ThrowingVariant v;
+  ToValuelessByException(v);
+  return v;
+}
+ThrowingVariant WithThrower() { return Thrower(39); }
+ThrowingVariant WithThrowerVec() {
+  return ThrowerVec{Thrower(1), Thrower(2), Thrower(3)};
+}
+ThrowingVariant WithCopyNoThrow() { return CopyNothrow(39); }
+ThrowingVariant WithMoveNoThrow() { return MoveNothrow(39); }
+
+TEST(VariantExceptionSafetyTest, DefaultConstructor) {
+  TestThrowingCtor<ThrowingVariant>();
+}
+
+TEST(VariantExceptionSafetyTest, CopyConstructor) {
+  {
+    ThrowingVariant v(ExpectedThrower());
+    TestThrowingCtor<ThrowingVariant>(v);
+  }
+  {
+    ThrowingVariant v(ExpectedThrowerVec());
+    TestThrowingCtor<ThrowingVariant>(v);
+  }
+  {
+    ThrowingVariant v(ValuelessByException());
+    TestThrowingCtor<ThrowingVariant>(v);
+  }
+}
+
+TEST(VariantExceptionSafetyTest, MoveConstructor) {
+  {
+    ThrowingVariant v(ExpectedThrower());
+    TestThrowingCtor<ThrowingVariant>(std::move(v));
+  }
+  {
+    ThrowingVariant v(ExpectedThrowerVec());
+    TestThrowingCtor<ThrowingVariant>(std::move(v));
+  }
+  {
+    ThrowingVariant v(ValuelessByException());
+    TestThrowingCtor<ThrowingVariant>(std::move(v));
+  }
+}
+
+TEST(VariantExceptionSafetyTest, ValueConstructor) {
+  TestThrowingCtor<ThrowingVariant>(ExpectedThrower());
+  TestThrowingCtor<ThrowingVariant>(ExpectedThrowerVec());
+}
+
+TEST(VariantExceptionSafetyTest, InPlaceTypeConstructor) {
+  TestThrowingCtor<ThrowingVariant>(absl::in_place_type_t<Thrower>{},
+                                    ExpectedThrower());
+  TestThrowingCtor<ThrowingVariant>(absl::in_place_type_t<ThrowerVec>{},
+                                    ExpectedThrowerVec());
+}
+
+TEST(VariantExceptionSafetyTest, InPlaceIndexConstructor) {
+  TestThrowingCtor<ThrowingVariant>(absl::in_place_index_t<0>{},
+                                    ExpectedThrower());
+  TestThrowingCtor<ThrowingVariant>(absl::in_place_index_t<3>{},
+                                    ExpectedThrowerVec());
+}
+
+TEST(VariantExceptionSafetyTest, CopyAssign) {
+  // variant& operator=(const variant& rhs);
+  // Let j be rhs.index()
+  {
+    // - neither *this nor rhs holds a value
+    const ThrowingVariant rhs = ValuelessByException();
+    ThrowingVariant lhs = ValuelessByException();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = rhs; }));
+  }
+  {
+    // - *this holds a value but rhs does not
+    const ThrowingVariant rhs = ValuelessByException();
+    ThrowingVariant lhs = WithThrower();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = rhs; }));
+  }
+  // - index() == j
+  {
+    const ThrowingVariant rhs(ExpectedThrower());
+    auto tester =
+        MakeExceptionSafetyTester()
+            .WithInitialValue(WithThrower())
+            .WithOperation([&rhs](ThrowingVariant* lhs) { *lhs = rhs; });
+    EXPECT_TRUE(tester.WithContracts(VariantInvariants).Test());
+    EXPECT_FALSE(tester.WithContracts(strong_guarantee).Test());
+  }
+  {
+    const ThrowingVariant rhs(ExpectedThrowerVec());
+    auto tester =
+        MakeExceptionSafetyTester()
+            .WithInitialValue(WithThrowerVec())
+            .WithOperation([&rhs](ThrowingVariant* lhs) { *lhs = rhs; });
+    EXPECT_TRUE(tester.WithContracts(VariantInvariants).Test());
+    EXPECT_FALSE(tester.WithContracts(strong_guarantee).Test());
+  }
+  // libstdc++ std::variant has bugs on copy assignment regarding exception
+  // safety.
+#if !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+  // index() != j
+  // if is_nothrow_copy_constructible_v<Tj> or
+  // !is_nothrow_move_constructible<Tj> is true, equivalent to
+  // emplace<j>(get<j>(rhs))
+  {
+    // is_nothrow_copy_constructible_v<Tj> == true
+    // should not throw because emplace() invokes Tj's copy ctor
+    // which should not throw.
+    const ThrowingVariant rhs(CopyNothrow{});
+    ThrowingVariant lhs = WithThrower();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = rhs; }));
+  }
+  {
+    // is_nothrow_copy_constructible<Tj> == false &&
+    // is_nothrow_move_constructible<Tj> == false
+    // should provide basic guarantee because emplace() invokes Tj's copy ctor
+    // which may throw.
+    const ThrowingVariant rhs(ExpectedThrower());
+    auto tester =
+        MakeExceptionSafetyTester()
+            .WithInitialValue(WithCopyNoThrow())
+            .WithOperation([&rhs](ThrowingVariant* lhs) { *lhs = rhs; });
+    EXPECT_TRUE(tester
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* lhs) {
+                                     return lhs->valueless_by_exception();
+                                   })
+                    .Test());
+    EXPECT_FALSE(tester.WithContracts(strong_guarantee).Test());
+  }
+#endif  // !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+  {
+    // is_nothrow_copy_constructible_v<Tj> == false &&
+    // is_nothrow_move_constructible_v<Tj> == true
+    // should provide strong guarantee because it is equivalent to
+    // operator=(variant(rhs)) which creates a temporary then invoke the move
+    // ctor which shouldn't throw.
+    const ThrowingVariant rhs(MoveNothrow{});
+    EXPECT_TRUE(MakeExceptionSafetyTester()
+                    .WithInitialValue(WithThrower())
+                    .WithContracts(VariantInvariants, strong_guarantee)
+                    .Test([&rhs](ThrowingVariant* lhs) { *lhs = rhs; }));
+  }
+}
+
+TEST(VariantExceptionSafetyTest, MoveAssign) {
+  // variant& operator=(variant&& rhs);
+  // Let j be rhs.index()
+  {
+    // - neither *this nor rhs holds a value
+    ThrowingVariant rhs = ValuelessByException();
+    ThrowingVariant lhs = ValuelessByException();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = std::move(rhs); }));
+  }
+  {
+    // - *this holds a value but rhs does not
+    ThrowingVariant rhs = ValuelessByException();
+    ThrowingVariant lhs = WithThrower();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = std::move(rhs); }));
+  }
+  {
+    // - index() == j
+    // assign get<j>(std::move(rhs)) to the value contained in *this.
+    // If an exception is thrown during call to Tj's move assignment, the state
+    // of the contained value is as defined by the exception safety guarantee of
+    // Tj's move assignment; index() will be j.
+    ThrowingVariant rhs(ExpectedThrower());
+    size_t j = rhs.index();
+    // Since Thrower's move assignment has basic guarantee, so should variant's.
+    auto tester = MakeExceptionSafetyTester()
+                      .WithInitialValue(WithThrower())
+                      .WithOperation([&](ThrowingVariant* lhs) {
+                        auto copy = rhs;
+                        *lhs = std::move(copy);
+                      });
+    EXPECT_TRUE(tester
+                    .WithContracts(
+                        VariantInvariants,
+                        [&](ThrowingVariant* lhs) { return lhs->index() == j; })
+                    .Test());
+    EXPECT_FALSE(tester.WithContracts(strong_guarantee).Test());
+  }
+  {
+    // libstdc++ introduced a regression between 2018-09-25 and 2019-01-06.
+    // The fix is targeted for gcc-9.
+    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87431#c7
+    // https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=267614
+#if !(defined(ABSL_USES_STD_VARIANT) && \
+      defined(_GLIBCXX_RELEASE) && _GLIBCXX_RELEASE == 8)
+    // - otherwise (index() != j), equivalent to
+    // emplace<j>(get<j>(std::move(rhs)))
+    // - If an exception is thrown during the call to Tj's move construction
+    // (with j being rhs.index()), the variant will hold no value.
+    ThrowingVariant rhs(CopyNothrow{});
+    EXPECT_TRUE(MakeExceptionSafetyTester()
+                    .WithInitialValue(WithThrower())
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* lhs) {
+                                     return lhs->valueless_by_exception();
+                                   })
+                    .Test([&](ThrowingVariant* lhs) {
+                      auto copy = rhs;
+                      *lhs = std::move(copy);
+                    }));
+#endif  // !(defined(ABSL_USES_STD_VARIANT) &&
+        //   defined(_GLIBCXX_RELEASE) && _GLIBCXX_RELEASE == 8)
+  }
+}
+
+TEST(VariantExceptionSafetyTest, ValueAssign) {
+  // template<class T> variant& operator=(T&& t);
+  // Let Tj be the type that is selected by overload resolution to be assigned.
+  {
+    // If *this holds a Tj, assigns std::forward<T>(t) to the value contained in
+    // *this. If  an exception is thrown during the assignment of
+    // std::forward<T>(t) to the value contained in *this, the state of the
+    // contained value and t are as defined by the exception safety guarantee of
+    // the assignment expression; valueless_by_exception() will be false.
+    // Since Thrower's copy/move assignment has basic guarantee, so should
+    // variant's.
+    Thrower rhs = ExpectedThrower();
+    // copy assign
+    auto copy_tester =
+        MakeExceptionSafetyTester()
+            .WithInitialValue(WithThrower())
+            .WithOperation([rhs](ThrowingVariant* lhs) { *lhs = rhs; });
+    EXPECT_TRUE(copy_tester
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* lhs) {
+                                     return !lhs->valueless_by_exception();
+                                   })
+                    .Test());
+    EXPECT_FALSE(copy_tester.WithContracts(strong_guarantee).Test());
+    // move assign
+    auto move_tester = MakeExceptionSafetyTester()
+                           .WithInitialValue(WithThrower())
+                           .WithOperation([&](ThrowingVariant* lhs) {
+                             auto copy = rhs;
+                             *lhs = std::move(copy);
+                           });
+    EXPECT_TRUE(move_tester
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* lhs) {
+                                     return !lhs->valueless_by_exception();
+                                   })
+                    .Test());
+
+    EXPECT_FALSE(move_tester.WithContracts(strong_guarantee).Test());
+  }
+  // Otherwise (*this holds something else), if is_nothrow_constructible_v<Tj,
+  // T> || !is_nothrow_move_constructible_v<Tj> is true, equivalent to
+  // emplace<j>(std::forward<T>(t)).
+  // We simplify the test by letting T = `const Tj&`  or `Tj&&`, so we can reuse
+  // the CopyNothrow and MoveNothrow types.
+
+  // if is_nothrow_constructible_v<Tj, T>
+  // (i.e. is_nothrow_copy/move_constructible_v<Tj>) is true, emplace() just
+  // invokes the copy/move constructor and it should not throw.
+  {
+    const CopyNothrow rhs;
+    ThrowingVariant lhs = WithThrower();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = rhs; }));
+  }
+  {
+    MoveNothrow rhs;
+    ThrowingVariant lhs = WithThrower();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs = std::move(rhs); }));
+  }
+  // if is_nothrow_constructible_v<Tj, T> == false &&
+  // is_nothrow_move_constructible<Tj> == false
+  // emplace() invokes the copy/move constructor which may throw so it should
+  // provide basic guarantee and variant object might not hold a value.
+  {
+    Thrower rhs = ExpectedThrower();
+    // copy
+    auto copy_tester =
+        MakeExceptionSafetyTester()
+            .WithInitialValue(WithCopyNoThrow())
+            .WithOperation([&rhs](ThrowingVariant* lhs) { *lhs = rhs; });
+    EXPECT_TRUE(copy_tester
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* lhs) {
+                                     return lhs->valueless_by_exception();
+                                   })
+                    .Test());
+    EXPECT_FALSE(copy_tester.WithContracts(strong_guarantee).Test());
+    // move
+    auto move_tester = MakeExceptionSafetyTester()
+                           .WithInitialValue(WithCopyNoThrow())
+                           .WithOperation([](ThrowingVariant* lhs) {
+                             *lhs = ExpectedThrower(testing::nothrow_ctor);
+                           });
+    EXPECT_TRUE(move_tester
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* lhs) {
+                                     return lhs->valueless_by_exception();
+                                   })
+                    .Test());
+    EXPECT_FALSE(move_tester.WithContracts(strong_guarantee).Test());
+  }
+  // Otherwise (if is_nothrow_constructible_v<Tj, T> == false &&
+  // is_nothrow_move_constructible<Tj> == true),
+  // equivalent to operator=(variant(std::forward<T>(t)))
+  // This should have strong guarantee because it creates a temporary variant
+  // and operator=(variant&&) invokes Tj's move ctor which doesn't throw.
+  // libstdc++ std::variant has bugs on conversion assignment regarding
+  // exception safety.
+#if !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+  {
+    MoveNothrow rhs;
+    EXPECT_TRUE(MakeExceptionSafetyTester()
+                    .WithInitialValue(WithThrower())
+                    .WithContracts(VariantInvariants, strong_guarantee)
+                    .Test([&rhs](ThrowingVariant* lhs) { *lhs = rhs; }));
+  }
+#endif  // !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+}
+
+TEST(VariantExceptionSafetyTest, Emplace) {
+  // If an exception during the initialization of the contained value, the
+  // variant might not hold a value. The standard requires emplace() to provide
+  // only basic guarantee.
+  {
+    Thrower args = ExpectedThrower();
+    auto tester = MakeExceptionSafetyTester()
+                      .WithInitialValue(WithThrower())
+                      .WithOperation([&args](ThrowingVariant* v) {
+                        v->emplace<Thrower>(args);
+                      });
+    EXPECT_TRUE(tester
+                    .WithContracts(VariantInvariants,
+                                   [](ThrowingVariant* v) {
+                                     return v->valueless_by_exception();
+                                   })
+                    .Test());
+    EXPECT_FALSE(tester.WithContracts(strong_guarantee).Test());
+  }
+}
+
+TEST(VariantExceptionSafetyTest, Swap) {
+  // if both are valueless_by_exception(), no effect
+  {
+    ThrowingVariant rhs = ValuelessByException();
+    ThrowingVariant lhs = ValuelessByException();
+    EXPECT_TRUE(TestNothrowOp([&]() { lhs.swap(rhs); }));
+  }
+  // if index() == rhs.index(), calls swap(get<i>(*this), get<i>(rhs))
+  // where i is index().
+  {
+    ThrowingVariant rhs = ExpectedThrower();
+    EXPECT_TRUE(MakeExceptionSafetyTester()
+                    .WithInitialValue(WithThrower())
+                    .WithContracts(VariantInvariants)
+                    .Test([&](ThrowingVariant* lhs) {
+                      auto copy = rhs;
+                      lhs->swap(copy);
+                    }));
+  }
+  // Otherwise, exchanges the value of rhs and *this. The exception safety
+  // involves variant in moved-from state which is not specified in the
+  // standard, and since swap is 3-step it's impossible for it to provide a
+  // overall strong guarantee. So, we are only checking basic guarantee here.
+  {
+    ThrowingVariant rhs = ExpectedThrower();
+    EXPECT_TRUE(MakeExceptionSafetyTester()
+                    .WithInitialValue(WithCopyNoThrow())
+                    .WithContracts(VariantInvariants)
+                    .Test([&](ThrowingVariant* lhs) {
+                      auto copy = rhs;
+                      lhs->swap(copy);
+                    }));
+  }
+  {
+    ThrowingVariant rhs = ExpectedThrower();
+    EXPECT_TRUE(MakeExceptionSafetyTester()
+                    .WithInitialValue(WithCopyNoThrow())
+                    .WithContracts(VariantInvariants)
+                    .Test([&](ThrowingVariant* lhs) {
+                      auto copy = rhs;
+                      copy.swap(*lhs);
+                    }));
+  }
+}
+
+}  // namespace
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // !defined(ABSL_INTERNAL_MSVC_2017_DBG_MODE)
+
+#endif  // #if !defined(ABSL_USES_STD_VARIANT) && defined(ABSL_HAVE_EXCEPTIONS)
diff --git a/third_party/abseil_cpp/absl/types/variant_test.cc b/third_party/abseil_cpp/absl/types/variant_test.cc
new file mode 100644
index 0000000000..cf8f7f3374
--- /dev/null
+++ b/third_party/abseil_cpp/absl/types/variant_test.cc
@@ -0,0 +1,2716 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Unit tests for the variant template. The 'is' and 'IsEmpty' methods
+// of variant are not explicitly tested because they are used repeatedly
+// in building other tests. All other public variant methods should have
+// explicit tests.
+
+#include "absl/types/variant.h"
+
+// This test is a no-op when absl::variant is an alias for std::variant.
+#if !defined(ABSL_USES_STD_VARIANT)
+
+#include <algorithm>
+#include <cstddef>
+#include <functional>
+#include <initializer_list>
+#include <memory>
+#include <ostream>
+#include <queue>
+#include <type_traits>
+#include <unordered_set>
+#include <utility>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/base/port.h"
+#include "absl/memory/memory.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/string_view.h"
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+
+#define ABSL_VARIANT_TEST_EXPECT_FAIL(expr, exception_t, text) \
+  EXPECT_THROW(expr, exception_t)
+
+#else
+
+#define ABSL_VARIANT_TEST_EXPECT_FAIL(expr, exception_t, text) \
+  EXPECT_DEATH_IF_SUPPORTED(expr, text)
+
+#endif  // ABSL_HAVE_EXCEPTIONS
+
+#define ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(...)                 \
+  ABSL_VARIANT_TEST_EXPECT_FAIL((void)(__VA_ARGS__), absl::bad_variant_access, \
+                                "Bad variant access")
+
+struct Hashable {};
+
+namespace std {
+template <>
+struct hash<Hashable> {
+  size_t operator()(const Hashable&);
+};
+}  // namespace std
+
+struct NonHashable {};
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace {
+
+using ::testing::DoubleEq;
+using ::testing::Pointee;
+using ::testing::VariantWith;
+
+struct MoveCanThrow {
+  MoveCanThrow() : v(0) {}
+  MoveCanThrow(int v) : v(v) {}  // NOLINT(runtime/explicit)
+  MoveCanThrow(const MoveCanThrow& other) : v(other.v) {}
+  MoveCanThrow& operator=(const MoveCanThrow& /*other*/) { return *this; }
+  int v;
+};
+
+bool operator==(MoveCanThrow lhs, MoveCanThrow rhs) { return lhs.v == rhs.v; }
+bool operator!=(MoveCanThrow lhs, MoveCanThrow rhs) { return lhs.v != rhs.v; }
+bool operator<(MoveCanThrow lhs, MoveCanThrow rhs) { return lhs.v < rhs.v; }
+bool operator<=(MoveCanThrow lhs, MoveCanThrow rhs) { return lhs.v <= rhs.v; }
+bool operator>=(MoveCanThrow lhs, MoveCanThrow rhs) { return lhs.v >= rhs.v; }
+bool operator>(MoveCanThrow lhs, MoveCanThrow rhs) { return lhs.v > rhs.v; }
+
+// This helper class allows us to determine if it was swapped with std::swap()
+// or with its friend swap() function.
+struct SpecialSwap {
+  explicit SpecialSwap(int i) : i(i) {}
+  friend void swap(SpecialSwap& a, SpecialSwap& b) {
+    a.special_swap = b.special_swap = true;
+    std::swap(a.i, b.i);
+  }
+  bool operator==(SpecialSwap other) const { return i == other.i; }
+  int i;
+  bool special_swap = false;
+};
+
+struct MoveOnlyWithListConstructor {
+  MoveOnlyWithListConstructor() = default;
+  explicit MoveOnlyWithListConstructor(std::initializer_list<int> /*ilist*/,
+                                       int value)
+      : value(value) {}
+  MoveOnlyWithListConstructor(MoveOnlyWithListConstructor&&) = default;
+  MoveOnlyWithListConstructor& operator=(MoveOnlyWithListConstructor&&) =
+      default;
+
+  int value = 0;
+};
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+
+struct ConversionException {};
+
+template <class T>
+struct ExceptionOnConversion {
+  operator T() const {  // NOLINT(runtime/explicit)
+    throw ConversionException();
+  }
+};
+
+// Forces a variant into the valueless by exception state.
+template <class H, class... T>
+void ToValuelessByException(absl::variant<H, T...>& v) {  // NOLINT
+  try {
+    v.template emplace<0>(ExceptionOnConversion<H>());
+  } catch (ConversionException& /*e*/) {
+    // This space intentionally left blank.
+  }
+}
+
+#endif  // ABSL_HAVE_EXCEPTIONS
+
+// An indexed sequence of distinct structures holding a single
+// value of type T
+template<typename T, size_t N>
+struct ValueHolder {
+  explicit ValueHolder(const T& x) : value(x) {}
+  typedef T value_type;
+  value_type value;
+  static const size_t kIndex = N;
+};
+template<typename T, size_t N>
+const size_t ValueHolder<T, N>::kIndex;
+
+// The following three functions make ValueHolder compatible with
+// EXPECT_EQ and EXPECT_NE
+template<typename T, size_t N>
+inline bool operator==(const ValueHolder<T, N>& left,
+                       const ValueHolder<T, N>& right) {
+  return left.value == right.value;
+}
+
+template<typename T, size_t N>
+inline bool operator!=(const ValueHolder<T, N>& left,
+                       const ValueHolder<T, N>& right) {
+  return left.value != right.value;
+}
+
+template<typename T, size_t N>
+inline std::ostream& operator<<(
+    std::ostream& stream, const ValueHolder<T, N>& object) {
+  return stream << object.value;
+}
+
+// Makes a variant holding twelve uniquely typed T wrappers.
+template<typename T>
+struct VariantFactory {
+  typedef variant<ValueHolder<T, 1>, ValueHolder<T, 2>, ValueHolder<T, 3>,
+                  ValueHolder<T, 4>>
+      Type;
+};
+
+// A typelist in 1:1 with VariantFactory, to use type driven unit tests.
+typedef ::testing::Types<ValueHolder<size_t, 1>, ValueHolder<size_t, 2>,
+                         ValueHolder<size_t, 3>,
+                         ValueHolder<size_t, 4>> VariantTypes;
+
+// Increments the provided counter pointer in the destructor
+struct IncrementInDtor {
+  explicit IncrementInDtor(int* counter) : counter(counter) {}
+  ~IncrementInDtor() { *counter += 1; }
+  int* counter;
+};
+
+struct IncrementInDtorCopyCanThrow {
+  explicit IncrementInDtorCopyCanThrow(int* counter) : counter(counter) {}
+  IncrementInDtorCopyCanThrow(IncrementInDtorCopyCanThrow&& other) noexcept =
+      default;
+  IncrementInDtorCopyCanThrow(const IncrementInDtorCopyCanThrow& other)
+      : counter(other.counter) {}
+  IncrementInDtorCopyCanThrow& operator=(
+      IncrementInDtorCopyCanThrow&&) noexcept = default;
+  IncrementInDtorCopyCanThrow& operator=(
+      IncrementInDtorCopyCanThrow const& other) {
+    counter = other.counter;
+    return *this;
+  }
+  ~IncrementInDtorCopyCanThrow() { *counter += 1; }
+  int* counter;
+};
+
+// This is defined so operator== for ValueHolder<IncrementInDtor> will
+// return true if two IncrementInDtor objects increment the same
+// counter
+inline bool operator==(const IncrementInDtor& left,
+                       const IncrementInDtor& right) {
+  return left.counter == right.counter;
+}
+
+// This is defined so EXPECT_EQ can work with IncrementInDtor
+inline std::ostream& operator<<(
+    std::ostream& stream, const IncrementInDtor& object) {
+  return stream << object.counter;
+}
+
+// A class that can be copied, but not assigned.
+class CopyNoAssign {
+ public:
+  explicit CopyNoAssign(int value) : foo(value) {}
+  CopyNoAssign(const CopyNoAssign& other) : foo(other.foo) {}
+  int foo;
+ private:
+  const CopyNoAssign& operator=(const CopyNoAssign&);
+};
+
+// A class that can neither be copied nor assigned. We provide
+// overloads for the constructor with up to four parameters so we can
+// test the overloads of variant::emplace.
+class NonCopyable {
+ public:
+  NonCopyable()
+      : value(0) {}
+  explicit NonCopyable(int value1)
+      : value(value1) {}
+
+  NonCopyable(int value1, int value2)
+      : value(value1 + value2) {}
+
+  NonCopyable(int value1, int value2, int value3)
+      : value(value1 + value2 + value3) {}
+
+  NonCopyable(int value1, int value2, int value3, int value4)
+      : value(value1 + value2 + value3 + value4) {}
+  NonCopyable(const NonCopyable&) = delete;
+  NonCopyable& operator=(const NonCopyable&) = delete;
+  int value;
+};
+
+// A typed test and typed test case over the VariantTypes typelist,
+// from which we derive a number of tests that will execute for one of
+// each type.
+template <typename T>
+class VariantTypesTest : public ::testing::Test {};
+TYPED_TEST_SUITE(VariantTypesTest, VariantTypes);
+
+////////////////////
+// [variant.ctor] //
+////////////////////
+
+struct NonNoexceptDefaultConstructible {
+  NonNoexceptDefaultConstructible() {}
+  int value = 5;
+};
+
+struct NonDefaultConstructible {
+  NonDefaultConstructible() = delete;
+};
+
+TEST(VariantTest, TestDefaultConstructor) {
+  {
+    using X = variant<int>;
+    constexpr variant<int> x{};
+    ASSERT_FALSE(x.valueless_by_exception());
+    ASSERT_EQ(0, x.index());
+    EXPECT_EQ(0, absl::get<0>(x));
+    EXPECT_TRUE(std::is_nothrow_default_constructible<X>::value);
+  }
+
+  {
+    using X = variant<NonNoexceptDefaultConstructible>;
+    X x{};
+    ASSERT_FALSE(x.valueless_by_exception());
+    ASSERT_EQ(0, x.index());
+    EXPECT_EQ(5, absl::get<0>(x).value);
+    EXPECT_FALSE(std::is_nothrow_default_constructible<X>::value);
+  }
+
+  {
+    using X = variant<int, NonNoexceptDefaultConstructible>;
+    X x{};
+    ASSERT_FALSE(x.valueless_by_exception());
+    ASSERT_EQ(0, x.index());
+    EXPECT_EQ(0, absl::get<0>(x));
+    EXPECT_TRUE(std::is_nothrow_default_constructible<X>::value);
+  }
+
+  {
+    using X = variant<NonNoexceptDefaultConstructible, int>;
+    X x{};
+    ASSERT_FALSE(x.valueless_by_exception());
+    ASSERT_EQ(0, x.index());
+    EXPECT_EQ(5, absl::get<0>(x).value);
+    EXPECT_FALSE(std::is_nothrow_default_constructible<X>::value);
+  }
+  EXPECT_FALSE(
+      std::is_default_constructible<variant<NonDefaultConstructible>>::value);
+  EXPECT_FALSE((std::is_default_constructible<
+                variant<NonDefaultConstructible, int>>::value));
+  EXPECT_TRUE((std::is_default_constructible<
+               variant<int, NonDefaultConstructible>>::value));
+}
+
+// Test that for each slot, copy constructing a variant with that type
+// produces a sensible object that correctly reports its type, and
+// that copies the provided value.
+TYPED_TEST(VariantTypesTest, TestCopyCtor) {
+  typedef typename VariantFactory<typename TypeParam::value_type>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  using value_type2 = absl::variant_alternative_t<1, Variant>;
+  using value_type3 = absl::variant_alternative_t<2, Variant>;
+  using value_type4 = absl::variant_alternative_t<3, Variant>;
+  const TypeParam value(TypeParam::kIndex);
+  Variant original(value);
+  Variant copied(original);
+  EXPECT_TRUE(absl::holds_alternative<value_type1>(copied) ||
+              TypeParam::kIndex != 1);
+  EXPECT_TRUE(absl::holds_alternative<value_type2>(copied) ||
+              TypeParam::kIndex != 2);
+  EXPECT_TRUE(absl::holds_alternative<value_type3>(copied) ||
+              TypeParam::kIndex != 3);
+  EXPECT_TRUE(absl::holds_alternative<value_type4>(copied) ||
+              TypeParam::kIndex != 4);
+  EXPECT_TRUE((absl::get_if<value_type1>(&original) ==
+               absl::get_if<value_type1>(&copied)) ||
+              TypeParam::kIndex == 1);
+  EXPECT_TRUE((absl::get_if<value_type2>(&original) ==
+               absl::get_if<value_type2>(&copied)) ||
+              TypeParam::kIndex == 2);
+  EXPECT_TRUE((absl::get_if<value_type3>(&original) ==
+               absl::get_if<value_type3>(&copied)) ||
+              TypeParam::kIndex == 3);
+  EXPECT_TRUE((absl::get_if<value_type4>(&original) ==
+               absl::get_if<value_type4>(&copied)) ||
+              TypeParam::kIndex == 4);
+  EXPECT_TRUE((absl::get_if<value_type1>(&original) ==
+               absl::get_if<value_type1>(&copied)) ||
+              TypeParam::kIndex == 1);
+  EXPECT_TRUE((absl::get_if<value_type2>(&original) ==
+               absl::get_if<value_type2>(&copied)) ||
+              TypeParam::kIndex == 2);
+  EXPECT_TRUE((absl::get_if<value_type3>(&original) ==
+               absl::get_if<value_type3>(&copied)) ||
+              TypeParam::kIndex == 3);
+  EXPECT_TRUE((absl::get_if<value_type4>(&original) ==
+               absl::get_if<value_type4>(&copied)) ||
+              TypeParam::kIndex == 4);
+  const TypeParam* ovalptr = absl::get_if<TypeParam>(&original);
+  const TypeParam* cvalptr = absl::get_if<TypeParam>(&copied);
+  ASSERT_TRUE(ovalptr != nullptr);
+  ASSERT_TRUE(cvalptr != nullptr);
+  EXPECT_EQ(*ovalptr, *cvalptr);
+  TypeParam* mutable_ovalptr = absl::get_if<TypeParam>(&original);
+  TypeParam* mutable_cvalptr = absl::get_if<TypeParam>(&copied);
+  ASSERT_TRUE(mutable_ovalptr != nullptr);
+  ASSERT_TRUE(mutable_cvalptr != nullptr);
+  EXPECT_EQ(*mutable_ovalptr, *mutable_cvalptr);
+}
+
+template <class>
+struct MoveOnly {
+  MoveOnly() = default;
+  explicit MoveOnly(int value) : value(value) {}
+  MoveOnly(MoveOnly&&) = default;
+  MoveOnly& operator=(MoveOnly&&) = default;
+  int value = 5;
+};
+
+TEST(VariantTest, TestMoveConstruct) {
+  using V = variant<MoveOnly<class A>, MoveOnly<class B>, MoveOnly<class C>>;
+
+  V v(in_place_index<1>, 10);
+  V v2 = absl::move(v);
+  EXPECT_EQ(10, absl::get<1>(v2).value);
+}
+
+// Used internally to emulate missing triviality traits for tests.
+template <class T>
+union SingleUnion {
+  T member;
+};
+
+// NOTE: These don't work with types that can't be union members.
+//       They are just for testing.
+template <class T>
+struct is_trivially_move_constructible
+    : std::is_move_constructible<SingleUnion<T>>::type {};
+
+template <class T>
+struct is_trivially_move_assignable
+    : absl::is_move_assignable<SingleUnion<T>>::type {};
+
+TEST(VariantTest, NothrowMoveConstructible) {
+  // Verify that variant is nothrow move constructible iff its template
+  // arguments are.
+  using U = std::unique_ptr<int>;
+  struct E {
+    E(E&&) {}
+  };
+  static_assert(std::is_nothrow_move_constructible<variant<U>>::value, "");
+  static_assert(std::is_nothrow_move_constructible<variant<U, int>>::value, "");
+  static_assert(!std::is_nothrow_move_constructible<variant<U, E>>::value, "");
+}
+
+// Test that for each slot, constructing a variant with that type
+// produces a sensible object that correctly reports its type, and
+// that copies the provided value.
+TYPED_TEST(VariantTypesTest, TestValueCtor) {
+  typedef typename VariantFactory<typename TypeParam::value_type>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  using value_type2 = absl::variant_alternative_t<1, Variant>;
+  using value_type3 = absl::variant_alternative_t<2, Variant>;
+  using value_type4 = absl::variant_alternative_t<3, Variant>;
+  const TypeParam value(TypeParam::kIndex);
+  Variant v(value);
+  EXPECT_TRUE(absl::holds_alternative<value_type1>(v) ||
+              TypeParam::kIndex != 1);
+  EXPECT_TRUE(absl::holds_alternative<value_type2>(v) ||
+              TypeParam::kIndex != 2);
+  EXPECT_TRUE(absl::holds_alternative<value_type3>(v) ||
+              TypeParam::kIndex != 3);
+  EXPECT_TRUE(absl::holds_alternative<value_type4>(v) ||
+              TypeParam::kIndex != 4);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type1>(&v) ||
+              TypeParam::kIndex != 1);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type2>(&v) ||
+              TypeParam::kIndex != 2);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type3>(&v) ||
+              TypeParam::kIndex != 3);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type4>(&v) ||
+              TypeParam::kIndex != 4);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type1>(&v) ||
+              TypeParam::kIndex != 1);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type2>(&v) ||
+              TypeParam::kIndex != 2);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type3>(&v) ||
+              TypeParam::kIndex != 3);
+  EXPECT_TRUE(nullptr != absl::get_if<value_type4>(&v) ||
+              TypeParam::kIndex != 4);
+  const TypeParam* valptr = absl::get_if<TypeParam>(&v);
+  ASSERT_TRUE(nullptr != valptr);
+  EXPECT_EQ(value.value, valptr->value);
+  const TypeParam* mutable_valptr = absl::get_if<TypeParam>(&v);
+  ASSERT_TRUE(nullptr != mutable_valptr);
+  EXPECT_EQ(value.value, mutable_valptr->value);
+}
+
+TEST(VariantTest, AmbiguousValueConstructor) {
+  EXPECT_FALSE((std::is_convertible<int, absl::variant<int, int>>::value));
+  EXPECT_FALSE((std::is_constructible<absl::variant<int, int>, int>::value));
+}
+
+TEST(VariantTest, InPlaceType) {
+  using Var = variant<int, std::string, NonCopyable, std::vector<int>>;
+
+  Var v1(in_place_type_t<int>(), 7);
+  ASSERT_TRUE(absl::holds_alternative<int>(v1));
+  EXPECT_EQ(7, absl::get<int>(v1));
+
+  Var v2(in_place_type_t<std::string>(), "ABC");
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v2));
+  EXPECT_EQ("ABC", absl::get<std::string>(v2));
+
+  Var v3(in_place_type_t<std::string>(), "ABC", 2);
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v3));
+  EXPECT_EQ("AB", absl::get<std::string>(v3));
+
+  Var v4(in_place_type_t<NonCopyable>{});
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v4));
+
+  Var v5(in_place_type_t<std::vector<int>>(), {1, 2, 3});
+  ASSERT_TRUE(absl::holds_alternative<std::vector<int>>(v5));
+  EXPECT_THAT(absl::get<std::vector<int>>(v5), ::testing::ElementsAre(1, 2, 3));
+}
+
+TEST(VariantTest, InPlaceTypeVariableTemplate) {
+  using Var = variant<int, std::string, NonCopyable, std::vector<int>>;
+
+  Var v1(in_place_type<int>, 7);
+  ASSERT_TRUE(absl::holds_alternative<int>(v1));
+  EXPECT_EQ(7, absl::get<int>(v1));
+
+  Var v2(in_place_type<std::string>, "ABC");
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v2));
+  EXPECT_EQ("ABC", absl::get<std::string>(v2));
+
+  Var v3(in_place_type<std::string>, "ABC", 2);
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v3));
+  EXPECT_EQ("AB", absl::get<std::string>(v3));
+
+  Var v4(in_place_type<NonCopyable>);
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v4));
+
+  Var v5(in_place_type<std::vector<int>>, {1, 2, 3});
+  ASSERT_TRUE(absl::holds_alternative<std::vector<int>>(v5));
+  EXPECT_THAT(absl::get<std::vector<int>>(v5), ::testing::ElementsAre(1, 2, 3));
+}
+
+TEST(VariantTest, InPlaceTypeInitializerList) {
+  using Var =
+      variant<int, std::string, NonCopyable, MoveOnlyWithListConstructor>;
+
+  Var v1(in_place_type_t<MoveOnlyWithListConstructor>(), {1, 2, 3, 4, 5}, 6);
+  ASSERT_TRUE(absl::holds_alternative<MoveOnlyWithListConstructor>(v1));
+  EXPECT_EQ(6, absl::get<MoveOnlyWithListConstructor>(v1).value);
+}
+
+TEST(VariantTest, InPlaceTypeInitializerListVariabletemplate) {
+  using Var =
+      variant<int, std::string, NonCopyable, MoveOnlyWithListConstructor>;
+
+  Var v1(in_place_type<MoveOnlyWithListConstructor>, {1, 2, 3, 4, 5}, 6);
+  ASSERT_TRUE(absl::holds_alternative<MoveOnlyWithListConstructor>(v1));
+  EXPECT_EQ(6, absl::get<MoveOnlyWithListConstructor>(v1).value);
+}
+
+TEST(VariantTest, InPlaceIndex) {
+  using Var = variant<int, std::string, NonCopyable, std::vector<int>>;
+
+  Var v1(in_place_index_t<0>(), 7);
+  ASSERT_TRUE(absl::holds_alternative<int>(v1));
+  EXPECT_EQ(7, absl::get<int>(v1));
+
+  Var v2(in_place_index_t<1>(), "ABC");
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v2));
+  EXPECT_EQ("ABC", absl::get<std::string>(v2));
+
+  Var v3(in_place_index_t<1>(), "ABC", 2);
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v3));
+  EXPECT_EQ("AB", absl::get<std::string>(v3));
+
+  Var v4(in_place_index_t<2>{});
+  EXPECT_TRUE(absl::holds_alternative<NonCopyable>(v4));
+
+  // Verify that a variant with only non-copyables can still be constructed.
+  EXPECT_TRUE(absl::holds_alternative<NonCopyable>(
+      variant<NonCopyable>(in_place_index_t<0>{})));
+
+  Var v5(in_place_index_t<3>(), {1, 2, 3});
+  ASSERT_TRUE(absl::holds_alternative<std::vector<int>>(v5));
+  EXPECT_THAT(absl::get<std::vector<int>>(v5), ::testing::ElementsAre(1, 2, 3));
+}
+
+TEST(VariantTest, InPlaceIndexVariableTemplate) {
+  using Var = variant<int, std::string, NonCopyable, std::vector<int>>;
+
+  Var v1(in_place_index<0>, 7);
+  ASSERT_TRUE(absl::holds_alternative<int>(v1));
+  EXPECT_EQ(7, absl::get<int>(v1));
+
+  Var v2(in_place_index<1>, "ABC");
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v2));
+  EXPECT_EQ("ABC", absl::get<std::string>(v2));
+
+  Var v3(in_place_index<1>, "ABC", 2);
+  ASSERT_TRUE(absl::holds_alternative<std::string>(v3));
+  EXPECT_EQ("AB", absl::get<std::string>(v3));
+
+  Var v4(in_place_index<2>);
+  EXPECT_TRUE(absl::holds_alternative<NonCopyable>(v4));
+
+  // Verify that a variant with only non-copyables can still be constructed.
+  EXPECT_TRUE(absl::holds_alternative<NonCopyable>(
+      variant<NonCopyable>(in_place_index<0>)));
+
+  Var v5(in_place_index<3>, {1, 2, 3});
+  ASSERT_TRUE(absl::holds_alternative<std::vector<int>>(v5));
+  EXPECT_THAT(absl::get<std::vector<int>>(v5), ::testing::ElementsAre(1, 2, 3));
+}
+
+TEST(VariantTest, InPlaceIndexInitializerList) {
+  using Var =
+      variant<int, std::string, NonCopyable, MoveOnlyWithListConstructor>;
+
+  Var v1(in_place_index_t<3>(), {1, 2, 3, 4, 5}, 6);
+  ASSERT_TRUE(absl::holds_alternative<MoveOnlyWithListConstructor>(v1));
+  EXPECT_EQ(6, absl::get<MoveOnlyWithListConstructor>(v1).value);
+}
+
+TEST(VariantTest, InPlaceIndexInitializerListVariableTemplate) {
+  using Var =
+      variant<int, std::string, NonCopyable, MoveOnlyWithListConstructor>;
+
+  Var v1(in_place_index<3>, {1, 2, 3, 4, 5}, 6);
+  ASSERT_TRUE(absl::holds_alternative<MoveOnlyWithListConstructor>(v1));
+  EXPECT_EQ(6, absl::get<MoveOnlyWithListConstructor>(v1).value);
+}
+
+////////////////////
+// [variant.dtor] //
+////////////////////
+
+// Make sure that the destructor destroys the contained value
+TEST(VariantTest, TestDtor) {
+  typedef VariantFactory<IncrementInDtor>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  using value_type2 = absl::variant_alternative_t<1, Variant>;
+  using value_type3 = absl::variant_alternative_t<2, Variant>;
+  using value_type4 = absl::variant_alternative_t<3, Variant>;
+  int counter = 0;
+  IncrementInDtor counter_adjuster(&counter);
+  EXPECT_EQ(0, counter);
+
+  value_type1 value1(counter_adjuster);
+  { Variant object(value1); }
+  EXPECT_EQ(1, counter);
+
+  value_type2 value2(counter_adjuster);
+  { Variant object(value2); }
+  EXPECT_EQ(2, counter);
+
+  value_type3 value3(counter_adjuster);
+  { Variant object(value3); }
+  EXPECT_EQ(3, counter);
+
+  value_type4 value4(counter_adjuster);
+  { Variant object(value4); }
+  EXPECT_EQ(4, counter);
+}
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+
+// See comment in absl/base/config.h
+#if defined(ABSL_INTERNAL_MSVC_2017_DBG_MODE)
+TEST(VariantTest, DISABLED_TestDtorValuelessByException)
+#else
+// Test destruction when in the valueless_by_exception state.
+TEST(VariantTest, TestDtorValuelessByException)
+#endif
+{
+  int counter = 0;
+  IncrementInDtor counter_adjuster(&counter);
+
+  {
+    using Variant = VariantFactory<IncrementInDtor>::Type;
+
+    Variant v(in_place_index<0>, counter_adjuster);
+    EXPECT_EQ(0, counter);
+
+    ToValuelessByException(v);
+    ASSERT_TRUE(v.valueless_by_exception());
+    EXPECT_EQ(1, counter);
+  }
+  EXPECT_EQ(1, counter);
+}
+
+#endif  // ABSL_HAVE_EXCEPTIONS
+
+//////////////////////
+// [variant.assign] //
+//////////////////////
+
+// Test that self-assignment doesn't destroy the current value
+TEST(VariantTest, TestSelfAssignment) {
+  typedef VariantFactory<IncrementInDtor>::Type Variant;
+  int counter = 0;
+  IncrementInDtor counter_adjuster(&counter);
+  absl::variant_alternative_t<0, Variant> value(counter_adjuster);
+  Variant object(value);
+  object.operator=(object);
+  EXPECT_EQ(0, counter);
+
+  // A string long enough that it's likely to defeat any inline representation
+  // optimization.
+  const std::string long_str(128, 'a');
+
+  std::string foo = long_str;
+  foo = *&foo;
+  EXPECT_EQ(long_str, foo);
+
+  variant<int, std::string> so = long_str;
+  ASSERT_EQ(1, so.index());
+  EXPECT_EQ(long_str, absl::get<1>(so));
+  so = *&so;
+
+  ASSERT_EQ(1, so.index());
+  EXPECT_EQ(long_str, absl::get<1>(so));
+}
+
+// Test that assigning a variant<..., T, ...> to a variant<..., T, ...> produces
+// a variant<..., T, ...> with the correct value.
+TYPED_TEST(VariantTypesTest, TestAssignmentCopiesValueSameTypes) {
+  typedef typename VariantFactory<typename TypeParam::value_type>::Type Variant;
+  const TypeParam value(TypeParam::kIndex);
+  const Variant source(value);
+  Variant target(TypeParam(value.value + 1));
+  ASSERT_TRUE(absl::holds_alternative<TypeParam>(source));
+  ASSERT_TRUE(absl::holds_alternative<TypeParam>(target));
+  ASSERT_NE(absl::get<TypeParam>(source), absl::get<TypeParam>(target));
+  target = source;
+  ASSERT_TRUE(absl::holds_alternative<TypeParam>(source));
+  ASSERT_TRUE(absl::holds_alternative<TypeParam>(target));
+  EXPECT_EQ(absl::get<TypeParam>(source), absl::get<TypeParam>(target));
+}
+
+// Test that assisnging a variant<..., T, ...> to a variant<1, ...>
+// produces a variant<..., T, ...> with the correct value.
+TYPED_TEST(VariantTypesTest, TestAssignmentCopiesValuesVaryingSourceType) {
+  typedef typename VariantFactory<typename TypeParam::value_type>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  const TypeParam value(TypeParam::kIndex);
+  const Variant source(value);
+  ASSERT_TRUE(absl::holds_alternative<TypeParam>(source));
+  Variant target(value_type1(1));
+  ASSERT_TRUE(absl::holds_alternative<value_type1>(target));
+  target = source;
+  EXPECT_TRUE(absl::holds_alternative<TypeParam>(source));
+  EXPECT_TRUE(absl::holds_alternative<TypeParam>(target));
+  EXPECT_EQ(absl::get<TypeParam>(source), absl::get<TypeParam>(target));
+}
+
+// Test that assigning a variant<1, ...> to a variant<..., T, ...>
+// produces a variant<1, ...> with the correct value.
+TYPED_TEST(VariantTypesTest, TestAssignmentCopiesValuesVaryingTargetType) {
+  typedef typename VariantFactory<typename TypeParam::value_type>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  const Variant source(value_type1(1));
+  ASSERT_TRUE(absl::holds_alternative<value_type1>(source));
+  const TypeParam value(TypeParam::kIndex);
+  Variant target(value);
+  ASSERT_TRUE(absl::holds_alternative<TypeParam>(target));
+  target = source;
+  EXPECT_TRUE(absl::holds_alternative<value_type1>(target));
+  EXPECT_TRUE(absl::holds_alternative<value_type1>(source));
+  EXPECT_EQ(absl::get<value_type1>(source), absl::get<value_type1>(target));
+}
+
+// Test that operator=<T> works, that assigning a new value destroys
+// the old and that assigning the new value again does not redestroy
+// the old
+TEST(VariantTest, TestAssign) {
+  typedef VariantFactory<IncrementInDtor>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  using value_type2 = absl::variant_alternative_t<1, Variant>;
+  using value_type3 = absl::variant_alternative_t<2, Variant>;
+  using value_type4 = absl::variant_alternative_t<3, Variant>;
+
+  const int kSize = 4;
+  int counter[kSize];
+  std::unique_ptr<IncrementInDtor> counter_adjustor[kSize];
+  for (int i = 0; i != kSize; i++) {
+    counter[i] = 0;
+    counter_adjustor[i] = absl::make_unique<IncrementInDtor>(&counter[i]);
+  }
+
+  value_type1 v1(*counter_adjustor[0]);
+  value_type2 v2(*counter_adjustor[1]);
+  value_type3 v3(*counter_adjustor[2]);
+  value_type4 v4(*counter_adjustor[3]);
+
+  // Test that reassignment causes destruction of old value
+  {
+    Variant object(v1);
+    object = v2;
+    object = v3;
+    object = v4;
+    object = v1;
+  }
+
+  EXPECT_EQ(2, counter[0]);
+  EXPECT_EQ(1, counter[1]);
+  EXPECT_EQ(1, counter[2]);
+  EXPECT_EQ(1, counter[3]);
+
+  std::fill(std::begin(counter), std::end(counter), 0);
+
+  // Test that self-assignment does not cause destruction of old value
+  {
+    Variant object(v1);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[0]);
+  }
+  {
+    Variant object(v2);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[1]);
+  }
+  {
+    Variant object(v3);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[2]);
+  }
+  {
+    Variant object(v4);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[3]);
+  }
+
+  EXPECT_EQ(1, counter[0]);
+  EXPECT_EQ(1, counter[1]);
+  EXPECT_EQ(1, counter[2]);
+  EXPECT_EQ(1, counter[3]);
+}
+
+// This tests that we perform a backup if the copy-assign can throw but the move
+// cannot throw.
+TEST(VariantTest, TestBackupAssign) {
+  typedef VariantFactory<IncrementInDtorCopyCanThrow>::Type Variant;
+  using value_type1 = absl::variant_alternative_t<0, Variant>;
+  using value_type2 = absl::variant_alternative_t<1, Variant>;
+  using value_type3 = absl::variant_alternative_t<2, Variant>;
+  using value_type4 = absl::variant_alternative_t<3, Variant>;
+
+  const int kSize = 4;
+  int counter[kSize];
+  std::unique_ptr<IncrementInDtorCopyCanThrow> counter_adjustor[kSize];
+  for (int i = 0; i != kSize; i++) {
+    counter[i] = 0;
+    counter_adjustor[i].reset(new IncrementInDtorCopyCanThrow(&counter[i]));
+  }
+
+  value_type1 v1(*counter_adjustor[0]);
+  value_type2 v2(*counter_adjustor[1]);
+  value_type3 v3(*counter_adjustor[2]);
+  value_type4 v4(*counter_adjustor[3]);
+
+  // Test that reassignment causes destruction of old value
+  {
+    Variant object(v1);
+    object = v2;
+    object = v3;
+    object = v4;
+    object = v1;
+  }
+
+  // libstdc++ doesn't pass this test
+#if !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+  EXPECT_EQ(3, counter[0]);
+  EXPECT_EQ(2, counter[1]);
+  EXPECT_EQ(2, counter[2]);
+  EXPECT_EQ(2, counter[3]);
+#endif
+
+  std::fill(std::begin(counter), std::end(counter), 0);
+
+  // Test that self-assignment does not cause destruction of old value
+  {
+    Variant object(v1);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[0]);
+  }
+  {
+    Variant object(v2);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[1]);
+  }
+  {
+    Variant object(v3);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[2]);
+  }
+  {
+    Variant object(v4);
+    object.operator=(object);
+    EXPECT_EQ(0, counter[3]);
+  }
+
+  EXPECT_EQ(1, counter[0]);
+  EXPECT_EQ(1, counter[1]);
+  EXPECT_EQ(1, counter[2]);
+  EXPECT_EQ(1, counter[3]);
+}
+
+///////////////////
+// [variant.mod] //
+///////////////////
+
+TEST(VariantTest, TestEmplaceBasic) {
+  using Variant = variant<int, char>;
+
+  Variant v(absl::in_place_index<0>, 0);
+
+  {
+    char& emplace_result = v.emplace<char>();
+    ASSERT_TRUE(absl::holds_alternative<char>(v));
+    EXPECT_EQ(absl::get<char>(v), 0);
+    EXPECT_EQ(&emplace_result, &absl::get<char>(v));
+  }
+
+  // Make sure that another emplace does zero-initialization
+  absl::get<char>(v) = 'a';
+  v.emplace<char>('b');
+  ASSERT_TRUE(absl::holds_alternative<char>(v));
+  EXPECT_EQ(absl::get<char>(v), 'b');
+
+  {
+    int& emplace_result = v.emplace<int>();
+    EXPECT_TRUE(absl::holds_alternative<int>(v));
+    EXPECT_EQ(absl::get<int>(v), 0);
+    EXPECT_EQ(&emplace_result, &absl::get<int>(v));
+  }
+}
+
+TEST(VariantTest, TestEmplaceInitializerList) {
+  using Var =
+      variant<int, std::string, NonCopyable, MoveOnlyWithListConstructor>;
+
+  Var v1(absl::in_place_index<0>, 555);
+  MoveOnlyWithListConstructor& emplace_result =
+      v1.emplace<MoveOnlyWithListConstructor>({1, 2, 3, 4, 5}, 6);
+  ASSERT_TRUE(absl::holds_alternative<MoveOnlyWithListConstructor>(v1));
+  EXPECT_EQ(6, absl::get<MoveOnlyWithListConstructor>(v1).value);
+  EXPECT_EQ(&emplace_result, &absl::get<MoveOnlyWithListConstructor>(v1));
+}
+
+TEST(VariantTest, TestEmplaceIndex) {
+  using Variant = variant<int, char>;
+
+  Variant v(absl::in_place_index<0>, 555);
+
+  {
+    char& emplace_result = v.emplace<1>();
+    ASSERT_TRUE(absl::holds_alternative<char>(v));
+    EXPECT_EQ(absl::get<char>(v), 0);
+    EXPECT_EQ(&emplace_result, &absl::get<char>(v));
+  }
+
+  // Make sure that another emplace does zero-initialization
+  absl::get<char>(v) = 'a';
+  v.emplace<1>('b');
+  ASSERT_TRUE(absl::holds_alternative<char>(v));
+  EXPECT_EQ(absl::get<char>(v), 'b');
+
+  {
+    int& emplace_result = v.emplace<0>();
+    EXPECT_TRUE(absl::holds_alternative<int>(v));
+    EXPECT_EQ(absl::get<int>(v), 0);
+    EXPECT_EQ(&emplace_result, &absl::get<int>(v));
+  }
+}
+
+TEST(VariantTest, TestEmplaceIndexInitializerList) {
+  using Var =
+      variant<int, std::string, NonCopyable, MoveOnlyWithListConstructor>;
+
+  Var v1(absl::in_place_index<0>, 555);
+  MoveOnlyWithListConstructor& emplace_result =
+      v1.emplace<3>({1, 2, 3, 4, 5}, 6);
+  ASSERT_TRUE(absl::holds_alternative<MoveOnlyWithListConstructor>(v1));
+  EXPECT_EQ(6, absl::get<MoveOnlyWithListConstructor>(v1).value);
+  EXPECT_EQ(&emplace_result, &absl::get<MoveOnlyWithListConstructor>(v1));
+}
+
+//////////////////////
+// [variant.status] //
+//////////////////////
+
+TEST(VariantTest, Index) {
+  using Var = variant<int, std::string, double>;
+
+  Var v = 1;
+  EXPECT_EQ(0, v.index());
+  v = "str";
+  EXPECT_EQ(1, v.index());
+  v = 0.;
+  EXPECT_EQ(2, v.index());
+
+  Var v2 = v;
+  EXPECT_EQ(2, v2.index());
+  v2.emplace<int>(3);
+  EXPECT_EQ(0, v2.index());
+}
+
+TEST(VariantTest, NotValuelessByException) {
+  using Var = variant<int, std::string, double>;
+
+  Var v = 1;
+  EXPECT_FALSE(v.valueless_by_exception());
+  v = "str";
+  EXPECT_FALSE(v.valueless_by_exception());
+  v = 0.;
+  EXPECT_FALSE(v.valueless_by_exception());
+
+  Var v2 = v;
+  EXPECT_FALSE(v.valueless_by_exception());
+  v2.emplace<int>(3);
+  EXPECT_FALSE(v.valueless_by_exception());
+}
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+
+TEST(VariantTest, IndexValuelessByException) {
+  using Var = variant<MoveCanThrow, std::string, double>;
+
+  Var v(absl::in_place_index<0>);
+  EXPECT_EQ(0, v.index());
+  ToValuelessByException(v);
+  EXPECT_EQ(absl::variant_npos, v.index());
+  v = "str";
+  EXPECT_EQ(1, v.index());
+}
+
+TEST(VariantTest, ValuelessByException) {
+  using Var = variant<MoveCanThrow, std::string, double>;
+
+  Var v(absl::in_place_index<0>);
+  EXPECT_FALSE(v.valueless_by_exception());
+  ToValuelessByException(v);
+  EXPECT_TRUE(v.valueless_by_exception());
+  v = "str";
+  EXPECT_FALSE(v.valueless_by_exception());
+}
+
+#endif  // ABSL_HAVE_EXCEPTIONS
+
+////////////////////
+// [variant.swap] //
+////////////////////
+
+TEST(VariantTest, MemberSwap) {
+  SpecialSwap v1(3);
+  SpecialSwap v2(7);
+
+  variant<SpecialSwap> a = v1, b = v2;
+
+  EXPECT_THAT(a, VariantWith<SpecialSwap>(v1));
+  EXPECT_THAT(b, VariantWith<SpecialSwap>(v2));
+
+  a.swap(b);
+  EXPECT_THAT(a, VariantWith<SpecialSwap>(v2));
+  EXPECT_THAT(b, VariantWith<SpecialSwap>(v1));
+  EXPECT_TRUE(absl::get<SpecialSwap>(a).special_swap);
+
+  using V = variant<MoveCanThrow, std::string, int>;
+  int i = 33;
+  std::string s = "abc";
+  {
+    // lhs and rhs holds different alternative
+    V lhs(i), rhs(s);
+    lhs.swap(rhs);
+    EXPECT_THAT(lhs, VariantWith<std::string>(s));
+    EXPECT_THAT(rhs, VariantWith<int>(i));
+  }
+#ifdef ABSL_HAVE_EXCEPTIONS
+  V valueless(in_place_index<0>);
+  ToValuelessByException(valueless);
+  {
+    // lhs is valueless
+    V lhs(valueless), rhs(i);
+    lhs.swap(rhs);
+    EXPECT_THAT(lhs, VariantWith<int>(i));
+    EXPECT_TRUE(rhs.valueless_by_exception());
+  }
+  {
+    // rhs is valueless
+    V lhs(s), rhs(valueless);
+    lhs.swap(rhs);
+    EXPECT_THAT(rhs, VariantWith<std::string>(s));
+    EXPECT_TRUE(lhs.valueless_by_exception());
+  }
+  {
+    // both are valueless
+    V lhs(valueless), rhs(valueless);
+    lhs.swap(rhs);
+    EXPECT_TRUE(lhs.valueless_by_exception());
+    EXPECT_TRUE(rhs.valueless_by_exception());
+  }
+#endif  // ABSL_HAVE_EXCEPTIONS
+}
+
+//////////////////////
+// [variant.helper] //
+//////////////////////
+
+TEST(VariantTest, VariantSize) {
+  {
+    using Size1Variant = absl::variant<int>;
+    EXPECT_EQ(1, absl::variant_size<Size1Variant>::value);
+    EXPECT_EQ(1, absl::variant_size<const Size1Variant>::value);
+    EXPECT_EQ(1, absl::variant_size<volatile Size1Variant>::value);
+    EXPECT_EQ(1, absl::variant_size<const volatile Size1Variant>::value);
+  }
+
+  {
+    using Size3Variant = absl::variant<int, float, int>;
+    EXPECT_EQ(3, absl::variant_size<Size3Variant>::value);
+    EXPECT_EQ(3, absl::variant_size<const Size3Variant>::value);
+    EXPECT_EQ(3, absl::variant_size<volatile Size3Variant>::value);
+    EXPECT_EQ(3, absl::variant_size<const volatile Size3Variant>::value);
+  }
+}
+
+TEST(VariantTest, VariantAlternative) {
+  {
+    using V = absl::variant<float, int, const char*>;
+    EXPECT_TRUE(
+        (std::is_same<float, absl::variant_alternative_t<0, V>>::value));
+    EXPECT_TRUE((std::is_same<const float,
+                              absl::variant_alternative_t<0, const V>>::value));
+    EXPECT_TRUE(
+        (std::is_same<volatile float,
+                      absl::variant_alternative_t<0, volatile V>>::value));
+    EXPECT_TRUE((
+        std::is_same<const volatile float,
+                     absl::variant_alternative_t<0, const volatile V>>::value));
+
+    EXPECT_TRUE((std::is_same<int, absl::variant_alternative_t<1, V>>::value));
+    EXPECT_TRUE((std::is_same<const int,
+                              absl::variant_alternative_t<1, const V>>::value));
+    EXPECT_TRUE(
+        (std::is_same<volatile int,
+                      absl::variant_alternative_t<1, volatile V>>::value));
+    EXPECT_TRUE((
+        std::is_same<const volatile int,
+                     absl::variant_alternative_t<1, const volatile V>>::value));
+
+    EXPECT_TRUE(
+        (std::is_same<const char*, absl::variant_alternative_t<2, V>>::value));
+    EXPECT_TRUE((std::is_same<const char* const,
+                              absl::variant_alternative_t<2, const V>>::value));
+    EXPECT_TRUE(
+        (std::is_same<const char* volatile,
+                      absl::variant_alternative_t<2, volatile V>>::value));
+    EXPECT_TRUE((
+        std::is_same<const char* const volatile,
+                     absl::variant_alternative_t<2, const volatile V>>::value));
+  }
+
+  {
+    using V = absl::variant<float, volatile int, const char*>;
+    EXPECT_TRUE(
+        (std::is_same<float, absl::variant_alternative_t<0, V>>::value));
+    EXPECT_TRUE((std::is_same<const float,
+                              absl::variant_alternative_t<0, const V>>::value));
+    EXPECT_TRUE(
+        (std::is_same<volatile float,
+                      absl::variant_alternative_t<0, volatile V>>::value));
+    EXPECT_TRUE((
+        std::is_same<const volatile float,
+                     absl::variant_alternative_t<0, const volatile V>>::value));
+
+    EXPECT_TRUE(
+        (std::is_same<volatile int, absl::variant_alternative_t<1, V>>::value));
+    EXPECT_TRUE((std::is_same<const volatile int,
+                              absl::variant_alternative_t<1, const V>>::value));
+    EXPECT_TRUE(
+        (std::is_same<volatile int,
+                      absl::variant_alternative_t<1, volatile V>>::value));
+    EXPECT_TRUE((
+        std::is_same<const volatile int,
+                     absl::variant_alternative_t<1, const volatile V>>::value));
+
+    EXPECT_TRUE(
+        (std::is_same<const char*, absl::variant_alternative_t<2, V>>::value));
+    EXPECT_TRUE((std::is_same<const char* const,
+                              absl::variant_alternative_t<2, const V>>::value));
+    EXPECT_TRUE(
+        (std::is_same<const char* volatile,
+                      absl::variant_alternative_t<2, volatile V>>::value));
+    EXPECT_TRUE((
+        std::is_same<const char* const volatile,
+                     absl::variant_alternative_t<2, const volatile V>>::value));
+  }
+}
+
+///////////////////
+// [variant.get] //
+///////////////////
+
+TEST(VariantTest, HoldsAlternative) {
+  using Var = variant<int, std::string, double>;
+
+  Var v = 1;
+  EXPECT_TRUE(absl::holds_alternative<int>(v));
+  EXPECT_FALSE(absl::holds_alternative<std::string>(v));
+  EXPECT_FALSE(absl::holds_alternative<double>(v));
+  v = "str";
+  EXPECT_FALSE(absl::holds_alternative<int>(v));
+  EXPECT_TRUE(absl::holds_alternative<std::string>(v));
+  EXPECT_FALSE(absl::holds_alternative<double>(v));
+  v = 0.;
+  EXPECT_FALSE(absl::holds_alternative<int>(v));
+  EXPECT_FALSE(absl::holds_alternative<std::string>(v));
+  EXPECT_TRUE(absl::holds_alternative<double>(v));
+
+  Var v2 = v;
+  EXPECT_FALSE(absl::holds_alternative<int>(v2));
+  EXPECT_FALSE(absl::holds_alternative<std::string>(v2));
+  EXPECT_TRUE(absl::holds_alternative<double>(v2));
+  v2.emplace<int>(3);
+  EXPECT_TRUE(absl::holds_alternative<int>(v2));
+  EXPECT_FALSE(absl::holds_alternative<std::string>(v2));
+  EXPECT_FALSE(absl::holds_alternative<double>(v2));
+}
+
+TEST(VariantTest, GetIndex) {
+  using Var = variant<int, std::string, double, int>;
+
+  {
+    Var v(absl::in_place_index<0>, 0);
+
+    using LValueGetType = decltype(absl::get<0>(v));
+    using RValueGetType = decltype(absl::get<0>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, int&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, int&&>::value));
+    EXPECT_EQ(absl::get<0>(v), 0);
+    EXPECT_EQ(absl::get<0>(absl::move(v)), 0);
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<0>(const_v));
+    using ConstRValueGetType = decltype(absl::get<0>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const int&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const int&&>::value));
+    EXPECT_EQ(absl::get<0>(const_v), 0);
+    EXPECT_EQ(absl::get<0>(absl::move(const_v)), 0);
+  }
+
+  {
+    Var v = std::string("Hello");
+
+    using LValueGetType = decltype(absl::get<1>(v));
+    using RValueGetType = decltype(absl::get<1>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, std::string&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, std::string&&>::value));
+    EXPECT_EQ(absl::get<1>(v), "Hello");
+    EXPECT_EQ(absl::get<1>(absl::move(v)), "Hello");
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<1>(const_v));
+    using ConstRValueGetType = decltype(absl::get<1>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const std::string&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const std::string&&>::value));
+    EXPECT_EQ(absl::get<1>(const_v), "Hello");
+    EXPECT_EQ(absl::get<1>(absl::move(const_v)), "Hello");
+  }
+
+  {
+    Var v = 2.0;
+
+    using LValueGetType = decltype(absl::get<2>(v));
+    using RValueGetType = decltype(absl::get<2>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, double&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, double&&>::value));
+    EXPECT_EQ(absl::get<2>(v), 2.);
+    EXPECT_EQ(absl::get<2>(absl::move(v)), 2.);
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<2>(const_v));
+    using ConstRValueGetType = decltype(absl::get<2>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const double&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const double&&>::value));
+    EXPECT_EQ(absl::get<2>(const_v), 2.);
+    EXPECT_EQ(absl::get<2>(absl::move(const_v)), 2.);
+  }
+
+  {
+    Var v(absl::in_place_index<0>, 0);
+    v.emplace<3>(1);
+
+    using LValueGetType = decltype(absl::get<3>(v));
+    using RValueGetType = decltype(absl::get<3>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, int&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, int&&>::value));
+    EXPECT_EQ(absl::get<3>(v), 1);
+    EXPECT_EQ(absl::get<3>(absl::move(v)), 1);
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<3>(const_v));
+    using ConstRValueGetType = decltype(absl::get<3>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const int&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const int&&>::value));
+    EXPECT_EQ(absl::get<3>(const_v), 1);
+    EXPECT_EQ(absl::get<3>(absl::move(const_v)), 1);  // NOLINT
+  }
+}
+
+TEST(VariantTest, BadGetIndex) {
+  using Var = variant<int, std::string, double>;
+
+  {
+    Var v = 1;
+
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<1>(v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<1>(std::move(v)));
+
+    const Var& const_v = v;
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<1>(const_v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(
+        absl::get<1>(std::move(const_v)));  // NOLINT
+  }
+
+  {
+    Var v = std::string("Hello");
+
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<0>(v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<0>(std::move(v)));
+
+    const Var& const_v = v;
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<0>(const_v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(
+        absl::get<0>(std::move(const_v)));  // NOLINT
+  }
+}
+
+TEST(VariantTest, GetType) {
+  using Var = variant<int, std::string, double>;
+
+  {
+    Var v = 1;
+
+    using LValueGetType = decltype(absl::get<int>(v));
+    using RValueGetType = decltype(absl::get<int>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, int&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, int&&>::value));
+    EXPECT_EQ(absl::get<int>(v), 1);
+    EXPECT_EQ(absl::get<int>(absl::move(v)), 1);
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<int>(const_v));
+    using ConstRValueGetType = decltype(absl::get<int>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const int&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const int&&>::value));
+    EXPECT_EQ(absl::get<int>(const_v), 1);
+    EXPECT_EQ(absl::get<int>(absl::move(const_v)), 1);
+  }
+
+  {
+    Var v = std::string("Hello");
+
+    using LValueGetType = decltype(absl::get<1>(v));
+    using RValueGetType = decltype(absl::get<1>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, std::string&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, std::string&&>::value));
+    EXPECT_EQ(absl::get<std::string>(v), "Hello");
+    EXPECT_EQ(absl::get<std::string>(absl::move(v)), "Hello");
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<1>(const_v));
+    using ConstRValueGetType = decltype(absl::get<1>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const std::string&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const std::string&&>::value));
+    EXPECT_EQ(absl::get<std::string>(const_v), "Hello");
+    EXPECT_EQ(absl::get<std::string>(absl::move(const_v)), "Hello");
+  }
+
+  {
+    Var v = 2.0;
+
+    using LValueGetType = decltype(absl::get<2>(v));
+    using RValueGetType = decltype(absl::get<2>(absl::move(v)));
+
+    EXPECT_TRUE((std::is_same<LValueGetType, double&>::value));
+    EXPECT_TRUE((std::is_same<RValueGetType, double&&>::value));
+    EXPECT_EQ(absl::get<double>(v), 2.);
+    EXPECT_EQ(absl::get<double>(absl::move(v)), 2.);
+
+    const Var& const_v = v;
+    using ConstLValueGetType = decltype(absl::get<2>(const_v));
+    using ConstRValueGetType = decltype(absl::get<2>(absl::move(const_v)));
+    EXPECT_TRUE((std::is_same<ConstLValueGetType, const double&>::value));
+    EXPECT_TRUE((std::is_same<ConstRValueGetType, const double&&>::value));
+    EXPECT_EQ(absl::get<double>(const_v), 2.);
+    EXPECT_EQ(absl::get<double>(absl::move(const_v)), 2.);
+  }
+}
+
+TEST(VariantTest, BadGetType) {
+  using Var = variant<int, std::string, double>;
+
+  {
+    Var v = 1;
+
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<std::string>(v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(
+        absl::get<std::string>(std::move(v)));
+
+    const Var& const_v = v;
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(
+        absl::get<std::string>(const_v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(
+        absl::get<std::string>(std::move(const_v)));  // NOLINT
+  }
+
+  {
+    Var v = std::string("Hello");
+
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<int>(v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<int>(std::move(v)));
+
+    const Var& const_v = v;
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(absl::get<int>(const_v));
+    ABSL_VARIANT_TEST_EXPECT_BAD_VARIANT_ACCESS(
+        absl::get<int>(std::move(const_v)));  // NOLINT
+  }
+}
+
+TEST(VariantTest, GetIfIndex) {
+  using Var = variant<int, std::string, double, int>;
+
+  {
+    Var v(absl::in_place_index<0>, 0);
+    EXPECT_TRUE(noexcept(absl::get_if<0>(&v)));
+
+    {
+      auto* elem = absl::get_if<0>(&v);
+      EXPECT_TRUE((std::is_same<decltype(elem), int*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, 0);
+      {
+        auto* bad_elem = absl::get_if<1>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), std::string*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<2>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), double*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<3>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+    }
+
+    const Var& const_v = v;
+    EXPECT_TRUE(noexcept(absl::get_if<0>(&const_v)));
+
+    {
+      auto* elem = absl::get_if<0>(&const_v);
+      EXPECT_TRUE((std::is_same<decltype(elem), const int*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, 0);
+      {
+        auto* bad_elem = absl::get_if<1>(&const_v);
+        EXPECT_TRUE(
+            (std::is_same<decltype(bad_elem), const std::string*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<2>(&const_v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const double*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<3>(&const_v);
+        EXPECT_EQ(bad_elem, nullptr);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const int*>::value));
+      }
+    }
+  }
+
+  {
+    Var v = std::string("Hello");
+    EXPECT_TRUE(noexcept(absl::get_if<1>(&v)));
+
+    {
+      auto* elem = absl::get_if<1>(&v);
+      EXPECT_TRUE((std::is_same<decltype(elem), std::string*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, "Hello");
+      {
+        auto* bad_elem = absl::get_if<0>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<2>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), double*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<3>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+    }
+
+    const Var& const_v = v;
+    EXPECT_TRUE(noexcept(absl::get_if<1>(&const_v)));
+
+    {
+      auto* elem = absl::get_if<1>(&const_v);
+      EXPECT_TRUE((std::is_same<decltype(elem), const std::string*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, "Hello");
+      {
+        auto* bad_elem = absl::get_if<0>(&const_v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<2>(&const_v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const double*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<3>(&const_v);
+        EXPECT_EQ(bad_elem, nullptr);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const int*>::value));
+      }
+    }
+  }
+
+  {
+    Var v = 2.0;
+    EXPECT_TRUE(noexcept(absl::get_if<2>(&v)));
+
+    {
+      auto* elem = absl::get_if<2>(&v);
+      EXPECT_TRUE((std::is_same<decltype(elem), double*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, 2.0);
+      {
+        auto* bad_elem = absl::get_if<0>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<1>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), std::string*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<3>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+    }
+
+    const Var& const_v = v;
+    EXPECT_TRUE(noexcept(absl::get_if<2>(&const_v)));
+
+    {
+      auto* elem = absl::get_if<2>(&const_v);
+      EXPECT_TRUE((std::is_same<decltype(elem), const double*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, 2.0);
+      {
+        auto* bad_elem = absl::get_if<0>(&const_v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<1>(&const_v);
+        EXPECT_TRUE(
+            (std::is_same<decltype(bad_elem), const std::string*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<3>(&const_v);
+        EXPECT_EQ(bad_elem, nullptr);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const int*>::value));
+      }
+    }
+  }
+
+  {
+    Var v(absl::in_place_index<0>, 0);
+    v.emplace<3>(1);
+    EXPECT_TRUE(noexcept(absl::get_if<3>(&v)));
+
+    {
+      auto* elem = absl::get_if<3>(&v);
+      EXPECT_TRUE((std::is_same<decltype(elem), int*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, 1);
+      {
+        auto* bad_elem = absl::get_if<0>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<1>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), std::string*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<2>(&v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), double*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+    }
+
+    const Var& const_v = v;
+    EXPECT_TRUE(noexcept(absl::get_if<3>(&const_v)));
+
+    {
+      auto* elem = absl::get_if<3>(&const_v);
+      EXPECT_TRUE((std::is_same<decltype(elem), const int*>::value));
+      ASSERT_NE(elem, nullptr);
+      EXPECT_EQ(*elem, 1);
+      {
+        auto* bad_elem = absl::get_if<0>(&const_v);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const int*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<1>(&const_v);
+        EXPECT_TRUE(
+            (std::is_same<decltype(bad_elem), const std::string*>::value));
+        EXPECT_EQ(bad_elem, nullptr);
+      }
+      {
+        auto* bad_elem = absl::get_if<2>(&const_v);
+        EXPECT_EQ(bad_elem, nullptr);
+        EXPECT_TRUE((std::is_same<decltype(bad_elem), const double*>::value));
+      }
+    }
+  }
+}
+
+//////////////////////
+// [variant.relops] //
+//////////////////////
+
+TEST(VariantTest, OperatorEquals) {
+  variant<int, std::string> a(1), b(1);
+  EXPECT_TRUE(a == b);
+  EXPECT_TRUE(b == a);
+  EXPECT_FALSE(a != b);
+  EXPECT_FALSE(b != a);
+
+  b = "str";
+  EXPECT_FALSE(a == b);
+  EXPECT_FALSE(b == a);
+  EXPECT_TRUE(a != b);
+  EXPECT_TRUE(b != a);
+
+  b = 0;
+  EXPECT_FALSE(a == b);
+  EXPECT_FALSE(b == a);
+  EXPECT_TRUE(a != b);
+  EXPECT_TRUE(b != a);
+
+  a = b = "foo";
+  EXPECT_TRUE(a == b);
+  EXPECT_TRUE(b == a);
+  EXPECT_FALSE(a != b);
+  EXPECT_FALSE(b != a);
+
+  a = "bar";
+  EXPECT_FALSE(a == b);
+  EXPECT_FALSE(b == a);
+  EXPECT_TRUE(a != b);
+  EXPECT_TRUE(b != a);
+}
+
+TEST(VariantTest, OperatorRelational) {
+  variant<int, std::string> a(1), b(1);
+  EXPECT_FALSE(a < b);
+  EXPECT_FALSE(b < a);
+  EXPECT_FALSE(a > b);
+  EXPECT_FALSE(b > a);
+  EXPECT_TRUE(a <= b);
+  EXPECT_TRUE(b <= a);
+  EXPECT_TRUE(a >= b);
+  EXPECT_TRUE(b >= a);
+
+  b = "str";
+  EXPECT_TRUE(a < b);
+  EXPECT_FALSE(b < a);
+  EXPECT_FALSE(a > b);
+  EXPECT_TRUE(b > a);
+  EXPECT_TRUE(a <= b);
+  EXPECT_FALSE(b <= a);
+  EXPECT_FALSE(a >= b);
+  EXPECT_TRUE(b >= a);
+
+  b = 0;
+  EXPECT_FALSE(a < b);
+  EXPECT_TRUE(b < a);
+  EXPECT_TRUE(a > b);
+  EXPECT_FALSE(b > a);
+  EXPECT_FALSE(a <= b);
+  EXPECT_TRUE(b <= a);
+  EXPECT_TRUE(a >= b);
+  EXPECT_FALSE(b >= a);
+
+  a = b = "foo";
+  EXPECT_FALSE(a < b);
+  EXPECT_FALSE(b < a);
+  EXPECT_FALSE(a > b);
+  EXPECT_FALSE(b > a);
+  EXPECT_TRUE(a <= b);
+  EXPECT_TRUE(b <= a);
+  EXPECT_TRUE(a >= b);
+  EXPECT_TRUE(b >= a);
+
+  a = "bar";
+  EXPECT_TRUE(a < b);
+  EXPECT_FALSE(b < a);
+  EXPECT_FALSE(a > b);
+  EXPECT_TRUE(b > a);
+  EXPECT_TRUE(a <= b);
+  EXPECT_FALSE(b <= a);
+  EXPECT_FALSE(a >= b);
+  EXPECT_TRUE(b >= a);
+}
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+
+TEST(VariantTest, ValuelessOperatorEquals) {
+  variant<MoveCanThrow, std::string> int_v(1), string_v("Hello"),
+      valueless(absl::in_place_index<0>),
+      other_valueless(absl::in_place_index<0>);
+  ToValuelessByException(valueless);
+  ToValuelessByException(other_valueless);
+
+  EXPECT_TRUE(valueless == other_valueless);
+  EXPECT_TRUE(other_valueless == valueless);
+  EXPECT_FALSE(valueless == int_v);
+  EXPECT_FALSE(valueless == string_v);
+  EXPECT_FALSE(int_v == valueless);
+  EXPECT_FALSE(string_v == valueless);
+
+  EXPECT_FALSE(valueless != other_valueless);
+  EXPECT_FALSE(other_valueless != valueless);
+  EXPECT_TRUE(valueless != int_v);
+  EXPECT_TRUE(valueless != string_v);
+  EXPECT_TRUE(int_v != valueless);
+  EXPECT_TRUE(string_v != valueless);
+}
+
+TEST(VariantTest, ValuelessOperatorRelational) {
+  variant<MoveCanThrow, std::string> int_v(1), string_v("Hello"),
+      valueless(absl::in_place_index<0>),
+      other_valueless(absl::in_place_index<0>);
+  ToValuelessByException(valueless);
+  ToValuelessByException(other_valueless);
+
+  EXPECT_FALSE(valueless < other_valueless);
+  EXPECT_FALSE(other_valueless < valueless);
+  EXPECT_TRUE(valueless < int_v);
+  EXPECT_TRUE(valueless < string_v);
+  EXPECT_FALSE(int_v < valueless);
+  EXPECT_FALSE(string_v < valueless);
+
+  EXPECT_TRUE(valueless <= other_valueless);
+  EXPECT_TRUE(other_valueless <= valueless);
+  EXPECT_TRUE(valueless <= int_v);
+  EXPECT_TRUE(valueless <= string_v);
+  EXPECT_FALSE(int_v <= valueless);
+  EXPECT_FALSE(string_v <= valueless);
+
+  EXPECT_TRUE(valueless >= other_valueless);
+  EXPECT_TRUE(other_valueless >= valueless);
+  EXPECT_FALSE(valueless >= int_v);
+  EXPECT_FALSE(valueless >= string_v);
+  EXPECT_TRUE(int_v >= valueless);
+  EXPECT_TRUE(string_v >= valueless);
+
+  EXPECT_FALSE(valueless > other_valueless);
+  EXPECT_FALSE(other_valueless > valueless);
+  EXPECT_FALSE(valueless > int_v);
+  EXPECT_FALSE(valueless > string_v);
+  EXPECT_TRUE(int_v > valueless);
+  EXPECT_TRUE(string_v > valueless);
+}
+
+#endif
+
+/////////////////////
+// [variant.visit] //
+/////////////////////
+
+template <typename T>
+struct ConvertTo {
+  template <typename U>
+  T operator()(const U& u) const {
+    return u;
+  }
+};
+
+TEST(VariantTest, VisitSimple) {
+  variant<std::string, const char*> v = "A";
+
+  std::string str = absl::visit(ConvertTo<std::string>{}, v);
+  EXPECT_EQ("A", str);
+
+  v = std::string("B");
+
+  absl::string_view piece = absl::visit(ConvertTo<absl::string_view>{}, v);
+  EXPECT_EQ("B", piece);
+
+  struct StrLen {
+    int operator()(const char* s) const { return strlen(s); }
+    int operator()(const std::string& s) const { return s.size(); }
+  };
+
+  v = "SomeStr";
+  EXPECT_EQ(7, absl::visit(StrLen{}, v));
+  v = std::string("VeryLargeThisTime");
+  EXPECT_EQ(17, absl::visit(StrLen{}, v));
+}
+
+TEST(VariantTest, VisitRValue) {
+  variant<std::string> v = std::string("X");
+  struct Visitor {
+    bool operator()(const std::string&) const { return false; }
+    bool operator()(std::string&&) const { return true; }  // NOLINT
+
+    int operator()(const std::string&, const std::string&) const { return 0; }
+    int operator()(const std::string&, std::string&&) const {
+      return 1;
+    }  // NOLINT
+    int operator()(std::string&&, const std::string&) const {
+      return 2;
+    }                                                                 // NOLINT
+    int operator()(std::string&&, std::string&&) const { return 3; }  // NOLINT
+  };
+  EXPECT_FALSE(absl::visit(Visitor{}, v));
+  EXPECT_TRUE(absl::visit(Visitor{}, absl::move(v)));
+
+  // Also test the variadic overload.
+  EXPECT_EQ(0, absl::visit(Visitor{}, v, v));
+  EXPECT_EQ(1, absl::visit(Visitor{}, v, absl::move(v)));
+  EXPECT_EQ(2, absl::visit(Visitor{}, absl::move(v), v));
+  EXPECT_EQ(3, absl::visit(Visitor{}, absl::move(v), absl::move(v)));
+}
+
+TEST(VariantTest, VisitRValueVisitor) {
+  variant<std::string> v = std::string("X");
+  struct Visitor {
+    bool operator()(const std::string&) const& { return false; }
+    bool operator()(const std::string&) && { return true; }
+  };
+  Visitor visitor;
+  EXPECT_FALSE(absl::visit(visitor, v));
+  EXPECT_TRUE(absl::visit(Visitor{}, v));
+}
+
+TEST(VariantTest, VisitResultTypeDifferent) {
+  variant<std::string> v = std::string("X");
+  struct LValue_LValue {};
+  struct RValue_LValue {};
+  struct LValue_RValue {};
+  struct RValue_RValue {};
+  struct Visitor {
+    LValue_LValue operator()(const std::string&) const& { return {}; }
+    RValue_LValue operator()(std::string&&) const& { return {}; }  // NOLINT
+    LValue_RValue operator()(const std::string&) && { return {}; }
+    RValue_RValue operator()(std::string&&) && { return {}; }  // NOLINT
+  } visitor;
+
+  EXPECT_TRUE(
+      (std::is_same<LValue_LValue, decltype(absl::visit(visitor, v))>::value));
+  EXPECT_TRUE(
+      (std::is_same<RValue_LValue,
+                    decltype(absl::visit(visitor, absl::move(v)))>::value));
+  EXPECT_TRUE((
+      std::is_same<LValue_RValue, decltype(absl::visit(Visitor{}, v))>::value));
+  EXPECT_TRUE(
+      (std::is_same<RValue_RValue,
+                    decltype(absl::visit(Visitor{}, absl::move(v)))>::value));
+}
+
+TEST(VariantTest, VisitVariadic) {
+  using A = variant<int, std::string>;
+  using B = variant<std::unique_ptr<int>, absl::string_view>;
+
+  struct Visitor {
+    std::pair<int, int> operator()(int a, std::unique_ptr<int> b) const {
+      return {a, *b};
+    }
+    std::pair<int, int> operator()(absl::string_view a,
+                                   std::unique_ptr<int> b) const {
+      return {static_cast<int>(a.size()), static_cast<int>(*b)};
+    }
+    std::pair<int, int> operator()(int a, absl::string_view b) const {
+      return {a, static_cast<int>(b.size())};
+    }
+    std::pair<int, int> operator()(absl::string_view a,
+                                   absl::string_view b) const {
+      return {static_cast<int>(a.size()), static_cast<int>(b.size())};
+    }
+  };
+
+  EXPECT_THAT(absl::visit(Visitor(), A(1), B(std::unique_ptr<int>(new int(7)))),
+              ::testing::Pair(1, 7));
+  EXPECT_THAT(absl::visit(Visitor(), A(1), B(absl::string_view("ABC"))),
+              ::testing::Pair(1, 3));
+  EXPECT_THAT(absl::visit(Visitor(), A(std::string("BBBBB")),
+                          B(std::unique_ptr<int>(new int(7)))),
+              ::testing::Pair(5, 7));
+  EXPECT_THAT(absl::visit(Visitor(), A(std::string("BBBBB")),
+                          B(absl::string_view("ABC"))),
+              ::testing::Pair(5, 3));
+}
+
+TEST(VariantTest, VisitNoArgs) {
+  EXPECT_EQ(5, absl::visit([] { return 5; }));
+}
+
+struct ConstFunctor {
+  int operator()(int a, int b) const { return a - b; }
+};
+
+struct MutableFunctor {
+  int operator()(int a, int b) { return a - b; }
+};
+
+struct Class {
+  int Method(int a, int b) { return a - b; }
+  int ConstMethod(int a, int b) const { return a - b; }
+
+  int member;
+};
+
+TEST(VariantTest, VisitReferenceWrapper) {
+  ConstFunctor cf;
+  MutableFunctor mf;
+  absl::variant<int> three = 3;
+  absl::variant<int> two = 2;
+
+  EXPECT_EQ(1, absl::visit(std::cref(cf), three, two));
+  EXPECT_EQ(1, absl::visit(std::ref(cf), three, two));
+  EXPECT_EQ(1, absl::visit(std::ref(mf), three, two));
+}
+
+// libstdc++ std::variant doesn't support the INVOKE semantics.
+#if !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+TEST(VariantTest, VisitMemberFunction) {
+  absl::variant<std::unique_ptr<Class>> p(absl::make_unique<Class>());
+  absl::variant<std::unique_ptr<const Class>> cp(
+      absl::make_unique<const Class>());
+  absl::variant<int> three = 3;
+  absl::variant<int> two = 2;
+
+  EXPECT_EQ(1, absl::visit(&Class::Method, p, three, two));
+  EXPECT_EQ(1, absl::visit(&Class::ConstMethod, p, three, two));
+  EXPECT_EQ(1, absl::visit(&Class::ConstMethod, cp, three, two));
+}
+
+TEST(VariantTest, VisitDataMember) {
+  absl::variant<std::unique_ptr<Class>> p(absl::make_unique<Class>(Class{42}));
+  absl::variant<std::unique_ptr<const Class>> cp(
+      absl::make_unique<const Class>(Class{42}));
+  EXPECT_EQ(42, absl::visit(&Class::member, p));
+
+  absl::visit(&Class::member, p) = 5;
+  EXPECT_EQ(5, absl::visit(&Class::member, p));
+
+  EXPECT_EQ(42, absl::visit(&Class::member, cp));
+}
+#endif  // !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+
+/////////////////////////
+// [variant.monostate] //
+/////////////////////////
+
+TEST(VariantTest, MonostateBasic) {
+  absl::monostate mono;
+  (void)mono;
+
+  // TODO(mattcalabrese) Expose move triviality metafunctions in absl.
+  EXPECT_TRUE(absl::is_trivially_default_constructible<absl::monostate>::value);
+  EXPECT_TRUE(is_trivially_move_constructible<absl::monostate>::value);
+  EXPECT_TRUE(absl::is_trivially_copy_constructible<absl::monostate>::value);
+  EXPECT_TRUE(is_trivially_move_assignable<absl::monostate>::value);
+  EXPECT_TRUE(absl::is_trivially_copy_assignable<absl::monostate>::value);
+  EXPECT_TRUE(absl::is_trivially_destructible<absl::monostate>::value);
+}
+
+TEST(VariantTest, VariantMonostateDefaultConstruction) {
+  absl::variant<absl::monostate, NonDefaultConstructible> var;
+  EXPECT_EQ(var.index(), 0);
+}
+
+////////////////////////////////
+// [variant.monostate.relops] //
+////////////////////////////////
+
+TEST(VariantTest, MonostateComparisons) {
+  absl::monostate lhs, rhs;
+
+  EXPECT_EQ(lhs, lhs);
+  EXPECT_EQ(lhs, rhs);
+
+  EXPECT_FALSE(lhs != lhs);
+  EXPECT_FALSE(lhs != rhs);
+  EXPECT_FALSE(lhs < lhs);
+  EXPECT_FALSE(lhs < rhs);
+  EXPECT_FALSE(lhs > lhs);
+  EXPECT_FALSE(lhs > rhs);
+
+  EXPECT_LE(lhs, lhs);
+  EXPECT_LE(lhs, rhs);
+  EXPECT_GE(lhs, lhs);
+  EXPECT_GE(lhs, rhs);
+
+  EXPECT_TRUE(noexcept(std::declval<absl::monostate>() ==
+                       std::declval<absl::monostate>()));
+  EXPECT_TRUE(noexcept(std::declval<absl::monostate>() !=
+                       std::declval<absl::monostate>()));
+  EXPECT_TRUE(noexcept(std::declval<absl::monostate>() <
+                       std::declval<absl::monostate>()));
+  EXPECT_TRUE(noexcept(std::declval<absl::monostate>() >
+                       std::declval<absl::monostate>()));
+  EXPECT_TRUE(noexcept(std::declval<absl::monostate>() <=
+                       std::declval<absl::monostate>()));
+  EXPECT_TRUE(noexcept(std::declval<absl::monostate>() >=
+                       std::declval<absl::monostate>()));
+}
+
+///////////////////////
+// [variant.specalg] //
+///////////////////////
+
+TEST(VariantTest, NonmemberSwap) {
+  using std::swap;
+
+  SpecialSwap v1(3);
+  SpecialSwap v2(7);
+
+  variant<SpecialSwap> a = v1, b = v2;
+
+  EXPECT_THAT(a, VariantWith<SpecialSwap>(v1));
+  EXPECT_THAT(b, VariantWith<SpecialSwap>(v2));
+
+  std::swap(a, b);
+  EXPECT_THAT(a, VariantWith<SpecialSwap>(v2));
+  EXPECT_THAT(b, VariantWith<SpecialSwap>(v1));
+#ifndef ABSL_USES_STD_VARIANT
+  EXPECT_FALSE(absl::get<SpecialSwap>(a).special_swap);
+#endif
+
+  swap(a, b);
+  EXPECT_THAT(a, VariantWith<SpecialSwap>(v1));
+  EXPECT_THAT(b, VariantWith<SpecialSwap>(v2));
+  EXPECT_TRUE(absl::get<SpecialSwap>(b).special_swap);
+}
+
+//////////////////////////
+// [variant.bad.access] //
+//////////////////////////
+
+TEST(VariantTest, BadAccess) {
+  EXPECT_TRUE(noexcept(absl::bad_variant_access()));
+  absl::bad_variant_access exception_obj;
+  std::exception* base = &exception_obj;
+  (void)base;
+}
+
+////////////////////
+// [variant.hash] //
+////////////////////
+
+TEST(VariantTest, MonostateHash) {
+  absl::monostate mono, other_mono;
+  std::hash<absl::monostate> const hasher{};
+  static_assert(std::is_same<decltype(hasher(mono)), std::size_t>::value, "");
+  EXPECT_EQ(hasher(mono), hasher(other_mono));
+}
+
+TEST(VariantTest, Hash) {
+  static_assert(type_traits_internal::IsHashable<variant<int>>::value, "");
+  static_assert(type_traits_internal::IsHashable<variant<Hashable>>::value, "");
+  static_assert(type_traits_internal::IsHashable<variant<int, Hashable>>::value,
+                "");
+
+#if ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_
+  static_assert(!type_traits_internal::IsHashable<variant<NonHashable>>::value,
+                "");
+  static_assert(
+      !type_traits_internal::IsHashable<variant<Hashable, NonHashable>>::value,
+      "");
+#endif
+
+// MSVC std::hash<std::variant> does not use the index, thus produce the same
+// result on the same value as different alternative.
+#if !(defined(_MSC_VER) && defined(ABSL_USES_STD_VARIANT))
+  {
+    // same value as different alternative
+    variant<int, int> v0(in_place_index<0>, 42);
+    variant<int, int> v1(in_place_index<1>, 42);
+    std::hash<variant<int, int>> hash;
+    EXPECT_NE(hash(v0), hash(v1));
+  }
+#endif  // !(defined(_MSC_VER) && defined(ABSL_USES_STD_VARIANT))
+
+  {
+    std::hash<variant<int>> hash;
+    std::set<size_t> hashcodes;
+    for (int i = 0; i < 100; ++i) {
+      hashcodes.insert(hash(i));
+    }
+    EXPECT_GT(hashcodes.size(), 90);
+
+    // test const-qualified
+    static_assert(type_traits_internal::IsHashable<variant<const int>>::value,
+                  "");
+    static_assert(
+        type_traits_internal::IsHashable<variant<const Hashable>>::value, "");
+    std::hash<absl::variant<const int>> c_hash;
+    for (int i = 0; i < 100; ++i) {
+      EXPECT_EQ(hash(i), c_hash(i));
+    }
+  }
+}
+
+////////////////////////////////////////
+// Miscellaneous and deprecated tests //
+////////////////////////////////////////
+
+// Test that a set requiring a basic type conversion works correctly
+#if !defined(ABSL_USES_STD_VARIANT)
+TEST(VariantTest, TestConvertingSet) {
+  typedef variant<double> Variant;
+  Variant v(1.0);
+  const int two = 2;
+  v = two;
+  EXPECT_TRUE(absl::holds_alternative<double>(v));
+  ASSERT_TRUE(nullptr != absl::get_if<double>(&v));
+  EXPECT_DOUBLE_EQ(2, absl::get<double>(v));
+}
+#endif  // ABSL_USES_STD_VARIANT
+
+// Test that a vector of variants behaves reasonably.
+TEST(VariantTest, Container) {
+  typedef variant<int, float> Variant;
+
+  // Creation of vector should work
+  std::vector<Variant> vec;
+  vec.push_back(Variant(10));
+  vec.push_back(Variant(20.0f));
+
+  // Vector resizing should work if we supply a value for new slots
+  vec.resize(10, Variant(0));
+}
+
+// Test that a variant with a non-copyable type can be constructed and
+// manipulated to some degree.
+TEST(VariantTest, TestVariantWithNonCopyableType) {
+  typedef variant<int, NonCopyable> Variant;
+  const int kValue = 1;
+  Variant v(kValue);
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+  EXPECT_EQ(kValue, absl::get<int>(v));
+}
+
+// Test that a variant with a non-copyable type can be transformed to
+// the non-copyable type with a call to `emplace` for different numbers
+// of arguments. We do not need to test this for each of T1 ... T8
+// because `emplace` does not overload on T1 ... to T8, so if this
+// works for any one of T1 ... T8, then it works for all of them. We
+// do need to test that it works with varying numbers of parameters
+// though.
+TEST(VariantTest, TestEmplace) {
+  typedef variant<int, NonCopyable> Variant;
+  const int kValue = 1;
+  Variant v(kValue);
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+  EXPECT_EQ(kValue, absl::get<int>(v));
+
+  // emplace with zero arguments, then back to 'int'
+  v.emplace<NonCopyable>();
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v));
+  EXPECT_EQ(0, absl::get<NonCopyable>(v).value);
+  v = kValue;
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+
+  // emplace with one argument:
+  v.emplace<NonCopyable>(1);
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v));
+  EXPECT_EQ(1, absl::get<NonCopyable>(v).value);
+  v = kValue;
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+
+  // emplace with two arguments:
+  v.emplace<NonCopyable>(1, 2);
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v));
+  EXPECT_EQ(3, absl::get<NonCopyable>(v).value);
+  v = kValue;
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+
+  // emplace with three arguments
+  v.emplace<NonCopyable>(1, 2, 3);
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v));
+  EXPECT_EQ(6, absl::get<NonCopyable>(v).value);
+  v = kValue;
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+
+  // emplace with four arguments
+  v.emplace<NonCopyable>(1, 2, 3, 4);
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v));
+  EXPECT_EQ(10, absl::get<NonCopyable>(v).value);
+  v = kValue;
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+}
+
+TEST(VariantTest, TestEmplaceDestroysCurrentValue) {
+  typedef variant<int, IncrementInDtor, NonCopyable> Variant;
+  int counter = 0;
+  Variant v(0);
+  ASSERT_TRUE(absl::holds_alternative<int>(v));
+  v.emplace<IncrementInDtor>(&counter);
+  ASSERT_TRUE(absl::holds_alternative<IncrementInDtor>(v));
+  ASSERT_EQ(0, counter);
+  v.emplace<NonCopyable>();
+  ASSERT_TRUE(absl::holds_alternative<NonCopyable>(v));
+  EXPECT_EQ(1, counter);
+}
+
+TEST(VariantTest, TestMoveSemantics) {
+  typedef variant<std::unique_ptr<int>, std::unique_ptr<std::string>> Variant;
+
+  // Construct a variant by moving from an element value.
+  Variant v(absl::WrapUnique(new int(10)));
+  EXPECT_TRUE(absl::holds_alternative<std::unique_ptr<int>>(v));
+
+  // Construct a variant by moving from another variant.
+  Variant v2(absl::move(v));
+  ASSERT_TRUE(absl::holds_alternative<std::unique_ptr<int>>(v2));
+  ASSERT_NE(nullptr, absl::get<std::unique_ptr<int>>(v2));
+  EXPECT_EQ(10, *absl::get<std::unique_ptr<int>>(v2));
+
+  // Moving from a variant object leaves it holding moved-from value of the
+  // same element type.
+  EXPECT_TRUE(absl::holds_alternative<std::unique_ptr<int>>(v));
+  ASSERT_NE(nullptr, absl::get_if<std::unique_ptr<int>>(&v));
+  EXPECT_EQ(nullptr, absl::get<std::unique_ptr<int>>(v));
+
+  // Assign a variant from an element value by move.
+  v = absl::make_unique<std::string>("foo");
+  ASSERT_TRUE(absl::holds_alternative<std::unique_ptr<std::string>>(v));
+  EXPECT_EQ("foo", *absl::get<std::unique_ptr<std::string>>(v));
+
+  // Move-assign a variant.
+  v2 = absl::move(v);
+  ASSERT_TRUE(absl::holds_alternative<std::unique_ptr<std::string>>(v2));
+  EXPECT_EQ("foo", *absl::get<std::unique_ptr<std::string>>(v2));
+  EXPECT_TRUE(absl::holds_alternative<std::unique_ptr<std::string>>(v));
+}
+
+variant<int, std::string> PassThrough(const variant<int, std::string>& arg) {
+  return arg;
+}
+
+TEST(VariantTest, TestImplicitConversion) {
+  EXPECT_TRUE(absl::holds_alternative<int>(PassThrough(0)));
+
+  // We still need the explicit cast for std::string, because C++ won't apply
+  // two user-defined implicit conversions in a row.
+  EXPECT_TRUE(
+      absl::holds_alternative<std::string>(PassThrough(std::string("foo"))));
+}
+
+struct Convertible2;
+struct Convertible1 {
+  Convertible1() {}
+  Convertible1(const Convertible1&) {}
+  Convertible1& operator=(const Convertible1&) { return *this; }
+
+  // implicit conversion from Convertible2
+  Convertible1(const Convertible2&) {}  // NOLINT(runtime/explicit)
+};
+
+struct Convertible2 {
+  Convertible2() {}
+  Convertible2(const Convertible2&) {}
+  Convertible2& operator=(const Convertible2&) { return *this; }
+
+  // implicit conversion from Convertible1
+  Convertible2(const Convertible1&) {}  // NOLINT(runtime/explicit)
+};
+
+TEST(VariantTest, TestRvalueConversion) {
+#if !defined(ABSL_USES_STD_VARIANT)
+  variant<double, std::string> var(
+      ConvertVariantTo<variant<double, std::string>>(
+          variant<std::string, int>(0)));
+  ASSERT_TRUE(absl::holds_alternative<double>(var));
+  EXPECT_EQ(0.0, absl::get<double>(var));
+
+  var = ConvertVariantTo<variant<double, std::string>>(
+      variant<const char*, float>("foo"));
+  ASSERT_TRUE(absl::holds_alternative<std::string>(var));
+  EXPECT_EQ("foo", absl::get<std::string>(var));
+
+  variant<double> singleton(
+      ConvertVariantTo<variant<double>>(variant<int, float>(42)));
+  ASSERT_TRUE(absl::holds_alternative<double>(singleton));
+  EXPECT_EQ(42.0, absl::get<double>(singleton));
+
+  singleton = ConvertVariantTo<variant<double>>(variant<int, float>(3.14f));
+  ASSERT_TRUE(absl::holds_alternative<double>(singleton));
+  EXPECT_FLOAT_EQ(3.14f, static_cast<float>(absl::get<double>(singleton)));
+
+  singleton = ConvertVariantTo<variant<double>>(variant<int>(0));
+  ASSERT_TRUE(absl::holds_alternative<double>(singleton));
+  EXPECT_EQ(0.0, absl::get<double>(singleton));
+
+  variant<int32_t, uint32_t> variant2(
+      ConvertVariantTo<variant<int32_t, uint32_t>>(variant<int32_t>(42)));
+  ASSERT_TRUE(absl::holds_alternative<int32_t>(variant2));
+  EXPECT_EQ(42, absl::get<int32_t>(variant2));
+
+  variant2 = ConvertVariantTo<variant<int32_t, uint32_t>>(variant<uint32_t>(42));
+  ASSERT_TRUE(absl::holds_alternative<uint32_t>(variant2));
+  EXPECT_EQ(42, absl::get<uint32_t>(variant2));
+#endif  // !ABSL_USES_STD_VARIANT
+
+  variant<Convertible1, Convertible2> variant3(
+      ConvertVariantTo<variant<Convertible1, Convertible2>>(
+          (variant<Convertible2, Convertible1>(Convertible1()))));
+  ASSERT_TRUE(absl::holds_alternative<Convertible1>(variant3));
+
+  variant3 = ConvertVariantTo<variant<Convertible1, Convertible2>>(
+      variant<Convertible2, Convertible1>(Convertible2()));
+  ASSERT_TRUE(absl::holds_alternative<Convertible2>(variant3));
+}
+
+TEST(VariantTest, TestLvalueConversion) {
+#if !defined(ABSL_USES_STD_VARIANT)
+  variant<std::string, int> source1 = 0;
+  variant<double, std::string> destination(
+      ConvertVariantTo<variant<double, std::string>>(source1));
+  ASSERT_TRUE(absl::holds_alternative<double>(destination));
+  EXPECT_EQ(0.0, absl::get<double>(destination));
+
+  variant<const char*, float> source2 = "foo";
+  destination = ConvertVariantTo<variant<double, std::string>>(source2);
+  ASSERT_TRUE(absl::holds_alternative<std::string>(destination));
+  EXPECT_EQ("foo", absl::get<std::string>(destination));
+
+  variant<int, float> source3(42);
+  variant<double> singleton(ConvertVariantTo<variant<double>>(source3));
+  ASSERT_TRUE(absl::holds_alternative<double>(singleton));
+  EXPECT_EQ(42.0, absl::get<double>(singleton));
+
+  source3 = 3.14f;
+  singleton = ConvertVariantTo<variant<double>>(source3);
+  ASSERT_TRUE(absl::holds_alternative<double>(singleton));
+  EXPECT_FLOAT_EQ(3.14f, static_cast<float>(absl::get<double>(singleton)));
+
+  variant<int> source4(0);
+  singleton = ConvertVariantTo<variant<double>>(source4);
+  ASSERT_TRUE(absl::holds_alternative<double>(singleton));
+  EXPECT_EQ(0.0, absl::get<double>(singleton));
+
+  variant<int32_t> source5(42);
+  variant<int32_t, uint32_t> variant2(
+      ConvertVariantTo<variant<int32_t, uint32_t>>(source5));
+  ASSERT_TRUE(absl::holds_alternative<int32_t>(variant2));
+  EXPECT_EQ(42, absl::get<int32_t>(variant2));
+
+  variant<uint32_t> source6(42);
+  variant2 = ConvertVariantTo<variant<int32_t, uint32_t>>(source6);
+  ASSERT_TRUE(absl::holds_alternative<uint32_t>(variant2));
+  EXPECT_EQ(42, absl::get<uint32_t>(variant2));
+#endif
+
+  variant<Convertible2, Convertible1> source7((Convertible1()));
+  variant<Convertible1, Convertible2> variant3(
+      ConvertVariantTo<variant<Convertible1, Convertible2>>(source7));
+  ASSERT_TRUE(absl::holds_alternative<Convertible1>(variant3));
+
+  source7 = Convertible2();
+  variant3 = ConvertVariantTo<variant<Convertible1, Convertible2>>(source7);
+  ASSERT_TRUE(absl::holds_alternative<Convertible2>(variant3));
+}
+
+TEST(VariantTest, TestMoveConversion) {
+  using Variant =
+      variant<std::unique_ptr<const int>, std::unique_ptr<const std::string>>;
+  using OtherVariant =
+      variant<std::unique_ptr<int>, std::unique_ptr<std::string>>;
+
+  Variant var(
+      ConvertVariantTo<Variant>(OtherVariant{absl::make_unique<int>(0)}));
+  ASSERT_TRUE(absl::holds_alternative<std::unique_ptr<const int>>(var));
+  ASSERT_NE(absl::get<std::unique_ptr<const int>>(var), nullptr);
+  EXPECT_EQ(0, *absl::get<std::unique_ptr<const int>>(var));
+
+  var = ConvertVariantTo<Variant>(
+      OtherVariant(absl::make_unique<std::string>("foo")));
+  ASSERT_TRUE(absl::holds_alternative<std::unique_ptr<const std::string>>(var));
+  EXPECT_EQ("foo", *absl::get<std::unique_ptr<const std::string>>(var));
+}
+
+TEST(VariantTest, DoesNotMoveFromLvalues) {
+  // We use shared_ptr here because it's both copyable and movable, and
+  // a moved-from shared_ptr is guaranteed to be null, so we can detect
+  // whether moving or copying has occurred.
+  using Variant =
+      variant<std::shared_ptr<const int>, std::shared_ptr<const std::string>>;
+  using OtherVariant =
+      variant<std::shared_ptr<int>, std::shared_ptr<std::string>>;
+
+  Variant v1(std::make_shared<const int>(0));
+
+  // Test copy constructor
+  Variant v2(v1);
+  EXPECT_EQ(absl::get<std::shared_ptr<const int>>(v1),
+            absl::get<std::shared_ptr<const int>>(v2));
+
+  // Test copy-assignment operator
+  v1 = std::make_shared<const std::string>("foo");
+  v2 = v1;
+  EXPECT_EQ(absl::get<std::shared_ptr<const std::string>>(v1),
+            absl::get<std::shared_ptr<const std::string>>(v2));
+
+  // Test converting copy constructor
+  OtherVariant other(std::make_shared<int>(0));
+  Variant v3(ConvertVariantTo<Variant>(other));
+  EXPECT_EQ(absl::get<std::shared_ptr<int>>(other),
+            absl::get<std::shared_ptr<const int>>(v3));
+
+  other = std::make_shared<std::string>("foo");
+  v3 = ConvertVariantTo<Variant>(other);
+  EXPECT_EQ(absl::get<std::shared_ptr<std::string>>(other),
+            absl::get<std::shared_ptr<const std::string>>(v3));
+}
+
+TEST(VariantTest, TestRvalueConversionViaConvertVariantTo) {
+#if !defined(ABSL_USES_STD_VARIANT)
+  variant<double, std::string> var(
+      ConvertVariantTo<variant<double, std::string>>(
+          variant<std::string, int>(3)));
+  EXPECT_THAT(absl::get_if<double>(&var), Pointee(3.0));
+
+  var = ConvertVariantTo<variant<double, std::string>>(
+      variant<const char*, float>("foo"));
+  EXPECT_THAT(absl::get_if<std::string>(&var), Pointee(std::string("foo")));
+
+  variant<double> singleton(
+      ConvertVariantTo<variant<double>>(variant<int, float>(42)));
+  EXPECT_THAT(absl::get_if<double>(&singleton), Pointee(42.0));
+
+  singleton = ConvertVariantTo<variant<double>>(variant<int, float>(3.14f));
+  EXPECT_THAT(absl::get_if<double>(&singleton), Pointee(DoubleEq(3.14f)));
+
+  singleton = ConvertVariantTo<variant<double>>(variant<int>(3));
+  EXPECT_THAT(absl::get_if<double>(&singleton), Pointee(3.0));
+
+  variant<int32_t, uint32_t> variant2(
+      ConvertVariantTo<variant<int32_t, uint32_t>>(variant<int32_t>(42)));
+  EXPECT_THAT(absl::get_if<int32_t>(&variant2), Pointee(42));
+
+  variant2 = ConvertVariantTo<variant<int32_t, uint32_t>>(variant<uint32_t>(42));
+  EXPECT_THAT(absl::get_if<uint32_t>(&variant2), Pointee(42));
+#endif
+
+  variant<Convertible1, Convertible2> variant3(
+      ConvertVariantTo<variant<Convertible1, Convertible2>>(
+          (variant<Convertible2, Convertible1>(Convertible1()))));
+  ASSERT_TRUE(absl::holds_alternative<Convertible1>(variant3));
+
+  variant3 = ConvertVariantTo<variant<Convertible1, Convertible2>>(
+      variant<Convertible2, Convertible1>(Convertible2()));
+  ASSERT_TRUE(absl::holds_alternative<Convertible2>(variant3));
+}
+
+TEST(VariantTest, TestLvalueConversionViaConvertVariantTo) {
+#if !defined(ABSL_USES_STD_VARIANT)
+  variant<std::string, int> source1 = 3;
+  variant<double, std::string> destination(
+      ConvertVariantTo<variant<double, std::string>>(source1));
+  EXPECT_THAT(absl::get_if<double>(&destination), Pointee(3.0));
+
+  variant<const char*, float> source2 = "foo";
+  destination = ConvertVariantTo<variant<double, std::string>>(source2);
+  EXPECT_THAT(absl::get_if<std::string>(&destination),
+              Pointee(std::string("foo")));
+
+  variant<int, float> source3(42);
+  variant<double> singleton(ConvertVariantTo<variant<double>>(source3));
+  EXPECT_THAT(absl::get_if<double>(&singleton), Pointee(42.0));
+
+  source3 = 3.14f;
+  singleton = ConvertVariantTo<variant<double>>(source3);
+  EXPECT_FLOAT_EQ(3.14f, static_cast<float>(absl::get<double>(singleton)));
+  EXPECT_THAT(absl::get_if<double>(&singleton), Pointee(DoubleEq(3.14f)));
+
+  variant<int> source4(3);
+  singleton = ConvertVariantTo<variant<double>>(source4);
+  EXPECT_THAT(absl::get_if<double>(&singleton), Pointee(3.0));
+
+  variant<int32_t> source5(42);
+  variant<int32_t, uint32_t> variant2(
+      ConvertVariantTo<variant<int32_t, uint32_t>>(source5));
+  EXPECT_THAT(absl::get_if<int32_t>(&variant2), Pointee(42));
+
+  variant<uint32_t> source6(42);
+  variant2 = ConvertVariantTo<variant<int32_t, uint32_t>>(source6);
+  EXPECT_THAT(absl::get_if<uint32_t>(&variant2), Pointee(42));
+#endif  // !ABSL_USES_STD_VARIANT
+
+  variant<Convertible2, Convertible1> source7((Convertible1()));
+  variant<Convertible1, Convertible2> variant3(
+      ConvertVariantTo<variant<Convertible1, Convertible2>>(source7));
+  ASSERT_TRUE(absl::holds_alternative<Convertible1>(variant3));
+
+  source7 = Convertible2();
+  variant3 = ConvertVariantTo<variant<Convertible1, Convertible2>>(source7);
+  ASSERT_TRUE(absl::holds_alternative<Convertible2>(variant3));
+}
+
+TEST(VariantTest, TestMoveConversionViaConvertVariantTo) {
+  using Variant =
+      variant<std::unique_ptr<const int>, std::unique_ptr<const std::string>>;
+  using OtherVariant =
+      variant<std::unique_ptr<int>, std::unique_ptr<std::string>>;
+
+  Variant var(
+      ConvertVariantTo<Variant>(OtherVariant{absl::make_unique<int>(3)}));
+  EXPECT_THAT(absl::get_if<std::unique_ptr<const int>>(&var),
+              Pointee(Pointee(3)));
+
+  var = ConvertVariantTo<Variant>(
+      OtherVariant(absl::make_unique<std::string>("foo")));
+  EXPECT_THAT(absl::get_if<std::unique_ptr<const std::string>>(&var),
+              Pointee(Pointee(std::string("foo"))));
+}
+
+// If all alternatives are trivially copy/move constructible, variant should
+// also be trivially copy/move constructible. This is not required by the
+// standard and we know that libstdc++ variant doesn't have this feature.
+// For more details see the paper:
+// http://open-std.org/JTC1/SC22/WG21/docs/papers/2017/p0602r0.html
+#if !(defined(ABSL_USES_STD_VARIANT) && defined(__GLIBCXX__))
+#define ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY 1
+#endif
+
+TEST(VariantTest, TestCopyAndMoveTypeTraits) {
+  EXPECT_TRUE(std::is_copy_constructible<variant<std::string>>::value);
+  EXPECT_TRUE(absl::is_copy_assignable<variant<std::string>>::value);
+  EXPECT_TRUE(std::is_move_constructible<variant<std::string>>::value);
+  EXPECT_TRUE(absl::is_move_assignable<variant<std::string>>::value);
+  EXPECT_TRUE(std::is_move_constructible<variant<std::unique_ptr<int>>>::value);
+  EXPECT_TRUE(absl::is_move_assignable<variant<std::unique_ptr<int>>>::value);
+  EXPECT_FALSE(
+      std::is_copy_constructible<variant<std::unique_ptr<int>>>::value);
+  EXPECT_FALSE(absl::is_copy_assignable<variant<std::unique_ptr<int>>>::value);
+
+  EXPECT_FALSE(
+      absl::is_trivially_copy_constructible<variant<std::string>>::value);
+  EXPECT_FALSE(absl::is_trivially_copy_assignable<variant<std::string>>::value);
+#if ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY
+  EXPECT_TRUE(absl::is_trivially_copy_constructible<variant<int>>::value);
+  EXPECT_TRUE(absl::is_trivially_copy_assignable<variant<int>>::value);
+  EXPECT_TRUE(is_trivially_move_constructible<variant<int>>::value);
+  EXPECT_TRUE(is_trivially_move_assignable<variant<int>>::value);
+#endif  // ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY
+}
+
+TEST(VariantTest, TestVectorOfMoveonlyVariant) {
+  // Verify that variant<MoveonlyType> works correctly as a std::vector element.
+  std::vector<variant<std::unique_ptr<int>, std::string>> vec;
+  vec.push_back(absl::make_unique<int>(42));
+  vec.emplace_back("Hello");
+  vec.reserve(3);
+  auto another_vec = absl::move(vec);
+  // As a sanity check, verify vector contents.
+  ASSERT_EQ(2, another_vec.size());
+  EXPECT_EQ(42, *absl::get<std::unique_ptr<int>>(another_vec[0]));
+  EXPECT_EQ("Hello", absl::get<std::string>(another_vec[1]));
+}
+
+TEST(VariantTest, NestedVariant) {
+#if ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY
+  static_assert(absl::is_trivially_copy_constructible<variant<int>>(), "");
+  static_assert(absl::is_trivially_copy_assignable<variant<int>>(), "");
+  static_assert(is_trivially_move_constructible<variant<int>>(), "");
+  static_assert(is_trivially_move_assignable<variant<int>>(), "");
+
+  static_assert(absl::is_trivially_copy_constructible<variant<variant<int>>>(),
+                "");
+  static_assert(absl::is_trivially_copy_assignable<variant<variant<int>>>(),
+                "");
+  static_assert(is_trivially_move_constructible<variant<variant<int>>>(), "");
+  static_assert(is_trivially_move_assignable<variant<variant<int>>>(), "");
+#endif  // ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY
+
+  variant<int> x(42);
+  variant<variant<int>> y(x);
+  variant<variant<int>> z(y);
+  EXPECT_TRUE(absl::holds_alternative<variant<int>>(z));
+  EXPECT_EQ(x, absl::get<variant<int>>(z));
+}
+
+struct TriviallyDestructible {
+  TriviallyDestructible(TriviallyDestructible&&) {}
+  TriviallyDestructible(const TriviallyDestructible&) {}
+  TriviallyDestructible& operator=(TriviallyDestructible&&) { return *this; }
+  TriviallyDestructible& operator=(const TriviallyDestructible&) {
+    return *this;
+  }
+};
+
+struct TriviallyMovable {
+  TriviallyMovable(TriviallyMovable&&) = default;
+  TriviallyMovable(TriviallyMovable const&) {}
+  TriviallyMovable& operator=(const TriviallyMovable&) { return *this; }
+};
+
+struct TriviallyCopyable {
+  TriviallyCopyable(const TriviallyCopyable&) = default;
+  TriviallyCopyable& operator=(const TriviallyCopyable&) { return *this; }
+};
+
+struct TriviallyMoveAssignable {
+  TriviallyMoveAssignable(TriviallyMoveAssignable&&) = default;
+  TriviallyMoveAssignable(const TriviallyMoveAssignable&) {}
+  TriviallyMoveAssignable& operator=(TriviallyMoveAssignable&&) = default;
+  TriviallyMoveAssignable& operator=(const TriviallyMoveAssignable&) {
+    return *this;
+  }
+};
+
+struct TriviallyCopyAssignable {};
+
+#if ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY
+TEST(VariantTest, TestTriviality) {
+  {
+    using TrivDestVar = absl::variant<TriviallyDestructible>;
+
+    EXPECT_FALSE(is_trivially_move_constructible<TrivDestVar>::value);
+    EXPECT_FALSE(absl::is_trivially_copy_constructible<TrivDestVar>::value);
+    EXPECT_FALSE(is_trivially_move_assignable<TrivDestVar>::value);
+    EXPECT_FALSE(absl::is_trivially_copy_assignable<TrivDestVar>::value);
+    EXPECT_TRUE(absl::is_trivially_destructible<TrivDestVar>::value);
+  }
+
+  {
+    using TrivMoveVar = absl::variant<TriviallyMovable>;
+
+    EXPECT_TRUE(is_trivially_move_constructible<TrivMoveVar>::value);
+    EXPECT_FALSE(absl::is_trivially_copy_constructible<TrivMoveVar>::value);
+    EXPECT_FALSE(is_trivially_move_assignable<TrivMoveVar>::value);
+    EXPECT_FALSE(absl::is_trivially_copy_assignable<TrivMoveVar>::value);
+    EXPECT_TRUE(absl::is_trivially_destructible<TrivMoveVar>::value);
+  }
+
+  {
+    using TrivCopyVar = absl::variant<TriviallyCopyable>;
+
+    EXPECT_TRUE(is_trivially_move_constructible<TrivCopyVar>::value);
+    EXPECT_TRUE(absl::is_trivially_copy_constructible<TrivCopyVar>::value);
+    EXPECT_FALSE(is_trivially_move_assignable<TrivCopyVar>::value);
+    EXPECT_FALSE(absl::is_trivially_copy_assignable<TrivCopyVar>::value);
+    EXPECT_TRUE(absl::is_trivially_destructible<TrivCopyVar>::value);
+  }
+
+  {
+    using TrivMoveAssignVar = absl::variant<TriviallyMoveAssignable>;
+
+    EXPECT_TRUE(is_trivially_move_constructible<TrivMoveAssignVar>::value);
+    EXPECT_FALSE(
+        absl::is_trivially_copy_constructible<TrivMoveAssignVar>::value);
+    EXPECT_TRUE(is_trivially_move_assignable<TrivMoveAssignVar>::value);
+    EXPECT_FALSE(absl::is_trivially_copy_assignable<TrivMoveAssignVar>::value);
+    EXPECT_TRUE(absl::is_trivially_destructible<TrivMoveAssignVar>::value);
+  }
+
+  {
+    using TrivCopyAssignVar = absl::variant<TriviallyCopyAssignable>;
+
+    EXPECT_TRUE(is_trivially_move_constructible<TrivCopyAssignVar>::value);
+    EXPECT_TRUE(
+        absl::is_trivially_copy_constructible<TrivCopyAssignVar>::value);
+    EXPECT_TRUE(is_trivially_move_assignable<TrivCopyAssignVar>::value);
+    EXPECT_TRUE(absl::is_trivially_copy_assignable<TrivCopyAssignVar>::value);
+    EXPECT_TRUE(absl::is_trivially_destructible<TrivCopyAssignVar>::value);
+  }
+}
+#endif  // ABSL_VARIANT_PROPAGATE_COPY_MOVE_TRIVIALITY
+
+// To verify that absl::variant correctly use the nontrivial move ctor of its
+// member rather than use the trivial copy constructor.
+TEST(VariantTest, MoveCtorBug) {
+  // To simulate std::tuple in libstdc++.
+  struct TrivialCopyNontrivialMove {
+    TrivialCopyNontrivialMove() = default;
+    TrivialCopyNontrivialMove(const TrivialCopyNontrivialMove&) = default;
+    TrivialCopyNontrivialMove(TrivialCopyNontrivialMove&&) { called = true; }
+    bool called = false;
+  };
+  {
+    using V = absl::variant<TrivialCopyNontrivialMove, int>;
+    V v1(absl::in_place_index<0>);
+    // this should invoke the move ctor, rather than the trivial copy ctor.
+    V v2(std::move(v1));
+    EXPECT_TRUE(absl::get<0>(v2).called);
+  }
+  {
+    // this case failed to compile before our fix due to a GCC bug.
+    using V = absl::variant<int, TrivialCopyNontrivialMove>;
+    V v1(absl::in_place_index<1>);
+    // this should invoke the move ctor, rather than the trivial copy ctor.
+    V v2(std::move(v1));
+    EXPECT_TRUE(absl::get<1>(v2).called);
+  }
+}
+
+}  // namespace
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // #if !defined(ABSL_USES_STD_VARIANT)