Export of internal Abseil changes.

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78293ba4eb4981991ae7e6edd25eb9245fcd7515 by Andy Soffer <asoffer@google.com>:

internal changes

PiperOrigin-RevId: 247073879

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7bd97e3aad0c3012b89a39392a6ad3f254e9f3c3 by Derek Mauro <dmauro@google.com>:

Release commandline flags

PiperOrigin-RevId: 247065920

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2a991849fd7b140a43b073076d194b61533fd199 by Tom Manshreck <shreck@google.com>:

Add documentation for built-in usage flags

PiperOrigin-RevId: 247058863

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14157b0de45841706bbd631284191fd94c313db9 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 247058292

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ed67e0a80468596e30540b367727a250fa415b68 by Abseil Team <absl-team@google.com>:

Internal Change.

PiperOrigin-RevId: 246828655

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e1bc8c2aa3f90b3d56c55c5b7244e718c919265d by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 246822325

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907a68f287199f749cb9bdb48571b50bc34731e1 by Eric Fiselier <ericwf@google.com>:

Accept vector<bool>::reference in StrCat and friends.

Converting vector<bool>::reference to alphanum requires
two user defined conversions, which isn't allowed.
In order to accept this, we need a special constructor that
is only enabled for the bool proxy types.

PiperOrigin-RevId: 246626732

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fe4295fa95cc65dee8c881ba12dd8f516e68c40d by Abseil Team <absl-team@google.com>:

Clarify the proper way to define AbslHashValue, and fix confusing indentation.

PiperOrigin-RevId: 246406528

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d7174681a72d4a25c8fd2b4d9f515a0763eff87c by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 246358214

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a7fdc19683cf1a5885e9e1af52fcdb2db1eda53b by Abseil Team <absl-team@google.com>:

Fix sample template instantiation.

PiperOrigin-RevId: 246354617

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29a23c6835f872948d09b24d890385bf195bc995 by Abseil Team <absl-team@google.com>:

Fix incorrectly copy-pasted static_assert in absl::optional::value_or

The static_assert for a move-constructible type previously said the type must be copy-constructible.

PiperOrigin-RevId: 246313827

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41884d5872d4ea2c67875b00144b8c8a5859a295 by Greg Falcon <gfalcon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 245418790

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7f90a7f94cdd5e21232c749efe952a750b5c43a2 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 245412658

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730a329cf047d54b46971fce1781edd857208c2a by Greg Falcon <gfalcon@google.com>:

internal change

PiperOrigin-RevId: 245293234

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cf0216be6338200cbb18167d3f3b2e98e372be77 by Greg Falcon <gfalcon@google.com>:

Internal change

PiperOrigin-RevId: 245288164
GitOrigin-RevId: 78293ba4eb4981991ae7e6edd25eb9245fcd7515
Change-Id: I5ea9a852c36c722bae2d6be65fb7f72473d94ab6

1 files changed, 103 insertions, 0 deletions

diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
new file mode 100644
index 000000000000..6402866f2249
--- /dev/null
+++ b/absl/flags/internal/flag.h
@@ -0,0 +1,103 @@
+//
+// 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_FLAGS_INTERNAL_FLAG_H_
+#define ABSL_FLAGS_INTERNAL_FLAG_H_
+
+#include "absl/flags/internal/commandlineflag.h"
+#include "absl/flags/internal/registry.h"
+
+namespace absl {
+namespace flags_internal {
+
+// This is "unspecified" implementation of absl::Flag<T> type.
+template <typename T>
+class Flag {
+ public:
+  constexpr Flag(const char* name, const flags_internal::HelpGenFunc help_gen,
+                 const char* filename,
+                 const flags_internal::FlagMarshallingOpFn marshalling_op,
+                 const flags_internal::InitialValGenFunc initial_value_gen)
+      : internal(name, flags_internal::HelpText::FromFunctionPointer(help_gen),
+                 filename, &flags_internal::FlagOps<T>, marshalling_op,
+                 initial_value_gen,
+                 /*retired_arg=*/false, /*def_arg=*/nullptr,
+                 /*cur_arg=*/nullptr) {}
+
+  // Not copyable/assignable.
+  Flag(const Flag<T>&) = delete;
+  Flag<T>& operator=(const Flag<T>&) = delete;
+
+  absl::string_view Name() const { return internal.Name(); }
+  std::string Help() const { return internal.Help(); }
+  std::string Filename() const { return internal.Filename(); }
+
+  absl::flags_internal::CommandLineFlag internal;
+
+  void SetCallback(const flags_internal::FlagCallback mutation_callback) {
+    internal.SetCallback(mutation_callback);
+  }
+
+ private:
+  // TODO(rogeeff): add these validations once UnparseFlag invocation is fixed
+  // for built-in types and when we cleanup existing code from operating on
+  // forward declared types.
+  //  auto IsCopyConstructible(const T& v) -> decltype(T(v));
+  //  auto HasAbslParseFlag(absl::string_view in, T* dst, std::string* err)
+  //      -> decltype(AbslParseFlag(in, dst, GlobalStringADLGuard(err)));
+  //  auto HasAbslUnparseFlag(const T& v) -> decltype(AbslUnparseFlag(v));
+};
+
+// This class facilitates Flag object registration and tail expression-based
+// flag definition, for example:
+// ABSL_FLAG(int, foo, 42, "Foo help").OnUpdate(NotifyFooWatcher);
+template <typename T, bool do_register>
+class FlagRegistrar {
+ public:
+  explicit FlagRegistrar(Flag<T>* flag) : flag_(flag) {
+    if (do_register) flags_internal::RegisterCommandLineFlag(&flag_->internal);
+  }
+
+  FlagRegistrar& OnUpdate(flags_internal::FlagCallback cb) && {
+    flag_->SetCallback(cb);
+    return *this;
+  }
+
+  // Make the registrar "die" gracefully as a bool on a line where registration
+  // happens. Registrar objects are intended to live only as temporary.
+  operator bool() const { return true; }  // NOLINT
+
+ private:
+  Flag<T>* flag_;  // Flag being registered (not owned).
+};
+
+// This struct and corresponding overload to MakeDefaultValue are used to
+// facilitate usage of {} as default value in ABSL_FLAG macro.
+struct EmptyBraces {};
+
+template <typename T>
+T* MakeFromDefaultValue(T t) {
+  return new T(std::move(t));
+}
+
+template <typename T>
+T* MakeFromDefaultValue(EmptyBraces) {
+  return new T;
+}
+
+}  // namespace flags_internal
+}  // namespace absl
+
+#endif  // ABSL_FLAGS_INTERNAL_FLAG_H_