Changes imported from Abseil "staging" branch:

  - 8bcd472c6f1a7c8a3a7aac07d7e5e3f90685fe5e Create an exception-safety testing framework for Abseil by Jon Cohen <cohenjon@google.com>
  - 17cc4bb19ba86e2bc45e9381bd07450c06134903 Fix typo. by Abseil Team <absl-team@google.com>

GitOrigin-RevId: 8bcd472c6f1a7c8a3a7aac07d7e5e3f90685fe5e
Change-Id: Ia1f4f12d25c375e0af34fea052a4a82dc964eeff

7 files changed, 1297 insertions, 67 deletions

diff --git a/absl/base/BUILD.bazel b/absl/base/BUILD.bazel
index e68c4500e561..207051254d21 100644
--- a/absl/base/BUILD.bazel
+++ b/absl/base/BUILD.bazel
@@ -226,6 +226,37 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "pretty_function",
+    hdrs = ["internal/pretty_function.h"],
+)
+
+cc_library(
+    name = "exception_safety_testing",
+    testonly = 1,
+    srcs = ["internal/exception_safety_testing.cc"],
+    hdrs = ["internal/exception_safety_testing.h"],
+    copts = ABSL_TEST_COPTS + ABSL_EXCEPTIONS_FLAG,
+    deps = [
+        ":config",
+        ":pretty_function",
+        "//absl/meta:type_traits",
+        "//absl/strings",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_test(
+    name = "exception_safety_testing_test",
+    srcs = ["exception_safety_testing_test.cc"],
+    copts = ABSL_TEST_COPTS + ABSL_EXCEPTIONS_FLAG,
+    deps = [
+        ":exception_safety_testing",
+        "//absl/memory",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "invoke_test",
     size = "small",
diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index ddf44584130d..6f3cfe4cbdae 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -260,7 +260,7 @@
 // ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED
 //
 // Tells the UndefinedSanitizer to ignore a given function. Useful for cases
-// where certain behavior (eg. devision by zero) is being used intentionally.
+// where certain behavior (eg. division by zero) is being used intentionally.
 // NOTE: GCC supports UndefinedBehaviorSanitizer(ubsan) since 4.9.
 // https://gcc.gnu.org/gcc-4.9/changes.html
 #if defined(__GNUC__) && \
diff --git a/absl/base/exception_safety_testing_test.cc b/absl/base/exception_safety_testing_test.cc
new file mode 100644
index 000000000000..365732c6721a
--- /dev/null
+++ b/absl/base/exception_safety_testing_test.cc
@@ -0,0 +1,546 @@
+#include "absl/base/internal/exception_safety_testing.h"
+
+#include <cstddef>
+#include <exception>
+#include <iostream>
+#include <list>
+#include <vector>
+
+#include "gtest/gtest-spi.h"
+#include "gtest/gtest.h"
+#include "absl/memory/memory.h"
+
+namespace absl {
+namespace {
+using ::absl::exceptions_internal::TestException;
+
+void SetCountdown() { exceptions_internal::countdown = 0; }
+
+void UnsetCountdown() { exceptions_internal::countdown = -1; }
+
+// EXPECT_NO_THROW can't inspect the thrown inspection in general.
+template <typename F>
+void ExpectNoThrow(const F& f) {
+  try {
+    f();
+  } catch (TestException e) {
+    ADD_FAILURE() << "Unexpected exception thrown from " << e.what();
+  }
+}
+
+class ThrowingValueTest : public ::testing::Test {
+ protected:
+  void SetUp() override { UnsetCountdown(); }
+
+ private:
+  AllocInspector clouseau_;
+};
+
+TEST_F(ThrowingValueTest, Throws) {
+  SetCountdown();
+  EXPECT_THROW(ThrowingValue<> bomb, TestException);
+
+  // It's not guaranteed that every operator only throws *once*.  The default
+  // ctor only throws once, though, so use it to make sure we only throw when
+  // the countdown hits 0
+  exceptions_internal::countdown = 2;
+  ExpectNoThrow([]() { ThrowingValue<> bomb; });
+  ExpectNoThrow([]() { ThrowingValue<> bomb; });
+  EXPECT_THROW(ThrowingValue<> bomb, TestException);
+}
+
+// Tests that an operation throws when the countdown is at 0, doesn't throw when
+// the countdown doesn't hit 0, and doesn't modify the state of the
+// ThrowingValue if it throws
+template <typename F>
+void TestOp(F&& f) {
+  UnsetCountdown();
+  ExpectNoThrow(f);
+
+  SetCountdown();
+  EXPECT_THROW(f(), TestException);
+  UnsetCountdown();
+}
+
+TEST_F(ThrowingValueTest, ThrowingCtors) {
+  ThrowingValue<> bomb;
+
+  TestOp([]() { ThrowingValue<> bomb(1); });
+  TestOp([&]() { ThrowingValue<> bomb1 = bomb; });
+  TestOp([&]() { ThrowingValue<> bomb1 = std::move(bomb); });
+}
+
+TEST_F(ThrowingValueTest, ThrowingAssignment) {
+  ThrowingValue<> bomb, bomb1;
+
+  TestOp([&]() { bomb = bomb1; });
+  TestOp([&]() { bomb = std::move(bomb1); });
+}
+
+TEST_F(ThrowingValueTest, ThrowingComparisons) {
+  ThrowingValue<> bomb1, bomb2;
+  TestOp([&]() { return bomb1 == bomb2; });
+  TestOp([&]() { return bomb1 != bomb2; });
+  TestOp([&]() { return bomb1 < bomb2; });
+  TestOp([&]() { return bomb1 <= bomb2; });
+  TestOp([&]() { return bomb1 > bomb2; });
+  TestOp([&]() { return bomb1 >= bomb2; });
+}
+
+TEST_F(ThrowingValueTest, ThrowingArithmeticOps) {
+  ThrowingValue<> bomb1(1), bomb2(2);
+
+  TestOp([&bomb1]() { +bomb1; });
+  TestOp([&bomb1]() { -bomb1; });
+  TestOp([&bomb1]() { ++bomb1; });
+  TestOp([&bomb1]() { bomb1++; });
+  TestOp([&bomb1]() { --bomb1; });
+  TestOp([&bomb1]() { bomb1--; });
+
+  TestOp([&]() { bomb1 + bomb2; });
+  TestOp([&]() { bomb1 - bomb2; });
+  TestOp([&]() { bomb1* bomb2; });
+  TestOp([&]() { bomb1 / bomb2; });
+  TestOp([&]() { bomb1 << 1; });
+  TestOp([&]() { bomb1 >> 1; });
+}
+
+TEST_F(ThrowingValueTest, ThrowingLogicalOps) {
+  ThrowingValue<> bomb1, bomb2;
+
+  TestOp([&bomb1]() { !bomb1; });
+  TestOp([&]() { bomb1&& bomb2; });
+  TestOp([&]() { bomb1 || bomb2; });
+}
+
+TEST_F(ThrowingValueTest, ThrowingBitwiseOps) {
+  ThrowingValue<> bomb1, bomb2;
+
+  TestOp([&bomb1]() { ~bomb1; });
+  TestOp([&]() { bomb1& bomb2; });
+  TestOp([&]() { bomb1 | bomb2; });
+  TestOp([&]() { bomb1 ^ bomb2; });
+}
+
+TEST_F(ThrowingValueTest, ThrowingCompoundAssignmentOps) {
+  ThrowingValue<> bomb1(1), bomb2(2);
+
+  TestOp([&]() { bomb1 += bomb2; });
+  TestOp([&]() { bomb1 -= bomb2; });
+  TestOp([&]() { bomb1 *= bomb2; });
+  TestOp([&]() { bomb1 /= bomb2; });
+  TestOp([&]() { bomb1 %= bomb2; });
+  TestOp([&]() { bomb1 &= bomb2; });
+  TestOp([&]() { bomb1 |= bomb2; });
+  TestOp([&]() { bomb1 ^= bomb2; });
+  TestOp([&]() { bomb1 *= bomb2; });
+}
+
+TEST_F(ThrowingValueTest, ThrowingStreamOps) {
+  ThrowingValue<> bomb;
+
+  TestOp([&]() { std::cin >> bomb; });
+  TestOp([&]() { std::cout << bomb; });
+}
+
+TEST_F(ThrowingValueTest, ThrowingAllocatingOps) {
+  // make_unique calls unqualified operator new, so these exercise the
+  // ThrowingValue overloads.
+  TestOp([]() { return absl::make_unique<ThrowingValue<>>(1); });
+  TestOp([]() { return absl::make_unique<ThrowingValue<>[]>(2); });
+}
+
+TEST_F(ThrowingValueTest, NonThrowingMoveCtor) {
+  ThrowingValue<NoThrow::kMoveCtor> nothrow_ctor;
+
+  SetCountdown();
+  ExpectNoThrow([&nothrow_ctor]() {
+    ThrowingValue<NoThrow::kMoveCtor> nothrow1 = std::move(nothrow_ctor);
+  });
+}
+
+TEST_F(ThrowingValueTest, NonThrowingMoveAssign) {
+  ThrowingValue<NoThrow::kMoveAssign> nothrow_assign1, nothrow_assign2;
+
+  SetCountdown();
+  ExpectNoThrow([&nothrow_assign1, &nothrow_assign2]() {
+    nothrow_assign1 = std::move(nothrow_assign2);
+  });
+}
+
+TEST_F(ThrowingValueTest, ThrowingSwap) {
+  ThrowingValue<> bomb1, bomb2;
+  TestOp([&]() { std::swap(bomb1, bomb2); });
+
+  ThrowingValue<NoThrow::kMoveCtor> bomb3, bomb4;
+  TestOp([&]() { std::swap(bomb3, bomb4); });
+
+  ThrowingValue<NoThrow::kMoveAssign> bomb5, bomb6;
+  TestOp([&]() { std::swap(bomb5, bomb6); });
+}
+
+TEST_F(ThrowingValueTest, NonThrowingSwap) {
+  ThrowingValue<NoThrow::kMoveAssign | NoThrow::kMoveCtor> bomb1, bomb2;
+  ExpectNoThrow([&]() { std::swap(bomb1, bomb2); });
+}
+
+TEST_F(ThrowingValueTest, NonThrowingAllocation) {
+  ThrowingValue<NoThrow::kAllocation>* allocated;
+  ThrowingValue<NoThrow::kAllocation>* array;
+
+  ExpectNoThrow([&allocated]() {
+    allocated = new ThrowingValue<NoThrow::kAllocation>(1);
+    delete allocated;
+  });
+  ExpectNoThrow([&array]() {
+    array = new ThrowingValue<NoThrow::kAllocation>[2];
+    delete[] array;
+  });
+}
+
+TEST_F(ThrowingValueTest, NonThrowingDelete) {
+  auto* allocated = new ThrowingValue<>(1);
+  auto* array = new ThrowingValue<>[2];
+
+  SetCountdown();
+  ExpectNoThrow([allocated]() { delete allocated; });
+  SetCountdown();
+  ExpectNoThrow([array]() { delete[] array; });
+}
+
+using Storage =
+    absl::aligned_storage_t<sizeof(ThrowingValue<>), alignof(ThrowingValue<>)>;
+
+TEST_F(ThrowingValueTest, NonThrowingPlacementDelete) {
+  constexpr int kArrayLen = 2;
+  // We intentionally create extra space to store the tag allocated by placement
+  // new[].
+  constexpr int kStorageLen = 4;
+
+  Storage buf;
+  Storage array_buf[kStorageLen];
+  auto* placed = new (&buf) ThrowingValue<>(1);
+  auto placed_array = new (&array_buf) ThrowingValue<>[kArrayLen];
+
+  SetCountdown();
+  ExpectNoThrow([placed, &buf]() {
+    placed->~ThrowingValue<>();
+    ThrowingValue<>::operator delete(placed, &buf);
+  });
+
+  SetCountdown();
+  ExpectNoThrow([&, placed_array]() {
+    for (int i = 0; i < kArrayLen; ++i) placed_array[i].~ThrowingValue<>();
+    ThrowingValue<>::operator delete[](placed_array, &array_buf);
+  });
+}
+
+TEST_F(ThrowingValueTest, NonThrowingDestructor) {
+  auto* allocated = new ThrowingValue<>();
+  SetCountdown();
+  ExpectNoThrow([allocated]() { delete allocated; });
+}
+
+TEST(ThrowingBoolTest, ThrowingBool) {
+  UnsetCountdown();
+  ThrowingBool t = true;
+
+  // Test that it's contextually convertible to bool
+  if (t) {  // NOLINT(whitespace/empty_if_body)
+  }
+  EXPECT_TRUE(t);
+
+  TestOp([&]() { (void)!t; });
+}
+
+class ThrowingAllocatorTest : public ::testing::Test {
+ protected:
+  void SetUp() override { UnsetCountdown(); }
+
+ private:
+  AllocInspector borlu_;
+};
+
+TEST_F(ThrowingAllocatorTest, MemoryManagement) {
+  // Just exercise the memory management capabilities under LSan to make sure we
+  // don't leak.
+  ThrowingAllocator<int> int_alloc;
+  int* ip = int_alloc.allocate(1);
+  int_alloc.deallocate(ip, 1);
+  int* i_array = int_alloc.allocate(2);
+  int_alloc.deallocate(i_array, 2);
+
+  ThrowingAllocator<ThrowingValue<>> ef_alloc;
+  ThrowingValue<>* efp = ef_alloc.allocate(1);
+  ef_alloc.deallocate(efp, 1);
+  ThrowingValue<>* ef_array = ef_alloc.allocate(2);
+  ef_alloc.deallocate(ef_array, 2);
+}
+
+TEST_F(ThrowingAllocatorTest, CallsGlobalNew) {
+  ThrowingAllocator<ThrowingValue<>, NoThrow::kNoThrow> nothrow_alloc;
+  ThrowingValue<>* ptr;
+
+  SetCountdown();
+  // This will only throw if ThrowingValue::new is called.
+  ExpectNoThrow([&]() { ptr = nothrow_alloc.allocate(1); });
+  nothrow_alloc.deallocate(ptr, 1);
+}
+
+TEST_F(ThrowingAllocatorTest, ThrowingConstructors) {
+  ThrowingAllocator<int> int_alloc;
+  int* ip = nullptr;
+
+  SetCountdown();
+  EXPECT_THROW(ip = int_alloc.allocate(1), TestException);
+  ExpectNoThrow([&]() { ip = int_alloc.allocate(1); });
+
+  *ip = 1;
+  SetCountdown();
+  EXPECT_THROW(int_alloc.construct(ip, 2), TestException);
+  EXPECT_EQ(*ip, 1);
+  int_alloc.deallocate(ip, 1);
+}
+
+TEST_F(ThrowingAllocatorTest, NonThrowingConstruction) {
+  {
+    ThrowingAllocator<int, NoThrow::kNoThrow> int_alloc;
+    int* ip = nullptr;
+
+    SetCountdown();
+    ExpectNoThrow([&]() { ip = int_alloc.allocate(1); });
+    SetCountdown();
+    ExpectNoThrow([&]() { int_alloc.construct(ip, 2); });
+    EXPECT_EQ(*ip, 2);
+    int_alloc.deallocate(ip, 1);
+  }
+
+  UnsetCountdown();
+  {
+    ThrowingAllocator<int> int_alloc;
+    int* ip = nullptr;
+    ExpectNoThrow([&]() { ip = int_alloc.allocate(1); });
+    ExpectNoThrow([&]() { int_alloc.construct(ip, 2); });
+    EXPECT_EQ(*ip, 2);
+    int_alloc.deallocate(ip, 1);
+  }
+
+  UnsetCountdown();
+  {
+    ThrowingAllocator<ThrowingValue<NoThrow::kIntCtor>, NoThrow::kNoThrow>
+        ef_alloc;
+    ThrowingValue<NoThrow::kIntCtor>* efp;
+    SetCountdown();
+    ExpectNoThrow([&]() { efp = ef_alloc.allocate(1); });
+    SetCountdown();
+    ExpectNoThrow([&]() { ef_alloc.construct(efp, 2); });
+    EXPECT_EQ(efp->Get(), 2);
+    ef_alloc.destroy(efp);
+    ef_alloc.deallocate(efp, 1);
+  }
+
+  UnsetCountdown();
+  {
+    ThrowingAllocator<int> a;
+    SetCountdown();
+    ExpectNoThrow([&]() { ThrowingAllocator<double> a1 = a; });
+    SetCountdown();
+    ExpectNoThrow([&]() { ThrowingAllocator<double> a1 = std::move(a); });
+  }
+}
+
+TEST_F(ThrowingAllocatorTest, ThrowingAllocatorConstruction) {
+  ThrowingAllocator<int> a;
+  TestOp([]() { ThrowingAllocator<int> a; });
+  TestOp([&]() { a.select_on_container_copy_construction(); });
+}
+
+TEST_F(ThrowingAllocatorTest, State) {
+  ThrowingAllocator<int> a1, a2;
+  EXPECT_NE(a1, a2);
+
+  auto a3 = a1;
+  EXPECT_EQ(a3, a1);
+  int* ip = a1.allocate(1);
+  EXPECT_EQ(a3, a1);
+  a3.deallocate(ip, 1);
+  EXPECT_EQ(a3, a1);
+}
+
+TEST_F(ThrowingAllocatorTest, InVector) {
+  std::vector<ThrowingValue<>, ThrowingAllocator<ThrowingValue<>>> v;
+  for (int i = 0; i < 20; ++i) v.push_back({});
+  for (int i = 0; i < 20; ++i) v.pop_back();
+}
+
+TEST_F(ThrowingAllocatorTest, InList) {
+  std::list<ThrowingValue<>, ThrowingAllocator<ThrowingValue<>>> l;
+  for (int i = 0; i < 20; ++i) l.push_back({});
+  for (int i = 0; i < 20; ++i) l.pop_back();
+  for (int i = 0; i < 20; ++i) l.push_front({});
+  for (int i = 0; i < 20; ++i) l.pop_front();
+}
+
+struct CallOperator {
+  template <typename T>
+  void operator()(T* t) const {
+    (*t)();
+  }
+};
+
+struct FailsBasicGuarantee {
+  void operator()() {
+    --i;
+    ThrowingValue<> bomb;
+    ++i;
+  }
+
+  bool operator!=(const FailsBasicGuarantee& other) const {
+    return i != other.i;
+  }
+
+  friend bool AbslCheckInvariants(const FailsBasicGuarantee& g) {
+    return g.i >= 0;
+  }
+
+  int i = 0;
+};
+
+TEST(ExceptionCheckTest, BasicGuaranteeFailure) {
+  FailsBasicGuarantee g;
+  EXPECT_FALSE(TestBasicGuarantee(&g, CallOperator{}));
+}
+
+struct FollowsBasicGuarantee {
+  void operator()() {
+    ++i;
+    ThrowingValue<> bomb;
+  }
+
+  bool operator!=(const FollowsBasicGuarantee& other) const {
+    return i != other.i;
+  }
+
+  friend bool AbslCheckInvariants(const FollowsBasicGuarantee& g) {
+    return g.i >= 0;
+  }
+
+  int i = 0;
+};
+
+TEST(ExceptionCheckTest, BasicGuarantee) {
+  FollowsBasicGuarantee g;
+  EXPECT_TRUE(TestBasicGuarantee(&g, CallOperator{}));
+}
+
+TEST(ExceptionCheckTest, StrongGuaranteeFailure) {
+  {
+    FailsBasicGuarantee g;
+    EXPECT_FALSE(TestStrongGuarantee(&g, CallOperator{}));
+  }
+
+  {
+    FollowsBasicGuarantee g;
+    EXPECT_FALSE(TestStrongGuarantee(&g, CallOperator{}));
+  }
+}
+
+struct FollowsStrongGuarantee {
+  void operator()() { ThrowingValue<> bomb; }
+
+  bool operator!=(const FollowsStrongGuarantee& other) const {
+    return i != other.i;
+  }
+
+  friend bool AbslCheckInvariants(const FollowsStrongGuarantee& g) {
+    return g.i >= 0;
+  }
+
+  int i = 0;
+};
+
+TEST(ExceptionCheckTest, StrongGuarantee) {
+  FollowsStrongGuarantee g;
+  EXPECT_TRUE(TestBasicGuarantee(&g, CallOperator{}));
+  EXPECT_TRUE(TestStrongGuarantee(&g, CallOperator{}));
+}
+
+template <typename T>
+struct InstructionCounter {
+  void operator()() {
+    ++counter;
+    T b1;
+    static_cast<void>(b1);
+    ++counter;
+    T b2;
+    static_cast<void>(b2);
+    ++counter;
+    T b3;
+    static_cast<void>(b3);
+    ++counter;
+  }
+
+  bool operator!=(const InstructionCounter<ThrowingValue<>>& other) const {
+    return false;
+  }
+
+  friend bool AbslCheckInvariants(const InstructionCounter&) { return true; }
+
+  static int counter;
+};
+template <typename T>
+int InstructionCounter<T>::counter = 0;
+
+TEST(ExceptionCheckTest, Exhaustiveness) {
+  InstructionCounter<int> int_factory;
+  EXPECT_TRUE(TestBasicGuarantee(&int_factory, CallOperator{}));
+  EXPECT_EQ(InstructionCounter<int>::counter, 4);
+
+  InstructionCounter<ThrowingValue<>> bomb_factory;
+  EXPECT_TRUE(TestBasicGuarantee(&bomb_factory, CallOperator{}));
+  EXPECT_EQ(InstructionCounter<ThrowingValue<>>::counter, 10);
+
+  InstructionCounter<ThrowingValue<>>::counter = 0;
+  EXPECT_TRUE(TestStrongGuarantee(&bomb_factory, CallOperator{}));
+  EXPECT_EQ(InstructionCounter<ThrowingValue<>>::counter, 10);
+}
+
+struct Tracked : private exceptions_internal::TrackedObject {
+  Tracked() : TrackedObject(ABSL_PRETTY_FUNCTION) {}
+};
+
+TEST(AllocInspectorTest, Pass) {
+  AllocInspector javert;
+  Tracked t;
+}
+
+TEST(AllocInspectorTest, NotDestroyed) {
+  absl::aligned_storage_t<sizeof(Tracked), alignof(Tracked)> storage;
+  EXPECT_NONFATAL_FAILURE(
+      {
+        AllocInspector gadget;
+        new (&storage) Tracked;
+      },
+      "not destroyed");
+}
+
+TEST(AllocInspectorTest, DestroyedTwice) {
+  EXPECT_NONFATAL_FAILURE(
+      {
+        Tracked t;
+        t.~Tracked();
+      },
+      "destroyed improperly");
+}
+
+TEST(AllocInspectorTest, ConstructedTwice) {
+  absl::aligned_storage_t<sizeof(Tracked), alignof(Tracked)> storage;
+  EXPECT_NONFATAL_FAILURE(
+      {
+        new (&storage) Tracked;
+        new (&storage) Tracked;
+      },
+      "re-constructed");
+}
+}  // namespace
+}  // namespace absl
diff --git a/absl/base/internal/exception_safety_testing.cc b/absl/base/internal/exception_safety_testing.cc
new file mode 100644
index 000000000000..383c9c595251
--- /dev/null
+++ b/absl/base/internal/exception_safety_testing.cc
@@ -0,0 +1,21 @@
+#include "absl/base/internal/exception_safety_testing.h"
+
+#include "gtest/gtest.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+namespace exceptions_internal {
+
+int countdown = -1;
+
+void MaybeThrow(absl::string_view msg) {
+  if (countdown-- == 0) throw TestException(msg);
+}
+
+testing::AssertionResult FailureMessage(const TestException& e,
+                                        int countdown) noexcept {
+  return testing::AssertionFailure()
+         << "Exception number " << countdown + 1 << " thrown from " << e.what();
+}
+}  // namespace exceptions_internal
+}  // namespace absl
diff --git a/absl/base/internal/exception_safety_testing.h b/absl/base/internal/exception_safety_testing.h
new file mode 100644
index 000000000000..aca27a575c34
--- /dev/null
+++ b/absl/base/internal/exception_safety_testing.h
@@ -0,0 +1,679 @@
+// Utilities for testing exception-safety
+
+#ifndef ABSL_BASE_INTERNAL_EXCEPTION_TESTING_H_
+#define ABSL_BASE_INTERNAL_EXCEPTION_TESTING_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <iosfwd>
+#include <string>
+#include <unordered_map>
+
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/pretty_function.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/string_view.h"
+#include "absl/strings/substitute.h"
+
+namespace absl {
+struct AllocInspector;
+
+// A configuration enum for Throwing*.  Operations whose flags are set will
+// throw, everything else won't.  This isn't meant to be exhaustive, more flags
+// can always be made in the future.
+enum class NoThrow : uint8_t {
+  kNone = 0,
+  kMoveCtor = 1,
+  kMoveAssign = 1 << 1,
+  kAllocation = 1 << 2,
+  kIntCtor = 1 << 3,
+  kNoThrow = static_cast<uint8_t>(-1)
+};
+
+constexpr NoThrow operator|(NoThrow a, NoThrow b) {
+  using T = absl::underlying_type_t<NoThrow>;
+  return static_cast<NoThrow>(static_cast<T>(a) | static_cast<T>(b));
+}
+
+constexpr NoThrow operator&(NoThrow a, NoThrow b) {
+  using T = absl::underlying_type_t<NoThrow>;
+  return static_cast<NoThrow>(static_cast<T>(a) & static_cast<T>(b));
+}
+
+namespace exceptions_internal {
+constexpr bool ThrowingAllowed(NoThrow flags, NoThrow flag) {
+  return !static_cast<bool>(flags & flag);
+}
+
+// A simple exception class.  We throw this so that test code can catch
+// exceptions specifically thrown by ThrowingValue.
+class TestException {
+ public:
+  explicit TestException(absl::string_view msg) : msg_(msg) {}
+  absl::string_view what() const { return msg_; }
+
+ private:
+  std::string msg_;
+};
+
+extern int countdown;
+
+void MaybeThrow(absl::string_view msg);
+
+testing::AssertionResult FailureMessage(const TestException& e,
+                                        int countdown) noexcept;
+
+class TrackedObject {
+ protected:
+  explicit TrackedObject(absl::string_view child_ctor) {
+    if (!GetAllocs().emplace(this, child_ctor).second) {
+      ADD_FAILURE() << "Object at address " << static_cast<void*>(this)
+                    << " re-constructed in ctor " << child_ctor;
+    }
+  }
+
+  TrackedObject(const TrackedObject&) = delete;
+  TrackedObject(TrackedObject&&) = delete;
+
+  static std::unordered_map<TrackedObject*, absl::string_view>& GetAllocs() {
+    static auto* m =
+        new std::unordered_map<TrackedObject*, absl::string_view>();
+    return *m;
+  }
+
+  ~TrackedObject() noexcept {
+    if (GetAllocs().erase(this) == 0) {
+      ADD_FAILURE() << "Object at address " << static_cast<void*>(this)
+                    << " destroyed improperly";
+    }
+  }
+
+  friend struct ::absl::AllocInspector;
+};
+}  // namespace exceptions_internal
+
+// A test class which is contextually convertible to bool.  The conversion can
+// be instrumented to throw at a controlled time.
+class ThrowingBool {
+ public:
+  ThrowingBool(bool b) noexcept : b_(b) {}  // NOLINT(runtime/explicit)
+  explicit operator bool() const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return b_;
+  }
+
+ private:
+  bool b_;
+};
+
+// A testing class instrumented to throw an exception at a controlled time.
+//
+// ThrowingValue implements a slightly relaxed version of the Regular concept --
+// that is it's a value type with the expected semantics.  It also implements
+// arithmetic operations.  It doesn't implement member and pointer operators
+// like operator-> or operator[].
+//
+// ThrowingValue can be instrumented to have certain operations be noexcept by
+// using compile-time bitfield flag template arguments.  That is, to make an
+// ThrowingValue which has a noexcept move constructor and noexcept move
+// assignment, use
+// ThrowingValue<absl::NoThrow::kMoveCtor | absl::NoThrow::kMoveAssign>.
+template <NoThrow Flags = NoThrow::kNone>
+class ThrowingValue : private exceptions_internal::TrackedObject {
+ public:
+  ThrowingValue() : TrackedObject(ABSL_PRETTY_FUNCTION) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ = 0;
+  }
+
+  ThrowingValue(const ThrowingValue& other)
+      : TrackedObject(ABSL_PRETTY_FUNCTION) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ = other.dummy_;
+  }
+
+  ThrowingValue(ThrowingValue&& other) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveCtor))
+      : TrackedObject(ABSL_PRETTY_FUNCTION) {
+    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveCtor)) {
+      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    }
+    dummy_ = other.dummy_;
+  }
+
+  explicit ThrowingValue(int i) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kIntCtor))
+      : TrackedObject(ABSL_PRETTY_FUNCTION) {
+    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kIntCtor)) {
+      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    }
+    dummy_ = i;
+  }
+
+  // absl expects nothrow destructors
+  ~ThrowingValue() noexcept = default;
+
+  ThrowingValue& operator=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ = other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator=(ThrowingValue&& other) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveAssign)) {
+    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveAssign)) {
+      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    }
+    dummy_ = other.dummy_;
+    return *this;
+  }
+
+  // Arithmetic Operators
+  ThrowingValue operator+(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ + other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator+() const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator-(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ - other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator-() const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(-dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue& operator++() {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    ++dummy_;
+    return *this;
+  }
+
+  ThrowingValue operator++(int) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    auto out = ThrowingValue(dummy_, NoThrowTag{});
+    ++dummy_;
+    return out;
+  }
+
+  ThrowingValue& operator--() {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    --dummy_;
+    return *this;
+  }
+
+  ThrowingValue operator--(int) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    auto out = ThrowingValue(dummy_, NoThrowTag{});
+    --dummy_;
+    return out;
+  }
+
+  ThrowingValue operator*(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ * other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator/(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ / other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator%(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ % other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator<<(int shift) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ << shift, NoThrowTag{});
+  }
+
+  ThrowingValue operator>>(int shift) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ >> shift, NoThrowTag{});
+  }
+
+  // Comparison Operators
+  friend ThrowingBool operator==(const ThrowingValue& a,
+                                 const ThrowingValue& b) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return a.dummy_ == b.dummy_;
+  }
+  friend ThrowingBool operator!=(const ThrowingValue& a,
+                                 const ThrowingValue& b) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return a.dummy_ != b.dummy_;
+  }
+  friend ThrowingBool operator<(const ThrowingValue& a,
+                                const ThrowingValue& b) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return a.dummy_ < b.dummy_;
+  }
+  friend ThrowingBool operator<=(const ThrowingValue& a,
+                                 const ThrowingValue& b) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return a.dummy_ <= b.dummy_;
+  }
+  friend ThrowingBool operator>(const ThrowingValue& a,
+                                const ThrowingValue& b) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return a.dummy_ > b.dummy_;
+  }
+  friend ThrowingBool operator>=(const ThrowingValue& a,
+                                 const ThrowingValue& b) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return a.dummy_ >= b.dummy_;
+  }
+
+  // Logical Operators
+  ThrowingBool operator!() const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return !dummy_;
+  }
+
+  ThrowingBool operator&&(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return dummy_ && other.dummy_;
+  }
+
+  ThrowingBool operator||(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return dummy_ || other.dummy_;
+  }
+
+  // Bitwise Logical Operators
+  ThrowingValue operator~() const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(~dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator&(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ & other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator|(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ | other.dummy_, NoThrowTag{});
+  }
+
+  ThrowingValue operator^(const ThrowingValue& other) const {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return ThrowingValue(dummy_ ^ other.dummy_, NoThrowTag{});
+  }
+
+  // Compound Assignment operators
+  ThrowingValue& operator+=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ += other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator-=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ -= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator*=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ *= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator/=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ /= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator%=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ %= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator&=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ &= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator|=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ |= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator^=(const ThrowingValue& other) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ ^= other.dummy_;
+    return *this;
+  }
+
+  ThrowingValue& operator<<=(int shift) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ <<= shift;
+    return *this;
+  }
+
+  ThrowingValue& operator>>=(int shift) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ >>= shift;
+    return *this;
+  }
+
+  // Pointer operators
+  void operator&() const = delete;  // NOLINT(runtime/operator)
+
+  // Stream operators
+  friend std::ostream& operator<<(std::ostream& os, const ThrowingValue&) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return os;
+  }
+
+  friend std::istream& operator>>(std::istream& is, const ThrowingValue&) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    return is;
+  }
+
+  // Memory management operators
+  // Args.. allows us to overload regular and placement new in one shot
+  template <typename... Args>
+  static void* operator new(size_t s, Args&&... args) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
+    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
+      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    }
+    return ::operator new(s, std::forward<Args>(args)...);
+  }
+
+  template <typename... Args>
+  static void* operator new[](size_t s, Args&&... args) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
+    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
+      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    }
+    return ::operator new[](s, std::forward<Args>(args)...);
+  }
+
+  // Abseil doesn't support throwing overloaded operator delete.  These are
+  // provided so a throwing operator-new can clean up after itself.
+  //
+  // We provide both regular and templated operator delete because if only the
+  // templated version is provided as we did with operator new, the compiler has
+  // no way of knowing which overload of operator delete to call. See
+  // http://en.cppreference.com/w/cpp/memory/new/operator_delete and
+  // http://en.cppreference.com/w/cpp/language/delete for the gory details.
+  void operator delete(void* p) noexcept { ::operator delete(p); }
+
+  template <typename... Args>
+  void operator delete(void* p, Args&&... args) noexcept {
+    ::operator delete(p, std::forward<Args>(args)...);
+  }
+
+  void operator delete[](void* p) noexcept { return ::operator delete[](p); }
+
+  template <typename... Args>
+  void operator delete[](void* p, Args&&... args) noexcept {
+    return ::operator delete[](p, std::forward<Args>(args)...);
+  }
+
+  // Non-standard access to the actual contained value.  No need for this to
+  // throw.
+  int& Get() noexcept { return dummy_; }
+  const int& Get() const noexcept { return dummy_; }
+
+ private:
+  struct NoThrowTag {};
+  ThrowingValue(int i, NoThrowTag) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(i) {}
+
+  int dummy_;
+};
+// While not having to do with exceptions, explicitly delete comma operator, to
+// make sure we don't use it on user-supplied types.
+template <NoThrow N, typename T>
+void operator,(const ThrowingValue<N>& ef, T&& t) = delete;
+template <NoThrow N, typename T>
+void operator,(T&& t, const ThrowingValue<N>& ef) = delete;
+
+// An allocator type which is instrumented to throw at a controlled time, or not
+// to throw, using NoThrow.  The supported settings are the default of every
+// function which is allowed to throw in a conforming allocator possibly
+// throwing, or nothing throws, in line with the ABSL_ALLOCATOR_THROWS
+// configuration macro.
+template <typename T, NoThrow Flags = NoThrow::kNone>
+class ThrowingAllocator : private exceptions_internal::TrackedObject {
+  static_assert(Flags == NoThrow::kNone || Flags == NoThrow::kNoThrow,
+                "Invalid flag");
+
+ public:
+  using pointer = T*;
+  using const_pointer = const T*;
+  using reference = T&;
+  using const_reference = const T&;
+  using void_pointer = void*;
+  using const_void_pointer = const void*;
+  using value_type = T;
+  using size_type = size_t;
+  using difference_type = ptrdiff_t;
+
+  using is_nothrow = std::integral_constant<bool, Flags == NoThrow::kNoThrow>;
+  using propagate_on_container_copy_assignment = std::true_type;
+  using propagate_on_container_move_assignment = std::true_type;
+  using propagate_on_container_swap = std::true_type;
+  using is_always_equal = std::false_type;
+
+  ThrowingAllocator() : TrackedObject(ABSL_PRETTY_FUNCTION) {
+    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
+    dummy_ = std::make_shared<const int>(next_id_++);
+  }
+
+  template <typename U>
+  ThrowingAllocator(  // NOLINT
+      const ThrowingAllocator<U, Flags>& other) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(other.State()) {}
+
+  ThrowingAllocator(const ThrowingAllocator& other) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(other.State()) {}
+
+  template <typename U>
+  ThrowingAllocator(  // NOLINT
+      ThrowingAllocator<U, Flags>&& other) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(std::move(other.State())) {}
+
+  ThrowingAllocator(ThrowingAllocator&& other) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(std::move(other.State())) {}
+
+  ~ThrowingAllocator() noexcept = default;
+
+  template <typename U>
+  ThrowingAllocator& operator=(
+      const ThrowingAllocator<U, Flags>& other) noexcept {
+    dummy_ = other.State();
+    return *this;
+  }
+
+  template <typename U>
+  ThrowingAllocator& operator=(ThrowingAllocator<U, Flags>&& other) noexcept {
+    dummy_ = std::move(other.State());
+    return *this;
+  }
+
+  template <typename U>
+  struct rebind {
+    using other = ThrowingAllocator<U, Flags>;
+  };
+
+  pointer allocate(size_type n) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
+    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
+    return static_cast<pointer>(::operator new(n * sizeof(T)));
+  }
+  pointer allocate(size_type n, const_void_pointer) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
+    return allocate(n);
+  }
+
+  void deallocate(pointer ptr, size_type) noexcept {
+    ReadState();
+    ::operator delete(static_cast<void*>(ptr));
+  }
+
+  template <typename U, typename... Args>
+  void construct(U* ptr, Args&&... args) noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
+    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
+    ::new (static_cast<void*>(ptr)) U(std::forward<Args>(args)...);
+  }
+
+  template <typename U>
+  void destroy(U* p) noexcept {
+    ReadState();
+    p->~U();
+  }
+
+  size_type max_size() const
+      noexcept(!exceptions_internal::ThrowingAllowed(Flags,
+                                                     NoThrow::kNoThrow)) {
+    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
+    return std::numeric_limits<difference_type>::max() / sizeof(value_type);
+  }
+
+  ThrowingAllocator select_on_container_copy_construction() noexcept(
+      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
+    auto& out = *this;
+    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
+    return out;
+  }
+
+  template <typename U>
+  bool operator==(const ThrowingAllocator<U, Flags>& other) const noexcept {
+    return dummy_ == other.dummy_;
+  }
+
+  template <typename U>
+  bool operator!=(const ThrowingAllocator<U, Flags>& other) const noexcept {
+    return dummy_ != other.dummy_;
+  }
+
+  template <typename U, NoThrow B>
+  friend class ThrowingAllocator;
+
+ private:
+  const std::shared_ptr<const int>& State() const { return dummy_; }
+  std::shared_ptr<const int>& State() { return dummy_; }
+
+  void ReadState() {
+    // we know that this will never be true, but the compiler doesn't, so this
+    // should safely force a read of the value.
+    if (*dummy_ < 0) std::abort();
+  }
+
+  void ReadStateAndMaybeThrow(absl::string_view msg) const {
+    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
+      exceptions_internal::MaybeThrow(
+          absl::Substitute("Allocator id $0 threw from $1", *dummy_, msg));
+    }
+  }
+
+  static int next_id_;
+  std::shared_ptr<const int> dummy_;
+};
+
+template <typename T, NoThrow Throws>
+int ThrowingAllocator<T, Throws>::next_id_ = 0;
+
+// Inspects the constructions and destructions of anything inheriting from
+// TrackedObject.  Place this as a member variable in a test fixture to ensure
+// that every ThrowingValue was constructed and destroyed correctly.
+struct AllocInspector {
+  AllocInspector() = default;
+  ~AllocInspector() {
+    auto& allocs = exceptions_internal::TrackedObject::GetAllocs();
+    for (const auto& kv : allocs) {
+      ADD_FAILURE() << "Object at address " << static_cast<void*>(kv.first)
+                    << " constructed from " << kv.second << " not destroyed";
+    }
+    allocs.clear();
+  }
+};
+
+// Tests that performing operation Op on a T follows the basic exception safety
+// guarantee.
+//
+// Parameters:
+//   * T: the type under test.
+//   * FunctionFromTPtrToVoid: A functor exercising the function under test.  It
+//     should take a T* and return void.
+//
+//  There must also be a function named `AbslCheckInvariants` in an associated
+//  namespace of T which takes a const T& and returns true if the T's class
+//  invariants hold, and false if they don't.
+template <typename T, typename FunctionFromTPtrToVoid>
+testing::AssertionResult TestBasicGuarantee(T* t, FunctionFromTPtrToVoid&& op) {
+  for (int countdown = 0;; ++countdown) {
+    exceptions_internal::countdown = countdown;
+    try {
+      op(t);
+      break;
+    } catch (const exceptions_internal::TestException& e) {
+      if (!AbslCheckInvariants(*t)) {
+        return exceptions_internal::FailureMessage(e, countdown)
+               << " broke invariants.";
+      }
+    }
+  }
+  exceptions_internal::countdown = -1;
+  return testing::AssertionSuccess();
+}
+
+// Tests that performing operation Op on a T follows the strong exception safety
+// guarantee.
+//
+// Parameters:
+//   * T: the type under test. T must be copy-constructable and
+//   equality-comparible.
+//   * FunctionFromTPtrToVoid: A functor exercising the function under test.  It
+//     should take a T* and return void.
+//
+//  There must also be a function named `AbslCheckInvariants` in an associated
+//  namespace of T which takes a const T& and returns true if the T's class
+//  invariants hold, and false if they don't.
+template <typename T, typename FunctionFromTPtrToVoid>
+testing::AssertionResult TestStrongGuarantee(T* t,
+                                             FunctionFromTPtrToVoid&& op) {
+  exceptions_internal::countdown = -1;
+  for (auto countdown = 0;; ++countdown) {
+    T dup = *t;
+    exceptions_internal::countdown = countdown;
+    try {
+      op(t);
+      break;
+    } catch (const exceptions_internal::TestException& e) {
+      if (!AbslCheckInvariants(*t)) {
+        return exceptions_internal::FailureMessage(e, countdown)
+               << " broke invariants.";
+      }
+      if (dup != *t)
+        return exceptions_internal::FailureMessage(e, countdown)
+               << " changed state.";
+    }
+  }
+  exceptions_internal::countdown = -1;
+  return testing::AssertionSuccess();
+}
+
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_EXCEPTION_SAFETY_TESTING_H_
diff --git a/absl/base/internal/pretty_function.h b/absl/base/internal/pretty_function.h
new file mode 100644
index 000000000000..6be3936f7c24
--- /dev/null
+++ b/absl/base/internal/pretty_function.h
@@ -0,0 +1,19 @@
+#ifndef ABSL_BASE_INTERNAL_PRETTY_FUNCTION_H_
+#define ABSL_BASE_INTERNAL_PRETTY_FUNCTION_H_
+
+// ABSL_PRETTY_FUNCTION
+//
+// In C++11, __func__ gives the undecorated name of the current function.  That
+// is, "main", not "int main()".  Various compilers give extra macros to get the
+// decorated function name, including return type and arguments, to
+// differentiate between overload sets.  ABSL_PRETTY_FUNCTION is a portable
+// version of these macros which forwards to the correct macro on each compiler.
+#if defined(_MSC_VER)
+#define ABSL_PRETTY_FUNCTION __FUNCSIG__
+#elif defined(__GNUC__)
+#define ABSL_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#else
+#error "Unsupported compiler"
+#endif
+
+#endif  // ABSL_BASE_INTERNAL_PRETTY_FUNCTION_H_
diff --git a/absl/strings/ascii_ctype.h b/absl/strings/ascii_ctype.h
deleted file mode 100644
index e1ba9e24a3d5..000000000000
--- a/absl/strings/ascii_ctype.h
+++ /dev/null
@@ -1,66 +0,0 @@
-// 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
-//
-//      http://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_STRINGS_ASCII_CTYPE_H_
-#define ABSL_STRINGS_ASCII_CTYPE_H_
-
-#include "absl/strings/ascii.h"
-
-inline bool ascii_isalpha(unsigned char c) {
-  return absl::ascii_isalpha(c);
-}
-inline bool ascii_isalnum(unsigned char c) {
-  return absl::ascii_isalnum(c);
-}
-inline bool ascii_isspace(unsigned char c) {
-  return absl::ascii_isspace(c);
-}
-inline bool ascii_ispunct(unsigned char c) {
-  return absl::ascii_ispunct(c);
-}
-inline bool ascii_isblank(unsigned char c) {
-  return absl::ascii_isblank(c);
-}
-inline bool ascii_iscntrl(unsigned char c) {
-  return absl::ascii_iscntrl(c);
-}
-inline bool ascii_isxdigit(unsigned char c) {
-  return absl::ascii_isxdigit(c);
-}
-inline bool ascii_isdigit(unsigned char c) {
-  return absl::ascii_isdigit(c);
-}
-inline bool ascii_isprint(unsigned char c) {
-  return absl::ascii_isprint(c);
-}
-inline bool ascii_isgraph(unsigned char c) {
-  return absl::ascii_isgraph(c);
-}
-inline bool ascii_isupper(unsigned char c) {
-  return absl::ascii_isupper(c);
-}
-inline bool ascii_islower(unsigned char c) {
-  return absl::ascii_islower(c);
-}
-inline bool ascii_isascii(unsigned char c) {
-  return absl::ascii_isascii(c);
-}
-inline char ascii_tolower(unsigned char c) {
-  return absl::ascii_tolower(c);
-}
-inline char ascii_toupper(unsigned char c) {
-  return absl::ascii_toupper(c);
-}
-
-#endif  // ABSL_STRINGS_ASCII_CTYPE_H_