5 files changed, 609 insertions, 0 deletions
diff --git a/absl/cleanup/BUILD.bazel b/absl/cleanup/BUILD.bazel
new file mode 100644
index 00000000..5cca898f
--- /dev/null
+++ b/absl/cleanup/BUILD.bazel
@@ -0,0 +1,66 @@
+# Copyright 2021 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"])
+
+cc_library(
+    name = "cleanup_internal",
+    hdrs = ["internal/cleanup.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/base:base_internal",
+        "//absl/base:core_headers",
+        "//absl/utility",
+    ],
+)
+
+cc_library(
+    name = "cleanup",
+    hdrs = [
+        "cleanup.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":cleanup_internal",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+    ],
+)
+
+cc_test(
+    name = "cleanup_test",
+    size = "small",
+    srcs = [
+        "cleanup_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":cleanup",
+        "//absl/base:config",
+        "//absl/utility",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
diff --git a/absl/cleanup/CMakeLists.txt b/absl/cleanup/CMakeLists.txt
new file mode 100644
index 00000000..a2dd78a8
--- /dev/null
+++ b/absl/cleanup/CMakeLists.txt
@@ -0,0 +1,55 @@
+# Copyright 2021 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
+    cleanup_internal
+  HDRS
+    "internal/cleanup.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::base_internal
+    absl::core_headers
+    absl::utility
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    cleanup
+  HDRS
+    "cleanup.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::cleanup_internal
+    absl::config
+    absl::core_headers
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    cleanup_test
+  SRCS
+    "cleanup_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::cleanup
+    absl::config
+    absl::utility
+    gmock_main
+)
diff --git a/absl/cleanup/cleanup.h b/absl/cleanup/cleanup.h
new file mode 100644
index 00000000..61b53d55
--- /dev/null
+++ b/absl/cleanup/cleanup.h
@@ -0,0 +1,140 @@
+// Copyright 2021 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.
+//
+// -----------------------------------------------------------------------------
+// File: cleanup.h
+// -----------------------------------------------------------------------------
+//
+// `absl::Cleanup` implements the scope guard idiom, invoking the contained
+// callback's `operator()() &&` on scope exit.
+//
+// Example:
+//
+// ```
+//   absl::Status CopyGoodData(const char* source_path, const char* sink_path) {
+//     FILE* source_file = fopen(source_path, "r");
+//     if (source_file == nullptr) {
+//       return absl::NotFoundError("No source file");  // No cleanups execute
+//     }
+//
+//     // C++17 style cleanup using class template argument deduction
+//     absl::Cleanup source_closer = [source_file] { fclose(source_file); };
+//
+//     FILE* sink_file = fopen(sink_path, "w");
+//     if (sink_file == nullptr) {
+//       return absl::NotFoundError("No sink file");  // First cleanup executes
+//     }
+//
+//     // C++11 style cleanup using the factory function
+//     auto sink_closer = absl::MakeCleanup([sink_file] { fclose(sink_file); });
+//
+//     Data data;
+//     while (ReadData(source_file, &data)) {
+//       if (!data.IsGood()) {
+//         absl::Status result = absl::FailedPreconditionError("Read bad data");
+//         return result;  // Both cleanups execute
+//       }
+//       SaveData(sink_file, &data);
+//     }
+//
+//     return absl::OkStatus();  // Both cleanups execute
+//   }
+// ```
+//
+// Methods:
+//
+// `std::move(cleanup).Cancel()` will prevent the callback from executing.
+//
+// `std::move(cleanup).Invoke()` will execute the callback early, before
+// destruction, and prevent the callback from executing in the destructor.
+//
+// Usage:
+//
+// `absl::Cleanup` is not an interface type. It is only intended to be used
+// within the body of a function. It is not a value type and instead models a
+// control flow construct. Check out `defer` in Golang for something similar.
+
+#ifndef ABSL_CLEANUP_CLEANUP_H_
+#define ABSL_CLEANUP_CLEANUP_H_
+
+#include <utility>
+
+#include "absl/base/config.h"
+#include "absl/base/macros.h"
+#include "absl/cleanup/internal/cleanup.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+template <typename Arg, typename Callback = void()>
+class ABSL_MUST_USE_RESULT Cleanup final {
+  static_assert(cleanup_internal::WasDeduced<Arg>(),
+                "Explicit template parameters are not supported.");
+
+  static_assert(cleanup_internal::ReturnsVoid<Callback>(),
+                "Callbacks that return values are not supported.");
+
+ public:
+  Cleanup(Callback callback)  // NOLINT
+      : storage_(std::move(callback), /* is_callback_engaged = */ true) {}
+
+  Cleanup(Cleanup&& other) = default;
+
+  void Cancel() && {
+    ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged());
+    storage_.DisengageCallback();
+  }
+
+  void Invoke() && {
+    ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged());
+    storage_.DisengageCallback();
+    storage_.InvokeCallback();
+  }
+
+  ~Cleanup() {
+    if (storage_.IsCallbackEngaged()) {
+      storage_.InvokeCallback();
+    }
+  }
+
+ private:
+  cleanup_internal::Storage<Callback> storage_;
+};
+
+// `absl::Cleanup c = /* callback */;`
+//
+// C++17 type deduction API for creating an instance of `absl::Cleanup`
+#if defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
+template <typename Callback>
+Cleanup(Callback callback) -> Cleanup<cleanup_internal::Tag, Callback>;
+#endif  // defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
+
+// `auto c = absl::MakeCleanup(/* callback */);`
+//
+// C++11 type deduction API for creating an instance of `absl::Cleanup`
+template <typename... Args, typename Callback>
+absl::Cleanup<cleanup_internal::Tag, Callback> MakeCleanup(Callback callback) {
+  static_assert(cleanup_internal::WasDeduced<cleanup_internal::Tag, Args...>(),
+                "Explicit template parameters are not supported.");
+
+  static_assert(cleanup_internal::ReturnsVoid<Callback>(),
+                "Callbacks that return values are not supported.");
+
+  return {std::move(callback)};
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CLEANUP_CLEANUP_H_
diff --git a/absl/cleanup/cleanup_test.cc b/absl/cleanup/cleanup_test.cc
new file mode 100644
index 00000000..792595d6
--- /dev/null
+++ b/absl/cleanup/cleanup_test.cc
@@ -0,0 +1,267 @@
+// Copyright 2021 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/cleanup/cleanup.h"
+
+#include <functional>
+#include <type_traits>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/utility/utility.h"
+
+namespace {
+
+using Tag = absl::cleanup_internal::Tag;
+
+template <typename Type1, typename Type2>
+constexpr bool IsSame() {
+  return (std::is_same<Type1, Type2>::value);
+}
+
+struct IdentityFactory {
+  template <typename Callback>
+  static Callback AsCallback(Callback callback) {
+    return Callback(std::move(callback));
+  }
+};
+
+// `FunctorClass` is a type used for testing `absl::Cleanup`. It is intended to
+// represent users that make their own move-only callback types outside of
+// `std::function` and lambda literals.
+class FunctorClass {
+  using Callback = std::function<void()>;
+
+ public:
+  explicit FunctorClass(Callback callback) : callback_(std::move(callback)) {}
+
+  FunctorClass(FunctorClass&& other)
+      : callback_(absl::exchange(other.callback_, Callback())) {}
+
+  FunctorClass(const FunctorClass&) = delete;
+
+  FunctorClass& operator=(const FunctorClass&) = delete;
+
+  FunctorClass& operator=(FunctorClass&&) = delete;
+
+  void operator()() const& = delete;
+
+  void operator()() && {
+    ASSERT_TRUE(callback_);
+    callback_();
+    callback_ = nullptr;
+  }
+
+ private:
+  Callback callback_;
+};
+
+struct FunctorClassFactory {
+  template <typename Callback>
+  static FunctorClass AsCallback(Callback callback) {
+    return FunctorClass(std::move(callback));
+  }
+};
+
+struct StdFunctionFactory {
+  template <typename Callback>
+  static std::function<void()> AsCallback(Callback callback) {
+    return std::function<void()>(std::move(callback));
+  }
+};
+
+using CleanupTestParams =
+    ::testing::Types<IdentityFactory, FunctorClassFactory, StdFunctionFactory>;
+template <typename>
+struct CleanupTest : public ::testing::Test {};
+TYPED_TEST_SUITE(CleanupTest, CleanupTestParams);
+
+bool fn_ptr_called = false;
+void FnPtrFunction() { fn_ptr_called = true; }
+
+TYPED_TEST(CleanupTest, FactoryProducesCorrectType) {
+  {
+    auto callback = TypeParam::AsCallback([] {});
+    auto cleanup = absl::MakeCleanup(std::move(callback));
+
+    static_assert(
+        IsSame<absl::Cleanup<Tag, decltype(callback)>, decltype(cleanup)>(),
+        "");
+  }
+
+  {
+    auto cleanup = absl::MakeCleanup(&FnPtrFunction);
+
+    static_assert(IsSame<absl::Cleanup<Tag, void (*)()>, decltype(cleanup)>(),
+                  "");
+  }
+
+  {
+    auto cleanup = absl::MakeCleanup(FnPtrFunction);
+
+    static_assert(IsSame<absl::Cleanup<Tag, void (*)()>, decltype(cleanup)>(),
+                  "");
+  }
+}
+
+#if defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
+TYPED_TEST(CleanupTest, CTADProducesCorrectType) {
+  {
+    auto callback = TypeParam::AsCallback([] {});
+    absl::Cleanup cleanup = std::move(callback);
+
+    static_assert(
+        IsSame<absl::Cleanup<Tag, decltype(callback)>, decltype(cleanup)>(),
+        "");
+  }
+
+  {
+    absl::Cleanup cleanup = &FnPtrFunction;
+
+    static_assert(IsSame<absl::Cleanup<Tag, void (*)()>, decltype(cleanup)>(),
+                  "");
+  }
+
+  {
+    absl::Cleanup cleanup = FnPtrFunction;
+
+    static_assert(IsSame<absl::Cleanup<Tag, void (*)()>, decltype(cleanup)>(),
+                  "");
+  }
+}
+
+TYPED_TEST(CleanupTest, FactoryAndCTADProduceSameType) {
+  {
+    auto callback = IdentityFactory::AsCallback([] {});
+    auto factory_cleanup = absl::MakeCleanup(callback);
+    absl::Cleanup deduction_cleanup = callback;
+
+    static_assert(
+        IsSame<decltype(factory_cleanup), decltype(deduction_cleanup)>(), "");
+  }
+
+  {
+    auto factory_cleanup =
+        absl::MakeCleanup(FunctorClassFactory::AsCallback([] {}));
+    absl::Cleanup deduction_cleanup = FunctorClassFactory::AsCallback([] {});
+
+    static_assert(
+        IsSame<decltype(factory_cleanup), decltype(deduction_cleanup)>(), "");
+  }
+
+  {
+    auto factory_cleanup =
+        absl::MakeCleanup(StdFunctionFactory::AsCallback([] {}));
+    absl::Cleanup deduction_cleanup = StdFunctionFactory::AsCallback([] {});
+
+    static_assert(
+        IsSame<decltype(factory_cleanup), decltype(deduction_cleanup)>(), "");
+  }
+
+  {
+    auto factory_cleanup = absl::MakeCleanup(&FnPtrFunction);
+    absl::Cleanup deduction_cleanup = &FnPtrFunction;
+
+    static_assert(
+        IsSame<decltype(factory_cleanup), decltype(deduction_cleanup)>(), "");
+  }
+
+  {
+    auto factory_cleanup = absl::MakeCleanup(FnPtrFunction);
+    absl::Cleanup deduction_cleanup = FnPtrFunction;
+
+    static_assert(
+        IsSame<decltype(factory_cleanup), decltype(deduction_cleanup)>(), "");
+  }
+}
+#endif  // defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
+
+TYPED_TEST(CleanupTest, BasicUsage) {
+  bool called = false;
+
+  {
+    auto cleanup =
+        absl::MakeCleanup(TypeParam::AsCallback([&called] { called = true; }));
+    EXPECT_FALSE(called);  // Constructor shouldn't invoke the callback
+  }
+
+  EXPECT_TRUE(called);  // Destructor should invoke the callback
+}
+
+TYPED_TEST(CleanupTest, BasicUsageWithFunctionPointer) {
+  fn_ptr_called = false;
+
+  {
+    auto cleanup = absl::MakeCleanup(TypeParam::AsCallback(&FnPtrFunction));
+    EXPECT_FALSE(fn_ptr_called);  // Constructor shouldn't invoke the callback
+  }
+
+  EXPECT_TRUE(fn_ptr_called);  // Destructor should invoke the callback
+}
+
+TYPED_TEST(CleanupTest, Cancel) {
+  bool called = false;
+
+  {
+    auto cleanup =
+        absl::MakeCleanup(TypeParam::AsCallback([&called] { called = true; }));
+    EXPECT_FALSE(called);  // Constructor shouldn't invoke the callback
+
+    std::move(cleanup).Cancel();
+    EXPECT_FALSE(called);  // Cancel shouldn't invoke the callback
+  }
+
+  EXPECT_FALSE(called);  // Destructor shouldn't invoke the callback
+}
+
+TYPED_TEST(CleanupTest, Invoke) {
+  bool called = false;
+
+  {
+    auto cleanup =
+        absl::MakeCleanup(TypeParam::AsCallback([&called] { called = true; }));
+    EXPECT_FALSE(called);  // Constructor shouldn't invoke the callback
+
+    std::move(cleanup).Invoke();
+    EXPECT_TRUE(called);  // Invoke should invoke the callback
+
+    called = false;  // Reset tracker before destructor runs
+  }
+
+  EXPECT_FALSE(called);  // Destructor shouldn't invoke the callback
+}
+
+TYPED_TEST(CleanupTest, Move) {
+  bool called = false;
+
+  {
+    auto moved_from_cleanup =
+        absl::MakeCleanup(TypeParam::AsCallback([&called] { called = true; }));
+    EXPECT_FALSE(called);  // Constructor shouldn't invoke the callback
+
+    {
+      auto moved_to_cleanup = std::move(moved_from_cleanup);
+      EXPECT_FALSE(called);  // Move shouldn't invoke the callback
+    }
+
+    EXPECT_TRUE(called);  // Destructor should invoke the callback
+
+    called = false;  // Reset tracker before destructor runs
+  }
+
+  EXPECT_FALSE(called);  // Destructor shouldn't invoke the callback
+}
+
+}  // namespace
diff --git a/absl/cleanup/internal/cleanup.h b/absl/cleanup/internal/cleanup.h
new file mode 100644
index 00000000..b4c40737
--- /dev/null
+++ b/absl/cleanup/internal/cleanup.h
@@ -0,0 +1,81 @@
+// Copyright 2021 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_CLEANUP_INTERNAL_CLEANUP_H_
+#define ABSL_CLEANUP_INTERNAL_CLEANUP_H_
+
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/invoke.h"
+#include "absl/base/thread_annotations.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace cleanup_internal {
+
+struct Tag {};
+
+template <typename Arg, typename... Args>
+constexpr bool WasDeduced() {
+  return (std::is_same<cleanup_internal::Tag, Arg>::value) &&
+         (sizeof...(Args) == 0);
+}
+
+template <typename Callback>
+constexpr bool ReturnsVoid() {
+  return (std::is_same<base_internal::invoke_result_t<Callback>, void>::value);
+}
+
+template <typename Callback>
+class Storage {
+ public:
+  Storage() = delete;
+
+  Storage(Callback callback, bool is_callback_engaged)
+      : callback_(std::move(callback)),
+        is_callback_engaged_(is_callback_engaged) {}
+
+  Storage(Storage&& other)
+      : callback_(std::move(other.callback_)),
+        is_callback_engaged_(
+            absl::exchange(other.is_callback_engaged_, false)) {}
+
+  Storage(const Storage& other) = delete;
+
+  Storage& operator=(Storage&& other) = delete;
+
+  Storage& operator=(const Storage& other) = delete;
+
+  bool IsCallbackEngaged() const { return is_callback_engaged_; }
+
+  void DisengageCallback() { is_callback_engaged_ = false; }
+
+  void InvokeCallback() ABSL_NO_THREAD_SAFETY_ANALYSIS {
+    std::move(callback_)();
+  }
+
+ private:
+  Callback callback_;
+  bool is_callback_engaged_;
+};
+
+}  // namespace cleanup_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CLEANUP_INTERNAL_CLEANUP_H_