Add Nullability annotations to Abseil.

PiperOrigin-RevId: 541915097
Change-Id: I7ebfbafc36db38b59b30ab5b312cd7e22082a805

CMake/AbseilDll.cmake

@@ -26,6 +26,7 @@ set(ABSL_INTERNAL_DLL_FILES
   "base/internal/low_level_alloc.cc"
   "base/internal/low_level_alloc.cc"
   "base/internal/low_level_alloc.h"
   "base/internal/low_level_alloc.h"
   "base/internal/low_level_scheduling.h"
   "base/internal/low_level_scheduling.h"
+  "base/internal/nullability_impl.h"
   "base/internal/per_thread_tls.h"
   "base/internal/per_thread_tls.h"
   "base/internal/prefetch.h"
   "base/internal/prefetch.h"
   "base/prefetch.h"
   "base/prefetch.h"
@@ -56,6 +57,7 @@ set(ABSL_INTERNAL_DLL_FILES
   "base/log_severity.cc"
   "base/log_severity.cc"
   "base/log_severity.h"
   "base/log_severity.h"
   "base/macros.h"
   "base/macros.h"
+  "base/nullability.h"
   "base/optimization.h"
   "base/optimization.h"
   "base/options.h"
   "base/options.h"
   "base/policy_checks.h"
   "base/policy_checks.h"

absl/base/BUILD.bazel

@@ -63,6 +63,18 @@ cc_library(
 )
 )
 
 
 cc_library(
 cc_library(
+    name = "nullability",
+    srcs = ["internal/nullability_impl.h"],
+    hdrs = ["nullability.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":core_headers",
+        "//absl/meta:type_traits",
+    ],
+)
+
+cc_library(
     name = "raw_logging_internal",
     name = "raw_logging_internal",
     srcs = ["internal/raw_logging.cc"],
     srcs = ["internal/raw_logging.cc"],
     hdrs = ["internal/raw_logging.h"],
     hdrs = ["internal/raw_logging.h"],
@@ -553,6 +565,16 @@ cc_test(
 )
 )
 
 
 cc_test(
 cc_test(
+    name = "nullability_test",
+    srcs = ["nullability_test.cc"],
+    deps = [
+        ":core_headers",
+        ":nullability",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
     name = "raw_logging_test",
     name = "raw_logging_test",
     srcs = ["raw_logging_test.cc"],
     srcs = ["raw_logging_test.cc"],
     copts = ABSL_TEST_COPTS,
     copts = ABSL_TEST_COPTS,

absl/base/CMakeLists.txt

@@ -54,6 +54,33 @@ absl_cc_library(
     ${ABSL_DEFAULT_COPTS}
     ${ABSL_DEFAULT_COPTS}
 )
 )
 
 
+absl_cc_library(
+  NAME
+    nullability
+  HDRS
+    "nullability.h"
+  SRCS
+    "internal/nullability_impl.h"
+  DEPS
+    absl::core_headers
+    absl::type_traits
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+)
+
+absl_cc_test(
+  NAME
+    nullability_test
+  SRCS
+    "nullability_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::core_headers
+    absl::nullability
+    GTest::gtest_main
+)
+
 # Internal-only target, do not depend on directly.
 # Internal-only target, do not depend on directly.
 absl_cc_library(
 absl_cc_library(
   NAME
   NAME

absl/base/internal/nullability_impl.h

+// Copyright 2023 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_BASE_INTERNAL_NULLABILITY_IMPL_H_
+#define ABSL_BASE_INTERNAL_NULLABILITY_IMPL_H_
+
+#include <memory>
+#include <type_traits>
+
+#include "absl/base/attributes.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+
+namespace nullability_internal {
+
+// `IsNullabilityCompatible` checks whether its first argument is a class
+// explicitly tagged as supporting nullability annotations. The tag is the type
+// declaration `absl_nullability_compatible`.
+template <typename, typename = void>
+struct IsNullabilityCompatible : std::false_type {};
+
+template <typename T>
+struct IsNullabilityCompatible<
+    T, absl::void_t<typename T::absl_nullability_compatible>> : std::true_type {
+};
+
+template <typename T>
+constexpr bool IsSupportedType = IsNullabilityCompatible<T>::value;
+
+template <typename T>
+constexpr bool IsSupportedType<T*> = true;
+
+template <typename T, typename U>
+constexpr bool IsSupportedType<T U::*> = true;
+
+template <typename T, typename... Deleter>
+constexpr bool IsSupportedType<std::unique_ptr<T, Deleter...>> = true;
+
+template <typename T>
+constexpr bool IsSupportedType<std::shared_ptr<T>> = true;
+
+template <typename T>
+struct EnableNullable {
+  static_assert(nullability_internal::IsSupportedType<std::remove_cv_t<T>>,
+                "Template argument must be a raw or supported smart pointer "
+                "type. See absl/base/nullability.h.");
+  using type = T;
+};
+
+template <typename T>
+struct EnableNonNull {
+  static_assert(nullability_internal::IsSupportedType<std::remove_cv_t<T>>,
+                "Template argument must be a raw or supported smart pointer "
+                "type. See absl/base/nullability.h.");
+  using type = T;
+};
+
+template <typename T>
+struct EnableNullabilityUnknown {
+  static_assert(nullability_internal::IsSupportedType<std::remove_cv_t<T>>,
+                "Template argument must be a raw or supported smart pointer "
+                "type. See absl/base/nullability.h.");
+  using type = T;
+};
+
+// Note: we do not apply Clang nullability attributes (e.g. _Nullable).  These
+// only support raw pointers, and conditionally enabling them only for raw
+// pointers inhibits template arg deduction.  Ideally, they would support all
+// pointer-like types.
+template <typename T, typename = typename EnableNullable<T>::type>
+using NullableImpl
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::annotate)
+    [[clang::annotate("Nullable")]]
+#endif
+    = T;
+
+template <typename T, typename = typename EnableNonNull<T>::type>
+using NonNullImpl
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::annotate)
+    [[clang::annotate("Nonnull")]]
+#endif
+    = T;
+
+template <typename T, typename = typename EnableNullabilityUnknown<T>::type>
+using NullabilityUnknownImpl
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::annotate)
+    [[clang::annotate("Nullability_Unspecified")]]
+#endif
+    = T;
+
+}  // namespace nullability_internal
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_NULLABILITY_IMPL_H_

absl/base/nullability_test.cc

+// Copyright 2023 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/base/nullability.h"
+
+#include <cassert>
+#include <memory>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/base/attributes.h"
+
+namespace {
+using ::absl::NonNull;
+using ::absl::NullabilityUnknown;
+using ::absl::Nullable;
+
+void funcWithNonnullArg(NonNull<int*> /*arg*/) {}
+template <typename T>
+void funcWithDeducedNonnullArg(NonNull<T*> /*arg*/) {}
+
+TEST(NonNullTest, NonNullArgument) {
+  int var = 0;
+  funcWithNonnullArg(&var);
+  funcWithDeducedNonnullArg(&var);
+}
+
+NonNull<int*> funcWithNonnullReturn() {
+  static int var = 0;
+  return &var;
+}
+
+TEST(NonNullTest, NonNullReturn) {
+  auto var = funcWithNonnullReturn();
+  (void)var;
+}
+
+TEST(PassThroughTest, PassesThroughRawPointerToInt) {
+  EXPECT_TRUE((std::is_same<NonNull<int*>, int*>::value));
+  EXPECT_TRUE((std::is_same<Nullable<int*>, int*>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<int*>, int*>::value));
+}
+
+TEST(PassThroughTest, PassesThroughRawPointerToVoid) {
+  EXPECT_TRUE((std::is_same<NonNull<void*>, void*>::value));
+  EXPECT_TRUE((std::is_same<Nullable<void*>, void*>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<void*>, void*>::value));
+}
+
+TEST(PassThroughTest, PassesThroughUniquePointerToInt) {
+  using T = std::unique_ptr<int>;
+  EXPECT_TRUE((std::is_same<NonNull<T>, T>::value));
+  EXPECT_TRUE((std::is_same<Nullable<T>, T>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<T>, T>::value));
+}
+
+TEST(PassThroughTest, PassesThroughSharedPointerToInt) {
+  using T = std::shared_ptr<int>;
+  EXPECT_TRUE((std::is_same<NonNull<T>, T>::value));
+  EXPECT_TRUE((std::is_same<Nullable<T>, T>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<T>, T>::value));
+}
+
+TEST(PassThroughTest, PassesThroughSharedPointerToVoid) {
+  using T = std::shared_ptr<void>;
+  EXPECT_TRUE((std::is_same<NonNull<T>, T>::value));
+  EXPECT_TRUE((std::is_same<Nullable<T>, T>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<T>, T>::value));
+}
+
+TEST(PassThroughTest, PassesThroughPointerToMemberObject) {
+  using T = decltype(&std::pair<int, int>::first);
+  EXPECT_TRUE((std::is_same<NonNull<T>, T>::value));
+  EXPECT_TRUE((std::is_same<Nullable<T>, T>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<T>, T>::value));
+}
+
+TEST(PassThroughTest, PassesThroughPointerToMemberFunction) {
+  using T = decltype(&std::unique_ptr<int>::reset);
+  EXPECT_TRUE((std::is_same<NonNull<T>, T>::value));
+  EXPECT_TRUE((std::is_same<Nullable<T>, T>::value));
+  EXPECT_TRUE((std::is_same<NullabilityUnknown<T>, T>::value));
+}
+
+}  // namespace
+
+// Nullable ADL lookup test
+namespace util {
+// Helper for NullableAdlTest.  Returns true, denoting that argument-dependent
+// lookup found this implementation of DidAdlWin.  Must be in namespace
+// util itself, not a nested anonymous namespace.
+template <typename T>
+bool DidAdlWin(T*) {
+  return true;
+}
+
+// Because this type is defined in namespace util, an unqualified call to
+// DidAdlWin with a pointer to MakeAdlWin will find the above implementation.
+struct MakeAdlWin {};
+}  // namespace util
+
+namespace {
+// Returns false, denoting that ADL did not inspect namespace util.  If it
+// had, the better match (T*) above would have won out over the (...) here.
+bool DidAdlWin(...) { return false; }
+
+TEST(NullableAdlTest, NullableAddsNothingToArgumentDependentLookup) {
+  // Treatment: util::Nullable<int*> contributes nothing to ADL because
+  // int* itself doesn't.
+  EXPECT_FALSE(DidAdlWin((int*)nullptr));
+  EXPECT_FALSE(DidAdlWin((Nullable<int*>)nullptr));
+
+  // Control: Argument-dependent lookup does find the implementation in
+  // namespace util when the underlying pointee type resides there.
+  EXPECT_TRUE(DidAdlWin((util::MakeAdlWin*)nullptr));
+  EXPECT_TRUE(DidAdlWin((Nullable<util::MakeAdlWin*>)nullptr));
+}
+}  // namespace