Remove the implementation of absl::variant, which was only needed

prior to C++17. `absl::variant` is now an alias for `std::variant`.
It is recommended that clients simply use `std::variant`.

PiperOrigin-RevId: 730940936
Change-Id: I7157612a62eec036abf61dd1ad42c5945afeac1d

Author: derekmauro

CMake/AbseilDll.cmake

@@ -430,10 +430,7 @@ set(ABSL_INTERNAL_DLL_FILES
   "time/internal/cctz/src/tzfile.h"
   "time/internal/cctz/src/zone_info_source.cc"
   "types/any.h"
-  "types/bad_variant_access.cc"
-  "types/bad_variant_access.h"
   "types/compare.h"
-  "types/internal/variant.h"
   "types/optional.h"
   "types/span.h"
   "types/internal/span.h"
@@ -488,7 +485,6 @@ set(ABSL_INTERNAL_DLL_TARGETS
   "any"
   "any_invocable"
   "atomic_hook"
-  "bad_variant_access"
   "base"
   "base_internal"
   "bind_front"

absl/base/config.h

@@ -522,19 +522,8 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define ABSL_USES_STD_ANY 1
 #define ABSL_HAVE_STD_OPTIONAL 1
 #define ABSL_USES_STD_OPTIONAL 1
-
-// ABSL_HAVE_STD_VARIANT
-//
-// Checks whether C++17 std::variant is available.
-#ifdef ABSL_HAVE_STD_VARIANT
-#error "ABSL_HAVE_STD_VARIANT cannot be directly set."
-#elif defined(__cpp_lib_variant) && __cpp_lib_variant >= 201606L
-#define ABSL_HAVE_STD_VARIANT 1
-#elif defined(ABSL_INTERNAL_CPLUSPLUS_LANG) && \
-    ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L && \
-    !ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE
 #define ABSL_HAVE_STD_VARIANT 1
-#endif
+#define ABSL_USES_STD_VARIANT 1
 
 // ABSL_HAVE_STD_STRING_VIEW
 //
@@ -564,21 +553,6 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define ABSL_HAVE_STD_ORDERING 1
 #endif
 
-// ABSL_USES_STD_VARIANT
-//
-// Indicates whether absl::variant is an alias for std::variant.
-#if !defined(ABSL_OPTION_USE_STD_VARIANT)
-#error options.h is misconfigured.
-#elif ABSL_OPTION_USE_STD_VARIANT == 0 || \
-    (ABSL_OPTION_USE_STD_VARIANT == 2 && !defined(ABSL_HAVE_STD_VARIANT))
-#undef ABSL_USES_STD_VARIANT
-#elif ABSL_OPTION_USE_STD_VARIANT == 1 || \
-    (ABSL_OPTION_USE_STD_VARIANT == 2 && defined(ABSL_HAVE_STD_VARIANT))
-#define ABSL_USES_STD_VARIANT 1
-#else
-#error options.h is misconfigured.
-#endif
-
 // ABSL_USES_STD_STRING_VIEW
 //
 // Indicates whether absl::string_view is an alias for std::string_view.
@@ -612,14 +586,6 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #error options.h is misconfigured.
 #endif
 
-// In debug mode, MSVC 2017's std::variant throws a EXCEPTION_ACCESS_VIOLATION
-// SEH exception from emplace for variant<SomeStruct> when constructing the
-// struct can throw. This defeats some of variant_test and
-// variant_exception_safety_test.
-#if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_DEBUG)
-#define ABSL_INTERNAL_MSVC_2017_DBG_MODE
-#endif
-
 // ABSL_INTERNAL_MANGLED_NS
 // ABSL_INTERNAL_MANGLED_BACKREFERENCE
 //

absl/base/options.h

@@ -99,32 +99,6 @@
 
 #define ABSL_OPTION_USE_STD_STRING_VIEW 2
 
-// ABSL_OPTION_USE_STD_VARIANT
-//
-// This option controls whether absl::variant is implemented as an alias to
-// std::variant, or as an independent implementation.
-//
-// A value of 0 means to use Abseil's implementation.  This requires only C++11
-// support, and is expected to work on every toolchain we support.
-//
-// A value of 1 means to use an alias to std::variant.  This requires that all
-// code using Abseil is built in C++17 mode or later.
-//
-// A value of 2 means to detect the C++ version being used to compile Abseil,
-// and use an alias only if a working std::variant is available.  This option
-// is useful when you are building your program from source.  It should not be
-// used otherwise -- for example, if you are distributing Abseil in a binary
-// package manager -- since in mode 2, absl::variant will name a different
-// type, with a different mangled name and binary layout, depending on the
-// compiler flags passed by the end user.  For more info, see
-// https://abseil.io/about/design/dropin-types.
-//
-// User code should not inspect this macro.  To check in the preprocessor if
-// absl::variant is a typedef of std::variant, use the feature macro
-// ABSL_USES_STD_VARIANT.
-
-#define ABSL_OPTION_USE_STD_VARIANT 2
-
 // ABSL_OPTION_USE_STD_ORDERING
 //
 // This option controls whether absl::{partial,weak,strong}_ordering are

absl/types/BUILD.bazel

@@ -105,81 +105,30 @@ cc_library(
     deprecation = "bad_optional_access dependency is empty can be removed",
 )
 
-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_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",
-        "@googletest//:gtest",
-        "@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",
-        "@google_benchmark//:benchmark_main",
-        "@googletest//:gtest",
-    ],
+cc_library(
+    name = "bad_variant_access",
+    deprecation = "bad_variant_access dependency is empty can be removed",
 )
 
 cc_test(
-    name = "variant_exception_safety_test",
+    name = "variant_test",
     size = "small",
-    srcs = [
-        "variant_exception_safety_test.cc",
-    ],
+    srcs = ["variant_test.cc"],
     copts = ABSL_TEST_COPTS,
     linkopts = ABSL_DEFAULT_LINKOPTS,
     deps = [
         ":variant",
-        "//absl/base:config",
-        "//absl/base:exception_safety_testing",
-        "//absl/memory",
         "@googletest//:gtest",
         "@googletest//:gtest_main",
     ],

absl/types/CMakeLists.txt

@@ -100,36 +100,15 @@ absl_cc_library(
   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_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
 )
@@ -143,11 +122,6 @@ absl_cc_test(
     ${ABSL_TEST_COPTS}
   DEPS
     absl::variant
-    absl::config
-    absl::core_headers
-    absl::memory
-    absl::type_traits
-    absl::strings
     GTest::gmock_main
 )
 
@@ -177,18 +151,3 @@ absl_cc_test(
     absl::compare
     GTest::gmock_main
 )
-
-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
-    GTest::gmock_main
-)