Update C++ feature detection in gtest-port.h to rely on feature test macros where possible.

This also avoids conflating C++ language versions with standard library versions, which don't always align.

PiperOrigin-RevId: 567662118
Change-Id: I7c023bd043c81c540c9430eaeb7b450feaadb206

googletest/include/gtest/internal/gtest-port.h

@@ -281,6 +281,22 @@
 #error C++ versions less than C++14 are not supported.
 #endif
 
+// MSVC >= 19.11 (VS 2017 Update 3) supports __has_include.
+#ifdef __has_include
+#define GTEST_INTERNAL_HAS_INCLUDE __has_include
+#else
+#define GTEST_INTERNAL_HAS_INCLUDE(...) 0
+#endif
+
+// Detect C++ feature test macros as gracefully as possible.
+// MSVC >= 19.15, Clang >= 3.4.1, and GCC >= 4.1.2 support feature test macros.
+#if GTEST_INTERNAL_CPLUSPLUS_LANG >= 202002L && \
+    (!defined(__has_include) || GTEST_INTERNAL_HAS_INCLUDE(<version>))
+#include <version>  // C++20 and later
+#elif (!defined(__has_include) || GTEST_INTERNAL_HAS_INCLUDE(<ciso646>))
+#include <ciso646>  // Pre-C++20
+#endif
+
 #include <ctype.h>   // for isspace, etc
 #include <stddef.h>  // for ptrdiff_t
 #include <stdio.h>
@@ -2351,9 +2367,9 @@ using Any = ::absl::any;
 }  // namespace internal
 }  // namespace testing
 #else
-#ifdef __has_include
-#if __has_include(<any>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L && \
-    (!defined(_MSC_VER) || GTEST_HAS_RTTI)
+#if defined(__cpp_lib_any) || (GTEST_INTERNAL_HAS_INCLUDE(<any>) &&        \
+                               GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L && \
+                               (!defined(_MSC_VER) || GTEST_HAS_RTTI))
 // Otherwise for C++17 and higher use std::any for UniversalPrinter<>
 // specializations.
 #define GTEST_INTERNAL_HAS_ANY 1
@@ -2365,8 +2381,7 @@ using Any = ::std::any;
 }  // namespace testing
 // The case where absl is configured NOT to alias std::any is not
 // supported.
-#endif  // __has_include(<any>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L
-#endif  // __has_include
+#endif  // __cpp_lib_any
 #endif  // GTEST_HAS_ABSL
 
 #ifndef GTEST_INTERNAL_HAS_ANY
@@ -2386,8 +2401,8 @@ inline ::absl::nullopt_t Nullopt() { return ::absl::nullopt; }
 }  // namespace internal
 }  // namespace testing
 #else
-#ifdef __has_include
-#if __has_include(<optional>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L
+#if defined(__cpp_lib_optional) || (GTEST_INTERNAL_HAS_INCLUDE(<optional>) && \
+                                    GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L)
 // Otherwise for C++17 and higher use std::optional for UniversalPrinter<>
 // specializations.
 #define GTEST_INTERNAL_HAS_OPTIONAL 1
@@ -2401,19 +2416,17 @@ inline ::std::nullopt_t Nullopt() { return ::std::nullopt; }
 }  // namespace testing
 // The case where absl is configured NOT to alias std::optional is not
 // supported.
-#endif  // __has_include(<optional>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L
-#endif  // __has_include
+#endif  // __cpp_lib_optional
 #endif  // GTEST_HAS_ABSL
 
 #ifndef GTEST_INTERNAL_HAS_OPTIONAL
 #define GTEST_INTERNAL_HAS_OPTIONAL 0
 #endif
 
-#ifdef __has_include
-#if __has_include(<span>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 202002L
+#if defined(__cpp_lib_span) || (GTEST_INTERNAL_HAS_INCLUDE(<span>) && \
+                                GTEST_INTERNAL_CPLUSPLUS_LANG >= 202002L)
 #define GTEST_INTERNAL_HAS_STD_SPAN 1
-#endif  // __has_include(<span>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 202002L
-#endif  // __has_include
+#endif  // __cpp_lib_span
 
 #ifndef GTEST_INTERNAL_HAS_STD_SPAN
 #define GTEST_INTERNAL_HAS_STD_SPAN 0
@@ -2430,8 +2443,9 @@ using StringView = ::absl::string_view;
 }  // namespace internal
 }  // namespace testing
 #else
-#ifdef __has_include
-#if __has_include(<string_view>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L
+#if defined(__cpp_lib_string_view) ||             \
+    (GTEST_INTERNAL_HAS_INCLUDE(<string_view>) && \
+     GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L)
 // Otherwise for C++17 and higher use std::string_view for Matcher<>
 // specializations.
 #define GTEST_INTERNAL_HAS_STRING_VIEW 1
@@ -2443,9 +2457,7 @@ using StringView = ::std::string_view;
 }  // namespace testing
 // The case where absl is configured NOT to alias std::string_view is not
 // supported.
-#endif  // __has_include(<string_view>) && GTEST_INTERNAL_CPLUSPLUS_LANG >=
-        // 201703L
-#endif  // __has_include
+#endif  // __cpp_lib_string_view
 #endif  // GTEST_HAS_ABSL
 
 #ifndef GTEST_INTERNAL_HAS_STRING_VIEW
@@ -2464,8 +2476,8 @@ using Variant = ::absl::variant<T...>;
 }  // namespace internal
 }  // namespace testing
 #else
-#ifdef __has_include
-#if __has_include(<variant>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L
+#if defined(__cpp_lib_variant) || (GTEST_INTERNAL_HAS_INCLUDE(<variant>) && \
+                                   GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L)
 // Otherwise for C++17 and higher use std::variant for UniversalPrinter<>
 // specializations.
 #define GTEST_INTERNAL_HAS_VARIANT 1
@@ -2477,16 +2489,16 @@ using Variant = ::std::variant<T...>;
 }  // namespace internal
 }  // namespace testing
 // The case where absl is configured NOT to alias std::variant is not supported.
-#endif  // __has_include(<variant>) && GTEST_INTERNAL_CPLUSPLUS_LANG >= 201703L
-#endif  // __has_include
+#endif  // __cpp_lib_variant
 #endif  // GTEST_HAS_ABSL
 
 #ifndef GTEST_INTERNAL_HAS_VARIANT
 #define GTEST_INTERNAL_HAS_VARIANT 0
 #endif
 
-#if defined(GTEST_INTERNAL_CPLUSPLUS_LANG) && \
-    GTEST_INTERNAL_CPLUSPLUS_LANG < 201703L
+#if (defined(__cpp_constexpr) && !defined(__cpp_inline_variables)) || \
+    (defined(GTEST_INTERNAL_CPLUSPLUS_LANG) &&                        \
+     GTEST_INTERNAL_CPLUSPLUS_LANG < 201703L)
 #define GTEST_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL 1
 #endif