specialize UniversalPrinter<> for std::variant

googletest/include/gtest/gtest-printers.h

@@ -114,7 +114,6 @@
 #if GTEST_HAS_ABSL
 #include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
-#include "absl/types/variant.h"
 #endif  // GTEST_HAS_ABSL
 
 namespace testing {
@@ -699,14 +698,22 @@ class UniversalPrinter<::absl::optional<T>> {
   }
 };
 
-// Printer for absl::variant
+#endif  // GTEST_HAS_ABSL
+
+#if GTEST_INTERNAL_HAS_VARIANT
+
+// Printer for std::variant / absl::variant
 
 template <typename... T>
-class UniversalPrinter<::absl::variant<T...>> {
+class UniversalPrinter<Variant<T...>> {
  public:
-  static void Print(const ::absl::variant<T...>& value, ::std::ostream* os) {
+  static void Print(const Variant<T...>& value, ::std::ostream* os) {
     *os << '(';
-    absl::visit(Visitor{os}, value);
+#if GTEST_HAS_ABSL
+    absl::visit(Visitor{os, value.index()}, value);
+#else
+    std::visit(Visitor{os, value.index()}, value);
+#endif  // GTEST_HAS_ABSL
     *os << ')';
   }
 
@@ -714,14 +721,15 @@ class UniversalPrinter<::absl::variant<T...>> {
   struct Visitor {
     template <typename U>
     void operator()(const U& u) const {
-      *os << "'" << GetTypeName<U>() << "' with value ";
+      *os << "'" << GetTypeName<U>() << "(" << index << ")' with value ";
       UniversalPrint(u, os);
     }
     ::std::ostream* os;
+    std::size_t index;
   };
 };
 
-#endif  // GTEST_HAS_ABSL
+#endif  // GTEST_INTERNAL_HAS_VARIANT
 
 // UniversalPrintArray(begin, len, os) prints an array of 'len'
 // elements, starting at address 'begin'.

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

@@ -202,6 +202,8 @@
 //   GTEST_INTERNAL_HAS_STRING_VIEW - for enabling Matcher<std::string_view> or
 //                                    Matcher<absl::string_view>
 //                                    specializations.
+//   GTEST_INTERNAL_HAS_VARIANT - for enabling UniversalPrinter<std::variant> or
+//                                UniversalPrinter<absl::variant> specializations.
 //
 // Synchronization:
 //   Mutex, MutexLock, ThreadLocal, GetThreadCount()
@@ -2251,4 +2253,34 @@ using StringView = ::std::string_view;
 # endif  // __has_include
 #endif  // GTEST_HAS_ABSL
 
+#if GTEST_HAS_ABSL
+// Always use absl::variant for UniversalPrinter<> specializations if googletest
+// is built with absl support.
+# define GTEST_INTERNAL_HAS_VARIANT 1
+#include "absl/types/variant.h"
+namespace testing {
+namespace internal {
+template <typename... T>
+using Variant = ::absl::variant<T...>;
+}  // namespace internal
+}  // namespace testing
+#else
+# ifdef __has_include
+#   if __has_include(<variant>) && __cplusplus >= 201703L
+// Otherwise for C++17 and higher use std::variant for UniversalPrinter<>
+// specializations.
+#   define GTEST_INTERNAL_HAS_VARIANT 1
+#include <variant>
+namespace testing {
+namespace internal {
+template <typename... T>
+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>) && __cplusplus >= 201703L
+# endif  // __has_include
+#endif  // GTEST_HAS_ABSL
+
 #endif  // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_PORT_H_

googletest/test/googletest-printers-test.cc

@@ -1542,21 +1542,24 @@ TEST(PrintOptionalTest, Basic) {
   EXPECT_EQ("(\"A\")", PrintToString(absl::optional<std::string>{"A"}));
 }
 
+#endif  // GTEST_HAS_ABSL
+
+#if GTEST_INTERNAL_HAS_VARIANT
 struct NonPrintable {
   unsigned char contents = 17;
 };
 
 TEST(PrintOneofTest, Basic) {
-  using Type = absl::variant<int, StreamableInGlobal, NonPrintable>;
+  using Type = internal::Variant<int, StreamableInGlobal, NonPrintable>;
-  EXPECT_EQ("('int' with value 7)", PrintToString(Type(7)));
+  EXPECT_EQ("('int(0)' with value 7)", PrintToString(Type(7)));
-  EXPECT_EQ("('StreamableInGlobal' with value StreamableInGlobal)",
+  EXPECT_EQ("('StreamableInGlobal(1)' with value StreamableInGlobal)",
             PrintToString(Type(StreamableInGlobal{})));
   EXPECT_EQ(
-      "('testing::gtest_printers_test::NonPrintable' with value 1-byte object "
+      "('testing::gtest_printers_test::NonPrintable(2)' with value 1-byte object "
       "<11>)",
       PrintToString(Type(NonPrintable{})));
 }
-#endif  // GTEST_HAS_ABSL
+#endif  // GTEST_INTERNAL_HAS_VARIANT
 namespace {
 class string_ref;