Add support for printing C++20 std::*_ordering types to gtest.

Adds feature test macro for C++20 <compare> header, a pretty-printer, and tests.
Inexplicably, these types aren't enums, so can't be handled with a switch.

PiperOrigin-RevId: 704783038
Change-Id: I29688989d18f43520fe610c12a447a20d2f98c95

googletest/include/gtest/gtest-printers.h

@@ -126,6 +126,10 @@
 #include <span>  // NOLINT
 #endif           // GTEST_INTERNAL_HAS_STD_SPAN
 
+#if GTEST_INTERNAL_HAS_COMPARE_LIB
+#include <compare>  // NOLINT
+#endif              // GTEST_INTERNAL_HAS_COMPARE_LIB
+
 namespace testing {
 
 // Definitions in the internal* namespaces are subject to change without notice.
@@ -782,6 +786,41 @@ void PrintTo(const std::shared_ptr<T>& ptr, std::ostream* os) {
   (PrintSmartPointer<T>)(ptr, os, 0);
 }
 
+#if GTEST_INTERNAL_HAS_COMPARE_LIB
+template <typename T>
+void PrintOrderingHelper(T ordering, std::ostream* os) {
+  if (ordering == T::less) {
+    *os << "(less)";
+  } else if (ordering == T::greater) {
+    *os << "(greater)";
+  } else if (ordering == T::equivalent) {
+    *os << "(equivalent)";
+  } else {
+    *os << "(unknown ordering)";
+  }
+}
+
+inline void PrintTo(std::strong_ordering ordering, std::ostream* os) {
+  if (ordering == std::strong_ordering::equal) {
+    *os << "(equal)";
+  } else {
+    PrintOrderingHelper(ordering, os);
+  }
+}
+
+inline void PrintTo(std::partial_ordering ordering, std::ostream* os) {
+  if (ordering == std::partial_ordering::unordered) {
+    *os << "(unordered)";
+  } else {
+    PrintOrderingHelper(ordering, os);
+  }
+}
+
+inline void PrintTo(std::weak_ordering ordering, std::ostream* os) {
+  PrintOrderingHelper(ordering, os);
+}
+#endif
+
 // Helper function for printing a tuple.  T must be instantiated with
 // a tuple type.
 template <typename T>

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

@@ -2533,4 +2533,12 @@ using Variant = ::std::variant<T...>;
 #define GTEST_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL 1
 #endif
 
+#if (defined(__cpp_lib_three_way_comparison) || \
+     (GTEST_INTERNAL_HAS_INCLUDE(<compare>) &&  \
+      GTEST_INTERNAL_CPLUSPLUS_LANG >= 201907L))
+#define GTEST_INTERNAL_HAS_COMPARE_LIB 1
+#else
+#define GTEST_INTERNAL_HAS_COMPARE_LIB 0
+#endif
+
 #endif  // GOOGLETEST_INCLUDE_GTEST_INTERNAL_GTEST_PORT_H_

googletest/test/googletest-printers-test.cc

@@ -64,6 +64,10 @@
 #include <span>  // NOLINT
 #endif  // GTEST_INTERNAL_HAS_STD_SPAN
 
+#if GTEST_INTERNAL_HAS_COMPARE_LIB
+#include <compare>  // NOLINT
+#endif              // GTEST_INTERNAL_HAS_COMPARE_LIB
+
 // Some user-defined types for testing the universal value printer.
 
 // An anonymous enum type.
@@ -1970,6 +1974,26 @@ TEST(PrintOneofTest, Basic) {
       PrintToString(Type(NonPrintable{})));
 }
 #endif  // GTEST_INTERNAL_HAS_VARIANT
+
+#if GTEST_INTERNAL_HAS_COMPARE_LIB
+TEST(PrintOrderingTest, Basic) {
+  EXPECT_EQ("(less)", PrintToString(std::strong_ordering::less));
+  EXPECT_EQ("(greater)", PrintToString(std::strong_ordering::greater));
+  // equal == equivalent for strong_ordering.
+  EXPECT_EQ("(equal)", PrintToString(std::strong_ordering::equivalent));
+  EXPECT_EQ("(equal)", PrintToString(std::strong_ordering::equal));
+
+  EXPECT_EQ("(less)", PrintToString(std::weak_ordering::less));
+  EXPECT_EQ("(greater)", PrintToString(std::weak_ordering::greater));
+  EXPECT_EQ("(equivalent)", PrintToString(std::weak_ordering::equivalent));
+
+  EXPECT_EQ("(less)", PrintToString(std::partial_ordering::less));
+  EXPECT_EQ("(greater)", PrintToString(std::partial_ordering::greater));
+  EXPECT_EQ("(equivalent)", PrintToString(std::partial_ordering::equivalent));
+  EXPECT_EQ("(unordered)", PrintToString(std::partial_ordering::unordered));
+}
+#endif
+
 namespace {
 class string_ref;