Make AbslStringify usage public in GoogleTest

Fixes #4314

PiperOrigin-RevId: 549986457
Change-Id: Iff74f02ab1c106696f288540e9c623d56b76e3f7

googletest/include/gtest/gtest-printers.h

@@ -43,6 +43,9 @@
 //   1. foo::PrintTo(const T&, ostream*)
 //   2. operator<<(ostream&, const T&) defined in either foo or the
 //      global namespace.
+// * Prefer AbslStringify(..) to operator<<(..), per https://abseil.io/tips/215.
+// * Define foo::PrintTo(..) if the type already has AbslStringify(..), but an
+//   alternative presentation in test results is of interest.
 //
 // However if T is an STL-style container then it is printed element-wise
 // unless foo::PrintTo(const T&, ostream*) is defined. Note that
@@ -112,6 +115,10 @@
 #include <utility>
 #include <vector>
 
+#ifdef GTEST_HAS_ABSL
+#include "absl/strings/internal/has_absl_stringify.h"
+#include "absl/strings/str_cat.h"
+#endif  // GTEST_HAS_ABSL
 #include "gtest/internal/gtest-internal.h"
 #include "gtest/internal/gtest-port.h"
 
@@ -260,6 +267,18 @@ struct ConvertibleToStringViewPrinter {
 #endif
 };
 
+#ifdef GTEST_HAS_ABSL
+struct ConvertibleToAbslStringifyPrinter {
+  template <
+      typename T,
+      typename = typename std::enable_if<
+          absl::strings_internal::HasAbslStringify<T>::value>::type>  // NOLINT
+  static void PrintValue(const T& value, ::std::ostream* os) {
+    *os << absl::StrCat(value);
+  }
+};
+#endif  // GTEST_HAS_ABSL
+
 // Prints the given number of bytes in the given object to the given
 // ostream.
 GTEST_API_ void PrintBytesInObjectTo(const unsigned char* obj_bytes,
@@ -308,6 +327,9 @@ void PrintWithFallback(const T& value, ::std::ostream* os) {
   using Printer = typename FindFirstPrinter<
       T, void, ContainerPrinter, FunctionPointerPrinter, PointerPrinter,
       ProtobufPrinter,
+#ifdef GTEST_HAS_ABSL
+      ConvertibleToAbslStringifyPrinter,
+#endif  // GTEST_HAS_ABSL
       internal_stream_operator_without_lexical_name_lookup::StreamPrinter,
       ConvertibleToIntegerPrinter, ConvertibleToStringViewPrinter,
       RawBytesPrinter, FallbackPrinter>::type;

googletest/test/googletest-printers-test.cc

@@ -55,6 +55,10 @@
 #include "gtest/gtest-printers.h"
 #include "gtest/gtest.h"
 
+#ifdef GTEST_HAS_ABSL
+#include "absl/strings/str_format.h"
+#endif
+
 // Some user-defined types for testing the universal value printer.
 
 // An anonymous enum type.
@@ -119,6 +123,19 @@ void operator<<(::std::ostream& os, const StreamableInGlobal* /* x */) {
   os << "StreamableInGlobal*";
 }
 
+#ifdef GTEST_HAS_ABSL
+// A user-defined type with AbslStringify
+struct Point {
+  template <typename Sink>
+  friend void AbslStringify(Sink& sink, const Point& p) {
+    absl::Format(&sink, "(%d, %d)", p.x, p.y);
+  }
+
+  int x = 10;
+  int y = 20;
+};
+#endif
+
 namespace foo {
 
 // A user-defined unprintable type in a user namespace.
@@ -317,6 +334,11 @@ TEST(PrintEnumTest, EnumWithPrintTo) {
   EXPECT_EQ("invalid", Print(static_cast<EnumWithPrintTo>(0)));
 }
 
+#ifdef GTEST_HAS_ABSL
+// Tests printing a class that defines AbslStringify
+TEST(PrintClassTest, AbslStringify) { EXPECT_EQ("(10, 20)", Print(Point())); }
+#endif
+
 // Tests printing a class implicitly convertible to BiggestInt.
 
 TEST(PrintClassTest, BiggestIntConvertible) {
@@ -1636,6 +1658,12 @@ TEST(PrintToStringTest, PrintReferenceToStreamableInGlobal) {
   EXPECT_STREQ("StreamableInGlobal", PrintToString(r).c_str());
 }
 
+#ifdef GTEST_HAS_ABSL
+TEST(PrintToStringTest, AbslStringify) {
+  EXPECT_PRINT_TO_STRING_(Point(), "(10, 20)");
+}
+#endif
+
 TEST(IsValidUTF8Test, IllFormedUTF8) {
   // The following test strings are ill-formed UTF-8 and are printed
   // as hex only (or ASCII, in case of ASCII bytes) because IsValidUTF8() is