Merge pull request #2837 from inazarenko:duck_type_protos

googletest/include/gtest/gtest-printers.h

@@ -235,8 +235,9 @@ struct ProtobufPrinter {
   // DebugString() for better readability.
   static const size_t kProtobufOneLinerMaxLength = 50;
 
-  template <typename T, typename = typename std::enable_if<
-                            internal::IsAProtocolMessage<T>::value>::type>
+  template <typename T,
+            typename = typename std::enable_if<
+                internal::HasDebugStringAndShortDebugString<T>::value>::type>
   static void PrintValue(const T& value, ::std::ostream* os) {
     std::string pretty_str = value.ShortDebugString();
     if (pretty_str.length() > kProtobufOneLinerMaxLength) {

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

@@ -892,11 +892,34 @@ class GTEST_API_ Random {
 #define GTEST_REMOVE_REFERENCE_AND_CONST_(T) \
   typename std::remove_const<typename std::remove_reference<T>::type>::type
 
-// IsAProtocolMessage<T>::value is a compile-time bool constant that's
-// true if and only if T is type proto2::MessageLite or a subclass of it.
+// HasDebugStringAndShortDebugString<T>::value is a compile-time bool constant
+// that's true if and only if T has methods DebugString() and ShortDebugString()
+// that return std::string.
 template <typename T>
-struct IsAProtocolMessage
-    : public std::is_convertible<const T*, const ::proto2::MessageLite*> {};
+class HasDebugStringAndShortDebugString {
+ private:
+  template <typename C>
+  static constexpr auto CheckDebugString(C*) -> typename std::is_same<
+      std::string, decltype(std::declval<const C>().DebugString())>::type;
+  template <typename>
+  static constexpr std::false_type CheckDebugString(...);
+
+  template <typename C>
+  static constexpr auto CheckShortDebugString(C*) -> typename std::is_same<
+      std::string, decltype(std::declval<const C>().ShortDebugString())>::type;
+  template <typename>
+  static constexpr std::false_type CheckShortDebugString(...);
+
+  using HasDebugStringType = decltype(CheckDebugString<T>(nullptr));
+  using HasShortDebugStringType = decltype(CheckShortDebugString<T>(nullptr));
+
+ public:
+  static constexpr bool value =
+      HasDebugStringType::value && HasShortDebugStringType::value;
+};
+
+template <typename T>
+constexpr bool HasDebugStringAndShortDebugString<T>::value;
 
 // When the compiler sees expression IsContainerTest<C>(0), if C is an
 // STL-style container class, the first overload of IsContainerTest

googletest/test/gtest_unittest.cc

@@ -254,8 +254,8 @@ using testing::internal::GetTimeInMillis;
 using testing::internal::GetTypeId;
 using testing::internal::GetUnitTestImpl;
 using testing::internal::GTestFlagSaver;
+using testing::internal::HasDebugStringAndShortDebugString;
 using testing::internal::Int32FromEnvOrDie;
-using testing::internal::IsAProtocolMessage;
 using testing::internal::IsContainer;
 using testing::internal::IsContainerTest;
 using testing::internal::IsNotContainer;
@@ -7185,24 +7185,71 @@ GTEST_TEST(AlternativeNameTest, Works) {  // GTEST_TEST is the same as TEST.
 class ConversionHelperBase {};
 class ConversionHelperDerived : public ConversionHelperBase {};
 
-// Tests that IsAProtocolMessage<T>::value is a compile-time constant.
-TEST(IsAProtocolMessageTest, ValueIsCompileTimeConstant) {
-  GTEST_COMPILE_ASSERT_(IsAProtocolMessage<::proto2::MessageLite>::value,
-                        const_true);
-  GTEST_COMPILE_ASSERT_(!IsAProtocolMessage<int>::value, const_false);
-}
+struct HasDebugStringMethods {
+  std::string DebugString() const { return ""; }
+  std::string ShortDebugString() const { return ""; }
+};
+
+struct InheritsDebugStringMethods : public HasDebugStringMethods {};
 
-// Tests that IsAProtocolMessage<T>::value is true when T is
-// proto2::Message or a sub-class of it.
-TEST(IsAProtocolMessageTest, ValueIsTrueWhenTypeIsAProtocolMessage) {
-  EXPECT_TRUE(IsAProtocolMessage<::proto2::MessageLite>::value);
+struct WrongTypeDebugStringMethod {
+  std::string DebugString() const { return ""; }
+  int ShortDebugString() const { return 1; }
+};
+
+struct NotConstDebugStringMethod {
+  std::string DebugString() { return ""; }
+  std::string ShortDebugString() const { return ""; }
+};
+
+struct MissingDebugStringMethod {
+  std::string DebugString() { return ""; }
+};
+
+struct IncompleteType;
+
+// Tests that HasDebugStringAndShortDebugString<T>::value is a compile-time
+// constant.
+TEST(HasDebugStringAndShortDebugStringTest, ValueIsCompileTimeConstant) {
+  GTEST_COMPILE_ASSERT_(
+      HasDebugStringAndShortDebugString<HasDebugStringMethods>::value,
+      const_true);
+  GTEST_COMPILE_ASSERT_(
+      HasDebugStringAndShortDebugString<InheritsDebugStringMethods>::value,
+      const_true);
+  GTEST_COMPILE_ASSERT_(HasDebugStringAndShortDebugString<
+                            const InheritsDebugStringMethods>::value,
+                        const_true);
+  GTEST_COMPILE_ASSERT_(
+      !HasDebugStringAndShortDebugString<WrongTypeDebugStringMethod>::value,
+      const_false);
+  GTEST_COMPILE_ASSERT_(
+      !HasDebugStringAndShortDebugString<NotConstDebugStringMethod>::value,
+      const_false);
+  GTEST_COMPILE_ASSERT_(
+      !HasDebugStringAndShortDebugString<MissingDebugStringMethod>::value,
+      const_false);
+  GTEST_COMPILE_ASSERT_(
+      !HasDebugStringAndShortDebugString<IncompleteType>::value, const_false);
+  GTEST_COMPILE_ASSERT_(!HasDebugStringAndShortDebugString<int>::value,
+                        const_false);
+}
+
+// Tests that HasDebugStringAndShortDebugString<T>::value is true when T has
+// needed methods.
+TEST(HasDebugStringAndShortDebugStringTest,
+     ValueIsTrueWhenTypeHasDebugStringAndShortDebugString) {
+  EXPECT_TRUE(
+      HasDebugStringAndShortDebugString<InheritsDebugStringMethods>::value);
 }
 
-// Tests that IsAProtocolMessage<T>::value is false when T is neither
-// ::proto2::Message nor a sub-class of it.
-TEST(IsAProtocolMessageTest, ValueIsFalseWhenTypeIsNotAProtocolMessage) {
-  EXPECT_FALSE(IsAProtocolMessage<int>::value);
-  EXPECT_FALSE(IsAProtocolMessage<const ConversionHelperBase>::value);
+// Tests that HasDebugStringAndShortDebugString<T>::value is false when T
+// doesn't have needed methods.
+TEST(HasDebugStringAndShortDebugStringTest,
+     ValueIsFalseWhenTypeIsNotAProtocolMessage) {
+  EXPECT_FALSE(HasDebugStringAndShortDebugString<int>::value);
+  EXPECT_FALSE(
+      HasDebugStringAndShortDebugString<const ConversionHelperBase>::value);
 }
 
 // Tests GTEST_REMOVE_REFERENCE_AND_CONST_.