Add matcher for std::variant.

googlemock/include/gmock/gmock-matchers.h

@@ -3623,6 +3623,66 @@ GTEST_API_ std::string FormatMatcherDescription(bool negation,
                                                 const char* matcher_name,
                                                 const Strings& param_values);
 
+namespace variant_matcher {
+// Overloads to allow VariantMatcher to do proper ADL lookup.
+template <typename T>
+void holds_alternative() {}
+template <typename T>
+void get() {}
+
+// Implements a matcher that checks the value of a variant<> type variable.
+template <typename T>
+class VariantMatcher {
+ public:
+  explicit VariantMatcher(::testing::Matcher<const T&> matcher)
+      : matcher_(internal::move(matcher)) {}
+
+  template <typename Variant>
+  bool MatchAndExplain(const Variant& value,
+                       ::testing::MatchResultListener* listener) const {
+    if (!listener->IsInterested()) {
+      return holds_alternative<T>(value) && matcher_.Matches(get<T>(value));
+    }
+
+    if (!holds_alternative<T>(value)) {
+      *listener << "whose value is not of type '" << GetTypeName() << "'";
+      return false;
+    }
+
+    const T& elem = get<T>(value);
+    StringMatchResultListener elem_listener;
+    const bool match = matcher_.MatchAndExplain(elem, &elem_listener);
+    *listener << "whose value " << PrintToString(elem)
+              << (match ? " matches" : " doesn't match");
+    PrintIfNotEmpty(elem_listener.str(), listener->stream());
+    return match;
+  }
+
+  void DescribeTo(std::ostream* os) const {
+    *os << "is a variant<> with value of type '" << GetTypeName()
+        << "' and the value ";
+    matcher_.DescribeTo(os);
+  }
+
+  void DescribeNegationTo(std::ostream* os) const {
+    *os << "is a variant<> with value of type other than '" << GetTypeName()
+        << "' or the value ";
+    matcher_.DescribeNegationTo(os);
+  }
+
+ private:
+  static string GetTypeName() {
+#if GTEST_HAS_RTTI
+    return internal::GetTypeName<T>();
+#endif
+    return "the element type";
+  }
+
+  const ::testing::Matcher<const T&> matcher_;
+};
+
+}  // namespace variant_matcher
+
 }  // namespace internal
 
 // ElementsAreArray(first, last)
@@ -4397,6 +4457,17 @@ inline internal::AnyOfMatcher<Args...> AnyOf(const Args&... matchers) {
 template <typename InnerMatcher>
 inline InnerMatcher AllArgs(const InnerMatcher& matcher) { return matcher; }
 
+// Returns a matcher that matches the value of a variant<> type variable.
+// The matcher implementation uses ADL to find the holds_alternative and get
+// functions.
+// It is compatible with std::variant.
+template <typename T>
+PolymorphicMatcher<internal::variant_matcher::VariantMatcher<T> > VariantWith(
+    const Matcher<const T&>& matcher) {
+  return MakePolymorphicMatcher(
+      internal::variant_matcher::VariantMatcher<T>(matcher));
+}
+
 // These macros allow using matchers to check values in Google Test
 // tests.  ASSERT_THAT(value, matcher) and EXPECT_THAT(value, matcher)
 // succeed iff the value matches the matcher.  If the assertion fails,

googlemock/test/gmock-matchers_test.cc

@@ -5655,5 +5655,69 @@ TEST(UnorderedPointwiseTest, AllowsMonomorphicInnerMatcher) {
   EXPECT_THAT(lhs, UnorderedPointwise(m2, rhs));
 }
 
+class SampleVariantIntString {
+ public:
+  SampleVariantIntString(int i) : i_(i), has_int_(true) {}
+  SampleVariantIntString(const std::string& s) : s_(s), has_int_(false) {}
+
+  template <typename T>
+  friend bool holds_alternative(const SampleVariantIntString& value) {
+    return value.has_int_ == internal::IsSame<T, int>::value;
+  }
+
+  template <typename T>
+  friend const T& get(const SampleVariantIntString& value) {
+    return value.get_impl(static_cast<T*>(NULL));
+  }
+
+ private:
+  const int& get_impl(int*) const { return i_; }
+  const std::string& get_impl(std::string*) const { return s_; }
+
+  int i_;
+  std::string s_;
+  bool has_int_;
+};
+
+TEST(VariantTest, DescribesSelf) {
+  const Matcher<SampleVariantIntString> m = VariantWith<int>(Eq(1));
+  EXPECT_THAT(Describe(m), ContainsRegex("is a variant<> with value of type "
+                                         "'.*' and the value is equal to 1"));
+}
+
+TEST(VariantTest, ExplainsSelf) {
+  const Matcher<SampleVariantIntString> m = VariantWith<int>(Eq(1));
+  EXPECT_THAT(Explain(m, SampleVariantIntString(1)),
+              ContainsRegex("whose value 1"));
+  EXPECT_THAT(Explain(m, SampleVariantIntString("A")),
+              HasSubstr("whose value is not of type '"));
+  EXPECT_THAT(Explain(m, SampleVariantIntString(2)),
+              "whose value 2 doesn't match");
+}
+
+TEST(VariantTest, FullMatch) {
+  Matcher<SampleVariantIntString> m = VariantWith<int>(Eq(1));
+  EXPECT_TRUE(m.Matches(SampleVariantIntString(1)));
+
+  m = VariantWith<std::string>(Eq("1"));
+  EXPECT_TRUE(m.Matches(SampleVariantIntString("1")));
+}
+
+TEST(VariantTest, TypeDoesNotMatch) {
+  Matcher<SampleVariantIntString> m = VariantWith<int>(Eq(1));
+  EXPECT_FALSE(m.Matches(SampleVariantIntString("1")));
+
+  m = VariantWith<std::string>(Eq("1"));
+  EXPECT_FALSE(m.Matches(SampleVariantIntString(1)));
+}
+
+TEST(VariantTest, InnerDoesNotMatch) {
+  Matcher<SampleVariantIntString> m = VariantWith<int>(Eq(1));
+  EXPECT_FALSE(m.Matches(SampleVariantIntString(2)));
+
+  m = VariantWith<std::string>(Eq("1"));
+  EXPECT_FALSE(m.Matches(SampleVariantIntString("2")));
+}
+
 }  // namespace gmock_matchers_test
 }  // namespace testing