Optional(): Add support for std::optional<>-like types lacking bool conversion.

PiperOrigin-RevId: 681053268
Change-Id: If80ba667fd4c91340e1405a9691f5ca0350fa9eb

googlemock/include/gmock/gmock-matchers.h

@@ -561,6 +561,11 @@ Matcher<T> A();
 // and MUST NOT BE USED IN USER CODE!!!
 namespace internal {
 
+// Used per go/ranked-overloads for dispatching.
+struct Rank0 {};
+struct Rank1 : Rank0 {};
+using HighestRank = Rank1;
+
 // If the explanation is not empty, prints it to the ostream.
 inline void PrintIfNotEmpty(const std::string& explanation,
                             ::std::ostream* os) {
@@ -2955,10 +2960,6 @@ class EachMatcher {
   const M inner_matcher_;
 };
 
-// Use go/ranked-overloads for dispatching.
-struct Rank0 {};
-struct Rank1 : Rank0 {};
-
 namespace pair_getters {
 using std::get;
 template <typename T>
@@ -3912,6 +3913,21 @@ GTEST_API_ std::string FormatMatcherDescription(
     bool negation, const char* matcher_name,
     const std::vector<const char*>& param_names, const Strings& param_values);
 
+// Overloads to support `OptionalMatcher` being used with a type that either
+// supports implicit conversion to bool or a `has_value()` method.
+template <typename Optional>
+auto IsOptionalEngaged(const Optional& optional,
+                       Rank1) -> decltype(!!optional) {
+  // The use of double-negation here is to preserve historical behavior where
+  // the matcher used `operator!` rather than directly using `operator bool`.
+  return !static_cast<bool>(!optional);
+}
+template <typename Optional>
+auto IsOptionalEngaged(const Optional& optional,
+                       Rank0) -> decltype(!optional.has_value()) {
+  return optional.has_value();
+}
+
 // Implements a matcher that checks the value of a optional<> type variable.
 template <typename ValueMatcher>
 class OptionalMatcher {
@@ -3944,7 +3960,7 @@ class OptionalMatcher {
 
     bool MatchAndExplain(Optional optional,
                          MatchResultListener* listener) const override {
-      if (!optional) {
+      if (!IsOptionalEngaged(optional, HighestRank())) {
         *listener << "which is not engaged";
         return false;
       }
@@ -5266,9 +5282,10 @@ inline InnerMatcher AllArgs(const InnerMatcher& matcher) {
 }
 
 // Returns a matcher that matches the value of an optional<> type variable.
-// The matcher implementation only uses '!arg' and requires that the optional<>
-// type has a 'value_type' member type and that '*arg' is of type 'value_type'
-// and is printable using 'PrintToString'. It is compatible with
+// The matcher implementation only uses '!arg' (or 'arg.has_value()' if '!arg`
+// isn't a valid expression) and requires that the optional<> type has a
+// 'value_type' member type and that '*arg' is of type 'value_type' and is
+// printable using 'PrintToString'. It is compatible with
 // std::optional/std::experimental::optional.
 // Note that to compare an optional type variable against nullopt you should
 // use Eq(nullopt) and not Eq(Optional(nullopt)). The latter implies that the

googlemock/test/gmock-matchers-misc_test.cc

@@ -674,6 +674,8 @@ TEST_P(MatcherTupleTestP, ExplainsMatchFailure) {
                    // explanation.
 }
 
+#if GTEST_HAS_TYPED_TEST
+
 // Sample optional type implementation with minimal requirements for use with
 // Optional matcher.
 template <typename T>
@@ -691,38 +693,76 @@ class SampleOptional {
   bool has_value_;
 };
 
-TEST(OptionalTest, DescribesSelf) {
-  const Matcher<SampleOptional<int>> m = Optional(Eq(1));
+// Sample optional type implementation with alternative minimal requirements for
+// use with Optional matcher. In particular, while it doesn't have a bool
+// conversion operator, it does have a has_value() method.
+template <typename T>
+class SampleOptionalWithoutBoolConversion {
+ public:
+  using value_type = T;
+  explicit SampleOptionalWithoutBoolConversion(T value)
+      : value_(std::move(value)), has_value_(true) {}
+  SampleOptionalWithoutBoolConversion() : value_(), has_value_(false) {}
+  bool has_value() const { return has_value_; }
+  const T& operator*() const { return value_; }
+
+ private:
+  T value_;
+  bool has_value_;
+};
+
+template <typename T>
+class OptionalTest : public testing::Test {};
+
+using OptionalTestTypes =
+    testing::Types<SampleOptional<int>,
+                   SampleOptionalWithoutBoolConversion<int>>;
+
+TYPED_TEST_SUITE(OptionalTest, OptionalTestTypes);
+
+TYPED_TEST(OptionalTest, DescribesSelf) {
+  const Matcher<TypeParam> m = Optional(Eq(1));
   EXPECT_EQ("value is equal to 1", Describe(m));
 }
 
-TEST(OptionalTest, ExplainsSelf) {
-  const Matcher<SampleOptional<int>> m = Optional(Eq(1));
-  EXPECT_EQ("whose value 1 matches", Explain(m, SampleOptional<int>(1)));
-  EXPECT_EQ("whose value 2 doesn't match", Explain(m, SampleOptional<int>(2)));
+TYPED_TEST(OptionalTest, ExplainsSelf) {
+  const Matcher<TypeParam> m = Optional(Eq(1));
+  EXPECT_EQ("whose value 1 matches", Explain(m, TypeParam(1)));
+  EXPECT_EQ("whose value 2 doesn't match", Explain(m, TypeParam(2)));
 }
 
-TEST(OptionalTest, MatchesNonEmptyOptional) {
-  const Matcher<SampleOptional<int>> m1 = Optional(1);
-  const Matcher<SampleOptional<int>> m2 = Optional(Eq(2));
-  const Matcher<SampleOptional<int>> m3 = Optional(Lt(3));
-  SampleOptional<int> opt(1);
+TYPED_TEST(OptionalTest, MatchesNonEmptyOptional) {
+  const Matcher<TypeParam> m1 = Optional(1);
+  const Matcher<TypeParam> m2 = Optional(Eq(2));
+  const Matcher<TypeParam> m3 = Optional(Lt(3));
+  TypeParam opt(1);
   EXPECT_TRUE(m1.Matches(opt));
   EXPECT_FALSE(m2.Matches(opt));
   EXPECT_TRUE(m3.Matches(opt));
 }
 
-TEST(OptionalTest, DoesNotMatchNullopt) {
-  const Matcher<SampleOptional<int>> m = Optional(1);
-  SampleOptional<int> empty;
+TYPED_TEST(OptionalTest, DoesNotMatchNullopt) {
+  const Matcher<TypeParam> m = Optional(1);
+  TypeParam empty;
   EXPECT_FALSE(m.Matches(empty));
 }
 
-TEST(OptionalTest, WorksWithMoveOnly) {
-  Matcher<SampleOptional<std::unique_ptr<int>>> m = Optional(Eq(nullptr));
-  EXPECT_TRUE(m.Matches(SampleOptional<std::unique_ptr<int>>(nullptr)));
+template <typename T>
+class MoveOnlyOptionalTest : public testing::Test {};
+
+using MoveOnlyOptionalTestTypes =
+    testing::Types<SampleOptional<std::unique_ptr<int>>,
+                   SampleOptionalWithoutBoolConversion<std::unique_ptr<int>>>;
+
+TYPED_TEST_SUITE(MoveOnlyOptionalTest, MoveOnlyOptionalTestTypes);
+
+TYPED_TEST(MoveOnlyOptionalTest, WorksWithMoveOnly) {
+  Matcher<TypeParam> m = Optional(Eq(nullptr));
+  EXPECT_TRUE(m.Matches(TypeParam(nullptr)));
 }
 
+#endif  // GTEST_HAS_TYPED_TEST
+
 class SampleVariantIntString {
  public:
   SampleVariantIntString(int i) : i_(i), has_int_(true) {}