In MatcherCast, store the input value as its own type rather than as the Matcher type, to avoid dangling references

PiperOrigin-RevId: 769240838
Change-Id: I7b1ac23a0a88ba90b5d1ae6e20b97f679f381f31

Author: Abseil Team

googlemock/include/gmock/gmock-matchers.h

@@ -376,11 +376,16 @@ class MatcherCastImpl {
 
   // M can't be implicitly converted to Matcher<T>, so M isn't a polymorphic
   // matcher. It's a value of a type implicitly convertible to T. Use direct
-  // initialization to create a matcher.
+  // initialization or `ImplicitCastEqMatcher` to create a matcher.
   static Matcher<T> CastImpl(const M& value,
                              std::false_type /* convertible_to_matcher */,
                              std::true_type /* convertible_to_T */) {
-    return Matcher<T>(ImplicitCast_<T>(value));
+    using NoRefT = std::remove_cv_t<std::remove_reference_t<T>>;
+    if constexpr (std::is_same_v<M, NoRefT>) {
+      return Matcher<T>(value);
+    } else {
+      return ImplicitCastEqMatcher<NoRefT, std::decay_t<const M&>>(value);
+    }
   }
 
   // M can't be implicitly converted to either Matcher<T> or T. Attempt to use
@@ -391,11 +396,11 @@ class MatcherCastImpl {
   // latter calls bool operator==(const Lhs& lhs, const Rhs& rhs) in the end
   // which might be undefined even when Rhs is implicitly convertible to Lhs
   // (e.g. std::pair<const int, int> vs. std::pair<int, int>).
-  //
-  // We don't define this method inline as we need the declaration of Eq().
   static Matcher<T> CastImpl(const M& value,
                              std::false_type /* convertible_to_matcher */,
-                             std::false_type /* convertible_to_T */);
+                             std::false_type /* convertible_to_T */) {
+    return Eq(value);
+  }
 };
 
 // This more specialized version is used when MatcherCast()'s argument
@@ -4483,13 +4488,6 @@ inline Matcher<T> An() {
   return _;
 }
 
-template <typename T, typename M>
-Matcher<T> internal::MatcherCastImpl<T, M>::CastImpl(
-    const M& value, std::false_type /* convertible_to_matcher */,
-    std::false_type /* convertible_to_T */) {
-  return Eq(value);
-}
-
 // Creates a polymorphic matcher that matches any NULL pointer.
 inline PolymorphicMatcher<internal::IsNullMatcher> IsNull() {
   return MakePolymorphicMatcher(internal::IsNullMatcher());

googlemock/test/gmock-matchers-comparisons_test.cc

@@ -622,15 +622,42 @@ struct IntReferenceWrapper {
   const int* value;
 };
 
+// Compared the contained values
 bool operator==(const IntReferenceWrapper& a, const IntReferenceWrapper& b) {
-  return a.value == b.value;
+  return *a.value == *b.value;
 }
 
-TEST(MatcherCastTest, ValueIsNotCopied) {
-  int n = 42;
-  Matcher<IntReferenceWrapper> m = MatcherCast<IntReferenceWrapper>(n);
-  // Verify that the matcher holds a reference to n, not to its temporary copy.
-  EXPECT_TRUE(m.Matches(n));
+TEST(MatcherCastTest, ValueIsCopied) {
+  {
+    // When an IntReferenceWrapper is passed.
+    int n = 42;
+    Matcher<IntReferenceWrapper> m =
+        MatcherCast<IntReferenceWrapper>(IntReferenceWrapper(n));
+    {
+      int value = 42;
+      EXPECT_TRUE(m.Matches(value));
+      value = 10;
+      EXPECT_FALSE(m.Matches(value));
+      // This changes the stored reference.
+      n = 10;
+      EXPECT_TRUE(m.Matches(value));
+    }
+  }
+
+  {
+    // When an int is passed.
+    int n = 42;
+    Matcher<IntReferenceWrapper> m = MatcherCast<IntReferenceWrapper>(n);
+    {
+      int value = 42;
+      EXPECT_TRUE(m.Matches(value));
+      value = 10;
+      EXPECT_FALSE(m.Matches(value));
+      // This does not change the stored int.
+      n = 10;
+      EXPECT_FALSE(m.Matches(value));
+    }
+  }
 }
 
 class Base {

googletest/include/gtest/gtest-matchers.h

@@ -773,6 +773,35 @@ class GeMatcher
   static const char* NegatedDesc() { return "isn't >="; }
 };
 
+// Same as `EqMatcher<Rhs>`, except that the `rhs` is stored as `StoredRhs` and
+// must be implicitly convertible to `Rhs`.
+template <typename Rhs, typename StoredRhs>
+class ImplicitCastEqMatcher {
+ public:
+  explicit ImplicitCastEqMatcher(const StoredRhs& rhs) : stored_rhs_(rhs) {}
+
+  using is_gtest_matcher = void;
+
+  template <typename Lhs>
+  bool MatchAndExplain(const Lhs& lhs, std::ostream*) const {
+    return lhs == rhs();
+  }
+
+  void DescribeTo(std::ostream* os) const {
+    *os << "is equal to ";
+    UniversalPrint(rhs(), os);
+  }
+  void DescribeNegationTo(std::ostream* os) const {
+    *os << "isn't equal to ";
+    UniversalPrint(rhs(), os);
+  }
+
+ private:
+  Rhs rhs() const { return ImplicitCast_<Rhs>(stored_rhs_); }
+
+  StoredRhs stored_rhs_;
+};
+
 template <typename T, typename = typename std::enable_if<
                           std::is_constructible<std::string, T>::value>::type>
 using StringLike = T;