Cast mutable lvalue references to const from testing::ResultOf

PiperOrigin-RevId: 716343482
Change-Id: I125bc4725886958d026c88f3902a8289e476598b

Author: Abseil Team

googlemock/include/gmock/gmock-matchers.h

@@ -2281,14 +2281,17 @@ class ResultOfMatcher {
   class Impl : public MatcherInterface<T> {
     using ResultType = decltype(CallableTraits<Callable>::template Invoke<T>(
         std::declval<CallableStorageType>(), std::declval<T>()));
+    using InnerType = std::conditional_t<
+        std::is_lvalue_reference<ResultType>::value,
+        const typename std::remove_reference<ResultType>::type&, ResultType>;
 
    public:
     template <typename M>
     Impl(const std::string& result_description,
          const CallableStorageType& callable, const M& matcher)
         : result_description_(result_description),
           callable_(callable),
-          matcher_(MatcherCast<ResultType>(matcher)) {}
+          matcher_(MatcherCast<InnerType>(matcher)) {}
 
     void DescribeTo(::std::ostream* os) const override {
       if (result_description_.empty()) {
@@ -2318,7 +2321,7 @@ class ResultOfMatcher {
       // takes a non-const reference as argument.
       // Also, specifying template argument explicitly is needed because T could
       // be a non-const reference (e.g. Matcher<Uncopyable&>).
-      ResultType result =
+      InnerType result =
           CallableTraits<Callable>::template Invoke<T>(callable_, obj);
       return MatchPrintAndExplain(result, matcher_, listener);
     }
@@ -2331,7 +2334,7 @@ class ResultOfMatcher {
     // use stateful callables with ResultOf(), which doesn't guarantee
     // how many times the callable will be invoked.
     mutable CallableStorageType callable_;
-    const Matcher<ResultType> matcher_;
+    const Matcher<InnerType> matcher_;
   };  // class Impl
 
   const std::string result_description_;