Merge pull request #2527 from PiotrNycz:gmock_prevent_return_ref_to_store_temporaries_2

googlemock/include/gmock/gmock-actions.h

@@ -1052,6 +1052,10 @@ inline internal::ReturnRefAction<R> ReturnRef(R& x) {  // NOLINT
   return internal::ReturnRefAction<R>(x);
 }
 
+// Prevent using ReturnRef on reference to temporary.
+template <typename R, R* = nullptr>
+internal::ReturnRefAction<R> ReturnRef(R&&) = delete;
+
 // Creates an action that returns the reference to a copy of the
 // argument.  The copy is created when the action is constructed and
 // lives as long as the action.

googlemock/test/gmock-actions_test.cc

@@ -46,6 +46,7 @@
 #include <iterator>
 #include <memory>
 #include <string>
+#include <type_traits>
 #include "gmock/gmock.h"
 #include "gmock/internal/gmock-port.h"
 #include "gtest/gtest.h"
@@ -647,6 +648,41 @@ TEST(ReturnRefTest, IsCovariant) {
   EXPECT_EQ(&derived, &a.Perform(std::make_tuple()));
 }
 
+template <typename T, typename = decltype(ReturnRef(std::declval<T&&>()))>
+bool CanCallReturnRef(T&&) { return true; }
+bool CanCallReturnRef(Unused) { return false; }
+
+// Tests that ReturnRef(v) is working with non-temporaries (T&)
+TEST(ReturnRefTest, WorksForNonTemporary) {
+  int scalar_value = 123;
+  EXPECT_TRUE(CanCallReturnRef(scalar_value));
+
+  std::string non_scalar_value("ABC");
+  EXPECT_TRUE(CanCallReturnRef(non_scalar_value));
+
+  const int const_scalar_value{321};
+  EXPECT_TRUE(CanCallReturnRef(const_scalar_value));
+
+  const std::string const_non_scalar_value("CBA");
+  EXPECT_TRUE(CanCallReturnRef(const_non_scalar_value));
+}
+
+// Tests that ReturnRef(v) is not working with temporaries (T&&)
+TEST(ReturnRefTest, DoesNotWorkForTemporary) {
+  auto scalar_value = []()  -> int { return 123; };
+  EXPECT_FALSE(CanCallReturnRef(scalar_value()));
+
+  auto non_scalar_value = []() -> std::string { return "ABC"; };
+  EXPECT_FALSE(CanCallReturnRef(non_scalar_value()));
+
+  // cannot use here callable returning "const scalar type",
+  // because such const for scalar return type is ignored
+  EXPECT_FALSE(CanCallReturnRef(static_cast<const int>(321)));
+
+  auto const_non_scalar_value = []() -> const std::string { return "CBA"; };
+  EXPECT_FALSE(CanCallReturnRef(const_non_scalar_value()));
+}
+
 // Tests that ReturnRefOfCopy(v) works for reference types.
 TEST(ReturnRefOfCopyTest, WorksForReference) {
   int n = 42;