Use ResultOf()'s result_description when explaining match result.

PiperOrigin-RevId: 439389646
Change-Id: Ie34adcdd2b24378e85962efac53b7bb89ed93803

googlemock/include/gmock/gmock-matchers.h

@@ -2258,7 +2258,11 @@ class ResultOfMatcher {
     }
 
     bool MatchAndExplain(T obj, MatchResultListener* listener) const override {
-      *listener << "which is mapped by the given callable to ";
+      if (result_description_.empty()) {
+        *listener << "which is mapped by the given callable to ";
+      } else {
+        *listener << "whose " << result_description_ << " is ";
+      }
       // Cannot pass the return value directly to MatchPrintAndExplain, which
       // takes a non-const reference as argument.
       // Also, specifying template argument explicitly is needed because T could

googlemock/test/gmock-matchers-containers_test.cc

@@ -949,6 +949,17 @@ TEST(ResultOfTest, CanExplainMatchResult) {
             Explain(matcher, 36));
 }
 
+TEST(ResultOfTest, CanExplainMatchResultWithResultDescription) {
+  Matcher<int> matcher = ResultOf("magic int conversion", &IntFunction, Ge(85));
+  EXPECT_EQ("whose magic int conversion is 90" + OfType("int"),
+            Explain(matcher, 36));
+
+  matcher = ResultOf("magic int conversion", &IntFunction, GreaterThan(85));
+  EXPECT_EQ("whose magic int conversion is 90" + OfType("int") +
+                ", which is 5 more than 85",
+            Explain(matcher, 36));
+}
+
 // Tests that ResultOf(f, ...) compiles and works as expected when f(x)
 // returns a non-reference.
 TEST(ResultOfTest, WorksForNonReferenceResults) {