Googletest export

The gmock matchers have a concept of MatchAndExpain; where the details of the
matching are written to a "result listener". A matcher can avoid creating
expensive debug info by checking result_listener->IsInterested(); but,
unfortunately, the default matcher code (called from EXPECT_THAT) is always
"interested".

This change implements EXPECT_THAT matching to first run the matcher in a "not
interested" mode; and then run it a second time ("interested") only if the
match fails.

PiperOrigin-RevId: 224929783

googlemock/include/gmock/gmock-matchers.h

@@ -1296,14 +1296,24 @@ class PredicateFormatterFromMatcher {
     // We don't write MatcherCast<const T&> either, as that allows
     // potentially unsafe downcasting of the matcher argument.
     const Matcher<const T&> matcher = SafeMatcherCast<const T&>(matcher_);
-    StringMatchResultListener listener;
-    if (MatchPrintAndExplain(x, matcher, &listener))
+
+    // The expected path here is that the matcher should match (i.e. that most
+    // tests pass) so optimize for this case.
+    if (matcher.Matches(x)) {
       return AssertionSuccess();
+    }
 
     ::std::stringstream ss;
     ss << "Value of: " << value_text << "\n"
        << "Expected: ";
     matcher.DescribeTo(&ss);
+
+    // Rerun the matcher to "PrintAndExain" the failure.
+    StringMatchResultListener listener;
+    if (MatchPrintAndExplain(x, matcher, &listener)) {
+      ss << "\n  The matcher failed on the initial attempt; but passed when "
+            "rerun to generate the explanation.";
+    }
     ss << "\n  Actual: " << listener.str();
     return AssertionFailure() << ss.str();
   }

googlemock/test/gmock-matchers_test.cc

@@ -85,6 +85,7 @@ using std::pair;
 using std::set;
 using std::stringstream;
 using std::vector;
+using testing::_;
 using testing::A;
 using testing::AllArgs;
 using testing::AllOf;
@@ -110,12 +111,12 @@ using testing::Le;
 using testing::Lt;
 using testing::MakeMatcher;
 using testing::MakePolymorphicMatcher;
-using testing::MatchResultListener;
 using testing::Matcher;
 using testing::MatcherCast;
 using testing::MatcherInterface;
 using testing::Matches;
 using testing::MatchesRegex;
+using testing::MatchResultListener;
 using testing::NanSensitiveDoubleEq;
 using testing::NanSensitiveDoubleNear;
 using testing::NanSensitiveFloatEq;
@@ -135,15 +136,14 @@ using testing::StartsWith;
 using testing::StrCaseEq;
 using testing::StrCaseNe;
 using testing::StrEq;
-using testing::StrNe;
 using testing::StringMatchResultListener;
+using testing::StrNe;
 using testing::Truly;
 using testing::TypedEq;
 using testing::UnorderedPointwise;
 using testing::Value;
 using testing::WhenSorted;
 using testing::WhenSortedBy;
-using testing::_;
 using testing::internal::DummyMatchResultListener;
 using testing::internal::ElementMatcherPair;
 using testing::internal::ElementMatcherPairs;
@@ -152,10 +152,11 @@ using testing::internal::FloatingEqMatcher;
 using testing::internal::FormatMatcherDescription;
 using testing::internal::IsReadableTypeName;
 using testing::internal::MatchMatrix;
+using testing::internal::PredicateFormatterFromMatcher;
 using testing::internal::RE;
 using testing::internal::StreamMatchResultListener;
-using testing::internal::Strings;
 using testing::internal::string;
+using testing::internal::Strings;
 
 // For testing ExplainMatchResultTo().
 class GreaterThanMatcher : public MatcherInterface<int> {
@@ -4932,7 +4933,7 @@ TYPED_TEST(ContainerEqTest, DuplicateDifference) {
 }
 #endif  // GTEST_HAS_TYPED_TEST
 
-// Tests that mutliple missing values are reported.
+// Tests that multiple missing values are reported.
 // Using just vector here, so order is predictable.
 TEST(ContainerEqExtraTest, MultipleValuesMissing) {
   static const int vals[] = {1, 1, 2, 3, 5, 8};
@@ -6910,6 +6911,84 @@ TEST(ArgsTest, ExplainsMatchResultWithInnerExplanation) {
             Explain(m, std::make_tuple('\0', 42, 43)));
 }
 
+class PredicateFormatterFromMatcherTest : public ::testing::Test {
+ protected:
+  enum Behavior { kInitialSuccess, kAlwaysFail, kFlaky };
+
+  // A matcher that can return different results when used multiple times on the
+  // same input. No real matcher should do this; but this lets us test that we
+  // detect such behavior and fail appropriately.
+  class MockMatcher : public MatcherInterface<Behavior> {
+   public:
+    bool MatchAndExplain(Behavior behavior,
+                         MatchResultListener* listener) const override {
+      *listener << "[MatchAndExplain]";
+      switch (behavior) {
+        case kInitialSuccess:
+          // The first call to MatchAndExplain should use a "not interested"
+          // listener; so this is expected to return |true|. There should be no
+          // subsequent calls.
+          return !listener->IsInterested();
+
+        case kAlwaysFail:
+          return false;
+
+        case kFlaky:
+          // The first call to MatchAndExplain should use a "not interested"
+          // listener; so this will return |false|. Subsequent calls should have
+          // an "interested" listener; so this will return |true|, thus
+          // simulating a flaky matcher.
+          return listener->IsInterested();
+      }
+    }
+
+    void DescribeTo(ostream* os) const override { *os << "[DescribeTo]"; }
+
+    void DescribeNegationTo(ostream* os) const override {
+      *os << "[DescribeNegationTo]";
+    }
+  };
+
+  AssertionResult RunPredicateFormatter(Behavior behavior) {
+    auto matcher = MakeMatcher(new MockMatcher);
+    PredicateFormatterFromMatcher<Matcher<Behavior>> predicate_formatter(
+        matcher);
+    return predicate_formatter("dummy-name", behavior);
+  }
+
+  const std::string kMatcherType =
+      "testing::gmock_matchers_test::PredicateFormatterFromMatcherTest::"
+      "Behavior";
+};
+
+TEST_F(PredicateFormatterFromMatcherTest, ShortCircuitOnSuccess) {
+  AssertionResult result = RunPredicateFormatter(kInitialSuccess);
+  EXPECT_TRUE(result);  // Implicit cast to bool.
+  EXPECT_EQ("", result.message());
+}
+
+TEST_F(PredicateFormatterFromMatcherTest, NoShortCircuitOnFailure) {
+  AssertionResult result = RunPredicateFormatter(kAlwaysFail);
+  EXPECT_FALSE(result);  // Implicit cast to bool.
+  std::string expect =
+      "Value of: dummy-name\nExpected: [DescribeTo]\n"
+      "  Actual: 1" +
+      OfType(kMatcherType) + ", [MatchAndExplain]";
+  EXPECT_EQ(expect, result.message());
+}
+
+TEST_F(PredicateFormatterFromMatcherTest, DetectsFlakyShortCircuit) {
+  AssertionResult result = RunPredicateFormatter(kFlaky);
+  EXPECT_FALSE(result);  // Implicit cast to bool.
+  std::string expect =
+      "Value of: dummy-name\nExpected: [DescribeTo]\n"
+      "  The matcher failed on the initial attempt; but passed when rerun to "
+      "generate the explanation.\n"
+      "  Actual: 2" +
+      OfType(kMatcherType) + ", [MatchAndExplain]";
+  EXPECT_EQ(expect, result.message());
+}
+
 }  // namespace gmock_matchers_test
 }  // namespace testing