From 909b1ccfcacc9d6f920aa79e3f643c1a4e806eb2 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Tue, 25 Feb 2020 10:52:53 -0500
Subject: [PATCH] Googletest export

Relax the implementation of MatcherCast to allow conversion of `Matcher<T>` to
`Matcher<const T&>`. They have the same match signature.

PiperOrigin-RevId: 297115843
---
 googlemock/include/gmock/gmock-matchers.h | 13 ++++++++++---
 googlemock/test/gmock-matchers_test.cc    |  9 +++++----
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/googlemock/include/gmock/gmock-matchers.h b/googlemock/include/gmock/gmock-matchers.h
index 4b6ac563..fe88a7c7 100644
--- a/googlemock/include/gmock/gmock-matchers.h
+++ b/googlemock/include/gmock/gmock-matchers.h
@@ -424,7 +424,14 @@ class MatcherCastImpl<T, Matcher<U> > {
               !std::is_base_of<FromType, ToType>::value,
           "Can't implicitly convert from <base> to <derived>");
 
-      return source_matcher_.MatchAndExplain(static_cast<U>(x), listener);
+      // Do the cast to `U` explicitly if necessary.
+      // Otherwise, let implicit conversions do the trick.
+      using CastType =
+          typename std::conditional<std::is_convertible<T&, const U&>::value,
+                                    T&, U>::type;
+
+      return source_matcher_.MatchAndExplain(static_cast<CastType>(x),
+                                             listener);
     }
 
     void DescribeTo(::std::ostream* os) const override {
@@ -524,8 +531,8 @@ inline Matcher<T> SafeMatcherCast(const M& polymorphic_matcher_or_value) {
 template <typename T, typename U>
 inline Matcher<T> SafeMatcherCast(const Matcher<U>& matcher) {
   // Enforce that T can be implicitly converted to U.
-  GTEST_COMPILE_ASSERT_((std::is_convertible<T, U>::value),
-                        "T must be implicitly convertible to U");
+  static_assert(std::is_convertible<const T&, const U&>::value,
+                "T must be implicitly convertible to U");
   // Enforce that we are not converting a non-reference type T to a reference
   // type U.
   GTEST_COMPILE_ASSERT_(
diff --git a/googlemock/test/gmock-matchers_test.cc b/googlemock/test/gmock-matchers_test.cc
index c1949e63..3619959f 100644
--- a/googlemock/test/gmock-matchers_test.cc
+++ b/googlemock/test/gmock-matchers_test.cc
@@ -765,10 +765,11 @@ TEST(SafeMatcherCastTest, FromConstReferenceToReference) {
 
 // Tests that MatcherCast<const T&>(m) works when m is a Matcher<T>.
 TEST(SafeMatcherCastTest, FromNonReferenceToConstReference) {
-  Matcher<int> m1 = Eq(0);
-  Matcher<const int&> m2 = SafeMatcherCast<const int&>(m1);
-  EXPECT_TRUE(m2.Matches(0));
-  EXPECT_FALSE(m2.Matches(1));
+  Matcher<std::unique_ptr<int>> m1 = IsNull();
+  Matcher<const std::unique_ptr<int>&> m2 =
+      SafeMatcherCast<const std::unique_ptr<int>&>(m1);
+  EXPECT_TRUE(m2.Matches(std::unique_ptr<int>()));
+  EXPECT_FALSE(m2.Matches(std::unique_ptr<int>(new int)));
 }
 
 // Tests that SafeMatcherCast<T&>(m) works when m is a Matcher<T>.