Add StringView ctor to Matcher<std::string> and Matcher<const std::string&>

Currently, Matcher<StringView>::Matcher(StringView s) and
Matcher<const StringView&>::Matcher(StringView s) exist and explicitly copy
into a std::string so the matcher owns its data:

    Matcher<internal::StringView>::Matcher(internal::StringView s) {
      *this = Eq(std::string(s));
    }

But the symmetric Matcher<const std::string&>::Matcher(StringView) and
Matcher<std::string>::Matcher(StringView) do not exist. That asymmetric gap
silently miscompiles when callers pass a string_view temporary into matchers
whose target type is std::string -- e.g.

    Property(&Proto::string_field, std::format("{},{}", subkey, topic))

Property() builds Matcher<const std::string&> from the value. Since no
StringView constructor exists for Matcher<const std::string&>, the
string_view falls through to MatcherCastImpl, which builds a polymorphic
Eq(string_view). EqMatcher<string_view> stores the view by value, and the
matcher outlives the calling expression -- the underlying buffer (the
std::format temporary) is destroyed and the matcher dangles.

Allocator reuse in optimized builds reliably exposes this: subsequent
std::format calls reuse the same heap slot, and all stored matchers end up
pointing into the same recycled buffer with the last-written contents.

This patch adds the symmetric constructors that mirror the existing
Matcher<StringView>(StringView) impl: copy into a std::string via
Eq(std::string(s)) so the matcher owns its data.

Also adds:
  - StringMatcherTest.CanBeImplicitlyConstructedFromStringView
  - StringMatcherTest.StringViewCtorIsLifetimeSafe (regression test that
    exercises the matcher after the source buffer is destroyed/mutated)

Signed-off-by: Jason Cui <jcui@nuro.ai>

googlemock/test/gmock-matchers-comparisons_test.cc

@@ -272,6 +272,40 @@ TEST(StringViewMatcherTest, CanBeImplicitlyConstructedFromStringView) {
   EXPECT_TRUE(m2.Matches("cats"));
   EXPECT_FALSE(m2.Matches("dogs"));
 }
+
+// Tests that a StringView object can be implicitly converted to a
+// Matcher<std::string> or Matcher<const std::string&>. This is the symmetric
+// counterpart of CanBeImplicitlyConstructedFromString above; without these
+// constructors, a StringView falls through to a polymorphic Eq matcher that
+// stores the view by value and dangles past the constructing call.
+TEST(StringMatcherTest, CanBeImplicitlyConstructedFromStringView) {
+  Matcher<std::string> m1 = internal::StringView("cats");
+  EXPECT_TRUE(m1.Matches("cats"));
+  EXPECT_FALSE(m1.Matches("dogs"));
+
+  Matcher<const std::string&> m2 = internal::StringView("cats");
+  EXPECT_TRUE(m2.Matches("cats"));
+  EXPECT_FALSE(m2.Matches("dogs"));
+}
+
+// Tests that the matcher copies the string data and is safe to use after the
+// underlying buffer the StringView was constructed from is destroyed.
+TEST(StringMatcherTest, StringViewCtorIsLifetimeSafe) {
+  Matcher<std::string> m1;
+  Matcher<const std::string&> m2;
+  {
+    std::string buffer = "cats";
+    m1 = internal::StringView(buffer);
+    m2 = internal::StringView(buffer);
+    // Mutate buffer and let it go out of scope to ensure the matcher does not
+    // alias |buffer|'s storage.
+    buffer = "dogs";
+  }
+  EXPECT_TRUE(m1.Matches("cats"));
+  EXPECT_FALSE(m1.Matches("dogs"));
+  EXPECT_TRUE(m2.Matches("cats"));
+  EXPECT_FALSE(m2.Matches("dogs"));
+}
 #endif  // GTEST_INTERNAL_HAS_STRING_VIEW
 
 // Tests that a std::reference_wrapper<std::string> object can be implicitly

googletest/include/gtest/gtest-matchers.h

@@ -520,6 +520,13 @@ Matcher<const std::string&> : public internal::MatcherBase<const std::string&> {
 
   // Allows the user to write "foo" instead of Eq("foo") sometimes.
   Matcher(const char* s);  // NOLINT
+
+#if GTEST_INTERNAL_HAS_STRING_VIEW
+  // Allows the user to pass absl::string_views or std::string_views directly.
+  // Copies into a std::string so the matcher owns its data and does not alias
+  // a (possibly temporary) buffer in the caller.
+  Matcher(internal::StringView s);  // NOLINT
+#endif
 };
 
 template <>
@@ -544,6 +551,13 @@ Matcher<std::string> : public internal::MatcherBase<std::string> {
 
   // Allows the user to write "foo" instead of Eq("foo") sometimes.
   Matcher(const char* s);  // NOLINT
+
+#if GTEST_INTERNAL_HAS_STRING_VIEW
+  // Allows the user to pass absl::string_views or std::string_views directly.
+  // Copies into a std::string so the matcher owns its data and does not alias
+  // a (possibly temporary) buffer in the caller.
+  Matcher(internal::StringView s);  // NOLINT
+#endif
 };
 
 #if GTEST_INTERNAL_HAS_STRING_VIEW

googletest/src/gtest-matchers.cc

@@ -93,6 +93,18 @@ Matcher<internal::StringView>::Matcher(const char* s) {
 Matcher<internal::StringView>::Matcher(internal::StringView s) {
   *this = Eq(std::string(s));
 }
+
+// Constructs a matcher that matches a const std::string& whose value is
+// equal to s. Copies into a std::string so the matcher owns its data.
+Matcher<const std::string&>::Matcher(internal::StringView s) {
+  *this = Eq(std::string(s));
+}
+
+// Constructs a matcher that matches a std::string whose value is equal to s.
+// Copies into a std::string so the matcher owns its data.
+Matcher<std::string>::Matcher(internal::StringView s) {
+  *this = Eq(std::string(s));
+}
 #endif  // GTEST_INTERNAL_HAS_STRING_VIEW
 
 }  // namespace testing