Add IsEmpty overload for C-style strings

Fixes #3937

PiperOrigin-RevId: 463180144
Change-Id: I21b528acc4c3f3aba4234642be01fcead7fe7f00

googlemock/include/gmock/gmock-more-matchers.h

@@ -40,6 +40,9 @@
 #ifndef GOOGLEMOCK_INCLUDE_GMOCK_GMOCK_MORE_MATCHERS_H_
 #define GOOGLEMOCK_INCLUDE_GMOCK_GMOCK_MORE_MATCHERS_H_
 
+#include <ostream>
+#include <string>
+
 #include "gmock/gmock-matchers.h"
 
 namespace testing {
@@ -56,16 +59,44 @@ namespace testing {
 #endif
 #endif
 
-// Defines a matcher that matches an empty container. The container must
-// support both size() and empty(), which all STL-like containers provide.
-MATCHER(IsEmpty, negation ? "isn't empty" : "is empty") {
-  if (arg.empty()) {
+namespace internal {
+
+// Implements the polymorphic IsEmpty matcher, which
+// can be used as a Matcher<T> as long as T is either a container that defines
+// empty() and size() (e.g. std::vector or std::string), or a C-style string.
+class IsEmptyMatcher {
+ public:
+  // Matches anything that defines empty() and size().
+  template <typename MatcheeContainerType>
+  bool MatchAndExplain(const MatcheeContainerType& c,
+                       MatchResultListener* listener) const {
+    if (c.empty()) {
       return true;
     }
-  *result_listener << "whose size is " << arg.size();
+    *listener << "whose size is " << c.size();
     return false;
   }
 
+  // Matches C-style strings.
+  bool MatchAndExplain(const char* s, MatchResultListener* listener) const {
+    return MatchAndExplain(std::string(s), listener);
+  }
+
+  // Describes what this matcher matches.
+  void DescribeTo(std::ostream* os) const { *os << "is empty"; }
+
+  void DescribeNegationTo(std::ostream* os) const { *os << "isn't empty"; }
+};
+
+}  // namespace internal
+
+// Creates a polymorphic matcher that matches an empty container or C-style
+// string. The container must support both size() and empty(), which all
+// STL-like containers provide.
+inline PolymorphicMatcher<internal::IsEmptyMatcher> IsEmpty() {
+  return MakePolymorphicMatcher(internal::IsEmptyMatcher());
+}
+
 // Define a matcher that matches a value that evaluates in boolean
 // context to true.  Useful for types that define "explicit operator
 // bool" operators and so can't be compared for equality with true

googlemock/test/gmock-matchers-comparisons_test.cc

@@ -39,6 +39,8 @@
 #pragma warning(disable : 4100)
 #endif
 
+#include <vector>
+
 #include "test/gmock-matchers_test.h"
 
 namespace testing {
@@ -983,6 +985,30 @@ TEST(ComparisonBaseTest, WorksWithMoveOnly) {
   helper.Call(MoveOnly(1));
 }
 
+TEST(IsEmptyTest, MatchesContainer) {
+  const Matcher<std::vector<int>> m = IsEmpty();
+  std::vector<int> a = {};
+  std::vector<int> b = {1};
+  EXPECT_TRUE(m.Matches(a));
+  EXPECT_FALSE(m.Matches(b));
+}
+
+TEST(IsEmptyTest, MatchesStdString) {
+  const Matcher<std::string> m = IsEmpty();
+  std::string a = "z";
+  std::string b = "";
+  EXPECT_FALSE(m.Matches(a));
+  EXPECT_TRUE(m.Matches(b));
+}
+
+TEST(IsEmptyTest, MatchesCString) {
+  const Matcher<const char*> m = IsEmpty();
+  const char a[] = "";
+  const char b[] = "x";
+  EXPECT_TRUE(m.Matches(a));
+  EXPECT_FALSE(m.Matches(b));
+}
+
 // Tests that IsNull() matches any NULL pointer of any type.
 TEST(IsNullTest, MatchesNullPointer) {
   Matcher<int*> m1 = IsNull();