Make formatter override implicit conversion to a C string

test/core-test.cc

@@ -469,6 +469,10 @@ struct convertible_to_int {
   operator int() const { return 42; }
 };
 
+struct convertible_to_c_string {
+  operator const char*() const { return "foo"; }
+};
+
 FMT_BEGIN_NAMESPACE
 template <> struct formatter<convertible_to_int> {
   auto parse(format_parse_context& ctx) -> decltype(ctx.begin()) {
@@ -478,10 +482,21 @@ template <> struct formatter<convertible_to_int> {
     return std::copy_n("foo", 3, ctx.out());
   }
 };
+
+template <> struct formatter<convertible_to_c_string> {
+  auto parse(format_parse_context& ctx) -> decltype(ctx.begin()) {
+    return ctx.begin();
+  }
+  auto format(convertible_to_c_string, format_context& ctx)
+      -> decltype(ctx.out()) {
+    return std::copy_n("bar", 3, ctx.out());
+  }
+};
 FMT_END_NAMESPACE
 
 TEST(CoreTest, FormatterOverridesImplicitConversion) {
   EXPECT_EQ(fmt::format("{}", convertible_to_int()), "foo");
+  EXPECT_EQ(fmt::format("{}", convertible_to_c_string()), "bar");
 }
 
 namespace my_ns {

test/ostream-test.cc

@@ -264,17 +264,13 @@ struct explicitly_convertible_to_string_like {
   }
 };
 
-TEST(FormatterTest, FormatExplicitlyConvertibleToStringLike) {
-  EXPECT_EQ("foo", fmt::format("{}", explicitly_convertible_to_string_like()));
-}
-
 std::ostream& operator<<(std::ostream& os,
                          explicitly_convertible_to_string_like) {
   return os << "bar";
 }
 
-TEST(FormatterTest, FormatExplicitlyConvertibleToStringLikeIgnoreInserter) {
-  EXPECT_EQ("foo", fmt::format("{}", explicitly_convertible_to_string_like()));
+TEST(FormatterTest, FormatExplicitlyConvertibleToStringLike) {
+  EXPECT_EQ("bar", fmt::format("{}", explicitly_convertible_to_string_like()));
 }
 
 #ifdef FMT_USE_STRING_VIEW
@@ -284,17 +280,13 @@ struct explicitly_convertible_to_std_string_view {
   }
 };
 
-TEST(FormatterTest, FormatExplicitlyConvertibleToStdStringView) {
-  EXPECT_EQ("foo", fmt::format("{}", explicitly_convertible_to_string_like()));
-}
-
 std::ostream& operator<<(std::ostream& os,
                          explicitly_convertible_to_std_string_view) {
   return os << "bar";
 }
 
-TEST(FormatterTest, FormatExplicitlyConvertibleToStdStringViewIgnoreInserter) {
-  EXPECT_EQ("foo",
-            fmt::format("{}", explicitly_convertible_to_std_string_view()));
+TEST(FormatterTest, FormatExplicitlyConvertibleToStdStringView) {
+  EXPECT_EQ("bar", fmt::format("{}", explicitly_convertible_to_string_like()));
 }
+
 #endif  // FMT_USE_STRING_VIEW