Add format_as for enums

test/core-test.cc

@@ -755,7 +755,16 @@ template <> struct formatter<convertible_to_pointer_formattable> {
 };
 FMT_END_NAMESPACE
 
-enum class test_scoped_enum {};
+enum class unformattable_scoped_enum {};
+
+namespace test {
+enum class formattable_scoped_enum {};
+auto format_as(formattable_scoped_enum) -> int { return 42; }
+
+struct convertible_to_enum {
+  operator formattable_scoped_enum() const { return {}; }
+};
+}  // namespace test
 
 TEST(core_test, is_formattable) {
 #if 0
@@ -796,7 +805,9 @@ TEST(core_test, is_formattable) {
   struct s;
   static_assert(!fmt::is_formattable<int(s::*)>::value, "");
   static_assert(!fmt::is_formattable<int (s::*)()>::value, "");
-  static_assert(!fmt::is_formattable<test_scoped_enum>::value, "");
+  static_assert(!fmt::is_formattable<unformattable_scoped_enum>::value, "");
+  static_assert(fmt::is_formattable<test::formattable_scoped_enum>::value, "");
+  static_assert(!fmt::is_formattable<test::convertible_to_enum>::value, "");
 }
 
 TEST(core_test, format) { EXPECT_EQ(fmt::format("{}", 42), "42"); }
@@ -807,6 +818,10 @@ TEST(core_test, format_to) {
   EXPECT_EQ(s, "42");
 }
 
+TEST(core_test, format_as) {
+  EXPECT_EQ(fmt::format("{}", test::formattable_scoped_enum()), "42");
+}
+
 struct convertible_to_int {
   operator int() const { return 42; }
 };