More compile-time checks

include/fmt/xchar.h

@@ -82,6 +82,16 @@ auto vformat(basic_string_view<Char> format_str,
   return to_string(buffer);
 }
 
+#if !FMT_GCC_VERSION || FMT_GCC_VERSION >= 409
+template <typename... Args>
+using wformat_string = basic_format_string<wchar_t, type_identity_t<Args>...>;
+#endif
+
+template <typename... T>
+auto format(wformat_string<T...> fmt, T&&... args) -> std::wstring {
+  return vformat(fmt, fmt::make_wformat_args(args...));
+}
+
 // Pass char_t as a default template parameter instead of using
 // std::basic_string<char_t<S>> to reduce the symbol size.
 template <typename S, typename... Args, typename Char = char_t<S>,