enable named arguments check in compile-time checks (#2649)

works only if all named arguments are UDL-based

include/fmt/core.h

@@ -1109,6 +1109,11 @@ template <typename... Args> constexpr auto count_named_args() -> size_t {
   return count<is_named_arg<Args>::value...>();
 }
 
+template <typename... Args>
+constexpr auto count_statically_named_args() -> size_t {
+  return count<is_statically_named_arg<Args>::value...>();
+}
+
 enum class type {
   none_type,
   // Integer types should go first,
@@ -3043,7 +3048,8 @@ template <typename Char, typename... Args> class basic_format_string {
              std::is_reference<Args>::value)...>() == 0,
         "passing views as lvalues is disallowed");
 #ifdef FMT_HAS_CONSTEVAL
-    if constexpr (detail::count_named_args<Args...>() == 0) {
+    if constexpr (detail::count_named_args<Args...>() ==
+                  detail::count_statically_named_args<Args...>()) {
       using checker = detail::format_string_checker<Char, detail::error_handler,
                                                     remove_cvref_t<Args>...>;
       detail::parse_format_string<true>(str_, checker(s, {}));