#2968: Introduce additional compile-time predicate to detect recursive ranges and reject them in formatter specialization for ranges. In addition, introduce additional wrapper traits for the individual logical operands of the complete range constraints

include/fmt/ranges.h

@@ -390,23 +390,33 @@ using range_formatter_type = conditional_t<
 template <typename R>
 using maybe_const_range =
     conditional_t<has_const_begin_end<R>::value, const R, R>;
+
+template <typename R>
+struct is_not_recursive_range : std::bool_constant<
+    !std::is_same<detail::uncvref_type<R>, R>::value> {};
+
+template <typename R, typename Char>
+struct is_formattable_delayed : is_formattable<
+    detail::uncvref_type<detail::maybe_const_range<R>>, Char> {
+};
+
+template <typename R, typename Char>
+struct has_fallback_formatter_delayed : detail::has_fallback_formatter<
+    detail::uncvref_type<detail::maybe_const_range<R>>, Char> {
+};
+
 }  // namespace detail
 
 template <typename R, typename Char>
 struct formatter<
     R, Char,
     enable_if_t<
-        conjunction<fmt::is_range<R, Char>
-// Workaround a bug in MSVC 2017 and earlier.
-#if !FMT_MSC_VERSION || FMT_MSC_VERSION >= 1920
-        ,
-        disjunction<
-          is_formattable<detail::uncvref_type<detail::maybe_const_range<R>>,
-                         Char>,
-          detail::has_fallback_formatter<
-             detail::uncvref_type<detail::maybe_const_range<R>>, Char>
-        >
-#endif
+        conjunction<fmt::is_range<R, Char>,
+          detail::is_not_recursive_range<R>,
+          disjunction<
+              detail::is_formattable_delayed<R, Char>,
+              detail::has_fallback_formatter_delayed<R, Char>
+          >
         >::value
         >> {