From 26a28441d3aca9e412db7062d7bdfb5c4be2984d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Kr=C3=BCgler?= <daniel.kruegler@gmail.com>
Date: Wed, 6 Jul 2022 19:53:40 +0200
Subject: [PATCH] #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 | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index 10429fc8..0010f49e 100644
--- a/include/fmt/ranges.h
+++ b/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
         >> {