From b5f15775674c4bcfa91052611428e48a10da3f84 Mon Sep 17 00:00:00 2001
From: Matthias Moulin <matthias.moulin@gmail.com>
Date: Thu, 23 May 2024 20:55:29 +0200
Subject: [PATCH] Added formattable concept

---
 include/fmt/base.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index c840289572da8..48772c3a622de 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -149,6 +149,13 @@ import std;
 #  define FMT_USE_NONTYPE_TEMPLATE_ARGS 0
 #endif
 
+// Detect C++20 concepts
+#ifdef __cpp_concepts
+#  define FMT_USE_CONCEPTS 1
+#else
+#  define FMT_USE_CONCEPTS 0
+#endif
+
 // Check if exceptions are disabled.
 #ifdef FMT_EXCEPTIONS
 // Use the provided definition.
@@ -2007,6 +2014,11 @@ using is_formattable = bool_constant<!std::is_base_of<
     detail::unformattable, decltype(detail::arg_mapper<buffered_context<Char>>()
                                         .map(std::declval<T&>()))>::value>;
 
+#if FMT_USE_CONCEPTS
+template <typename T, typename Char = char>
+concept formattable = is_formattable<remove_reference_t<T>, Char>::value;
+#endif
+
 /**
   \rst
   Constructs an object that stores references to arguments and can be implicitly