From a8115267a6c80d22bd483cf075e8709cc68fbb60 Mon Sep 17 00:00:00 2001
From: Leonid Yuriev <leo@yuriev.ru>
Date: Mon, 26 Jul 2021 05:16:29 +0300
Subject: [PATCH] mdbx++: disable using C++20 concepts for CLANG < 12.

---
 mdbx.h++ | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mdbx.h++ b/mdbx.h++
index 654cee8b..d44f930d 100644
--- a/mdbx.h++
+++ b/mdbx.h++
@@ -192,7 +192,9 @@
 #endif /* MDBX_CXX20_UNLIKELY */
 
 #ifndef MDBX_CXX20_CONCEPT
-#if defined(DOXYGEN) || (defined(__cpp_concepts) && __cpp_concepts >= 201907L)
+#if defined(DOXYGEN) ||                                                        \
+    (defined(__cpp_concepts) && __cpp_concepts >= 201907L &&                   \
+     (!defined(__clang__) || __clang_major__ >= 12))
 #define MDBX_CXX20_CONCEPT(CONCEPT, NAME) CONCEPT NAME
 #else
 #define MDBX_CXX20_CONCEPT(CONCEPT, NAME) typename NAME
@@ -200,7 +202,9 @@
 #endif /* MDBX_CXX20_CONCEPT */
 
 #ifndef MDBX_ASSERT_CXX20_CONCEPT_SATISFIED
-#if defined(DOXYGEN) || (defined(__cpp_concepts) && __cpp_concepts >= 201907L)
+#if defined(DOXYGEN) ||                                                        \
+    (defined(__cpp_concepts) && __cpp_concepts >= 201907L &&                   \
+     (!defined(__clang__) || __clang_major__ >= 12))
 #define MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(CONCEPT, TYPE)                     \
   static_assert(CONCEPT<TYPE>)
 #else
@@ -466,7 +470,9 @@ static MDBX_CXX20_CONSTEXPR void *memcpy(void *dest, const void *src,
                                          size_t bytes) noexcept;
 //------------------------------------------------------------------------------
 
-#if defined(DOXYGEN) || (defined(__cpp_concepts) && __cpp_concepts >= 201907L)
+#if defined(DOXYGEN) ||                                                        \
+    (defined(__cpp_concepts) && __cpp_concepts >= 201907L &&                   \
+     (!defined(__clang__) || __clang_major__ >= 12))
 
 template <typename T>
 concept MutableByteProducer = requires(T a, char array[42]) {