From e00f827de76e73a21cfdd333d2fb66f84bcf6b73 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Thu, 21 Apr 2022 21:50:52 +0300
Subject: [PATCH] mdbx++: fix/refine detection of C++20 concepts accessibility.

---
 mdbx.h++ | 39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/mdbx.h++ b/mdbx.h++
index a2b1b176..abf214b8 100644
--- a/mdbx.h++
+++ b/mdbx.h++
@@ -209,14 +209,23 @@
 #endif
 #endif /* MDBX_CXX20_UNLIKELY */
 
-#ifndef MDBX_CXX20_CONCEPT
+#ifndef MDBX_HAVE_CXX20_CONCEPTS
 #if defined(DOXYGEN) ||                                                        \
     (defined(__cpp_concepts) && __cpp_concepts >= 201907L &&                   \
-     (!defined(__clang__) ||                                                   \
-      (__clang_major__ >= 12 && !defined(__APPLE__) &&                         \
-       !defined(__ANDROID_API__)) ||                                           \
-      __clang_major__ >=                                                       \
-          /* Hope Apple will fix concepts in AppleClang 14 */ 14))
+     (!defined(__clang__) || __has_include(<concepts>) ||                      \
+  (defined(__cpp_lib_concepts) && __cpp_lib_concepts >= 202002L)))
+#if __has_include(<concepts>) ||                                               \
+  (defined(__cpp_lib_concepts) && __cpp_lib_concepts >= 202002L)
+#include <concepts>
+#endif /* <concepts> */
+#define MDBX_HAVE_CXX20_CONCEPTS 1
+#else
+#define MDBX_HAVE_CXX20_CONCEPTS 0
+#endif
+#endif /* MDBX_HAVE_CXX20_CONCEPTS */
+
+#ifndef MDBX_CXX20_CONCEPT
+#if MDBX_HAVE_CXX20_CONCEPTS
 #define MDBX_CXX20_CONCEPT(CONCEPT, NAME) CONCEPT NAME
 #else
 #define MDBX_CXX20_CONCEPT(CONCEPT, NAME) typename NAME
@@ -224,13 +233,7 @@
 #endif /* MDBX_CXX20_CONCEPT */
 
 #ifndef MDBX_ASSERT_CXX20_CONCEPT_SATISFIED
-#if defined(DOXYGEN) ||                                                        \
-    (defined(__cpp_concepts) && __cpp_concepts >= 201907L &&                   \
-     (!defined(__clang__) ||                                                   \
-      (__clang_major__ >= 12 && !defined(__APPLE__) &&                         \
-       !defined(__ANDROID_API__)) ||                                           \
-      __clang_major__ >=                                                       \
-          /* Hope Apple will fix concepts in AppleClang 14 */ 14))
+#if MDBX_HAVE_CXX20_CONCEPTS
 #define MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(CONCEPT, TYPE)                     \
   static_assert(CONCEPT<TYPE>)
 #else
@@ -509,13 +512,7 @@ static MDBX_CXX20_CONSTEXPR void *memcpy(void *dest, const void *src,
                                          size_t bytes) noexcept;
 //------------------------------------------------------------------------------
 
-#if defined(DOXYGEN) ||                                                        \
-    (defined(__cpp_concepts) && __cpp_concepts >= 201907L &&                   \
-     (!defined(__clang__) ||                                                   \
-      (__clang_major__ >= 12 && !defined(__APPLE__) &&                         \
-       !defined(__ANDROID_API__)) ||                                           \
-      __clang_major__ >=                                                       \
-          /* Hope Apple will fix concepts in AppleClang 14 */ 14))
+#if MDBX_HAVE_CXX20_CONCEPTS
 
 template <typename T>
 concept MutableByteProducer = requires(T a, char array[42]) {
@@ -538,7 +535,7 @@ concept SliceTranscoder = ImmutableByteProducer<T> &&
   { a.is_erroneous() } -> std::same_as<bool>;
 };
 
-#endif /* __cpp_concepts >= 201907L*/
+#endif /* MDBX_HAVE_CXX20_CONCEPTS */
 
 template <class ALLOCATOR = legacy_allocator,
           typename CAPACITY_POLICY = default_capacity_policy,