From 4e1d3fb734903095a7c4ce50744288b3aaa0e0b7 Mon Sep 17 00:00:00 2001
From: marehr <marehr-github@marehr.dialup.fu-berlin.de>
Date: Wed, 16 Sep 2020 11:35:09 +0200
Subject: [PATCH] [FIX] workaround gcc versions that forgot to define
 __cpp_lib_remove_cvref

---
 include/seqan3/std/type_traits | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/seqan3/std/type_traits b/include/seqan3/std/type_traits
index 717aeccbe88..cc626ad3458 100644
--- a/include/seqan3/std/type_traits
+++ b/include/seqan3/std/type_traits
@@ -15,13 +15,25 @@
 
 #include <type_traits>
 
+//!\brief A workaround for __cpp_lib_remove_cvref for gcc version >=9.0 and <9.4 (in C++17 mode).
+//!       Those versions implemented std::remove_cvref_t, but did not define that feature detection macro.
+#ifndef SEQAN3_WORKAROUND_CPP_LIB_REMOVE_CVREF
+#   if defined(__cpp_lib_remove_cvref)
+#       define SEQAN3_WORKAROUND_CPP_LIB_REMOVE_CVREF 1
+#   elif defined(__GNUC__) && ((__GNUC__ == 9) && (__GNUC_MINOR__ < 4)) && __cplusplus > 201703L
+#       define SEQAN3_WORKAROUND_CPP_LIB_REMOVE_CVREF 1
+#   else
+#       define SEQAN3_WORKAROUND_CPP_LIB_REMOVE_CVREF 0
+#   endif
+#endif
+
 namespace std
 {
 
 // ----------------------------------------------------------------------------
 // remove_cvref_t
 // ----------------------------------------------------------------------------
-#ifndef __cpp_lib_remove_cvref
+#if !SEQAN3_WORKAROUND_CPP_LIB_REMOVE_CVREF
 /*!\brief Return the input type with `const`, `volatile` and references removed.
  * \tparam t The type to operate on.
  */
@@ -42,7 +54,7 @@ struct remove_cvref<t> // needed for gcc-9, it defines std::remove_cvref but doe
  */
 template <typename t>
 using remove_cvref_t = typename remove_cvref<t>::type;
-#endif // __cpp_lib_remove_cvref
+#endif // !SEQAN3_WORKAROUND_CPP_LIB_REMOVE_CVREF
 
 // ----------------------------------------------------------------------------
 // type_identity