https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103891
--- Comment #5 from Sergei Trofimovich <slyfox at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #4) > I suppose we could just do: > > --- a/libstdc++-v3/include/std/variant > +++ b/libstdc++-v3/include/std/variant > @@ -54,7 +54,7 @@ namespace std _GLIBCXX_VISIBILITY(default) > { > _GLIBCXX_BEGIN_NAMESPACE_VERSION > > -#if __cplusplus >= 202002L && __cpp_concepts > +#if __cplusplus >= 202002L && __cpp_concepts && __GNUC__ >= 12 > // P2231R1 constexpr needs constexpr unions and constrained destructors. > # define __cpp_lib_variant 202106L > #else > > And then improve it later if GCC updates __cpp_concepts That almost works: In file included from bug.cc:12: stdc++-include/c++/12.0.0/variant:300:18: error: no template named '__aligned_membuf' in namespace '__gnu_cxx' __gnu_cxx::__aligned_membuf<_Type> _M_storage; ~~~~~~~~~~~^ On clang it also needs `#include <ext/aligned_buffer.h>` as well.