https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94508
--- Comment #2 from Arseny Solokha <asolokha at gmx dot com> --- (In reply to Martin Liška from comment #1) > Confirmed, -fconcepts started with GCC 6. Is it a valid or invalid code? clang rejects it, but accepts the following one, on which g++ also ICEs: template<typename T> struct S4 { void foo() requires (this, true) { } }; void bar () { S4<int>{}.foo (); }