https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120917
--- Comment #15 from Jason Merrill <jason at gcc dot gnu.org> --- We always intended to diagnose Concepts TS features that didn't make it into C++20, but there was a bug in GCC 12 that we didn't diagnose that particular case because it hit the transformation from void f(S<auto>); to template <class T> void f(S<T>); before it hit the error; I fixed that bug in r14-1659 for GCC 14 by adding another error. I suppose we could downgrade the error to a permerror (to make it compile with -fpermissive), since the above transformation still works apart from the error. Would that be useful to you?
