https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120917
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- Yes the problem is that before GCC 14 the extension was silently accepted for C++20 and later, even with -pedantic. For C++17 it would warn, but tell you to use -std=c++20 or -fconcepts, so there was no clue that it as an extension enabled by -fconcepts-ts So if GCC never told you it was related to -fconcepts-ts and you never needed to use -fconcepts-ts to enable it, then you would never have seen the warning that -fconcepts-ts is deprecated.
