https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116071
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:8c71830b51e6fd10087ce3f6791de80eb1f10b96 commit r15-2277-g8c71830b51e6fd10087ce3f6791de80eb1f10b96 Author: Jason Merrill <ja...@redhat.com> Date: Wed Jul 24 16:20:33 2024 -0400 c++: parse error with -std=c++14 -fconcepts [PR116071] cp_parser_simple_type_specifier tries a variety of different things that might qualify as a user-defined type: an actual type-name, a constrained auto, a CTAD placeholder. In a context where a type-specifier is optional, this is all tentative. With -std=c++14 -fconcepts, we try type-name and constrained auto in sub-tentative parses, and when we run out of things to try we haven't found anything but also haven't failed the outer tentative parse, so parse_definitely succeeds, discarding the nested-name-specifier. Fixed by failing if we didn't find anything. I said in r14-3203 that we should disable this combination of flags if further problems arise, but this seems like a more general problem that only happened to occur with just this combination of flags. So it lives on. PR c++/116071 gcc/cp/ChangeLog: * parser.cc (cp_parser_simple_type_specifier): Call cp_parser_simulate_error if nothing worked. gcc/testsuite/ChangeLog: * g++.dg/parse/pr116071.C: New test.
