https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117778
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:e6e40cb7459c9b21b291fe28e46cd4ebcd924dff commit r15-7355-ge6e40cb7459c9b21b291fe28e46cd4ebcd924dff Author: Marek Polacek <pola...@redhat.com> Date: Wed Jan 29 15:58:38 2025 -0500 c++: auto in trailing-return-type in parameter [PR117778] This PR describes a few issues, both ICE and rejects-valid, but ultimately the problem is that we don't properly synthesize the second auto in: int g (auto fp() -> auto) { return fp (); } since r12-5860, which disabled auto_is_implicit_function_template_parm_p in cp_parser_parameter_declaration after parsing the decl-specifier-seq. If there is no trailing auto, there is no problem. So we have to make sure auto_is_implicit_function_template_parm_p is properly set when parsing the trailing auto. A complication is that one can write: auto f (auto fp(auto fp2() -> auto) -> auto) -> auto; ~~~~~~~ where only the underlined auto should be synthesized. So when we parse a parameter-declaration-clause inside another parameter-declaration-clause, we should not enable the flag. We have no flags to keep track of such nesting, but I think I can walk current_binding_level to see if we find ourselves in such an unlikely scenario. PR c++/117778 gcc/cp/ChangeLog: * parser.cc (cp_parser_late_return_type_opt): Maybe override auto_is_implicit_function_template_parm_p. (cp_parser_parameter_declaration): Move a make_temp_override below. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/lambda-generic-117778.C: New test. * g++.dg/cpp2a/abbrev-fn2.C: New test. * g++.dg/cpp2a/abbrev-fn3.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com>
