https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107188
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:147e276b580b674a46bc3b9c461ae7837fd48aba commit r13-4731-g147e276b580b674a46bc3b9c461ae7837fd48aba Author: Patrick Palka <ppa...@redhat.com> Date: Thu Dec 15 16:07:09 2022 -0500 c++: class-scope qualified constrained auto [PR107188] Here when parsing the class-scope auto constrained by a qualified concept-id, we first tentatively parse the overall member-declaration as a deprecated access-declaration, during which we parse C<int> as a standalone TEMPLATE_ID_EXPR (separate from the auto) and end up emitting the stray error concepts-placeholder11.C:9:6: error: wrong number of template arguments (1, should be 2) 9 | N::C<int> auto f() { return 0; } | ^~~~~~ concepts-placeholder11.C:5:34: note: provided for âtemplate<class, class> concept N::Câ 5 | template<class, class> concept C = true; | ^ from build_concept_id called from cp_parser_template_id_expr. We could fix this by adding a complain parameter to build_concept_id and passing tf_none when parsing tentatively. However, it seems this can also be fixed in a more general way that might benefit non-concepts code: when tentatively parsing an access-declaration, abort the parse early if the qualifying scope isn't possibly a class or enumeration type, so that we avoid parsing C<int> as a TEMPLATE_ID_EXPR here in the first place. This patch takes this latter approach. PR c++/107188 gcc/cp/ChangeLog: * parser.cc (cp_parser_using_declaration): Give up early if the scope of an access-declaration isn't possibly a class type. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-placeholder11.C: New test.
