https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89062
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <[email protected]>: https://gcc.gnu.org/g:6186708312780bb2139da01946abdde39667e985 commit r12-2859-g6186708312780bb2139da01946abdde39667e985 Author: Patrick Palka <[email protected]> Date: Wed Aug 11 15:58:30 2021 -0400 c++: most vexing parse and braced CTAD [PR89062] Here grokdeclarator is emitting the error error: class template placeholder âFooâ not permitted in this context during the tentative (and ultimately futile) parse of 'x' as a function declaration. This happens because when parsing 'Foo{1}', cp_parser_parameter_declaration yields a parameter declaration with no declarator and whose type is a CTAD placeholder, and stops short of consuming the '{'. The caller cp_parser_parameter_declaration_list then calls grokdeclarator on this declarator, hence the error, and soon thereafter we abort this tentative parse since the next token '{' doesn't make sense in the context of a parameter list. Note that we don't have this issue with parenthesized CTAD Foo<int> x(Foo(1)); because in this case cp_parser_direct_declarator (called indirectly from c_p_p_d) consumes the '(' and returns cp_error_declarator instead of a NULL declarator (and also simulates a parse error), and grokdeclarator exits early for this declarator without emitting any error. Since grokdeclarator doesn't take a 'complain' parameter, to fix this we need to avoid calling grokdeclarator in this situation. To that end this patch makes c_p_p_d simulate an error when a construct is a CTAD expression and definitely not a parameter declaration, so that c_p_p_d_l can avoid calling grokdeclarator by checking for this simulated error. Alternatively we could keep all this logic inside c_p_p_d_l and not touch c_p_p_d at all, but this approach seems slightly less adhoc. PR c++/89062 gcc/cp/ChangeLog: * parser.c (cp_parser_parameter_declaration_list): Don't call grokdeclarator if cp_parser_error_occurred. (cp_parser_parameter_declaration): Simulate an error if we see the beginning of a CTAD form, i.e. if we see an opening brace after the decl-specifier-seq and the type is a CTAD placeholder. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction97.C: New test.
