https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64679
--- Comment #5 from CVS 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:ee9128189623ce43343ce326caa8d5eec2eccfec commit r13-146-gee9128189623ce43343ce326caa8d5eec2eccfec Author: Marek Polacek <pola...@redhat.com> Date: Tue May 3 19:01:19 2022 -0400 c++: wrong error with MVP and pushdecl [PR64679] This patch fixes the second half of 64679. Here we issue a wrong "redefinition of 'int x'" for the following: struct Bar { Bar(int, int, int); }; int x = 1; Bar bar(int(x), int(x), int{x}); // #1 cp_parser_parameter_declaration_list does pushdecl every time it sees a named parameter, so the second "int(x)" causes the error. That's premature, since this turns out to be a constructor call after the third argument! If the first parameter is parenthesized, we can't push until we've established we're looking at a function declaration. Therefore this could be fixed by some kind of lookahead. I thought about introducing a lightweight variant of cp_parser_parameter_declaration_list that would not have any side effects and would return as soon as it figures out whether it's looking at a declaration or expression. Since that would require fairly nontrivial changes, I wanted something simpler. Something like delaying the pushdecl until we've reached the ')' following the parameter-declaration-clause. But we must push the parameters before processing a default argument, as in: Bar bar(int(a), int(b), int c = sizeof(a)); // valid Moreover, this code should still be accepted Bar f(int(i), decltype(i) j = 42); so this patch stashes parameters into a vector when parsing tentatively only when pushdecl-ing a parameter would result in a clash and an error about redefinition/redeclaration. The stashed parameters are pushed at the end of a parameter-declaration-clause if it's followed by a ')', so that we still diagnose redefining a parameter. PR c++/64679 gcc/cp/ChangeLog: * parser.cc (cp_parser_parameter_declaration_clause): Maintain a vector of parameters that haven't been pushed yet. Push them at the end of a valid parameter-declaration-clause. (cp_parser_parameter_declaration_list): Take a new auto_vec parameter. Do not pushdecl while parsing tentatively when pushdecl-ing a parameter would result in a hard error. (cp_parser_cache_defarg): Adjust the call to cp_parser_parameter_declaration_list. gcc/testsuite/ChangeLog: * g++.dg/parse/ambig11.C: New test. * g++.dg/parse/ambig12.C: New test. * g++.dg/parse/ambig13.C: New test. * g++.dg/parse/ambig14.C: New test.
