https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86773
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:43cb72263fb3b7b97a74fb38d71364a1d5cf0448 commit r11-4498-g43cb72263fb3b7b97a74fb38d71364a1d5cf0448 Author: Marek Polacek <pola...@redhat.com> Date: Mon Oct 26 15:04:58 2020 -0400 c++: GCC accepts junk before fold-expression [PR86773] Here we accept a bogus expression before a left fold: Recall that a fold expression looks like: fold-expression: ( cast-expression fold-operator ... ) ( ... fold-operator cast-expression ) ( cast-expression fold-operator ... fold-operator cast-expression ) but here we have ( cast-expression ... fold-operator cast-expression ) The best fix seems to just return error_mark_node when we know this code is invalid, and let the subsequent code report that a ) was expected. gcc/cp/ChangeLog: PR c++/86773 * parser.c (cp_parser_fold_expression): Return error_mark_node if a left fold is preceded by an expression. gcc/testsuite/ChangeLog: PR c++/86773 * g++.dg/cpp1z/fold12.C: New test.