[Bug c++/86773] GCC accepts junk before fold expressions

[cvs-commit at gcc dot gnu.org]

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 <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:43cb72263fb3b7b97a74fb38d71364a1d5cf0448

commit r11-4498-g43cb72263fb3b7b97a74fb38d71364a1d5cf0448
Author: Marek Polacek <polacek@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.