[Bug c++/124297] [16 Regression] ICE in write_type_constraint, at cp/mangle.cc:913 since r16-7491

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124297

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:d0d3d4dde0b4712a3c39970ec8dcfe0782434d3e

commit r16-7937-gd0d3d4dde0b4712a3c39970ec8dcfe0782434d3e
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Mar 6 17:59:11 2026 -0500

    c++: ICE mangling C auto... tparm [PR124297]

    After r16-7491, the constraint on a C auto... tparm is represented as a
    fold-expression (in TEMPLATE_PARM_CONSTRAINTS) instead of a concept-id (in
    PLACEHOLDER_TYPE_CONSTRAINTS).  So we now need to strip this
fold-expression
    before calling write_type_constraint, like we do in the type template
    parameter case a few lines below.

            PR c++/124297

    gcc/cp/ChangeLog:

            * mangle.cc (write_template_param_decl) <case PARM_DECL>:
            Strip fold-expression before calling write_type_constraint.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-variadic4.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>