[Bug c++/108206] [12 Regression] ICE: tree check: expected tree that contains 'decl minimal' structure, have 'error_mark' in merge_default_template_args, at cp/decl.cc:1563 since r12-7562-gfe548eb8436f3906

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108206

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:7048e8c1073fcf2bf6be1a3d079393a78864ca61

commit r12-9137-g7048e8c1073fcf2bf6be1a3d079393a78864ca61
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Jan 4 18:42:31 2023 +0100

    c++: Error recovery in merge_default_template_args [PR108206]

    We ICE on the following testcase during error recovery, both new_parm
    and old_parm are error_mark_node, the ICE is on
              error ("redefinition of default argument for %q+#D", new_parm);
              inform (DECL_SOURCE_LOCATION (old_parm),
                      "original definition appeared here");
    where we don't print anything useful for new_parm and ICE trying to
    access DECL_SOURCE_LOCATION of old_parm.  I think we shouldn't diagnose
    anything when either of the parms is erroneous, GCC 11 before
    merge_default_template_args has been added was doing
          if (TREE_VEC_ELT (tmpl_parms, i) == error_mark_node
              || TREE_VEC_ELT (parms, i) == error_mark_node)
            continue;

          tmpl_parm = TREE_VALUE (TREE_VEC_ELT (tmpl_parms, i));
          if (error_operand_p (tmpl_parm))
            return false;
    in redeclare_class_template.

    2023-01-04  Jakub Jelinek  <jakub@redhat.com>

            PR c++/108206
            * decl.cc (merge_default_template_args): Return false if either
            new_parm or old_parm are erroneous.

            * g++.dg/template/pr108206.C: New test.

    (cherry picked from commit fc349931adcf1024ee95e0a0cd98cf4a41996093)