[Bug c++/106259] [10/11/12 Regression] ICE in diag_mismatched_tags, at cp/parser.cc:33896

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106259

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:3a2310d4b229e707bbc5440150bf180e0499273a

commit r12-9217-g3a2310d4b229e707bbc5440150bf180e0499273a
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Mar 1 14:28:46 2023 -0500

    c++: ICE with -Wmismatched-tags and member template [PR106259]

    -Wmismatched-tags warns about the (harmless) struct/class mismatch.
    For, e.g.,

      template<typename T> struct A { };
      class A<int> a;

    it works by adding A<T> to the class2loc hash table while parsing the
    class-head and then, while parsing the elaborate type-specifier, we
    add A<int>.  At the end of c_parse_file we go through the table and
    warn about the class-key mismatches.  In this PR we crash though; we
    have

      template<typename T> struct A {
        template<typename U> struct W { };
      };
      struct A<int>::W<int> w; // #1

    where while parsing A and #1 we've stashed
       A<T>
       A<T>::W<U>
       A<int>::W<int>
    into class2loc.  Then in class_decl_loc_t::diag_mismatched_tags TYPE
    is A<int>::W<int>, and specialization_of gets us A<int>::W<U>, which
    is not in class2loc, so we crash on gcc_assert (cdlguide).  But it's
    OK not to have found A<int>::W<U>, we should just look one "level" up,
    that is, A<T>::W<U>.

    It's important to handle class specializations, so e.g.

      template<>
      struct A<char> {
        template<typename U>
        class W { };
      };

    where W's class-key is different than in the primary template above,
    so we should warn depending on whether we're looking into A<char>
    or into a different instantiation.

            PR c++/106259

    gcc/cp/ChangeLog:

            * parser.cc (class_decl_loc_t::diag_mismatched_tags): If the first
            lookup of SPEC didn't find anything, try to look for
            most_general_template.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wmismatched-tags-11.C: New test.

    (cherry picked from commit 71afd0628419c5d670701cb35bc9860380c7d9fb)