[Bug c++/117993] [15 regression] this->x is being rejected in a nested template class with a base of class of the outer templated class since r15-2117

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117993

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>:

https://gcc.gnu.org/g:57904dc27d5b27226912838cdd6b5272cec4d050

commit r15-6737-g57904dc27d5b27226912838cdd6b5272cec4d050
Author: Patrick Palka <ppa...@redhat.com>
Date:   Thu Jan 9 10:50:06 2025 -0500

    c++: current inst w/ indirect dependent bases [PR117993]

    In the first testcase we're overeagerly diagnosing qualified name lookup
    failure for f from the current instantiation B<T>::C ahead of time
    because we (correctly) deem C to not have any direct dependent bases:
    its direct base B<T> is part of the current instantiation and therefore
    not a dependent base, and we decide it's safe to diagnose name lookup
    failure ahead of time.

    But this testcase demonstrates it's not enough to consider only direct
    dependent bases: f is defined in A<T> which is a dependent base of
    B<T>, so qualified name lookup from C won't search it ahead of time and
    in turn won't be exhaustive, and so it's wrong to diagnose lookup
    failure ahead of time.  This ultimately suggests that
    any_dependent_bases_p needs to consider indirect bases as well.

    To that end it seems sufficient to make the predicate recurse into any
    !BINFO_DEPENDENT_BASE_P base since the recursive call will exit early
    for non-dependent types.  So effectively we'll only recurse into bases
    belonging to the current instantiation.

    I considered more narrowly making only dependentish_scope_p consider
    indirect dependent bases, but it seems other any_dependent_bases_p
    callers also want this behavior, e.g. build_new_method_call for benefit
    of the second testcase (which is an even older regression since GCC 7).

            PR c++/117993

    gcc/cp/ChangeLog:

            * search.cc (any_dependent_bases_p): Recurse into bases (of
            dependent type) that are not BINFO_DEPENDENT_BASE_P.  Document
            default argument.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/dependent-base4.C: New test.
            * g++.dg/template/dependent-base5.C: New test.

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