[Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:850a9ce8bcca59c7efabcdeeca14c5bd905e8363

commit r13-768-g850a9ce8bcca59c7efabcdeeca14c5bd905e8363
Author: Jason Merrill <jason@redhat.com>
Date:   Tue May 24 17:37:58 2022 -0400

    c++: deduction from auto fn [PR105623]

    Since my patch for PR90451, we defer mark_used of single functions as late
    as possible.  And since my r12-1273, we keep BASELINK from lookup around
    rather than reconstruct it later.  These both made us try to instantiate g
    with a function type that still had 'auto' as its return type.

            PR c++/105623

    gcc/cp/ChangeLog:

            * decl2.cc (mark_used): Copy type from fn to BASELINK.
            * pt.cc (unify_one_argument): Call mark_single_function.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/auto-fn62.C: New test.