[Bug c++/86747] [8 Regression] rejects-valid with redundant friend declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86747

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:3d99aab56d7237bb8260653ed07ca8b182fbf975

commit r8-10073-g3d99aab56d7237bb8260653ed07ca8b182fbf975
Author: Alexandre Oliva <aoliva@redhat.com>
Date:   Tue Feb 25 21:29:03 2020 -0500

    c++: tsubst friend tpl ctxt before looking it up for dupes [PR86747]

    When a member template is redeclared as a friend, we enter the context
    of the member before looking it up, and then we check that the decls
    are compatible.  However, when the member template references template
    types of the enclosing context, say an enclosing template class, the
    compare fails because the friend decl is already tsubsted, whereas the
    looked up name isn't.

    The problem is that the enclosing context is taken from the friend
    declaration before tsubsting it, so we look up in the context of the
    generic template instead of that of the tsubsted one we're
    specializing.  The solution is to tsubst the enclosing context when
    it's a non-namespace scope.

    gcc/cp/ChangeLog
    2020-02-25  Alexandre Oliva <aoliva@redhat.com>

        PR c++/86747
        * pt.c (tsubst_friend_class): Enter tsubsted class context.

    gcc/testsuite/ChangeLog
    2020-02-25  Alexandre Oliva <aoliva@redhat.com>

        PR c++/86747
        * g++.dg/pr86747.C: New.