[Bug c++/96106] [10/11 Regression] A friend abbreviated template function denies access to private members

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96106

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:f31dd9beb95f4beda1d2bd5c0526c42d0ce455c4

commit r11-2418-gf31dd9beb95f4beda1d2bd5c0526c42d0ce455c4
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Jul 29 22:06:36 2020 -0400

    c++: abbreviated function template friend matching [PR96106]

    In the below testcase, duplicate_decls wasn't merging the tsubsted
    friend declaration for 'void add(auto)' with its definition, because
    reduce_template_parm_level (during tsubst_friend_function) lost the
    DECL_VIRTUAL_P flag on the auto's invented template parameter, which
    caused template_heads_equivalent_p to deem the two template heads as not
    equivalent in C++20 mode.

    This patch makes reduce_template_parm_level carry over the
    DECL_VIRTUAL_P flag from the original TEMPLATE_PARM_DECL.

    gcc/cp/ChangeLog:

            PR c++/96106
            * pt.c (reduce_template_parm_level): Propagate DECL_VIRTUAL_P
            from the original TEMPLATE_PARM_DECL to the new lowered one.

    gcc/testsuite/ChangeLog:

            PR c++/96106
            * g++.dg/concepts/abbrev7.C: New test.