[Bug c++/108090] New: pack expansion of using declarations doesn't properly handle dependent conversion function names

[Bug c++/108090] New: pack expansion of using declarations doesn't properly handle dependent conversion function names

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108090

            Bug ID: 108090
           Summary: pack expansion of using declarations doesn't properly
                    handle dependent conversion function names
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richard-gccbugzilla at metafoo dot co.uk
  Target Milestone: ---

Testcase, which I believe is valid, and other compilers accept:

template<typename T> struct As { operator T(); };
template<typename ...T> struct AsAll : As<T>... {
  using As<T>::operator T...;
};
AsAll<int, float, char> x;

But GCC rejects:

<source>:3:26: error: parameter packs not expanded with '...':
    3 |   using As<T>::operator T...;
      |                          ^~~
<source>:3:26: note:         'T'

[Bug c++/108090] pack expansion of using declarations doesn't properly handle dependent conversion function names

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108090

--- Comment #1 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:e79d51963378b10ab90544a7d8eeb6266e9a57f6

commit r13-4734-ge79d51963378b10ab90544a7d8eeb6266e9a57f6
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Dec 15 18:50:16 2022 -0500

    c++: variadic using-decl with parm pack in terminal name [PR102104]

    There's a curious corner case with variadic member using-decls: the
    terminal name can also contain a parameter pack, and only through naming
    a conversion function, e.g.

      using A<Ts>::operator Ts...;

    We currently only handle parameter packs appearing in the qualifying
    scope of a variadic using-decl; this patch adds support for the above
    case as well, representing such a using-decl via two pack expansions,
    one for the qualifying scope and one for the terminal name (despite
    logically there being just one).  Then at instantiation time we manually
    merge them.

            PR c++/102104
            PR c++/108090

    gcc/cp/ChangeLog:

            * error.cc (dump_decl) <case USING_DECL>: Look through a
            pack expansion in the name as well.
            * parser.cc (cp_parser_using_declaration): Handle a parameter
            pack appearing in the terminal name of a variadic using-decl.
            * pt.cc (tsubst_decl) <case USING_DECL>: Likewise.  Combine the
            handling of variadic and non-variadic using-decls.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1z/using-variadic1.C: New test.
            * g++.dg/cpp1z/using-variadic1a.C: New test.
            * g++.dg/cpp1z/using-variadic1b.C: New test.
            * g++.dg/cpp1z/using-variadic1c.C: New test.
            * g++.dg/cpp1z/using-variadic2.C: New test.
            * g++.dg/cpp1z/using-variadic3.C: New test.

[Bug c++/108090] pack expansion of using declarations doesn't properly handle dependent conversion function names

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108090

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
   Target Milestone|---                         |13.0
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
                 CC|                            |ppalka at gcc dot gnu.org
         Resolution|---                         |FIXED

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13