[Bug c++/102104] New: parameter packs not expanded with '...' for operator conversions

[Bug c++/102104] New: parameter packs not expanded with '...' for operator conversions

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102104

            Bug ID: 102104
           Summary: parameter packs not expanded with '...' for operator
                    conversions
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Originally the second testcase from PR 79094 but the first one has since been
fixed.


Take -std=c++17:
template<typename A, typename B>
struct unvariadic: private A, private B {
    // okay, provided A and B each declare appropriate
    // target_type and operator target_type() members
    using A::operator typename A::target_type,
          B::operator typename B::target_type;
};

template<typename... Bases>
struct variadic: private Bases... {
    // error: parameter packs not expanded with '...':
    using Bases::operator typename Bases::target_type...;
};

This should compile just as ICC and clang do.

[Bug c++/102104] parameter packs not expanded with '...' for operator conversions

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102104

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-09-29
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
We also reject the following, with a different error message:

template<typename T, typename... Bases>
struct variadic: private Bases... {
    // error: expansion pattern ‘T’ contains no parameter packs
    using T::operator typename Bases::target_type...;
};

[Bug c++/102104] parameter packs not expanded with '...' for operator conversions

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102104

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/102104] parameter packs not expanded with '...' for operator conversions

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102104

--- Comment #2 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++/102104] parameter packs not expanded with '...' for operator conversions

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102104

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13.