[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-07-29
             Blocks|                            |67491
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67491
[Bug 67491] [meta-bug] concepts issues

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

--- Comment #1 from Ed Catmur <ed at catmur dot uk> ---
This becomes problematic when N::Q is std::hash; we are encouraged not to
reopen namespace std but to specialize std::hash from the root namespace.

Example:

#include <functional>
template<class> constexpr bool P = false;
template<class> constexpr bool Q = false;
template<class T> requires P<T> struct std::hash<T> { std::size_t operator()(T)
{ return 1; } };
template<class U> requires Q<U> struct std::hash<U> { std::size_t operator()(U)
{ return 2; } };
struct S {};
template<> constexpr bool P<S> = true;
int i = std::hash<S>()(S());

clang and MSVC correctly accept this.

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

--- Comment #2 from Ed Catmur <ed at catmur dot uk> ---
Sorry, meant to link this:
https://quuxplusone.github.io/blog/2021/10/27/dont-reopen-namespace-std/

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |florin at iucha dot net

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 103809 has been marked as a duplicate of this bug. ***

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fchelnokov at gmail dot com

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 103849 has been marked as a duplicate of this bug. ***

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

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
                 CC|                            |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

--- Comment #5 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:ce6054a22ae14594a2919d2ad87cd9478e616fb3

commit r12-6896-gce6054a22ae14594a2919d2ad87cd9478e616fb3
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jan 27 10:56:34 2022 -0500

    c++: constrained partial spec using qualified name [PR92944, PR103678]

    In the nested_name_specifier branch within cp_parser_class_head, we need
    to update 'type' with the result of maybe_process_partial_specialization
    like we do in the template_id_p branch.

            PR c++/92944
            PR c++/103678

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_class_head): Update 'type' with the result
            of maybe_process_partial_specialization in the
            nested_name_specifier branch.  Refactor nearby code to accomodate
            that maybe_process_partial_specialization returns a _TYPE, not a
            TYPE_DECL, and eliminate local variable 'class_type' in passing.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-partial-spec10.C: New test.
            * g++.dg/cpp2a/concepts-partial-spec11.C: New test.

[Bug c++/92944] [concepts] redefinition error when using constrained structure template inside namespace

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92944

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|---                         |12.0

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12, thanks for the bug report.