[Bug c++/95809] New: GCC treats inline namespace declaration as "ambiguous"

[Bug c++/95809] New: GCC treats inline namespace declaration as "ambiguous"

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95809

            Bug ID: 95809
           Summary: GCC treats inline namespace declaration as "ambiguous"
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

This code, bug.cc, GCC fails to compile it, while clang, icc, or msvc accepts
it well.

$cat bug.cc
namespace g_namespace {}
inline namespace {
    namespace g_namespace {}
}
namespace g_namespace {}

$g++ -c bug.cc
bug.cc:5:12: error: ‘namespace g_namespace’ is ambiguous
    5 | namespace  g_namespace {}
      |            ^~~~~~~~~~~
bug.cc:3:15: note: candidates are: ‘namespace <unnamed>::g_namespace { }’
    3 |     namespace g_namespace {}
      |               ^~~~~~~~~~~
bug.cc:1:11: note:                 ‘namespace g_namespace { }’
    1 | namespace g_namespace {}
      |           ^~~~~~~~~~~

My GCC version is
g++ (GCC) 11.0.0 20200605 (experimental)
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


When I remove the keyword "inline", GCC accepts it well. So, I guess GCC might
can not detect the inline namespace declaration and separate its inside
namespace from outside ones.

[Bug c++/95809] GCC treats inline namespace declaration as "ambiguous"

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95809

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nathan at gcc dot gnu.org

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This changed with r248521

    Implement DR2061

            gcc/
            Implement DR2061
            * name-lookup.c (push_inline_namespaces): New.
            (push_namespace): Look inside inline namespaces.

            testsuite/
            * g++.dg/cpp0x/dr2061.C: New.
            * g++.dg/parse/namespace-alias-1.C: Add more test.

I'm not sure the code is valid, but I'll let Nathan comment.

[Bug c++/95809] GCC treats inline namespace declaration as "ambiguous"

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95809

--- Comment #2 from Nathan Sidwell <nathan at gcc dot gnu.org> ---
yup, dr2061 made that ill-formed.  

p1701 (wg21.link/p1701) documents the behaviour and it appears EWG is exploring
another avenue to resolve the underlying problem 2061 was attempting to fix.

[Bug c++/95809] GCC treats inline namespace declaration as "ambiguous"

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95809

--- Comment #3 from Haoxin Tu <haoxintu at gmail dot com> ---
(In reply to Nathan Sidwell from comment #2)
> yup, dr2061 made that ill-formed.  
> 
> p1701 (wg21.link/p1701) documents the behaviour and it appears EWG is
> exploring another avenue to resolve the underlying problem 2061 was
> attempting to fix.

Thank you, Nathan, so this is a valid code, right?

[Bug c++/95809] GCC treats inline namespace declaration as "ambiguous"

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95809

--- Comment #4 from Nathan Sidwell <nathan at gcc dot gnu.org> ---
The code is invalid due to DR2061

[Bug c++/95809] [DR2061]GCC treats inline namespace declaration as "ambiguous"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95809

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Alias|                            |cwg2061
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Invalid as explained.