[Bug c++/59204] New: Incorrect metaprogram evaluation in SFINAE context

[Bug c++/59204] New: Incorrect metaprogram evaluation in SFINAE context

[webrown.cpp at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59204

            Bug ID: 59204
           Summary: Incorrect metaprogram evaluation in SFINAE context
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: webrown.cpp at gmail dot com

Created attachment 31255
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31255&action=edit
Demonstrating SFINAE failure to fail

Command:  g++-mp-4.9 -O3 -std=gnu++1y bug2.cc
Version: g++-mp-4.9 (MacPorts gcc49 4.9-20131110_0) 4.9.0 20131110
(experimental)

Attached program fails to compile because the 2nd static_assert incorrectly
leads to a diagnostic.

Used in a SFINAE context, it seems that the type expression
  void_t<typename T::type>
always yields the type void.  This seems too aggressive an outcome; when T has
no T::type member, the expression should instead be treated as invalid, hence
its context rejected due to SFINAE.

[Bug c++/59204] Incorrect metaprogram evaluation in SFINAE context

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59204

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-12-18
     Ever confirmed|0                           |1

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This works in mainline. I'm adding the testcase and closing the bug.

[Bug c++/59204] Incorrect metaprogram evaluation in SFINAE context

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59204

--- Comment #3 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Thu Dec 18 23:43:46 2014
New Revision: 218878

URL: https://gcc.gnu.org/viewcvs?rev=218878&root=gcc&view=rev
Log:
2014-12-18  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/59204
    * g++.dg/cpp0x/sfinae53.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/sfinae53.C
Modified:
    trunk/gcc/testsuite/ChangeLog

[Bug c++/59204] Incorrect metaprogram evaluation in SFINAE context

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59204

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.0

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Done. Note: in r217250 Jason implemented the resolution of Core/1558.