[Bug c++/50442] New: Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[Bug c++/50442] New: Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[zackw at panix dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

             Bug #: 50442
           Summary: Constructing T from implicit conversion to T&
                    ambiguous in C++0x mode, not C++98
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zackw@panix.com


This test case ...

    template <typename T> struct MoveRef { operator T& () {} };
    template <typename T> MoveRef <T> Move(T&) {}
    struct Thing {};
    Thing foo(const Thing* p) { return Thing(Move(*p)); }

... generates these diagnostics from g++ 4.6.1 in c++0x/gnu++0x mode, but not
in c++98/gnu++98 mode:

t.cc: In function ‘Thing foo(const Thing*)’:
t.cc:4:50: error: call of overloaded ‘Thing(MoveRef<const Thing>)’ is ambiguous
t.cc:4:50: note: candidates are:
t.cc:3:8: note: constexpr Thing::Thing(const Thing&)
t.cc:3:8: note: constexpr Thing::Thing(Thing&&)

This is a regression from g++ 4.5.x and earlier.

[Bug c++/50442] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[mh+gcc at glandium dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

Mike Hommey <mh+gcc at glandium dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mh+gcc at glandium dot org

--- Comment #1 from Mike Hommey <mh+gcc at glandium dot org> 2011-09-17 06:21:28 UTC ---
More specifically, r178746 from SVN gcc-4_6-branch is affected, while r178501
from the same branch is not.

[Bug c++/50442] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

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

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

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-17 09:45:11 UTC ---
maybe the fix for PR 49267 then, Jason?

[Bug c++/50442] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-17 09:48:55 UTC ---
yep, confirmed that r178552 changed the behaviour

[Bug c++/50442] [4.6 regression] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011-09-17
            Version|4.6.1                       |4.6.2
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
            Summary|Constructing T from         |[4.6 regression]
                   |implicit conversion to T&   |Constructing T from
                   |ambiguous in C++0x mode,    |implicit conversion to T&
                   |not C++98                   |ambiguous in C++0x mode,
                   |                            |not C++98
     Ever Confirmed|0                           |1

[Bug c++/50442] [4.6 regression] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> 2011-09-17 22:35:15 UTC ---
Author: jason
Date: Sat Sep 17 22:35:10 2011
New Revision: 178932

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=178932
Log:
    PR c++/50442
    Revert:
    PR c++/49267
    * call.c (compare_ics): rvaluedness_matches_p can differ
    based on the source type, not just target.

Removed:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/rv-conv1.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/call.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog

[Bug c++/50442] [4.6 regression] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.2

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> 2011-09-17 22:35:48 UTC ---
Fixed by reverting the earlier patch.

[Bug c++/50442] [4.6 regression] Constructing T from implicit conversion to T& ambiguous in C++0x mode, not C++98

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50442

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2011-09-20 19:25:36 UTC ---
Author: jason
Date: Tue Sep 20 19:25:32 2011
New Revision: 179015

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=179015
Log:
    PR c++/50442
    * g++.dg/overload/ref-conv1.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/overload/ref-conv1.C
Modified:
    trunk/gcc/testsuite/ChangeLog