[Bug c++/54890] New: Incorrect SFINAE Rejection

[Bug c++/54890] New: Incorrect SFINAE Rejection

[pmenso57 at comcast dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

             Bug #: 54890
           Summary: Incorrect SFINAE Rejection
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pmenso57@comcast.net


When explicitly specifying the template parameters to a function template in
the following context, the compiler incorrectly removes the function from the
overload set for a substitution failure which should not exist.

struct A {
    template<class T> struct apply { };
};

template<class T, class... U>
void f(typename T::template apply<U...>*) { }

int main() {
    f<A, int>(nullptr);
    return 0;
}

Output from the compiler is:

In function ‘int main()’:
error: no matching function for call to ‘f(std::nullptr_t)’
note: candidate is:
note: template<class T, class ... U> void f(typename T::apply<U ...>*)
note:   template argument deduction/substitution failed:
note:   mismatched types ‘A::apply<U ...>*’ and ‘std::nullptr_t’

Which I believe is incorrect.

[Bug c++/54890] Incorrect SFINAE Rejection

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-10-10
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-10-10 16:00:31 UTC ---
Confirmed. Honestly, I don't think the issue has much to do with SFINAE, but
anyway seems easy to fix.

[Bug c++/54890] Incorrect SFINAE Rejection

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.8.0

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-10-10 16:20:16 UTC ---
On it.

[Bug c++/54890] Incorrect SFINAE Rejection

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|paolo.carlini at oracle dot |unassigned at gcc dot
                   |com                         |gnu.org

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-10-10 17:32:16 UTC ---
Nope, I don't have a fix forthcoming, sorry.

I thought something was wrong in unify, because NULLPTR_TYPE isn't explicitly
handled, but actually I think this should work for 0 too, not just for nullptr
(indeed, for non-variadic it does already)

[Bug c++/54890] Incorrect SFINAE Rejection

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.0                       |4.8.1

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-22 14:45:50 UTC ---
GCC 4.8.0 is being released, adjusting target milestone.

[Bug c++/54890] Incorrect SFINAE Rejection

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.1                       |4.8.2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.1 has been released.

[Bug c++/54890] Incorrect SFINAE Rejection

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.2                       |4.8.3

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.2 has been released.

[Bug c++/54890] Incorrect SFINAE Rejection

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |UNCONFIRMED
     Ever confirmed|1                           |0

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Uhm, I note that both current clang and icc reject this.

[Bug c++/54890] Incorrect SFINAE Rejection

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

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

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

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Jason, can you help me (re-)triaging this?

[Bug c++/54890] Incorrect SFINAE Rejection

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ville.voutilainen at gmail dot com

--- Comment #9 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Ping. I don't know what to make of this. The code looks reasonable, but both
gcc and clang reject it, failing deduction.

[Bug c++/54890] [DR 1982] Incorrect SFINAE Rejection

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54890

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID
            Summary|Incorrect SFINAE Rejection  |[DR 1982] Incorrect SFINAE
                   |                            |Rejection

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> ---
This is 

http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_toc.html#1982

which was closed at the Urbana meeting.