[Bug c++/51989] New: std::deque::iterator recognised as container

[Bug c++/51989] New: std::deque::iterator recognised as container

[leonid at volnitsky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

             Bug #: 51989
           Summary: std::deque::iterator recognised as container
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: leonid@volnitsky.com


Created attachment 26450
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26450
deque-bug.cc

I need is_container<T> template which would recognize if T is a container. 
Code below works as expected.  With exception for std::deque::iterator -  gcc
can not compile code below:

------------------------------------------------------------------
#include <iostream>
#include <type_traits>
#include <vector>
#include <list>
#include <set>
#include <deque>

    template <typename T>
struct is_container {
    template <typename U>
    static char test(
        U* u,
        typename U::const_iterator b = ((U*)0)->begin(),
        typename U::const_iterator e = ((U*)0)->end()
    );
    template <typename U> static long test(...);

    enum { value = sizeof test<T>(0) == 1 };
};

int main() {
    std::cout <<  "void\t"            << is_container< void            
>::value << '\n';
    std::cout <<  "int\t"            << is_container< int              >::value
<< '\n';
    std::cout <<  "int*\t"            << is_container< int*            
>::value << '\n';
    std::cout <<  "vector<int>\t"        << is_container< std::vector<int>
>::value << '\n';
    std::cout <<  "deque<int>\t"        << is_container< std::deque<int> 
>::value << '\n';
    std::cout <<  "set<int>::iterator\t"    << is_container<
std::set<int>::iterator >::value << '\n';
    std::cout <<  "vector<int>::iterator\t"    << is_container<
std::vector<int>::iterator >::value << '\n';

    // gcc error
    std::cout <<  "deque<int>::iterator\t"    << is_container<
std::deque<int>::iterator >::value << '\n';
}
-----------------------------------------------------------------------

Compiling it with GCC (4.7.0-alpha20111203):

gcc -std=gnu++0x -Wall deque-bug.cc   -o deque-bug

Produce following error:

deque-bug.cc: In instantiation of ‘struct
is_container<std::_Deque_iterator<int, int&, int*> >’:
deque-bug.cc:31:84:   required from here
deque-bug.cc:18:7: error: ‘struct std::_Deque_iterator<int, int&, int*>’ has no
member named ‘begin’
deque-bug.cc:18:7: error: ‘struct std::_Deque_iterator<int, int&, int*>’ has no
member named ‘end’

Attached are source and -save-temps

[Bug c++/51989] std::deque::iterator recognised as container

[leonid at volnitsky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #1 from Leonid Volnitsky <leonid at volnitsky dot com> 2012-01-25 05:03:14 UTC ---
Created attachment 26451
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26451
deque-bug.ii

[Bug c++/51989] std::deque::iterator recognised as container

[leonid at volnitsky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #2 from Leonid Volnitsky <leonid at volnitsky dot com> 2012-01-25 05:04:00 UTC ---
Created attachment 26452
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26452
deque-bug.s

[Bug c++/51989] std::deque::iterator recognised as container

[leonid at volnitsky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #3 from Leonid Volnitsky <leonid at volnitsky dot com> 2012-01-25 05:04:56 UTC ---
Created attachment 26453
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26453
gcc error

[Bug c++/51989] std::deque::iterator recognised as container

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-25 09:48:32 UTC ---
not a gcc bug, you're code is invalid - values of default arguments are not
part of the function type and do not take part in deduction

you can do it in C++11 with decltype

[Bug c++/51989] std::deque::iterator recognised as container

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

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

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

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-25 09:55:25 UTC ---
However, I think it is a bug that this is rejected. 

template <typename T>
struct is_container {
    template <typename U, typename V = decltype(((U*)0)->begin())>
    static char test( U* u);

    template <typename U> static long test(...);

    enum { value = sizeof test<T>(0) == 1 };
};

int main() {
    return is_container< void >::value;
}

c.cc: In instantiation of ‘struct is_container<void>’:
c.cc:12:32:   required from here
c.cc:3:27: error: ‘void*’ is not a pointer-to-object type

Jason, shouldn't deduction fail for ((U*)0)->foo() with U=void instead of
giving an error?

[Bug c++/51989] std::deque::iterator recognised as container

[leonid at volnitsky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #6 from Leonid Volnitsky <leonid at volnitsky dot com> 2012-01-25 10:29:29 UTC ---
Also,  new is_container<T> with decltype, have value == 0 for any, non-void
type.

[Bug c++/51989] std::deque::iterator recognised as container

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-25 11:56:50 UTC ---
My code was only meant to show a possible problem with invalid expressions
using void* not to solve your issue.  GCC's bugzilla isn't a tutorial site and
"my code doesn't work" isn't a compiler bug.

[Bug c++/51989] std::deque::iterator recognised as container

[leonid at volnitsky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #8 from Leonid Volnitsky <leonid at volnitsky dot com> 2012-01-25 12:29:22 UTC ---
I understand that.  And thank you for giving me a hint and code for
is_container,  it was more than I expected if it was non-bug. I've made the
comment only because I've thought that it might help to diagnose the problem,
if there is a bug after all.

[Bug c++/51989] std::deque::iterator recognised as container

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-25 17:32:12 UTC ---
(In reply to comment #5)
> Jason, shouldn't deduction fail for ((U*)0)->foo() with U=void instead of
> giving an error?

Yep.  Need to pass complain into build_x_arrow.

[Bug c++/51989] std::deque::iterator recognised as container

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-01-25
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
     Ever Confirmed|0                           |1

--- Comment #10 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-01-25 20:29:07 UTC ---
Can do it.

[Bug c++/51989] std::deque::iterator recognised as container

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

--- Comment #11 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-03-02 16:18:34 UTC ---
Author: paolo
Date: Fri Mar  2 16:18:25 2012
New Revision: 184796

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=184796
Log:
/cp
2012-03-02  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/51989
    * typeck2.c (build_x_arrow): Take a tsubst_flags_t argument and
    propagate it.
    * cp-tree.h (build_x_arrow): Adjust prototype.
    * pt.c (tsubst_copy_and_build): Adjust call.
    * parser.c (cp_parser_postfix_dot_deref_expression): Likewise.

/testsuite
2012-03-02  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/51989
    * g++.dg/cpp0x/sfinae32.C: New.


Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/sfinae32.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/parser.c
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/typeck2.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/51989] std::deque::iterator recognised as container

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51989

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.8.0

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-24 12:12:51 UTC ---
Fixed for 4.8.0.