[Bug libstdc++/16021] New: Tests for container swap specialisations FAIL in debug mode

["redi at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

All testsuite/23_containers/*/modifiers/swap.cc files FAIL to compile
when _GLIBCXX_DEBUG is defined.

The following code is adapted from the testsuite:

    #define _GLIBCXX_DEBUG
    #include <vector>

    struct T { int i; };

    int swap_calls;

    namespace std
    {
      template<>
        void
        vector<T, allocator<T> >::swap(vector<T, allocator<T> >&)
        { ++swap_calls; }
    }

    // Should use vector specialization for swap.
    int main()
    {
      std::vector<T> A;
      std::vector<T> B;
      swap_calls = 0;
      std::swap(A, B);
      return swap_calls;
    }

Compiling this gives:

swap.cc:12: error: `allocator' was not declared in this scope
swap.cc:12: error: template argument 2 is invalid
swap.cc:12: error: variable or field `swap' declared void
swap.cc:12: error: `int __gnu_debug_def::vector<T, std::allocator<T> >::swap' is
 not a static member of `class __gnu_debug_def::vector<T, std::allocator<T> >'
swap.cc:12: error: expected primary-expression before ')' token
swap.cc:13: error: expected `;' before '{' token

The same error happens for all containers on 3.4 and mainline.

The diagnostic is confusing, it first says allocator is not found, then
identifies it as std::allocator in another diagnostic that seems to think
the member function is static.

A solution is to qualify allocator as std::allocator, but this shouldn't
be necessary because _GLIBCXX_DEBUG shouldn't change the meaning of any
conforming program.

I *think* what might be happening is that in debug mode the "std"
namespace is really "__gnu_debug" and the (non-debug) standard library
is really in "_GLIBCXX_STD". This means that the unqualified name
"allocator" looks up in __gnu_debug and the global namespace, and so
doesn't find "_GLIBCXX_STD::allocator". But I don't think I've got that
quite right.

-- 
           Summary: Tests for container swap specialisations FAIL in debug
                    mode
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: redi at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16021