[Bug c++/60019] New: [C++11] Bogus error: use of deleted function unique_ptr(const unique_ptr&)

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60019

            Bug ID: 60019
           Summary: [C++11] Bogus error: use of deleted function
                    unique_ptr(const unique_ptr&)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com

Google ref: b/12846752

Test:

#include <memory>
struct S {};
struct T : S {};

std::unique_ptr<T> F();
const std::unique_ptr<S> s = F();


Using recent trunk:
g++ (GCC) 4.9.0 20140129 (experimental)

t.cc:6:32: error: use of deleted function ‘std::unique_ptr<_Tp,
_Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = S; _Dp =
std::default_delete<S>]’
 const std::unique_ptr<S> s = F();
                                ^


There is a copy constructor in unique_ptr.h that
I believe is supposed to apply here:

      /** @brief Converting constructor from another type
       *
       * Requires that the pointer owned by @p __u is convertible to the
       * type of pointer owned by this object, @p __u does not own an array,
       * and @p __u has a compatible deleter type.
       */
      template<typename _Up, typename _Ep, typename = _Require<
               is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>,
               __not_<is_array<_Up>>,
               typename conditional<is_reference<_Dp>::value,
                                    is_same<_Ep, _Dp>,
                                    is_convertible<_Ep, _Dp>>::type>>
        unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
        : _M_t(__u.release(), std::forward<_Ep>(__u.get_deleter()))
        { }

but for some reason it doesn't kick in.

(Code builds fine under Clang.)