[Bug c++/59173] New: Alias template in partial specialization finds name from primary template

["jhs at edg dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59173

            Bug ID: 59173
           Summary: Alias template in partial specialization finds name
                    from primary template
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jhs at edg dot com

In code such as the following, which is present in the <ext/extptr_allocator.h>
and <ext/pointer.h> headers, the type in the alias template definition finds
the rebind from the primary template.  The correct behavior is to give an error
because "rebind<_Up>" should be preceded by the "template" keyword for
syntactic disambiguation.

This is also a defect in those two headers as the template keyword should be
added there.

template<typename _Ptr>
struct pointer_traits
{
  template<typename _Up> struct rebind {};
};

template<typename T> struct P {};

template<typename T>
struct pointer_traits<P<T> >
{
  template<typename _Up>
     using rebind = P<typename pointer_traits<T>::rebind<_Up>>;
};