[Bug c++/68731] New: [concepts] ICE when referencing struct type in specialization

[ryan.burn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68731

            Bug ID: 68731
           Summary: [concepts] ICE when referencing struct type in
                    specialization
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ryan.burn at gmail dot com
  Target Milestone: ---

The below code segfaults with g++ 20151123

///////////////////////////////////////////////////////////////
template <class T>
struct a_type {
};

template <class T>
  requires !requires { typename a_type<T>::type; }
struct a_type<T> {
  using type = T;
};

int main() {
  a_type<int> a;
  return 0;
}
///////////////////////////////////////////////////////////////