error[E0391]: unsupported cyclic reference between types/traits detected
  |
note: the cycle begins when computing layout of `S`...
note: ...which then requires computing layout of `std::option::Option<<S as Mirror>::It>`...
note: ...which then requires computing layout of `<S as Mirror>::It`...
  = note: ...which then again requires computing layout of `S`, completing the cycle.

error: aborting due to previous error