error[E0391]: cycle detected when computing layout of `S`
   |
   = note: ...which requires computing layout of `std::option::Option<<S as Mirror>::It>`...
   = note: ...which requires computing layout of `std::option::Option<S>`...
   = note: ...which again requires computing layout of `S`, completing the cycle
   = note: cycle used when computing layout of `std::option::Option<S>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0391`.