Function is_ty_fully_unsafe_celled 

fn is_ty_fully_unsafe_celled<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool

Checks that a Ty fully covered by one or more UnsafeCell.

This checks excludes ZST and PhantomData.

This check is an approximation and can return false for spurious reasons, but true is dependable.