error[E0605]: non-primitive cast: `()` as `usize`
  --> $DIR/issue-10991.rs:3:14
   |
LL |     let _t = nil as usize;
   |              ^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0605`.