error[E0605]: non-primitive cast: `()` as `u32`
  --> $DIR/cast-from-nil.rs:12:21
   |
LL | fn main() { let u = (assert!(true) as u32); }
   |                     ^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` trait

error: aborting due to previous error

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