error[E0277]: the trait bound `dyn Foo: CastTo<[i32]>` is not satisfied
  --> $DIR/issue-71659.rs:30:15
   |
LL |     let x = x.cast::<[i32]>();
   |               ^^^^ the trait `CastTo<[i32]>` is not implemented for `dyn Foo`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.