error[E0308]: mismatched types
  --> $DIR/upcast-wrong-substs.rs:9:30
   |
LL |     let y: &dyn Bar<usize> = x;
   |            ---------------   ^ expected trait `Bar`, found trait `Foo`
   |            |
   |            expected due to this
   |
   = note: expected reference `&dyn Bar<usize>`
              found reference `&dyn Foo`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.