error[E0308]: mismatched types
  --> $DIR/unsize_adt.rs:8:30
   |
LL | fn hello() -> Foo<[impl Sized; 2]> {
   |                    ---------- the found opaque type
...
LL |         let _: &Foo<[i32]> = &x;
   |                -----------   ^^ expected `&Foo<[i32]>`, found `&Foo<[impl Sized; 2]>`
   |                |
   |                expected due to this
   |
   = note: expected reference `&Foo<[i32]>`
              found reference `&Foo<[impl Sized; 2]>`

error: aborting due to 1 previous error

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