error[E0308]: mismatched types
  --> $DIR/not-matching-trait-refs-isnt-defining.rs:17:54
   |
LL |     type Assoc = impl Sized;
   |                  ---------- the expected opaque type
...
LL |         let _: <Self as Foo<DefinesOpaque>>::Assoc = "";
   |                -----------------------------------   ^^ expected opaque type, found `&str`
   |                |
   |                expected due to this
   |
   = note: expected opaque type `<() as Foo<DefinesOpaque>>::Assoc`
                found reference `&'static str`
note: this item must have the opaque type in its signature in order to be able to register hidden types
  --> $DIR/not-matching-trait-refs-isnt-defining.rs:16:8
   |
LL |     fn test() -> <() as Foo<NoOpaques>>::Assoc {
   |        ^^^^

error: aborting due to previous error

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