error[E0038]: the trait `Foo` cannot be made into an object
  --> $DIR/object-safety-err-ret.rs:17:16
   |
LL | fn use_dyn(v: &dyn Foo) {
   |                ^^^^^^^ `Foo` cannot be made into an object
   |
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> $DIR/object-safety-err-ret.rs:8:8
   |
LL | trait Foo {
   |       --- this trait cannot be made into an object...
LL |     fn test(&self) -> [u8; bar::<Self>()];
   |        ^^^^           ^^^^^^^^^^^^^^^^^^^ ...because method `test` references the `Self` type in its return type
   |        |
   |        ...because method `test` references the `Self` type in its `where` clause
   = help: consider moving `test` to another trait
   = help: only type `()` implements the trait, consider using it directly instead

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0038`.