error[E0307]: invalid `self` parameter type: `Bar`
  --> $DIR/arbitrary-self-opaque.rs:8:18
   |
LL |     fn foo(self: Bar) {}
   |                  ^^^
   |
   = note: type of `self` must be `Self` or a type that dereferences to it
   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)

error: item does not constrain `Bar::{opaque#0}`, but has it in its signature
  --> $DIR/arbitrary-self-opaque.rs:8:8
   |
LL |     fn foo(self: Bar) {}
   |        ^^^
   |
   = note: consider moving the opaque type's declaration and defining uses into a separate module
note: this opaque type is in the signature
  --> $DIR/arbitrary-self-opaque.rs:4:12
   |
LL | type Bar = impl Sized;
   |            ^^^^^^^^^^

error: unconstrained opaque type
  --> $DIR/arbitrary-self-opaque.rs:4:12
   |
LL | type Bar = impl Sized;
   |            ^^^^^^^^^^
   |
   = note: `Bar` must be used in combination with a concrete type within the same module

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0307`.