error[E0038]: the trait `A` is not dyn compatible
  --> $DIR/dyn-incompatible-trait-should-use-self.rs:2:13
   |
LL |     fn f(a: dyn A) -> dyn A;
   |             ^^^^^ `A` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/dyn-incompatible-trait-should-use-self.rs:1:10
   |
LL | trait A: Sized {
   |       -  ^^^^^ ...because it requires `Self: Sized`
   |       |
   |       this trait is not dyn compatible...
help: you might have meant to use `Self` to refer to the implementing type
   |
LL -     fn f(a: dyn A) -> dyn A;
LL +     fn f(a: Self) -> dyn A;
   |

error[E0038]: the trait `B` is not dyn compatible
  --> $DIR/dyn-incompatible-trait-should-use-self.rs:6:13
   |
LL |     fn f(a: dyn B) -> dyn B;
   |             ^^^^^ `B` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/dyn-incompatible-trait-should-use-self.rs:6:8
   |
LL | trait B {
   |       - this trait is not dyn compatible...
LL |     fn f(a: dyn B) -> dyn B;
   |        ^ ...because associated function `f` has no `self` parameter
help: consider turning `f` into a method by giving it a `&self` argument
   |
LL |     fn f(&self, a: dyn B) -> dyn B;
   |          ++++++
help: alternatively, consider constraining `f` so it does not apply to trait objects
   |
LL |     fn f(a: dyn B) -> dyn B where Self: Sized;
   |                             +++++++++++++++++
help: you might have meant to use `Self` to refer to the implementing type
   |
LL -     fn f(a: dyn B) -> dyn B;
LL +     fn f(a: Self) -> dyn B;
   |

error: aborting due to 2 previous errors

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