diagnostics: suggest "Self::" on missing type not found in trait definition

[matthiaskrgr]

trait A {
    type Bla;
    fn to_bla(&self) -> Bla;
}

yields

error[E0412]: cannot find type `Bla` in this scope
 --> src/main.rs:3:25
  |
3 |     fn to_bla(&self) -> Bla;
  |                         ^^^ not found in this scope

error: aborting due to previous error

it would be helpful to suggest to change the to_bla return type to Self::Bla; which fixes the error:

trait A {
    type Bla;
    fn to_bla(&self) -> Self::Bla;
}

fn main() {}

[matthiaskrgr]

@rustbot modify labels: A-diagnostics