Confusing suggestion when E0719 and E0191 occur at the same time.

[jendrikw]

Given the following code: play

trait A {
    type X;
}

trait B: A {
    type X; // note: this is legal
}

impl<X> Clone for Box<dyn B<X=X, X=X>> {
    fn clone(&self) -> Self {
        todo!()
    }
}

The current output is:

error[E0719]: the value of the associated type `X` (from trait `B`) is already specified
 --> src/lib.rs:9:34
  |
9 | impl<X> Clone for Box<dyn B<X=X, X=X>> {
  |                             ---  ^^^ re-bound here
  |                             |
  |                             `X` bound here first

error[E0191] the value of the associated type `X` (from trait `A`) must be specified
 --> src/lib.rs:9:27
  |
2 |     type X;
  |     ------- `X` defined here
...
9 | impl<X> Clone for Box<dyn B<X=X, X=X>> {
  |                           ^^^^^^^^^^^ help: specify the associated type: `B<X=X, X=X, X = Type>`

B<X=X, X=X, X = Type> is wrong, specifying another X=Type isn't going to fix the problem.

Writing just dyn B has a suggestion consider introducing a new type parameter, adding `where` constraints using the fully-qualified path to the associated types, which is good, but the concrete syntax would be nice.

[compiler-errors]

We probably should modify E0191 to hint that an supertrait's associated type is shadowed. I think E0719 here is fine to keep as-is, imo.

[jendrikw]

I agree the message for E0719 is good as-is.

[Abhicodes-crypto]

Is this issue fixed ? If not can I take this up, please.
Also how exactly should E0191 be modified. Imo, I don't think E0191 should pop up in this case as E0719 conveys the message. @compiler-errors

[Abhicodes-crypto]

@rustbot claim

[LittleFall]

@rustbot claim

[LittleFall]

Ask for help：
How do I specify the association type of supertrait with the same name? In other words, is there an easy way to modify the code in the issue to make it pass compilation?

Here's my clumsy way of creating a new trait.

trait A {
    type X;
}

trait B: A {
    type X; // note: this is legal
}

trait BP<P, Q>: A<X = P> + B<X = Q> {}

impl<T> Clone for Box<dyn BP<T, T>> {
    fn clone(&self) -> Self {
        todo!()
    }
}

fn main() {
    let v: Box<dyn BP<(), ()>>;
}