Associated types are not resolved in the IDE layer

[lnicola]

Like the T::S here:

trait D {}

trait Foo {
    type S;
}

trait Bar<T>
where
    T: Foo,
    T::S: D,
{
}

fn main() {}

CC #4991

Another one:

trait Foo {
    type Bar;

    fn foo(_: Self::Bar);
}

struct S;

impl Foo for S {
    type Bar = i32;

    fn foo(_: Self::Bar) {
        todo!()
    }
}

[flodiebold]

Not sure what you mean by "not resolved" here -- as far as I can see, e.g. within methods in Bar we can call methods of D on any T::S.

[lnicola]

Hmm, that's interesting. Yeah, it seems to work, but T::S shows up as unresolvedReference:

[flodiebold]

We don't handle this correctly in the IDE layer, that's true. Resolving T::S to the associated type happens during type lowering, which the IDE layer doesn't really access yet.

The type hint is correct, though we might consider displaying it differently. Since T::S doesn't normalize to any concrete type, it's represented as an associated type placeholder, which looks like this; but maybe we should display it as the projection <T as Foo>::S instead.

Actually both of these are a bit related to the type IR I've been working on slowly for a while, because I think it might also be the correct way to represent types for the IDE layer -- it would have T::S resolved, and it wouldn't have a representation of associated type placeholders (instead going back to it would convert them to projections)... 🤔

[mouse07410]

Thank you for working on this! Any idea what the time-frame for the incremental solution steps might be?

[lnicola]

#6387 fixed #5003 (comment), CC @bnjjj: