chalkify: Fix lowering of traits with supertraits

[tmandry]

Fixes #49953.

A little ugly, but also temporary 😃

[rust-highfive]

r? @cramertj

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[tmandry]

r? @nikomatsakis

[scalexm]

It seems like this would also skip a predicate of the form:

trait A where <Self as A>::Item: A {
    type Item;
}

or equivalently:

trait A {
    type Item: A;
}

since you are only relying on the def id. Actually maybe it would be better to just wait for your PR which removes the Self: Trait predicate...

[tmandry]

Ah, good catch. I'll try and make progress on that PR today. A patch that might possibly still work here is to filter out only the first predicate that matches this condition, but it still feels quite brittle!

[emilyalbini]

Thanks for the PR! Can @nikomatsakis or someone else from @rust-lang/compiler review this?

[oli-obk]

This is blocked on another PR. @tmandry can you link the PR here?

[tmandry]

It's still very much a WIP but I made one, #50183. This PR might be closed in favor of that one.

[bors]

☔ The latest upstream changes (presumably #49837) made this pull request unmergeable. Please resolve the merge conflicts.

[tmandry]

Closing in favor of #51895.