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d163e5e515
Check alias args for WF even if they have escaping bound vars
#### What
This PR stops skipping arguments of aliases if they have escaping bound vars, instead recursing into them and only discarding the resulting obligations referencing bounds vars.
#### An example:
From the test:
```
trait Trait {
type Gat<U: ?Sized>;
}
fn test<T>(f: for<'a> fn(<&'a T as Trait>::Gat<&'a [str]>)) where for<'a> &'a T: Trait {}
//~^ ERROR the size for values of type `[()]` cannot be known at compilation time
fn main() {}
```
We now prove that `str: Sized` in order for `&'a [str]` to be well-formed. We were previously unconditionally skipping over `&'a [str]` as it referenced a buond variable. We now recurse into it and instead only discard the `[str]: 'a` obligation because of the escaping bound vars.
#### Why?
This is a change that improves consistency about proving well-formedness earlier in the pipeline, which is necessary for future work on where-bounds in binders and correctly handling higher-ranked implied bounds. I don't expect this to fix any unsoundness.
#### What doesn't it fix?
Specifically, this doesn't check projection predicates' components are well-formed, because there are too many regressions: https://github.com/rust-lang/rust/pull/123737#issuecomment-2052198478
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|---|---|---|
| .. | ||
| leak-check | ||
| subtype | ||
| trait-bounds | ||
| builtin-closure-like-bounds.rs | ||
| closure-bound-codegen-ice.rs | ||
| erroneous-lifetime-bound.rs | ||
| erroneous-lifetime-bound.stderr | ||
| higher-lifetime-bounds.rs | ||
| higher-lifetime-bounds.stderr | ||
| higher-ranked-lifetime-equality.rs | ||
| higher-ranked-lifetime-equality.stderr | ||
| higher-ranked-lifetime-error.rs | ||
| higher-ranked-lifetime-error.stderr | ||
| structually-relate-aliases.rs | ||
| structually-relate-aliases.stderr | ||
| well-formed-aliases.rs | ||
| well-formed-aliases.stderr | ||