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Auto merge of #17939 - ShoyuVanilla:maybe-sized-fix, r=Veykril

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fix: Wrong `Sized` predicate for `generic_predicates_for_param`

I found this gathers wrong `Self: Sized` bound while implementing object safety, though I couldn't find proper test for this.

If we call `generic_predicates_for_param` to `Bar` in the following code;
```rust
trait Foo<T: ?Sized> {}
trait Bar<T: Foo<Self> + ?Sized> {}
```
it returns `T: Sized` and `Self: Sized` bound, because normaly, the `?Sized` bound applied properly in L1059 with;
3723e5910c/crates/hir-ty/src/lower.rs (L1035-L1061)

But we filter them before it is lowered with that function here;

3723e5910c/crates/hir-ty/src/lower.rs (L1540-L1586)

So, the `?Sized` bounded params are not gathered into `ctx.unsized_types` and thus we are applying them implicit `Sized` bound here;

3723e5910c/crates/hir-ty/src/lower.rs (L1591-L1602)
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bors 2024-08-22 08:38:27 +00:00
commit 011e3bb9ac
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4
crates/hir-ty/src/lower.rs
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@ -1551,6 +1551,10 @@ pub(crate) fn generic_predicates_for_param_query(
}
};
if invalid_target {
// If this is filtered out without lowering, `?Sized` is not gathered into `ctx.unsized_types`
if let TypeBound::Path(_, TraitBoundModifier::Maybe) = &**bound {
ctx.lower_where_predicate(pred, &def, true).for_each(drop);
}
return false;
}