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Rollup merge of #114267 - compiler-errors:rpitit-opaque-bounds, r=spastorino

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Map RPITIT's opaque type bounds back from projections to opaques

An RPITIT in a program's AST is eventually translated into both a projection GAT and an opaque. The opaque is used for default trait methods, like:

```
trait Foo {
  fn bar() -> impl Sized { 0i32 }
}
```

The item bounds for both the projection and opaque are identical, and both have a *projection* self ty. This is mostly okay, since we can normalize this projection within the default trait method body to the opaque, but it does two things:
1. it leads to bugs in places where we don't normalize item bounds, like `deduce_future_output_from_obligations`
2. it leads to extra match arms that are both suspicious looking and also easy to miss

This PR maps the opaque type bounds of the RPITIT's *opaque* back to the opaque's self type to avoid this quirk. Then we can fix the UI test for #108304 (1.) and also remove a bunch of match arms (2.).

Fixes #108304

r? `@spastorino`
This commit is contained in:
Matthias Krüger 2023-07-31 16:57:55 +02:00 • committed by GitHub
commit 692d764e53
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9 changed files with 54 additions and 72 deletions
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13
compiler/rustc_middle/src/ty/mod.rs
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@ -2625,19 +2625,6 @@ impl<'tcx> TyCtxt<'tcx> {
matches!(self.trait_of_item(def_id), Some(trait_id) if self.has_attr(trait_id, sym::const_trait))
}
pub fn impl_trait_in_trait_parent_fn(self, mut def_id: DefId) -> DefId {
match self.opt_rpitit_info(def_id) {
Some(ImplTraitInTraitData::Trait { fn_def_id, .. })
| Some(ImplTraitInTraitData::Impl { fn_def_id, .. }) => fn_def_id,
None => {
while let def_kind = self.def_kind(def_id) && def_kind != DefKind::AssocFn {
def_id = self.parent(def_id);
}
def_id
}
}
}
/// Returns the `DefId` of the item within which the `impl Trait` is declared.
/// For type-alias-impl-trait this is the `type` alias.
/// For impl-trait-in-assoc-type this is the assoc type.