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Auto merge of #101679 - compiler-errors:rpitit-default-body, r=nikomatsakis

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Support default-body trait functions with return-position `impl Trait` in traits

Introduce a new `Trait` candidate kind for the `ImplTraitInTrait` projection candidate, which just projects an RPITIT down to its opaque type form.

This is a hack until we lower RPITITs to regular associated types, after which we will need to rework how these default bodies are type-checked, so comments are left in a few places for us to clean up later.

Fixes #101665
This commit is contained in:
bors 2022-10-12 21:03:47 +00:00
commit 0938e1680d
14 changed files with 166 additions and 129 deletions
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16
compiler/rustc_privacy/src/lib.rs
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@ -122,8 +122,20 @@ where
&mut self,
projection: ty::ProjectionTy<'tcx>,
) -> ControlFlow<V::BreakTy> {
let (trait_ref, assoc_substs) =
projection.trait_ref_and_own_substs(self.def_id_visitor.tcx());
let tcx = self.def_id_visitor.tcx();
let (trait_ref, assoc_substs) = if tcx.def_kind(projection.item_def_id)
!= DefKind::ImplTraitPlaceholder
{
projection.trait_ref_and_own_substs(tcx)
} else {
// HACK(RPITIT): Remove this when RPITITs are lowered to regular assoc tys
let def_id = tcx.impl_trait_in_trait_parent(projection.item_def_id);
let trait_generics = tcx.generics_of(def_id);
(
ty::TraitRef { def_id, substs: projection.substs.truncate_to(tcx, trait_generics) },
&projection.substs[trait_generics.count()..],
)
};
self.visit_trait(trait_ref)?;
if self.def_id_visitor.shallow() {
ControlFlow::CONTINUE