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Rollup merge of #92006 - oli-obk:welcome_opaque_types_into_the_fold, r=nikomatsakis

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Welcome opaque types into the fold

r? ```@nikomatsakis``` because idk who else to bug on the type_op changes

The commits have explanations in them. The TLDR is that

* 5c46002273 stops the "recurse and replace" scheme that replaces opaque types with their canonical inference var by just doing that ahead of time
* bdeeb07bf6 does not affect anything on master afaict, but since opaque types generate obligations when instantiated, and lazy TAIT instantiates opaque types *everywhere*, we need to properly handle obligations here instead of just hoping no problematic obligations ever come up.
This commit is contained in:
Matthias Krüger 2022-01-13 08:11:19 +01:00 • committed by GitHub
commit b45a819bef
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4 changed files with 61 additions and 80 deletions
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20
compiler/rustc_infer/src/infer/opaque_types.rs
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@ -551,6 +551,22 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
let predicate = predicate.subst(tcx, substs);
debug!(?predicate);
let predicate = predicate.fold_with(&mut BottomUpFolder {
tcx,
ty_op: |ty| match *ty.kind() {
// Replace all other mentions of the same opaque type with the hidden type,
// as the bounds must hold on the hidden type after all.
ty::Opaque(def_id2, substs2) if def_id == def_id2 && substs == substs2 => {
ty_var
}
// Instantiate nested instances of `impl Trait`.
ty::Opaque(..) => self.instantiate_opaque_types_in_map(ty),
_ => ty,
},
lt_op: |lt| lt,
ct_op: |ct| ct,
});
// We can't normalize associated types from `rustc_infer`, but we can eagerly register inference variables for them.
let predicate = predicate.fold_with(&mut BottomUpFolder {
tcx,
@ -575,10 +591,6 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
return tcx.ty_error();
}
}
// Change the predicate to refer to the type variable,
// which will be the concrete type instead of the opaque type.
// This also instantiates nested instances of `impl Trait`.
let predicate = self.instantiate_opaque_types_in_map(predicate);
let cause =
traits::ObligationCause::new(self.value_span, self.body_id, traits::OpaqueType);