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Auto merge of #121679 - lcnr:opaque-wf-check-2, r=oli-obk

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stricter hidden type wf-check [based on #115008]

Original work by `@aliemjay` in #115008. A huge thanks to them for originally figuring out this approach ❤️

Fixes https://github.com/rust-lang/rust/issues/114728
Fixes https://github.com/rust-lang/rust/issues/114572

Instead of adding the `WellFormed` obligations when relating opaque types, we now always emit such an obligation when defining the hidden type.

This causes nested opaque types which aren't wf to error, see the comment below for the described impact. I believe this change to be desirable as it significantly reduces complexity by removing special-cases.

It also caused an issue with RPITIT: in defaulted trait methods, we add a `Projection(synthetic_assoc, rpit_of_trait_method)` clause to the `param_env`. This clause is not added to the `ParamEnv` of the nested coroutines. This caused a normalization failure in `fn check_coroutine_obligations` with the new solver. I fixed that by using the env of the typeck root instead.

r? `@oli-obk`
This commit is contained in:
bors 2024-03-06 10:04:26 +00:00
commit 09bc67b915
21 changed files with 313 additions and 136 deletions
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19
compiler/rustc_infer/src/infer/opaque_types.rs
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@ -592,8 +592,25 @@ impl<'tcx> InferCtxt<'tcx> {
obligations: &mut Vec<PredicateObligation<'tcx>>,
) {
let tcx = self.tcx;
let item_bounds = tcx.explicit_item_bounds(def_id);
// Require that the hidden type is well-formed. We have to
// make sure we wf-check the hidden type to fix #114728.
//
// However, we don't check that all types are well-formed.
// We only do so for types provided by the user or if they are
// "used", e.g. for method selection.
//
// This means we never check the wf requirements of the hidden
// type during MIR borrowck, causing us to infer the wrong
// lifetime for its member constraints which then results in
// unexpected region errors.
obligations.push(traits::Obligation::new(
tcx,
cause.clone(),
param_env,
ty::ClauseKind::WellFormed(hidden_ty.into()),
));
let item_bounds = tcx.explicit_item_bounds(def_id);
for (predicate, _) in item_bounds.iter_instantiated_copied(tcx, args) {
let predicate = predicate.fold_with(&mut BottomUpFolder {
tcx,