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Rollup merge of #92191 - jackh726:issue-89352, r=nikomatsakis

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Prefer projection candidates instead of param_env candidates for Sized predicates

Fixes #89352

Also includes some drive by logging and verbose printing changes that I found useful when debugging this, but I can remove this if needed.

This is a little hacky - but imo no more than the rest of `candidate_should_be_dropped_in_favor_of`. Importantly, in a Chalk-like world, both candidates should be completely compatible.

r? ```@nikomatsakis```
This commit is contained in:
Matthias Krüger 2022-01-15 02:25:14 +01:00 • committed by GitHub
commit 64716825b0
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13 changed files with 84 additions and 34 deletions
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9
compiler/rustc_trait_selection/src/traits/project.rs
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@ -1225,6 +1225,10 @@ fn assemble_candidates_from_object_ty<'cx, 'tcx>(
);
}
#[tracing::instrument(
level = "debug",
skip(selcx, candidate_set, ctor, env_predicates, potentially_unnormalized_candidates)
)]
fn assemble_candidates_from_predicates<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
@ -1233,8 +1237,6 @@ fn assemble_candidates_from_predicates<'cx, 'tcx>(
env_predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
potentially_unnormalized_candidates: bool,
) {
debug!(?obligation, "assemble_candidates_from_predicates");
let infcx = selcx.infcx();
for predicate in env_predicates {
debug!(?predicate);
@ -1270,13 +1272,12 @@ fn assemble_candidates_from_predicates<'cx, 'tcx>(
}
}
#[tracing::instrument(level = "debug", skip(selcx, obligation, candidate_set))]
fn assemble_candidates_from_impls<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
) {
debug!("assemble_candidates_from_impls");
// If we are resolving `<T as TraitRef<...>>::Item == Type`,
// start out by selecting the predicate `T as TraitRef<...>`:
let poly_trait_ref = ty::Binder::dummy(obligation.predicate.trait_ref(selcx.tcx()));