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Don't instantiate the binder twice when assembling object candidate

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This commit is contained in:
Michael Goulet 2023-11-06 23:41:25 +00:00
parent 24e14dd8b4
commit 171d5587ca
4 changed files with 45 additions and 17 deletions
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24
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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@ -628,18 +628,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}
self.infcx.probe(|_snapshot| {
// FIXME(non_lifetime_binders): Really, we care only to check that we don't
// have any non-region *escaping* bound vars, but that's hard to check and
// we shouldn't really ever encounter those anyways.
if obligation.self_ty().has_non_region_late_bound() {
return;
}
let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
let placeholder_trait_predicate =
self.infcx.instantiate_binder_with_placeholders(poly_trait_predicate);
// The code below doesn't care about regions, and the
// self-ty here doesn't escape this probe, so just erase
// any LBR.
let self_ty = self.tcx().erase_late_bound_regions(obligation.self_ty());
let poly_trait_ref = match self_ty.kind() {
let self_ty = placeholder_trait_predicate.self_ty();
let principal_trait_ref = match self_ty.kind() {
ty::Dynamic(ref data, ..) => {
if data.auto_traits().any(|did| did == obligation.predicate.def_id()) {
debug!(
@ -671,18 +665,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
_ => return,
};
debug!(?poly_trait_ref, "assemble_candidates_from_object_ty");
let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
let placeholder_trait_predicate =
self.infcx.instantiate_binder_with_placeholders(poly_trait_predicate);
debug!(?principal_trait_ref, "assemble_candidates_from_object_ty");
// Count only those upcast versions that match the trait-ref
// we are looking for. Specifically, do not only check for the
// correct trait, but also the correct type parameters.
// For example, we may be trying to upcast `Foo` to `Bar<i32>`,
// but `Foo` is declared as `trait Foo: Bar<u32>`.
let candidate_supertraits = util::supertraits(self.tcx(), poly_trait_ref)
let candidate_supertraits = util::supertraits(self.tcx(), principal_trait_ref)
.enumerate()
.filter(|&(_, upcast_trait_ref)| {
self.infcx.probe(|_| {