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EXPERIMENT: Assemble inherent pick for trait blanket impl #128560

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EXPERIMENT: Assemble inherent pick for trait blanket impl #128560

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37 changes: 36 additions & 1 deletion compiler/rustc_hir_typeck/src/method/probe.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,7 @@ pub(crate) enum CandidateKind<'tcx> {
InherentImplCandidate(DefId),
ObjectCandidate(ty::PolyTraitRef<'tcx>),
TraitCandidate(ty::PolyTraitRef<'tcx>),
TraitImplSelfCandidate(ty::TraitRef<'tcx>),
WhereClauseCandidate(ty::PolyTraitRef<'tcx>),
}

Expand Down Expand Up @@ -648,6 +649,24 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
for step in self.steps.iter() {
self.assemble_probe(&step.self_ty);
}

// HACK:
// Assemble an "inherent" candidate for the self type of the impl we're inside of.
if let Some(own_item) =
self.tcx.opt_associated_item(self.tcx.typeck_root_def_id(self.body_id.to_def_id()))
&& let ty::AssocItemContainer::ImplContainer = own_item.container
&& let Some(trait_ref) = self.tcx.impl_trait_ref(own_item.container_id(self.tcx))
&& let trait_ref = trait_ref.instantiate_identity()
&& matches!(trait_ref.self_ty().kind(), ty::Param(_))
{
for item in self.impl_or_trait_item(trait_ref.def_id) {
self.inherent_candidates.push(Candidate {
item,
import_ids: smallvec![],
kind: TraitImplSelfCandidate(trait_ref),
})
}
}
}

#[instrument(level = "debug", skip(self))]
Expand Down Expand Up @@ -1381,7 +1400,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
InherentImplCandidate(_) => {
CandidateSource::Impl(candidate.item.container_id(self.tcx))
}
ObjectCandidate(_) | WhereClauseCandidate(_) => {
ObjectCandidate(_) | WhereClauseCandidate(_) | TraitImplSelfCandidate(_) => {
CandidateSource::Trait(candidate.item.container_id(self.tcx))
}
TraitCandidate(trait_ref) => self.probe(|_| {
Expand Down Expand Up @@ -1467,6 +1486,18 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
impl_bounds,
));
}
TraitImplSelfCandidate(trait_ref) => {
(xform_self_ty, xform_ret_ty) =
self.xform_self_ty(probe.item, trait_ref.self_ty(), trait_ref.args);
xform_self_ty = ocx.normalize(cause, self.param_env, xform_self_ty);
match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
Ok(()) => {}
Err(err) => {
debug!("--> cannot relate self-types {:?}", err);
return ProbeResult::NoMatch;
}
}
}
TraitCandidate(poly_trait_ref) => {
// Some trait methods are excluded for arrays before 2021.
// (`array.into_iter()` wants a slice iterator for compatibility.)
Expand Down Expand Up @@ -1946,6 +1977,10 @@ impl<'tcx> Candidate<'tcx> {
InherentImplCandidate(_) => InherentImplPick,
ObjectCandidate(_) => ObjectPick,
TraitCandidate(_) => TraitPick,

// HACK:
TraitImplSelfCandidate(w) => WhereClausePick(ty::Binder::dummy(w)),

WhereClauseCandidate(trait_ref) => {
// Only trait derived from where-clauses should
// appear here, so they should not contain any
Expand Down