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Handle multiple applicable projection candidates

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This commit is contained in:
Matthew Jasper
2020-07-23 21:59:20 +01:00
parent bc08b791bc
commit cfee49593d
6 changed files with 82 additions and 37 deletions
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25
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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@@ -70,8 +70,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
Ok(ImplSource::AutoImpl(data))
}
ProjectionCandidate => {
let obligations = self.confirm_projection_candidate(obligation);
ProjectionCandidate(idx) => {
let obligations = self.confirm_projection_candidate(obligation, idx);
Ok(ImplSource::Param(obligations))
}
@@ -121,11 +121,22 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn confirm_projection_candidate(
&mut self,
obligation: &TraitObligation<'tcx>,
idx: usize,
) -> Vec<PredicateObligation<'tcx>> {
self.infcx.commit_unconditionally(|_| {
let candidate = self
.match_projection_obligation_against_definition_bounds(obligation)
.unwrap_or_else(|| bug!("Can't find selected projection candidate"));
let tcx = self.tcx();
let bound_self_ty = self.infcx.shallow_resolve(obligation.self_ty());
let (def_id, substs) = match bound_self_ty.skip_binder().kind {
ty::Projection(proj) => (proj.item_def_id, proj.substs),
ty::Opaque(def_id, substs) => (def_id, substs),
_ => bug!("projection candidate for unexpected type: {:?}", bound_self_ty),
};
let candidate_predicate = tcx.item_bounds(def_id)[idx].subst(tcx, substs);
let candidate = candidate_predicate
.to_opt_poly_trait_ref()
.expect("projection candidate is not a trait predicate");
let mut obligations = self
.infcx
.at(&obligation.cause, obligation.param_env)
@@ -139,7 +150,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
);
});
// Require that the projection is well-formed.
let self_ty = self.infcx.replace_bound_vars_with_placeholders(&obligation.self_ty());
let self_ty = self.infcx.replace_bound_vars_with_placeholders(&bound_self_ty);
let self_ty = normalize_with_depth_to(
self,
obligation.param_env,
@@ -152,7 +163,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation.param_env,
ty::PredicateKind::WellFormed(self_ty.into()).to_predicate(self.tcx()),
ty::PredicateKind::WellFormed(self_ty.into()).to_predicate(tcx),
));
obligations
})