Tweak FulfillProcessor.

Avoids some unnecessary references and lifetimes.

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -102,7 +102,7 @@ impl<'a, 'tcx> FulfillmentContext<'tcx> {
  }
 
  /// Attempts to select obligations using `selcx`.
- fn select(&mut self, selcx: &mut SelectionContext<'a, 'tcx>) -> Vec<FulfillmentError<'tcx>> {
+ fn select(&mut self, selcx: SelectionContext<'a, 'tcx>) -> Vec<FulfillmentError<'tcx>> {
  let span = debug_span!("select", obligation_forest_size = ?self.predicates.len());
  let _enter = span.enter();
 
@@ -197,8 +197,8 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
  &mut self,
  infcx: &InferCtxt<'_, 'tcx>,
  ) -> Vec<FulfillmentError<'tcx>> {
- let mut selcx = SelectionContext::new(infcx);
- self.select(&mut selcx)
+ let selcx = SelectionContext::new(infcx);
+ self.select(selcx)
  }
 
  fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
@@ -210,8 +210,8 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
  }
 }
 
-struct FulfillProcessor<'a, 'b, 'tcx> {
- selcx: &'a mut SelectionContext<'b, 'tcx>,
+struct FulfillProcessor<'a, 'tcx> {
+ selcx: SelectionContext<'a, 'tcx>,
 }
 
 fn mk_pending(os: Vec<PredicateObligation<'_>>) -> Vec<PendingPredicateObligation<'_>> {
@@ -220,7 +220,7 @@ fn mk_pending(os: Vec<PredicateObligation<'_>>) -> Vec<PendingPredicateObligatio
  .collect()
 }
 
-impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
+impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
  type Obligation = PendingPredicateObligation<'tcx>;
  type Error = FulfillmentErrorCode<'tcx>;
  type OUT = Outcome<Self::Obligation, Self::Error>;
@@ -291,7 +291,7 @@ impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
  if obligation.predicate.has_projections() {
  let mut obligations = Vec::new();
  let predicate = crate::traits::project::try_normalize_with_depth_to(
- self.selcx,
+ &mut self.selcx,
  obligation.param_env,
  obligation.cause.clone(),
  obligation.recursion_depth + 1,
@@ -608,7 +608,7 @@ impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
  }
 }
 
-impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
+impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
  #[instrument(level = "debug", skip(self, obligation, stalled_on))]
  fn process_trait_obligation(
  &mut self,
@@ -643,7 +643,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
  // information about the types in the trait.
  stalled_on.clear();
  stalled_on.extend(substs_infer_vars(
- self.selcx,
+ &self.selcx,
  trait_obligation.predicate.map_bound(|pred| pred.trait_ref.substs),
  ));
 
@@ -695,12 +695,12 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
  }
  }
 
- match project::poly_project_and_unify_type(self.selcx, &project_obligation) {
+ match project::poly_project_and_unify_type(&mut self.selcx, &project_obligation) {
  ProjectAndUnifyResult::Holds(os) => ProcessResult::Changed(mk_pending(os)),
  ProjectAndUnifyResult::FailedNormalization => {
  stalled_on.clear();
  stalled_on.extend(substs_infer_vars(
- self.selcx,
+ &self.selcx,
  project_obligation.predicate.map_bound(|pred| pred.projection_ty.substs),
  ));
  ProcessResult::Unchanged
@@ -718,7 +718,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
 
 /// Returns the set of inference variables contained in `substs`.
 fn substs_infer_vars<'a, 'tcx>(
- selcx: &mut SelectionContext<'a, 'tcx>,
+ selcx: &SelectionContext<'a, 'tcx>,
  substs: ty::Binder<'tcx, SubstsRef<'tcx>>,
 ) -> impl Iterator<Item = TyOrConstInferVar<'tcx>> {
  selcx