Remove unused part of return value from replace_bound_vars_with_placeholders

compiler/rustc_infer/src/infer/higher_ranked/mod.rs

@@ -2,7 +2,7 @@
 //! the end of the file for details.
 
 use super::combine::CombineFields;
-use super::{HigherRankedType, InferCtxt, PlaceholderMap};
+use super::{HigherRankedType, InferCtxt};
 
 use crate::infer::CombinedSnapshot;
 use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
@@ -33,7 +33,7 @@ impl<'a, 'tcx> CombineFields<'a, 'tcx> {
         self.infcx.commit_if_ok(|_| {
             // First, we instantiate each bound region in the supertype with a
             // fresh placeholder region.
-            let (b_prime, _) = self.infcx.replace_bound_vars_with_placeholders(&b);
+            let b_prime = self.infcx.replace_bound_vars_with_placeholders(&b);
 
             // Next, we instantiate each bound region in the subtype
             // with a fresh region variable. These region variables --
@@ -66,10 +66,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// the [rustc dev guide].
     ///
     /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
-    pub fn replace_bound_vars_with_placeholders<T>(
-        &self,
-        binder: &ty::Binder<T>,
-    ) -> (T, PlaceholderMap<'tcx>)
+    pub fn replace_bound_vars_with_placeholders<T>(&self, binder: &ty::Binder<T>) -> T
     where
         T: TypeFoldable<'tcx>,
     {
@@ -122,7 +119,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             next_universe, binder, result, map,
         );
 
-        (result, map)
+        result
     }
 
     /// See `infer::region_constraints::RegionConstraintCollector::leak_check`.

compiler/rustc_infer/src/infer/mod.rs

@@ -351,11 +351,6 @@ pub struct InferCtxt<'a, 'tcx> {
     universe: Cell<ty::UniverseIndex>,
 }
 
-/// A map returned by `replace_bound_vars_with_placeholders()`
-/// indicating the placeholder region that each late-bound region was
-/// replaced with.
-pub type PlaceholderMap<'tcx> = BTreeMap<ty::BoundRegion, ty::Region<'tcx>>;
-
 /// See the `error_reporting` module for more details.
 #[derive(Clone, Debug, PartialEq, Eq, TypeFoldable)]
 pub enum ValuePairs<'tcx> {
@@ -992,7 +987,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
 
         Some(self.commit_if_ok(|_snapshot| {
-            let (ty::SubtypePredicate { a_is_expected, a, b }, _) =
+            let ty::SubtypePredicate { a_is_expected, a, b } =
                 self.replace_bound_vars_with_placeholders(&predicate);
 
             let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
@@ -1007,7 +1002,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
     ) -> UnitResult<'tcx> {
         self.commit_if_ok(|_snapshot| {
-            let (ty::OutlivesPredicate(r_a, r_b), _) =
+            let ty::OutlivesPredicate(r_a, r_b) =
                 self.replace_bound_vars_with_placeholders(&predicate);
             let origin = SubregionOrigin::from_obligation_cause(cause, || {
                 RelateRegionParamBound(cause.span)

compiler/rustc_trait_selection/src/traits/project.rs

@@ -167,7 +167,7 @@ pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
 
     let infcx = selcx.infcx();
     infcx.commit_if_ok(|_snapshot| {
-        let (placeholder_predicate, _) =
+        let placeholder_predicate =
             infcx.replace_bound_vars_with_placeholders(&obligation.predicate);
 
         let placeholder_obligation = obligation.with(placeholder_predicate);

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -253,7 +253,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             let trait_obligations: Vec<PredicateObligation<'_>> =
                 self.infcx.commit_unconditionally(|_| {
                     let poly_trait_ref = obligation.predicate.to_poly_trait_ref();
-                    let (trait_ref, _) =
+                    let trait_ref =
                         self.infcx.replace_bound_vars_with_placeholders(&poly_trait_ref);
                     let cause = obligation.derived_cause(ImplDerivedObligation);
                     self.impl_or_trait_obligations(
@@ -437,7 +437,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!("confirm_trait_alias_candidate({:?}, {:?})", obligation, alias_def_id);
 
         self.infcx.commit_unconditionally(|_| {
-            let (predicate, _) =
+            let predicate =
                 self.infcx().replace_bound_vars_with_placeholders(&obligation.predicate);
             let trait_ref = predicate.trait_ref;
             let trait_def_id = trait_ref.def_id;

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1161,7 +1161,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
     ) -> Option<ty::PolyTraitRef<'tcx>> {
         let poly_trait_predicate = self.infcx().resolve_vars_if_possible(&obligation.predicate);
-        let (placeholder_trait_predicate, _) =
+        let placeholder_trait_predicate =
             self.infcx().replace_bound_vars_with_placeholders(&poly_trait_predicate);
         debug!(
             "match_projection_obligation_against_definition_bounds: \
@@ -1640,7 +1640,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let ty: ty::Binder<Ty<'tcx>> = ty::Binder::bind(ty); // <----/
 
                 self.infcx.commit_unconditionally(|_| {
-                    let (placeholder_ty, _) = self.infcx.replace_bound_vars_with_placeholders(&ty);
+                    let placeholder_ty = self.infcx.replace_bound_vars_with_placeholders(&ty);
                     let Normalized { value: normalized_ty, mut obligations } =
                         ensure_sufficient_stack(|| {
                             project::normalize_with_depth(
@@ -1708,7 +1708,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             return Err(());
         }
 
-        let (placeholder_obligation, _) =
+        let placeholder_obligation =
             self.infcx().replace_bound_vars_with_placeholders(&obligation.predicate);
         let placeholder_obligation_trait_ref = placeholder_obligation.trait_ref;