instantiate_own doesn't need to return a pair of vectors

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -209,9 +209,11 @@ fn compare_method_predicate_entailment<'tcx>(
     //
     // We then register the obligations from the impl_m and check to see
     // if all constraints hold.
-    hybrid_preds
+    hybrid_preds.predicates.extend(
-        .predicates
+        trait_m_predicates
-        .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
+            .instantiate_own(tcx, trait_to_placeholder_substs)
+            .map(|(predicate, _)| predicate),
+    );
 
     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
     // The key step here is to update the caller_bounds's predicates to be
@@ -230,7 +232,7 @@ fn compare_method_predicate_entailment<'tcx>(
     debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
 
     let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
-    for (predicate, span) in iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
+    for (predicate, span) in impl_m_own_bounds {
         let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id);
         let predicate = ocx.normalize(&normalize_cause, param_env, predicate);
 
@@ -1828,8 +1830,7 @@ fn compare_type_predicate_entailment<'tcx>(
     check_region_bounds_on_impl_item(tcx, impl_ty, trait_ty, false)?;
 
     let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
-
+    if impl_ty_own_bounds.len() == 0 {
-    if impl_ty_own_bounds.is_empty() {
         // Nothing to check.
         return Ok(());
     }
@@ -1844,9 +1845,11 @@ fn compare_type_predicate_entailment<'tcx>(
     // associated type in the trait are assumed.
     let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
-    hybrid_preds
+    hybrid_preds.predicates.extend(
-        .predicates
+        trait_ty_predicates
-        .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
+            .instantiate_own(tcx, trait_to_impl_substs)
+            .map(|(predicate, _)| predicate),
+    );
 
     debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
 
@@ -1862,9 +1865,7 @@ fn compare_type_predicate_entailment<'tcx>(
 
     debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
 
-    assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
+    for (predicate, span) in impl_ty_own_bounds {
-    for (span, predicate) in std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
-    {
         let cause = ObligationCause::misc(span, impl_ty_hir_id);
         let predicate = ocx.normalize(&cause, param_env, predicate);
 

compiler/rustc_middle/src/ty/generics.rs

@@ -341,15 +341,9 @@ impl<'tcx> GenericPredicates<'tcx> {
         &self,
         tcx: TyCtxt<'tcx>,
         substs: SubstsRef<'tcx>,
-    ) -> InstantiatedPredicates<'tcx> {
+    ) -> impl Iterator<Item = (Predicate<'tcx>, Span)> + DoubleEndedIterator + ExactSizeIterator
-        InstantiatedPredicates {
+    {
-            predicates: self
+        EarlyBinder(self.predicates).subst_iter_copied(tcx, substs)
-                .predicates
-                .iter()
-                .map(|(p, _)| EarlyBinder(*p).subst(tcx, substs))
-                .collect(),
-            spans: self.predicates.iter().map(|(_, sp)| *sp).collect(),
-        }
     }
 
     #[instrument(level = "debug", skip(self, tcx))]

compiler/rustc_middle/src/ty/subst.rs

@@ -639,6 +639,13 @@ where
     }
 }
 
+impl<'tcx, I: IntoIterator> ExactSizeIterator for SubstIter<'_, 'tcx, I>
+where
+    I::IntoIter: ExactSizeIterator,
+    I::Item: TypeFoldable<'tcx>,
+{
+}
+
 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
 where
     I::Item: Deref,
@@ -686,6 +693,14 @@ where
     }
 }
 
+impl<'tcx, I: IntoIterator> ExactSizeIterator for SubstIterCopied<'_, 'tcx, I>
+where
+    I::IntoIter: ExactSizeIterator,
+    I::Item: Deref,
+    <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
+{
+}
+
 pub struct EarlyBinderIter<T> {
     t: T,
 }

compiler/rustc_trait_selection/src/traits/project.rs

@@ -2303,10 +2303,10 @@ fn assoc_ty_own_obligations<'cx, 'tcx>(
     nested: &mut Vec<PredicateObligation<'tcx>>,
 ) {
     let tcx = selcx.tcx();
-    let own = tcx
+    let predicates = tcx
         .predicates_of(obligation.predicate.def_id)
         .instantiate_own(tcx, obligation.predicate.substs);
-    for (predicate, span) in std::iter::zip(own.predicates, own.spans) {
+    for (predicate, span) in predicates {
         let normalized = normalize_with_depth_to(
             selcx,
             obligation.param_env,

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

@@ -185,9 +185,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         })?);
 
         if let ty::Alias(ty::Projection, ..) = placeholder_self_ty.kind() {
-            let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs).predicates;
+            let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
-            debug!(?predicates, "projection predicates");
+            for (predicate, _) in predicates {
-            for predicate in predicates {
                 let normalized = normalize_with_depth_to(
                     self,
                     obligation.param_env,

compiler/rustc_trait_selection/src/traits/vtable.rs

@@ -261,7 +261,10 @@ fn vtable_entries<'tcx>(
                     // Note that this method could then never be called, so we
                     // do not want to try and codegen it, in that case (see #23435).
                     let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
-                    if impossible_predicates(tcx, predicates.predicates) {
+                    if impossible_predicates(
+                        tcx,
+                        predicates.map(|(predicate, _)| predicate).collect(),
+                    ) {
                         debug!("vtable_entries: predicates do not hold");
                         return VtblEntry::Vacant;
                     }