add subst_identity_iter and subst_identity_iter_copied methods on EarlyBinder; use this to simplify some EarlyBinder noise around explicit_item_bounds calls

2 files changed, 18 insertions, 26 deletions

diff --git a/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs b/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
index 1d410211403..15715c8fca0 100644
--- a/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
+++ b/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
@@ -74,9 +74,7 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
         // For every projection predicate in the opaque type's explicit bounds,
         // check that the type that we're assigning actually satisfies the bounds
         // of the associated type.
-        for bound in cx.tcx.explicit_item_bounds(def_id).transpose_iter() {
-            let (pred, pred_span) = bound.map_bound(|b| *b).subst_identity();
-
+        for (pred, pred_span) in cx.tcx.explicit_item_bounds(def_id).subst_identity_iter_copied() {
             // Liberate bound regions in the predicate since we
             // don't actually care about lifetimes in this check.
             let predicate = cx.tcx.liberate_late_bound_regions(def_id, pred.kind());
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 8de358cf8ab..eb175e96997 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -254,29 +254,23 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                 }
                 ty::Adt(def, _) => is_def_must_use(cx, def.did(), span),
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, .. }) => {
-                    elaborate(
-                        cx.tcx,
-                        cx.tcx
-                            .explicit_item_bounds(def)
-                            .transpose_iter()
-                            .map(|bound| bound.map_bound(|b| *b).subst_identity()),
-                    )
-                    // We only care about self bounds for the impl-trait
-                    .filter_only_self()
-                    .find_map(|(pred, _span)| {
-                        // We only look at the `DefId`, so it is safe to skip the binder here.
-                        if let ty::PredicateKind::Clause(ty::Clause::Trait(
-                            ref poly_trait_predicate,
-                        )) = pred.kind().skip_binder()
-                        {
-                            let def_id = poly_trait_predicate.trait_ref.def_id;
-
-                            is_def_must_use(cx, def_id, span)
-                        } else {
-                            None
-                        }
-                    })
-                    .map(|inner| MustUsePath::Opaque(Box::new(inner)))
+                    elaborate(cx.tcx, cx.tcx.explicit_item_bounds(def).subst_identity_iter_copied())
+                        // We only care about self bounds for the impl-trait
+                        .filter_only_self()
+                        .find_map(|(pred, _span)| {
+                            // We only look at the `DefId`, so it is safe to skip the binder here.
+                            if let ty::PredicateKind::Clause(ty::Clause::Trait(
+                                ref poly_trait_predicate,
+                            )) = pred.kind().skip_binder()
+                            {
+                                let def_id = poly_trait_predicate.trait_ref.def_id;
+
+                                is_def_must_use(cx, def_id, span)
+                            } else {
+                                None
+                            }
+                        })
+                        .map(|inner| MustUsePath::Opaque(Box::new(inner)))
                 }
                 ty::Dynamic(binders, _, _) => binders.iter().find_map(|predicate| {
                     if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder()