3 files changed, 9 insertions, 5 deletions

diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index 06187df56..c90a16720 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -152,7 +152,7 @@ impl<T> Canonicalized<T> {
             // eagerly replace projections in the type; we may be getting types
             // e.g. from where clauses where this hasn't happened yet
             let ty = ctx.normalize_associated_types_in(
-                ty.assert_ty_ref(&Interner).clone().subst_bound_vars(&new_vars),
+                new_vars.apply(ty.assert_ty_ref(&Interner).clone(), &Interner),
             );
             ctx.table.unify(&TyKind::InferenceVar(v, k).intern(&Interner), &ty);
         }
@@ -173,8 +173,8 @@ pub(crate) fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substitution> {
             // fallback to Unknown in the end (kind of hacky, as below)
             .map(|_| table.new_type_var()),
     );
-    let ty1_with_vars = tys.value.0.clone().subst_bound_vars(&vars);
-    let ty2_with_vars = tys.value.1.clone().subst_bound_vars(&vars);
+    let ty1_with_vars = vars.apply(tys.value.0.clone(), &Interner);
+    let ty2_with_vars = vars.apply(tys.value.1.clone(), &Interner);
     if !table.unify(&ty1_with_vars, &ty2_with_vars) {
         return None;
     }
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index a3c3ef6b2..66e72c814 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -477,7 +477,7 @@ impl<'a> TyLoweringContext<'a> {
                                     ),
                                 );
                                 let s = generics.type_params_subst(self.db);
-                                t.substitution.clone().subst_bound_vars(&s)
+                                s.apply(t.substitution.clone(), &Interner)
                             }
                             TypeParamLoweringMode::Variable => t.substitution.clone(),
                         };
diff --git a/crates/hir_ty/src/types.rs b/crates/hir_ty/src/types.rs
index 59678b45b..46c705a76 100644
--- a/crates/hir_ty/src/types.rs
+++ b/crates/hir_ty/src/types.rs
@@ -12,7 +12,7 @@ use smallvec::SmallVec;
 
 use crate::{
     AssocTypeId, CanonicalVarKinds, ChalkTraitId, ClosureId, FnDefId, FnSig, ForeignDefId,
-    InferenceVar, Interner, OpaqueTyId, PlaceholderIndex, VariableKinds,
+    InferenceVar, Interner, OpaqueTyId, PlaceholderIndex, TypeWalk, VariableKinds,
 };
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
@@ -286,6 +286,10 @@ impl Substitution {
         Substitution(elements.into_iter().casted(interner).collect())
     }
 
+    pub fn apply<T: TypeWalk>(&self, value: T, _interner: &Interner) -> T {
+        value.subst_bound_vars(self)
+    }
+
     // Temporary helper functions, to be removed
     pub fn intern(interned: SmallVec<[GenericArg; 2]>) -> Substitution {
         Substitution(interned)