4 files changed, 32 insertions, 23 deletions

diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index ccaae53e9..6966d26e7 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -419,7 +419,7 @@ impl<'a> InferenceContext<'a> {
                         self.result.record_field_resolutions.insert(field.expr, field_def);
                     }
                     let field_ty = field_def.map_or(self.err_ty(), |it| {
-                        field_types[it.local_id].clone().subst(&substs)
+                        field_types[it.local_id].clone().substitute(&Interner, &substs)
                     });
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
@@ -462,7 +462,7 @@ impl<'a> InferenceContext<'a> {
                                 Some(
                                     self.db.field_types((*s).into())[field.local_id]
                                         .clone()
-                                        .subst(&parameters),
+                                        .substitute(&Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -476,7 +476,7 @@ impl<'a> InferenceContext<'a> {
                                 Some(
                                     self.db.field_types((*u).into())[field.local_id]
                                         .clone()
-                                        .subst(&parameters),
+                                        .substitute(&Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -849,10 +849,10 @@ impl<'a> InferenceContext<'a> {
                 self.write_method_resolution(tgt_expr, func);
                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
             }
-            None => (receiver_ty, Binders::new(0, self.err_ty()), None),
+            None => (receiver_ty, Binders::empty(&Interner, self.err_ty()), None),
         };
         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
-        let method_ty = method_ty.subst(&substs);
+        let method_ty = method_ty.substitute(&Interner, &substs);
         let method_ty = self.insert_type_vars(method_ty);
         self.register_obligations_for_call(&method_ty);
         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
@@ -949,9 +949,11 @@ impl<'a> InferenceContext<'a> {
             let def: CallableDefId = from_chalk(self.db, *fn_def);
             let generic_predicates = self.db.generic_predicates(def.into());
             for predicate in generic_predicates.iter() {
-                let (predicate, binders) =
-                    predicate.clone().subst(parameters).into_value_and_skipped_binders();
-                always!(binders == 0); // quantified where clauses not yet handled
+                let (predicate, binders) = predicate
+                    .clone()
+                    .substitute(&Interner, parameters)
+                    .into_value_and_skipped_binders();
+                always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
                 self.push_obligation(predicate.cast(&Interner));
             }
             // add obligation for trait implementation, if this is a trait method
diff --git a/crates/hir_ty/src/infer/pat.rs b/crates/hir_ty/src/infer/pat.rs
index 469f37dd9..252ae914a 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -49,7 +49,9 @@ impl<'a> InferenceContext<'a> {
             let expected_ty = var_data
                 .as_ref()
                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
-                .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
+                .map_or(self.err_ty(), |field| {
+                    field_tys[field].clone().substitute(&Interner, &substs)
+                });
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat, &expected_ty, default_bm);
         }
@@ -83,8 +85,9 @@ impl<'a> InferenceContext<'a> {
                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
             }
 
-            let expected_ty = matching_field
-                .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
+            let expected_ty = matching_field.map_or(self.err_ty(), |field| {
+                field_tys[field].clone().substitute(&Interner, &substs)
+            });
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat.pat, &expected_ty, default_bm);
         }
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index 89d78e781..14f705173 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -81,9 +81,9 @@ impl<'a> InferenceContext<'a> {
             ValueNs::ImplSelf(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
                 let substs = generics.type_params_subst(self.db);
-                let ty = self.db.impl_self_ty(impl_id).subst(&substs);
+                let ty = self.db.impl_self_ty(impl_id).substitute(&Interner, &substs);
                 if let Some((AdtId::StructId(struct_id), substs)) = ty.as_adt() {
-                    let ty = self.db.value_ty(struct_id.into()).subst(&substs);
+                    let ty = self.db.value_ty(struct_id.into()).substitute(&Interner, &substs);
                     return Some(ty);
                 } else {
                     // FIXME: diagnostic, invalid Self reference
@@ -243,7 +243,8 @@ impl<'a> InferenceContext<'a> {
                         let impl_substs = TyBuilder::subst_for_def(self.db, impl_id)
                             .fill(iter::repeat_with(|| self.table.new_type_var()))
                             .build();
-                        let impl_self_ty = self.db.impl_self_ty(impl_id).subst(&impl_substs);
+                        let impl_self_ty =
+                            self.db.impl_self_ty(impl_id).substitute(&Interner, &impl_substs);
                         self.unify(&impl_self_ty, &ty);
                         Some(impl_substs)
                     }
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index 8370f2e1c..c90a16720 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -108,19 +108,22 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
 }
 
 impl<T> Canonicalized<T> {
-    pub(super) fn decanonicalize_ty(&self, mut ty: Ty) -> Ty {
-        ty.walk_mut_binders(
+    pub(super) fn decanonicalize_ty(&self, ty: Ty) -> Ty {
+        ty.fold_binders(
             &mut |ty, binders| {
-                if let &mut TyKind::BoundVar(bound) = ty.interned_mut() {
+                if let TyKind::BoundVar(bound) = ty.kind(&Interner) {
                     if bound.debruijn >= binders {
                         let (v, k) = self.free_vars[bound.index];
-                        *ty = TyKind::InferenceVar(v, k).intern(&Interner);
+                        TyKind::InferenceVar(v, k).intern(&Interner)
+                    } else {
+                        ty
                     }
+                } else {
+                    ty
                 }
             },
             DebruijnIndex::INNERMOST,
-        );
-        ty
+        )
     }
 
     pub(super) fn apply_solution(
@@ -149,7 +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);
         }
@@ -170,8 +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;
     }