4 files changed, 11 insertions, 12 deletions

diff --git a/crates/hir_ty/src/builder.rs b/crates/hir_ty/src/builder.rs
index ba158a749..4d3b4eade 100644
--- a/crates/hir_ty/src/builder.rs
+++ b/crates/hir_ty/src/builder.rs
@@ -99,6 +99,11 @@ impl TyBuilder<()> {
         }
     }
 
+    pub fn type_params_subst(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> Substitution {
+        let params = generics(db.upcast(), def.into());
+        params.type_params_subst(db)
+    }
+
     pub fn subst_for_def(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> TyBuilder<()> {
         let def = def.into();
         let params = generics(db.upcast(), def);
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 39e0b328d..385bd9405 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -19,8 +19,7 @@ use crate::{
     db::HirDatabase, from_assoc_type_id, from_foreign_def_id, from_placeholder_idx, primitive,
     to_assoc_type_id, traits::chalk::from_chalk, utils::generics, AdtId, AliasEq, AliasTy,
     CallableDefId, CallableSig, DomainGoal, GenericArg, ImplTraitId, Interner, Lifetime, OpaqueTy,
-    ProjectionTy, QuantifiedWhereClause, Scalar, TraitRef, Ty, TyExt, TyKind,
-    WhereClause,
+    ProjectionTy, QuantifiedWhereClause, Scalar, TraitRef, Ty, TyExt, TyKind, WhereClause,
 };
 
 pub struct HirFormatter<'a> {
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 6d6443ca3..a8c87eadf 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -462,12 +462,6 @@ impl Substitution {
     ) -> Self {
         Substitution(elements.into_iter().casted(interner).collect())
     }
-
-    /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub fn type_params(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> Substitution {
-        let params = generics(db.upcast(), def.into());
-        params.type_params_subst(db)
-    }
 }
 
 /// Return an index of a parameter in the generic type parameter list by it's id.
@@ -944,7 +938,7 @@ impl Ty {
                 let param_data = &generic_params.types[id.local_id];
                 match param_data.provenance {
                     hir_def::generics::TypeParamProvenance::ArgumentImplTrait => {
-                        let substs = Substitution::type_params(db, id.parent);
+                        let substs = TyBuilder::type_params_subst(db, id.parent);
                         let predicates = db
                             .generic_predicates(id.parent)
                             .into_iter()
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index f9a721fdf..214655807 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -470,12 +470,13 @@ impl<'a> TyLoweringContext<'a> {
                             TypeParamLoweringMode::Placeholder => {
                                 // if we're lowering to placeholders, we have to put
                                 // them in now
-                                let s = Substitution::type_params(
-                                    self.db,
+                                let generics = generics(
+                                    self.db.upcast(),
                                     self.resolver.generic_def().expect(
                                         "there should be generics if there's a generic param",
                                     ),
                                 );
+                                let s = generics.type_params_subst(self.db);
                                 t.substitution.clone().subst_bound_vars(&s)
                             }
                             TypeParamLoweringMode::Variable => t.substitution.clone(),
@@ -963,7 +964,7 @@ pub(crate) fn trait_environment_query(
         // function default implementations (and hypothetical code
         // inside consts or type aliases)
         cov_mark::hit!(trait_self_implements_self);
-        let substs = Substitution::type_params(db, trait_id);
+        let substs = TyBuilder::type_params_subst(db, trait_id);
         let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
         let pred = WhereClause::Implemented(trait_ref);
         let program_clause: chalk_ir::ProgramClause<Interner> = pred.to_chalk(db).cast(&Interner);