2 files changed, 10 insertions, 4 deletions

diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index a685e70c2..314be17b8 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -361,10 +361,16 @@ impl Substs {
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub(crate) fn type_params(generic_params: &Generics) -> Substs {
+    pub(crate) fn type_params_for_generics(generic_params: &Generics) -> Substs {
         Substs(generic_params.iter().map(|(id, _)| Ty::Param(id)).collect())
     }
 
+    /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
+    pub fn type_params(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> Substs {
+        let params = generics(db, def.into());
+        Substs::type_params_for_generics(&params)
+    }
+
     /// Return Substs that replace each parameter by a bound variable.
     pub(crate) fn bound_vars(generic_params: &Generics) -> Substs {
         Substs(generic_params.iter().enumerate().map(|(idx, _)| Ty::Bound(idx as u32)).collect())
@@ -1026,7 +1032,7 @@ impl HirDisplay for Ty {
                     TypeParamProvenance::ArgumentImplTrait => {
                         write!(f, "impl ")?;
                         let bounds = f.db.generic_predicates_for_param(*id);
-                        let substs = Substs::type_params(&generics);
+                        let substs = Substs::type_params_for_generics(&generics);
                         write_bounds_like_dyn_trait(&bounds.iter().map(|b| b.clone().subst(&substs)).collect::<Vec<_>>(), f)?;
                     }
                 }
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index 847111748..0d4c075af 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -276,7 +276,7 @@ impl Ty {
             TypeNs::SelfType(impl_id) => {
                 let generics = generics(ctx.db, impl_id.into());
                 let substs = match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => Substs::type_params(&generics),
+                    TypeParamLoweringMode::Placeholder => Substs::type_params_for_generics(&generics),
                     TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
                 };
                 ctx.db.impl_self_ty(impl_id).subst(&substs)
@@ -284,7 +284,7 @@ impl Ty {
             TypeNs::AdtSelfType(adt) => {
                 let generics = generics(ctx.db, adt.into());
                 let substs = match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => Substs::type_params(&generics),
+                    TypeParamLoweringMode::Placeholder => Substs::type_params_for_generics(&generics),
                     TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
                 };
                 ctx.db.ty(adt.into()).subst(&substs)