1 files changed, 15 insertions, 0 deletions

diff --git a/crates/hir_ty/src/types.rs b/crates/hir_ty/src/types.rs
index 6dffda1ca..4a626d5e7 100644
--- a/crates/hir_ty/src/types.rs
+++ b/crates/hir_ty/src/types.rs
@@ -360,6 +360,15 @@ impl<T: Clone> Binders<&T> {
     }
 }
 
+impl<T: TypeWalk> Binders<T> {
+    /// Substitutes all variables.
+    pub fn substitute(self, interner: &Interner, subst: &Substitution) -> T {
+        let (value, binders) = self.into_value_and_skipped_binders();
+        assert_eq!(subst.len(interner), binders.len(interner));
+        value.subst_bound_vars(subst)
+    }
+}
+
 impl<T: std::fmt::Debug> std::fmt::Debug for Binders<T> {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
         let Binders { ref binders, ref value } = *self;
@@ -375,6 +384,12 @@ pub struct TraitRef {
     pub substitution: Substitution,
 }
 
+impl TraitRef {
+    pub fn self_type_parameter(&self, interner: &Interner) -> &Ty {
+        &self.substitution.at(interner, 0).assert_ty_ref(interner)
+    }
+}
+
 /// Like `generics::WherePredicate`, but with resolved types: A condition on the
 /// parameters of a generic item.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]