1 files changed, 30 insertions, 1 deletions

diff --git a/crates/hir_ty/src/types.rs b/crates/hir_ty/src/types.rs
index dc64e6e2b..4a626d5e7 100644
--- a/crates/hir_ty/src/types.rs
+++ b/crates/hir_ty/src/types.rs
@@ -4,7 +4,7 @@
 use std::sync::Arc;
 
 use chalk_ir::{
-    cast::{CastTo, Caster},
+    cast::{Cast, CastTo, Caster},
     BoundVar, Mutability, Scalar, TyVariableKind,
 };
 use smallvec::SmallVec;
@@ -29,6 +29,12 @@ pub struct ProjectionTy {
     pub substitution: Substitution,
 }
 
+impl ProjectionTy {
+    pub fn self_type_parameter(&self, interner: &Interner) -> &Ty {
+        &self.substitution.interned()[0].assert_ty_ref(interner)
+    }
+}
+
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct DynTy {
     /// The unknown self type.
@@ -272,6 +278,14 @@ impl Substitution {
         self.0.iter()
     }
 
+    pub fn from1(_interner: &Interner, ty: Ty) -> Substitution {
+        Substitution::intern({
+            let mut v = SmallVec::new();
+            v.push(ty.cast(&Interner));
+            v
+        })
+    }
+
     pub fn from_iter(
         interner: &Interner,
         elements: impl IntoIterator<Item = impl CastTo<GenericArg>>,
@@ -346,6 +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;
@@ -361,6 +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)]