Add def_id() method to ty::Binder<.., ExistentialPredicate>

Author: ivarflakstad

compiler/rustc_type_ir/src/predicate.rs

@@ -275,6 +275,13 @@ pub enum ExistentialPredicate<I: Interner> {
 }
 
 impl<I: Interner> ty::Binder<I, ExistentialPredicate<I>> {
+    pub fn def_id(&self) -> I::DefId {
+        match self.skip_binder() {
+            ExistentialPredicate::Trait(tr) => tr.def_id,
+            ExistentialPredicate::Projection(p) => p.def_id,
+            ExistentialPredicate::AutoTrait(did) => did,
+        }
+    }
     /// Given an existential predicate like `?Self: PartialEq<u32>` (e.g., derived from `dyn PartialEq<u32>`),
     /// and a concrete type `self_ty`, returns a full predicate where the existentially quantified variable `?Self`
     /// has been replaced with `self_ty` (e.g., `self_ty: PartialEq<u32>`, in our example).