Make gen blocks implement the Iterator trait

compiler/rustc_trait_selection/src/traits/util.rs

@@ -297,6 +297,17 @@ pub fn future_trait_ref_and_outputs<'tcx>(
     sig.map_bound(|sig| (trait_ref, sig.return_ty))
 }
 
+pub fn iterator_trait_ref_and_outputs<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    iterator_def_id: DefId,
+    self_ty: Ty<'tcx>,
+    sig: ty::PolyGenSig<'tcx>,
+) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
+    assert!(!self_ty.has_escaping_bound_vars());
+    let trait_ref = ty::TraitRef::new(tcx, iterator_def_id, [self_ty]);
+    sig.map_bound(|sig| (trait_ref, sig.yield_ty))
+}
+
 pub fn impl_item_is_final(tcx: TyCtxt<'_>, assoc_item: &ty::AssocItem) -> bool {
     assoc_item.defaultness(tcx).is_final()
         && tcx.defaultness(assoc_item.container_id(tcx)).is_final()