{"ast_node_type":"variable","tokens":[{"end":97,"kind":"keyword","start":0,"text":"let"}]}
                    let impl_ty = self.tcx.type_of(impl_def_id).instantiate(self.tcx, impl_args);
                    let impl_args = self.fresh_args_for_item(self.span, impl_def_id);
                    (xform_self_ty, xform_ret_ty) =