{"ast_node_type":"variable","tokens":[{"end":32,"kind":"keyword","start":0,"text":"let"}]}
            let impl_trait_ref =
            let impl_args = self.fresh_args_for_item(base_expr.span, impl_def_id);
                self.tcx.impl_trait_ref(impl_def_id).unwrap().instantiate(self.tcx, impl_args);