{"ast_node_type":"variable","tokens":[{"end":83,"kind":"keyword","start":0,"text":"let"}]}
                        let used_mut_upvars = self.root_cx.used_mut_upvars(def_id);
                        let def_id = def_id.expect_local();
                        debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);