{"ast_node_type":"variable","tokens":[{"end":64,"kind":"keyword","start":0,"text":"let"}]}
        let expr = &self.infcx.tcx.hir_expect_expr(hir_id).kind;
        let hir_id = self.infcx.tcx.local_def_id_to_hir_id(def_id);
        debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);