{"ast_node_type":"variable","tokens":[{"end":73,"kind":"keyword","start":0,"text":"let"}]}
        let is_closure = self.infcx.tcx.is_closure_like(did.to_def_id());
        debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
        let fn_hir_id = self.infcx.tcx.local_def_id_to_hir_id(did);