{"ast_node_type":"variable","tokens":[{"end":90,"kind":"keyword","start":0,"text":"let"}]}
        let liberated_sig = self.normalize(self.tcx.def_span(expr_def_id), liberated_sig);
            self.tcx().liberate_late_bound_regions(expr_def_id.to_def_id(), bound_sig);
        ClosureSignatures { bound_sig, liberated_sig }