{"ast_node_type":"variable","tokens":[{"end":54,"kind":"keyword","start":0,"text":"let"}]}
    let body: &Body<'tcx> = tcx.optimized_mir(def_id);
    // Grab the optimized MIR. Analyze it to determine which arguments have been mutated.
    let mut deduce_read_only = DeduceReadOnly::new(body.arg_count);