{"ast_node_type":"variable","tokens":[{"end":44,"kind":"keyword","start":0,"text":"let"}]}
        let mut patch = MirPatch::new(body);
    fn run_pass<'tcx>(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
        let mut unreachable_blocks = FxHashSet::default();