{"ast_node_type":"variable","tokens":[{"end":84,"kind":"keyword","start":0,"text":"let"}]}
        let mut involving_tos = IndexVec::from_elem(Vec::new(), &body.basic_blocks);
    fn new(body: &Body<'_>, opportunities: Vec<ThreadingOpportunity>) -> OpportunitySet {
        for (index, to) in opportunities.iter().enumerate() {