{"ast_node_type":"other","tokens":[{"end":100,"kind":"keyword","start":0,"text":"debug!(\"gather_used_muts:"}]}
        debug!("gather_used_muts: never_initialized_mut_locals={:?}", never_initialized_mut_locals);
        // never initialized.
        self.used_mut = self.used_mut.union(&never_initialized_mut_locals).cloned().collect();