syntax_data: {"ast_node_type":"other","tokens":[{"end":58,"kind":"keyword","start":0,"text":"for"}]}
source_snippet:     for (arm, is_useful) in report.arm_usefulness.iter() {
context_before:     let sm = cx.tcx.sess.source_map();
context_after:         if let Usefulness::Redundant(explanation) = is_useful {