syntax_data: {"ast_node_type":"other","tokens":[{"end":62,"kind":"keyword","start":0,"text":"for"}]}
source_snippet:         for (arm, is_useful) in report.arm_usefulness.iter() {
context_before:         // Warn unreachable subpatterns.
context_after:             if let Usefulness::Useful(redundant_subpats) = is_useful