syntax_data: {"ast_node_type":"other","tokens":[{"end":37,"kind":"keyword","start":0,"text":"for"}]}
source_snippet:         for (&arm_id, branch) in it {
context_before:         let it = arms.iter().zip(built_match_tree.branches.iter());
context_after:             let pat = cx.lower_pat(&*self.thir.arms[arm_id].pattern);