syntax_data: {"ast_node_type":"variable","tokens":[{"end":92,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, expn_id.to_expn_id());
context_before:             debug_assert_eq!(expn_id, _eid);
context_after:             debug_assert!(_old_id.is_none());