syntax_data: {"ast_node_type":"variable","tokens":[{"end":77,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let _old_data = hygiene_data.foreign_expn_data.insert(expn_id, data);
context_before:     HygieneData::with(|hygiene_data| {
context_after:         let _old_hash = hygiene_data.foreign_expn_hashes.insert(expn_id, hash);