syntax_data: {"ast_node_type":"other","tokens":[{"end":45,"kind":"keyword","start":0,"text":"debug_assert!(_old_id.is_none());"}]}
source_snippet:             debug_assert!(_old_id.is_none());
context_before:             let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, expn_id.to_expn_id());
context_after:             expn_id