syntax_data: {"ast_node_type":"variable","tokens":[{"end":64,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let old_expn_data = &mut data.local_expn_data[self];
context_before:         HygieneData::with(|data| {
context_after:             assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");