syntax_data: {"ast_node_type":"variable","tokens":[{"end":45,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let expn_id = ExpnId { krate, local_id };
context_before:     debug_assert!(data.parent == ExpnId::root() || krate == data.parent.krate);
context_after:     HygieneData::with(|hygiene_data| {