syntax_data: {"ast_node_type":"other","tokens":[{"end":36,"kind":"keyword","start":0,"text":"allow_internal_unstable,"}]}
source_snippet:             allow_internal_unstable,
context_before:         let expn_data = ExpnData {
context_after:             ..ExpnData::default(ExpnKind::Desugaring(reason), self, edition, None, None)