syntax_data: {"ast_node_type":"other","tokens":[{"end":67,"kind":"keyword","start":0,"text":"allow_internal_unstable:"}]}
source_snippet:             allow_internal_unstable: Some(allow_internal_unstable),
context_before:         ExpnData {
context_after:             ..ExpnData::default(kind, call_site, edition, macro_def_id, parent_module)