syntax_data: {"ast_node_type":"other","tokens":[{"end":58,"kind":"keyword","start":0,"text":"mut"}]}
source_snippet:     mut item_and_field_ids: Vec<(LocalDefId, LocalDefId)>,
context_before:     tcx: TyCtxt<'_>,
context_after:     representable_ids: &FxHashSet<LocalDefId>,