syntax_data: {"ast_node_type":"variable","tokens":[{"end":88,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:                             if let Some(witness) = tcx.mir_coroutine_witnesses(def_id) {
context_before:                             queue_type(self, args.as_coroutine().resume_ty());
context_after:                                 for field_ty in &witness.field_tys {