syntax_data: {"ast_node_type":"variable","tokens":[{"end":70,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let option_args = tcx.mk_args(&[old_yield_ty.into()]);
context_before:                 let option_adt_ref = tcx.adt_def(option_did);
context_after:                 Ty::new_adt(tcx, option_adt_ref, option_args)