syntax_data: {"ast_node_type":"variable","tokens":[{"end":74,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                     let option_args = tcx.mk_args(&[sig.yield_ty.into()]);
context_before:                     let option_adt_ref = tcx.adt_def(option_did);
context_after:                     let ret_ty = Ty::new_adt(tcx, option_adt_ref, option_args);