{"ast_node_type":"other","tokens":[{"end":50,"kind":"keyword","start":0,"text":"mt_b:"}]}
                       mt_b: ty::TypeAndMut<'tcx>,
    let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
                       mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| {