{"ast_node_type":"other","tokens":[{"end":47,"kind":"keyword","start":0,"text":"infcx.enter_forall(b,"}]}
                    infcx.enter_forall(b, |b| {
                ty::Covariant => {
                        let a = infcx.instantiate_binder_with_fresh_vars(span, HigherRankedType, a);