Function assert_field_type_is_reborrow 

fn assert_field_type_is_reborrow<'tcx>(
    tcx: TyCtxt<'tcx>,
    infcx: &InferCtxt<'tcx>,
    reborrow_trait: DefId,
    impl_did: LocalDefId,
    param_env: ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    span: Span,
) -> Result<(), Vec<FulfillmentError<'tcx>>>