tests/eager_drop.rs

#[test]
fn map_ok() {
    use futures::future::{self, FutureExt, TryFutureExt};
    use futures_test::future::FutureTestExt;
    use std::sync::mpsc;

    // The closure given to `map_ok` should have been dropped by the time `map`
    // runs.
    let (tx1, rx1) = mpsc::channel::<()>();
    let (tx2, rx2) = mpsc::channel::<()>();

    future::ready::<Result<i32, i32>>(Err(1))
        .map_ok(move |_| { let _tx1 = tx1; panic!("should not run"); })
        .map(move |_| {
            assert!(rx1.recv().is_err());
            tx2.send(()).unwrap()
        })
        .run_in_background();

    rx2.recv().unwrap();
}

#[test]
fn map_err() {
    use futures::future::{self, FutureExt, TryFutureExt};
    use futures_test::future::FutureTestExt;
    use std::sync::mpsc;

    // The closure given to `map_err` should have been dropped by the time `map`
    // runs.
    let (tx1, rx1) = mpsc::channel::<()>();
    let (tx2, rx2) = mpsc::channel::<()>();

    future::ready::<Result<i32, i32>>(Ok(1))
        .map_err(move |_| { let _tx1 = tx1; panic!("should not run"); })
        .map(move |_| {
            assert!(rx1.recv().is_err());
            tx2.send(()).unwrap()
        })
        .run_in_background();

    rx2.recv().unwrap();
}

mod channelled {
    use futures::future::Future;
    use futures::task::{Context,Poll};
    use pin_project::pin_project;
    use std::pin::Pin;

    #[pin_project]
    struct FutureData<F, T> {
        _data: T,
        #[pin]
        future: F,
    }

    impl<F: Future, T: Send + 'static> Future for FutureData<F, T> {
        type Output = F::Output;

        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<F::Output> {
            self.project().future.poll(cx)
        }
    }

    #[test]
    fn then_drops_eagerly() {
        use futures::channel::oneshot;
        use futures::future::{self, FutureExt, TryFutureExt};
        use futures_test::future::FutureTestExt;
        use std::sync::mpsc;

        let (tx0, rx0) = oneshot::channel::<()>();
        let (tx1, rx1) = mpsc::channel::<()>();
        let (tx2, rx2) = mpsc::channel::<()>();

        FutureData { _data: tx1, future: rx0.unwrap_or_else(|_| { panic!() }) }
            .then(move |_| {
                assert!(rx1.recv().is_err()); // tx1 should have been dropped
                tx2.send(()).unwrap();
                future::ready(())
            })
            .run_in_background();

        assert_eq!(Err(mpsc::TryRecvError::Empty), rx2.try_recv());
        tx0.send(()).unwrap();
        rx2.recv().unwrap();
    }

    #[test]
    fn and_then_drops_eagerly() {
        use futures::channel::oneshot;
        use futures::future::{self, TryFutureExt};
        use futures_test::future::FutureTestExt;
        use std::sync::mpsc;

        let (tx0, rx0) = oneshot::channel::<Result<(), ()>>();
        let (tx1, rx1) = mpsc::channel::<()>();
        let (tx2, rx2) = mpsc::channel::<()>();

        FutureData { _data: tx1, future: rx0.unwrap_or_else(|_| { panic!() }) }
            .and_then(move |_| {
                assert!(rx1.recv().is_err()); // tx1 should have been dropped
                tx2.send(()).unwrap();
                future::ready(Ok(()))
            })
            .run_in_background();

        assert_eq!(Err(mpsc::TryRecvError::Empty), rx2.try_recv());
        tx0.send(Ok(())).unwrap();
        rx2.recv().unwrap();
    }

    #[test]
    fn or_else_drops_eagerly() {
        use futures::channel::oneshot;
        use futures::future::{self, TryFutureExt};
        use futures_test::future::FutureTestExt;
        use std::sync::mpsc;

        let (tx0, rx0) = oneshot::channel::<Result<(), ()>>();
        let (tx1, rx1) = mpsc::channel::<()>();
        let (tx2, rx2) = mpsc::channel::<()>();

        FutureData { _data: tx1, future: rx0.unwrap_or_else(|_| { panic!() }) }
            .or_else(move |_| {
                assert!(rx1.recv().is_err()); // tx1 should have been dropped
                tx2.send(()).unwrap();
                future::ready::<Result<(), ()>>(Ok(()))
            })
            .run_in_background();

        assert_eq!(Err(mpsc::TryRecvError::Empty), rx2.try_recv());
        tx0.send(Err(())).unwrap();
        rx2.recv().unwrap();
    }
}