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diff --git a/third_party/rust/futures-util/src/stream/select_with_strategy.rs b/third_party/rust/futures-util/src/stream/select_with_strategy.rs
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+++ b/third_party/rust/futures-util/src/stream/select_with_strategy.rs
@@ -0,0 +1,304 @@
+use super::assert_stream;
+use core::{fmt, pin::Pin};
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+/// Type to tell [`SelectWithStrategy`] which stream to poll next.
+#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
+pub enum PollNext {
+    /// Poll the first stream.
+    Left,
+    /// Poll the second stream.
+    Right,
+}
+
+impl PollNext {
+    /// Toggle the value and return the old one.
+    pub fn toggle(&mut self) -> Self {
+        let old = *self;
+        *self = self.other();
+        old
+    }
+
+    fn other(&self) -> PollNext {
+        match self {
+            PollNext::Left => PollNext::Right,
+            PollNext::Right => PollNext::Left,
+        }
+    }
+}
+
+impl Default for PollNext {
+    fn default() -> Self {
+        PollNext::Left
+    }
+}
+
+enum InternalState {
+    Start,
+    LeftFinished,
+    RightFinished,
+    BothFinished,
+}
+
+impl InternalState {
+    fn finish(&mut self, ps: PollNext) {
+        match (&self, ps) {
+            (InternalState::Start, PollNext::Left) => {
+                *self = InternalState::LeftFinished;
+            }
+            (InternalState::Start, PollNext::Right) => {
+                *self = InternalState::RightFinished;
+            }
+            (InternalState::LeftFinished, PollNext::Right)
+            | (InternalState::RightFinished, PollNext::Left) => {
+                *self = InternalState::BothFinished;
+            }
+            _ => {}
+        }
+    }
+}
+
+pin_project! {
+    /// Stream for the [`select_with_strategy()`] function. See function docs for details.
+    #[must_use = "streams do nothing unless polled"]
+    #[project = SelectWithStrategyProj]
+    pub struct SelectWithStrategy<St1, St2, Clos, State> {
+        #[pin]
+        stream1: St1,
+        #[pin]
+        stream2: St2,
+        internal_state: InternalState,
+        state: State,
+        clos: Clos,
+    }
+}
+
+/// This function will attempt to pull items from both streams. You provide a
+/// closure to tell [`SelectWithStrategy`] which stream to poll. The closure can
+/// store state on `SelectWithStrategy` to which it will receive a `&mut` on every
+/// invocation. This allows basing the strategy on prior choices.
+///
+/// After one of the two input streams completes, the remaining one will be
+/// polled exclusively. The returned stream completes when both input
+/// streams have completed.
+///
+/// Note that this function consumes both streams and returns a wrapped
+/// version of them.
+///
+/// ## Examples
+///
+/// ### Priority
+/// This example shows how to always prioritize the left stream.
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt };
+///
+/// let left = repeat(1);
+/// let right = repeat(2);
+///
+/// // We don't need any state, so let's make it an empty tuple.
+/// // We must provide some type here, as there is no way for the compiler
+/// // to infer it. As we don't need to capture variables, we can just
+/// // use a function pointer instead of a closure.
+/// fn prio_left(_: &mut ()) -> PollNext { PollNext::Left }
+///
+/// let mut out = select_with_strategy(left, right, prio_left);
+///
+/// for _ in 0..100 {
+///     // Whenever we poll out, we will alwas get `1`.
+///     assert_eq!(1, out.select_next_some().await);
+/// }
+/// # });
+/// ```
+///
+/// ### Round Robin
+/// This example shows how to select from both streams round robin.
+/// Note: this special case is provided by [`futures-util::stream::select`].
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt };
+///
+/// let left = repeat(1);
+/// let right = repeat(2);
+///
+/// let rrobin = |last: &mut PollNext| last.toggle();
+///
+/// let mut out = select_with_strategy(left, right, rrobin);
+///
+/// for _ in 0..100 {
+///     // We should be alternating now.
+///     assert_eq!(1, out.select_next_some().await);
+///     assert_eq!(2, out.select_next_some().await);
+/// }
+/// # });
+/// ```
+pub fn select_with_strategy<St1, St2, Clos, State>(
+    stream1: St1,
+    stream2: St2,
+    which: Clos,
+) -> SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+    Clos: FnMut(&mut State) -> PollNext,
+    State: Default,
+{
+    assert_stream::<St1::Item, _>(SelectWithStrategy {
+        stream1,
+        stream2,
+        state: Default::default(),
+        internal_state: InternalState::Start,
+        clos: which,
+    })
+}
+
+impl<St1, St2, Clos, State> SelectWithStrategy<St1, St2, Clos, State> {
+    /// Acquires a reference to the underlying streams that this combinator is
+    /// pulling from.
+    pub fn get_ref(&self) -> (&St1, &St2) {
+        (&self.stream1, &self.stream2)
+    }
+
+    /// Acquires a mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_mut(&mut self) -> (&mut St1, &mut St2) {
+        (&mut self.stream1, &mut self.stream2)
+    }
+
+    /// Acquires a pinned mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>) {
+        let this = self.project();
+        (this.stream1, this.stream2)
+    }
+
+    /// Consumes this combinator, returning the underlying streams.
+    ///
+    /// Note that this may discard intermediate state of this combinator, so
+    /// care should be taken to avoid losing resources when this is called.
+    pub fn into_inner(self) -> (St1, St2) {
+        (self.stream1, self.stream2)
+    }
+}
+
+impl<St1, St2, Clos, State> FusedStream for SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+    Clos: FnMut(&mut State) -> PollNext,
+{
+    fn is_terminated(&self) -> bool {
+        match self.internal_state {
+            InternalState::BothFinished => true,
+            _ => false,
+        }
+    }
+}
+
+#[inline]
+fn poll_side<St1, St2, Clos, State>(
+    select: &mut SelectWithStrategyProj<'_, St1, St2, Clos, State>,
+    side: PollNext,
+    cx: &mut Context<'_>,
+) -> Poll<Option<St1::Item>>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    match side {
+        PollNext::Left => select.stream1.as_mut().poll_next(cx),
+        PollNext::Right => select.stream2.as_mut().poll_next(cx),
+    }
+}
+
+#[inline]
+fn poll_inner<St1, St2, Clos, State>(
+    select: &mut SelectWithStrategyProj<'_, St1, St2, Clos, State>,
+    side: PollNext,
+    cx: &mut Context<'_>,
+) -> Poll<Option<St1::Item>>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    let first_done = match poll_side(select, side, cx) {
+        Poll::Ready(Some(item)) => return Poll::Ready(Some(item)),
+        Poll::Ready(None) => {
+            select.internal_state.finish(side);
+            true
+        }
+        Poll::Pending => false,
+    };
+    let other = side.other();
+    match poll_side(select, other, cx) {
+        Poll::Ready(None) => {
+            select.internal_state.finish(other);
+            if first_done {
+                Poll::Ready(None)
+            } else {
+                Poll::Pending
+            }
+        }
+        a => a,
+    }
+}
+
+impl<St1, St2, Clos, State> Stream for SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+    Clos: FnMut(&mut State) -> PollNext,
+{
+    type Item = St1::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> {
+        let mut this = self.project();
+
+        match this.internal_state {
+            InternalState::Start => {
+                let next_side = (this.clos)(this.state);
+                poll_inner(&mut this, next_side, cx)
+            }
+            InternalState::LeftFinished => match this.stream2.poll_next(cx) {
+                Poll::Ready(None) => {
+                    *this.internal_state = InternalState::BothFinished;
+                    Poll::Ready(None)
+                }
+                a => a,
+            },
+            InternalState::RightFinished => match this.stream1.poll_next(cx) {
+                Poll::Ready(None) => {
+                    *this.internal_state = InternalState::BothFinished;
+                    Poll::Ready(None)
+                }
+                a => a,
+            },
+            InternalState::BothFinished => Poll::Ready(None),
+        }
+    }
+}
+
+impl<St1, St2, Clos, State> fmt::Debug for SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: fmt::Debug,
+    St2: fmt::Debug,
+    State: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SelectWithStrategy")
+            .field("stream1", &self.stream1)
+            .field("stream2", &self.stream2)
+            .field("state", &self.state)
+            .finish()
+    }
+}