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diff --git a/third_party/rust/futures-sink/src/lib.rs b/third_party/rust/futures-sink/src/lib.rs
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+//! Asynchronous sinks
+//!
+//! This crate contains the `Sink` trait which allows values to be sent
+//! asynchronously.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![warn(missing_debug_implementations, missing_docs, rust_2018_idioms, unreachable_pub)]
+// It cannot be included in the published code because this lints have false positives in the minimum required version.
+#![cfg_attr(test, warn(single_use_lifetimes))]
+#![doc(test(
+    no_crate_inject,
+    attr(
+        deny(warnings, rust_2018_idioms, single_use_lifetimes),
+        allow(dead_code, unused_assignments, unused_variables)
+    )
+))]
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
+
+use core::ops::DerefMut;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+/// A `Sink` is a value into which other values can be sent, asynchronously.
+///
+/// Basic examples of sinks include the sending side of:
+///
+/// - Channels
+/// - Sockets
+/// - Pipes
+///
+/// In addition to such "primitive" sinks, it's typical to layer additional
+/// functionality, such as buffering, on top of an existing sink.
+///
+/// Sending to a sink is "asynchronous" in the sense that the value may not be
+/// sent in its entirety immediately. Instead, values are sent in a two-phase
+/// way: first by initiating a send, and then by polling for completion. This
+/// two-phase setup is analogous to buffered writing in synchronous code, where
+/// writes often succeed immediately, but internally are buffered and are
+/// *actually* written only upon flushing.
+///
+/// In addition, the `Sink` may be *full*, in which case it is not even possible
+/// to start the sending process.
+///
+/// As with `Future` and `Stream`, the `Sink` trait is built from a few core
+/// required methods, and a host of default methods for working in a
+/// higher-level way. The `Sink::send_all` combinator is of particular
+/// importance: you can use it to send an entire stream to a sink, which is
+/// the simplest way to ultimately consume a stream.
+#[must_use = "sinks do nothing unless polled"]
+pub trait Sink<Item> {
+    /// The type of value produced by the sink when an error occurs.
+    type Error;
+
+    /// Attempts to prepare the `Sink` to receive a value.
+    ///
+    /// This method must be called and return `Poll::Ready(Ok(()))` prior to
+    /// each call to `start_send`.
+    ///
+    /// This method returns `Poll::Ready` once the underlying sink is ready to
+    /// receive data. If this method returns `Poll::Pending`, the current task
+    /// is registered to be notified (via `cx.waker().wake_by_ref()`) when `poll_ready`
+    /// should be called again.
+    ///
+    /// In most cases, if the sink encounters an error, the sink will
+    /// permanently be unable to receive items.
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+
+    /// Begin the process of sending a value to the sink.
+    /// Each call to this function must be preceded by a successful call to
+    /// `poll_ready` which returned `Poll::Ready(Ok(()))`.
+    ///
+    /// As the name suggests, this method only *begins* the process of sending
+    /// the item. If the sink employs buffering, the item isn't fully processed
+    /// until the buffer is fully flushed. Since sinks are designed to work with
+    /// asynchronous I/O, the process of actually writing out the data to an
+    /// underlying object takes place asynchronously. **You *must* use
+    /// `poll_flush` or `poll_close` in order to guarantee completion of a
+    /// send**.
+    ///
+    /// Implementations of `poll_ready` and `start_send` will usually involve
+    /// flushing behind the scenes in order to make room for new messages.
+    /// It is only necessary to call `poll_flush` if you need to guarantee that
+    /// *all* of the items placed into the `Sink` have been sent.
+    ///
+    /// In most cases, if the sink encounters an error, the sink will
+    /// permanently be unable to receive items.
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error>;
+
+    /// Flush any remaining output from this sink.
+    ///
+    /// Returns `Poll::Ready(Ok(()))` when no buffered items remain. If this
+    /// value is returned then it is guaranteed that all previous values sent
+    /// via `start_send` have been flushed.
+    ///
+    /// Returns `Poll::Pending` if there is more work left to do, in which
+    /// case the current task is scheduled (via `cx.waker().wake_by_ref()`) to wake up when
+    /// `poll_flush` should be called again.
+    ///
+    /// In most cases, if the sink encounters an error, the sink will
+    /// permanently be unable to receive items.
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+
+    /// Flush any remaining output and close this sink, if necessary.
+    ///
+    /// Returns `Poll::Ready(Ok(()))` when no buffered items remain and the sink
+    /// has been successfully closed.
+    ///
+    /// Returns `Poll::Pending` if there is more work left to do, in which
+    /// case the current task is scheduled (via `cx.waker().wake_by_ref()`) to wake up when
+    /// `poll_close` should be called again.
+    ///
+    /// If this function encounters an error, the sink should be considered to
+    /// have failed permanently, and no more `Sink` methods should be called.
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
+}
+
+impl<S: ?Sized + Sink<Item> + Unpin, Item> Sink<Item> for &mut S {
+    type Error = S::Error;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Pin::new(&mut **self).poll_ready(cx)
+    }
+
+    fn start_send(mut self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        Pin::new(&mut **self).start_send(item)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Pin::new(&mut **self).poll_flush(cx)
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Pin::new(&mut **self).poll_close(cx)
+    }
+}
+
+impl<P, Item> Sink<Item> for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: Sink<Item>,
+{
+    type Error = <P::Target as Sink<Item>>::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.get_mut().as_mut().poll_ready(cx)
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        self.get_mut().as_mut().start_send(item)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.get_mut().as_mut().poll_flush(cx)
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.get_mut().as_mut().poll_close(cx)
+    }
+}
+
+#[cfg(feature = "alloc")]
+mod if_alloc {
+    use super::*;
+    use core::convert::Infallible as Never;
+
+    impl<T> Sink<T> for alloc::vec::Vec<T> {
+        type Error = Never;
+
+        fn poll_ready(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn start_send(self: Pin<&mut Self>, item: T) -> Result<(), Self::Error> {
+            // TODO: impl<T> Unpin for Vec<T> {}
+            unsafe { self.get_unchecked_mut() }.push(item);
+            Ok(())
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    impl<T> Sink<T> for alloc::collections::VecDeque<T> {
+        type Error = Never;
+
+        fn poll_ready(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn start_send(self: Pin<&mut Self>, item: T) -> Result<(), Self::Error> {
+            // TODO: impl<T> Unpin for Vec<T> {}
+            unsafe { self.get_unchecked_mut() }.push_back(item);
+            Ok(())
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    impl<S: ?Sized + Sink<Item> + Unpin, Item> Sink<Item> for alloc::boxed::Box<S> {
+        type Error = S::Error;
+
+        fn poll_ready(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Result<(), Self::Error>> {
+            Pin::new(&mut **self).poll_ready(cx)
+        }
+
+        fn start_send(mut self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+            Pin::new(&mut **self).start_send(item)
+        }
+
+        fn poll_flush(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Result<(), Self::Error>> {
+            Pin::new(&mut **self).poll_flush(cx)
+        }
+
+        fn poll_close(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> Poll<Result<(), Self::Error>> {
+            Pin::new(&mut **self).poll_close(cx)
+        }
+    }
+}