1 files changed, 56 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/future/poll_fn.rs b/third_party/rust/futures-util/src/future/poll_fn.rs
new file mode 100644
index 0000000000..b7b10be85d
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/poll_fn.rs
@@ -0,0 +1,56 @@
+//! Definition of the `PollFn` adapter combinator
+
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`poll_fn`] function.
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct PollFn<F> {
+    f: F,
+}
+
+impl<F> Unpin for PollFn<F> {}
+
+/// Creates a new future wrapping around a function returning [`Poll`].
+///
+/// Polling the returned future delegates to the wrapped function.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future::poll_fn;
+/// use futures::task::{Context, Poll};
+///
+/// fn read_line(_cx: &mut Context<'_>) -> Poll<String> {
+///     Poll::Ready("Hello, World!".into())
+/// }
+///
+/// let read_future = poll_fn(read_line);
+/// assert_eq!(read_future.await, "Hello, World!".to_owned());
+/// # });
+/// ```
+pub fn poll_fn<T, F>(f: F) -> PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>
+{
+    PollFn { f }
+}
+
+impl<F> fmt::Debug for PollFn<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PollFn").finish()
+    }
+}
+
+impl<T, F> Future for PollFn<F>
+    where F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        (&mut self.f)(cx)
+    }
+}