1 files changed, 167 insertions, 0 deletions
diff --git a/library/core/src/task/poll.rs b/library/core/src/task/poll.rs
new file mode 100644
index 00000000000..b3a4bd20b8f
--- /dev/null
+++ b/library/core/src/task/poll.rs
@@ -0,0 +1,167 @@
+#![stable(feature = "futures_api", since = "1.36.0")]
+
+use crate::ops::Try;
+use crate::result::Result;
+
+/// Indicates whether a value is available or if the current task has been
+/// scheduled to receive a wakeup instead.
+#[must_use = "this `Poll` may be a `Pending` variant, which should be handled"]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[stable(feature = "futures_api", since = "1.36.0")]
+pub enum Poll<T> {
+    /// Represents that a value is immediately ready.
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    Ready(#[stable(feature = "futures_api", since = "1.36.0")] T),
+
+    /// Represents that a value is not ready yet.
+    ///
+    /// When a function returns `Pending`, the function *must* also
+    /// ensure that the current task is scheduled to be awoken when
+    /// progress can be made.
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    Pending,
+}
+
+impl<T> Poll<T> {
+    /// Changes the ready value of this `Poll` with the closure provided.
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    pub fn map<U, F>(self, f: F) -> Poll<U>
+    where
+        F: FnOnce(T) -> U,
+    {
+        match self {
+            Poll::Ready(t) => Poll::Ready(f(t)),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+
+    /// Returns `true` if this is `Poll::Ready`
+    #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    pub fn is_ready(&self) -> bool {
+        matches!(*self, Poll::Ready(_))
+    }
+
+    /// Returns `true` if this is `Poll::Pending`
+    #[inline]
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    pub fn is_pending(&self) -> bool {
+        !self.is_ready()
+    }
+}
+
+impl<T, E> Poll<Result<T, E>> {
+    /// Changes the success value of this `Poll` with the closure provided.
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>
+    where
+        F: FnOnce(T) -> U,
+    {
+        match self {
+            Poll::Ready(Ok(t)) => Poll::Ready(Ok(f(t))),
+            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+
+    /// Changes the error value of this `Poll` with the closure provided.
+    #[stable(feature = "futures_api", since = "1.36.0")]
+    pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>
+    where
+        F: FnOnce(E) -> U,
+    {
+        match self {
+            Poll::Ready(Ok(t)) => Poll::Ready(Ok(t)),
+            Poll::Ready(Err(e)) => Poll::Ready(Err(f(e))),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+impl<T, E> Poll<Option<Result<T, E>>> {
+    /// Changes the success value of this `Poll` with the closure provided.
+    #[unstable(feature = "poll_map", issue = "63514")]
+    pub fn map_ok<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>
+    where
+        F: FnOnce(T) -> U,
+    {
+        match self {
+            Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(Ok(f(t)))),
+            Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e))),
+            Poll::Ready(None) => Poll::Ready(None),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+
+    /// Changes the error value of this `Poll` with the closure provided.
+    #[unstable(feature = "poll_map", issue = "63514")]
+    pub fn map_err<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>
+    where
+        F: FnOnce(E) -> U,
+    {
+        match self {
+            Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(Ok(t))),
+            Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(f(e)))),
+            Poll::Ready(None) => Poll::Ready(None),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+#[stable(feature = "futures_api", since = "1.36.0")]
+impl<T> From<T> for Poll<T> {
+    fn from(t: T) -> Poll<T> {
+        Poll::Ready(t)
+    }
+}
+
+#[stable(feature = "futures_api", since = "1.36.0")]
+impl<T, E> Try for Poll<Result<T, E>> {
+    type Ok = Poll<T>;
+    type Error = E;
+
+    #[inline]
+    fn into_result(self) -> Result<Self::Ok, Self::Error> {
+        match self {
+            Poll::Ready(Ok(x)) => Ok(Poll::Ready(x)),
+            Poll::Ready(Err(e)) => Err(e),
+            Poll::Pending => Ok(Poll::Pending),
+        }
+    }
+
+    #[inline]
+    fn from_error(e: Self::Error) -> Self {
+        Poll::Ready(Err(e))
+    }
+
+    #[inline]
+    fn from_ok(x: Self::Ok) -> Self {
+        x.map(Ok)
+    }
+}
+
+#[stable(feature = "futures_api", since = "1.36.0")]
+impl<T, E> Try for Poll<Option<Result<T, E>>> {
+    type Ok = Poll<Option<T>>;
+    type Error = E;
+
+    #[inline]
+    fn into_result(self) -> Result<Self::Ok, Self::Error> {
+        match self {
+            Poll::Ready(Some(Ok(x))) => Ok(Poll::Ready(Some(x))),
+            Poll::Ready(Some(Err(e))) => Err(e),
+            Poll::Ready(None) => Ok(Poll::Ready(None)),
+            Poll::Pending => Ok(Poll::Pending),
+        }
+    }
+
+    #[inline]
+    fn from_error(e: Self::Error) -> Self {
+        Poll::Ready(Some(Err(e)))
+    }
+
+    #[inline]
+    fn from_ok(x: Self::Ok) -> Self {
+        x.map(|x| x.map(Ok))
+    }
+}