sync: deprecate mpsc::RecvError (#3833)

tokio/src/sync/mpsc/bounded.rs

@@ -65,7 +65,7 @@ pub struct Receiver<T> {
 /// with backpressure.
 ///
 /// The channel will buffer up to the provided number of messages.  Once the
-/// buffer is full, attempts to `send` new messages will wait until a message is
+/// buffer is full, attempts to send new messages will wait until a message is
 /// received from the channel. The provided buffer capacity must be at least 1.
 ///
 /// All data sent on `Sender` will become available on `Receiver` in the same
@@ -76,7 +76,7 @@ pub struct Receiver<T> {
 ///
 /// If the `Receiver` is disconnected while trying to `send`, the `send` method
 /// will return a `SendError`. Similarly, if `Sender` is disconnected while
-/// trying to `recv`, the `recv` method will return a `RecvError`.
+/// trying to `recv`, the `recv` method will return `None`.
 ///
 /// # Panics
 ///

tokio/src/sync/mpsc/error.rs

@@ -55,14 +55,18 @@ impl<T> From<SendError<T>> for TrySendError<T> {
 
 /// Error returned by `Receiver`.
 #[derive(Debug)]
+#[doc(hidden)]
+#[deprecated(note = "This type is unused because recv returns an Option.")]
 pub struct RecvError(());
 
+#[allow(deprecated)]
 impl fmt::Display for RecvError {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(fmt, "channel closed")
     }
 }
 
+#[allow(deprecated)]
 impl Error for RecvError {}
 
 cfg_time! {