From 676824988e12d21878ede2d91b773354b6b0981c Mon Sep 17 00:00:00 2001
From: Thomas Lacroix <toto.rigolo@free.fr>
Date: Tue, 12 Mar 2019 16:51:23 +0100
Subject: sync: impl `Error` for oneshot and watch error types (#967)

Refs: #937
---
 tokio-sync/src/oneshot.rs  | 32 ++++++++++++++++++++++++++++++++
 tokio-sync/src/watch.rs    | 32 ++++++++++++++++++++++++++++++++
 tokio-sync/tests/errors.rs | 22 +++++++++++++++++++---
 3 files changed, 83 insertions(+), 3 deletions(-)

diff --git a/tokio-sync/src/oneshot.rs b/tokio-sync/src/oneshot.rs
index f8e82567..bb11d4e6 100644
--- a/tokio-sync/src/oneshot.rs
+++ b/tokio-sync/src/oneshot.rs
@@ -32,6 +32,8 @@ pub struct Receiver<T> {
 pub mod error {
     //! Oneshot error types
 
+    use std::fmt;
+
     /// Error returned by the `Future` implementation for `Receiver`.
     #[derive(Debug)]
     pub struct RecvError(pub(super) ());
@@ -39,6 +41,36 @@ pub mod error {
     /// Error returned by the `try_recv` function on `Receiver`.
     #[derive(Debug)]
     pub struct TryRecvError(pub(super) ());
+
+    // ===== impl RecvError =====
+
+    impl fmt::Display for RecvError {
+        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            use std::error::Error;
+            write!(fmt, "{}", self.description())
+        }
+    }
+
+    impl ::std::error::Error for RecvError {
+        fn description(&self) -> &str {
+            "channel closed"
+        }
+    }
+
+    // ===== impl TryRecvError =====
+
+    impl fmt::Display for TryRecvError {
+        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            use std::error::Error;
+            write!(fmt, "{}", self.description())
+        }
+    }
+
+    impl ::std::error::Error for TryRecvError {
+        fn description(&self) -> &str {
+            "channel closed"
+        }
+    }
 }
 
 use self::error::*;
diff --git a/tokio-sync/src/watch.rs b/tokio-sync/src/watch.rs
index 4c2b2972..b3303bdc 100644
--- a/tokio-sync/src/watch.rs
+++ b/tokio-sync/src/watch.rs
@@ -104,6 +104,8 @@ pub struct Ref<'a, T: 'a> {
 pub mod error {
     //! Watch error types
 
+    use std::fmt;
+
     /// Error produced when receiving a value fails.
     #[derive(Debug)]
     pub struct RecvError {
@@ -115,6 +117,36 @@ pub mod error {
     pub struct SendError<T> {
         pub(crate) inner: T,
     }
+
+    // ===== impl RecvError =====
+
+    impl fmt::Display for RecvError {
+        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            use std::error::Error;
+            write!(fmt, "{}", self.description())
+        }
+    }
+
+    impl ::std::error::Error for RecvError {
+        fn description(&self) -> &str {
+            "channel closed"
+        }
+    }
+
+    // ===== impl SendError =====
+
+    impl<T: fmt::Debug> fmt::Display for SendError<T> {
+        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            use std::error::Error;
+            write!(fmt, "{}", self.description())
+        }
+    }
+
+    impl<T: fmt::Debug> ::std::error::Error for SendError<T> {
+        fn description(&self) -> &str {
+            "channel closed"
+        }
+    }
 }
 
 #[derive(Debug)]
diff --git a/tokio-sync/tests/errors.rs b/tokio-sync/tests/errors.rs
index 0e56cc1a..129cbfc2 100644
--- a/tokio-sync/tests/errors.rs
+++ b/tokio-sync/tests/errors.rs
@@ -2,12 +2,12 @@
 
 extern crate tokio_sync;
 
-use tokio_sync::mpsc::error;
-
 fn is_error<T: ::std::error::Error + Send + Sync>() {}
 
 #[test]
-fn error_bound() {
+fn mpsc_error_bound() {
+    use tokio_sync::mpsc::error;
+
     is_error::<error::RecvError>();
     is_error::<error::SendError>();
     is_error::<error::TrySendError<()>>();
@@ -15,3 +15,19 @@ fn error_bound() {
     is_error::<error::UnboundedSendError>();
     is_error::<error::UnboundedTrySendError<()>>();
 }
+
+#[test]
+fn oneshot_error_bound() {
+    use tokio_sync::oneshot::error;
+
+    is_error::<error::RecvError>();
+    is_error::<error::TryRecvError>();
+}
+
+#[test]
+fn watch_error_bound() {
+    use tokio_sync::watch::error;
+
+    is_error::<error::RecvError>();
+    is_error::<error::SendError<()>>();
+}
-- 
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