sync: bounded channel can not have 0 size (#879)

tokio-sync/src/mpsc/bounded.rs

@@ -111,6 +111,7 @@ pub struct RecvError(());
 /// }));
 /// ```
 pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
+    assert_eq!(buffer >= 1, true);
     let semaphore = (::semaphore::Semaphore::new(buffer), buffer);
     let (tx, rx) = chan::channel(semaphore);
 

tokio-sync/tests/mpsc.rs

@@ -65,6 +65,12 @@ fn send_recv_with_buffer() {
     assert!(val.is_none());
 }
 
+#[test]
+#[should_panic]
+fn buffer_gteq_one() {
+    mpsc::channel::<i32>(0);
+}
+
 #[test]
 fn send_recv_unbounded() {
     let (mut tx, mut rx) = mpsc::unbounded_channel::<i32>();