feat(watch): allow non-Clone channel values

CHANGELOG.md

@@ -39,6 +39,7 @@ All notable changes to this project will be documented in this file.
 
 ### Improvements
 
+* Allow `watch::channel` to store non-`Clone` values for publication and change notification; only owning reads through `Receiver::get` and `Receiver::recv` require `Clone`.
 * Finish releasing buffered bounded MPSC messages even if one message destructor panics.
 * Improve unbounded MPSC throughput with batched receiving and incremental storage reclamation; empty-buffer retention is bounded independently of previous peak occupancy.
 * Make completed and abandoned `Completion` waits lock-free while preserving cancellable pending registration.

asyncband/src/watch/mod.rs

@@ -90,7 +90,7 @@ use crate::internal::wakerset::WakerToken;
 /// let (_tx, rx) = watch::channel("ready");
 /// assert_eq!(rx.get(), "ready");
 /// ```
-pub fn channel<T: Clone>(initial: T) -> (Sender<T>, Receiver<T>) {
+pub fn channel<T>(initial: T) -> (Sender<T>, Receiver<T>) {
     let shared = Arc::new(Shared {
         state: Mutex::new(State {
             value: initial,

tests-integration/tests/watch_test.rs

@@ -59,6 +59,8 @@ impl Clone for PanicOnceClone {
     }
 }
 
+struct NonClone(usize);
+
 #[test]
 fn initial_value_is_observed_and_updates_coalesce() {
     let (tx, mut rx) = watch::channel(0);
@@ -147,6 +149,22 @@ fn subscriptions_start_at_the_current_version() {
     assert_eq!(FutureExt::block_on(subscribed.recv()).unwrap(), 2);
 }
 
+#[test]
+fn non_clone_values_support_publication_and_change_tracking() {
+    let (tx, mut rx) = watch::channel(NonClone(0));
+
+    assert_eq!(rx.has_changed(), Ok(false));
+
+    tx.send(NonClone(1)).unwrap();
+    assert_eq!(rx.has_changed(), Ok(true));
+    FutureExt::block_on(rx.changed()).unwrap();
+    assert_eq!(rx.has_changed(), Ok(false));
+
+    let previous = tx.send_replace(NonClone(2));
+    assert_eq!(previous.0, 1);
+    assert_eq!(rx.has_changed(), Ok(true));
+}
+
 #[test]
 fn final_unseen_value_is_reported_before_disconnection() {
     let (tx, mut first) = watch::channel(0);