Pass Dispatch as owned value

As an alternative to tokio-rs#1045, this PR switches `set_default` and `with_default` to take an owned `Dispatch` instead of a ref.

See [comment here](tokio-rs#1045 (comment)) for motivation.

Closes tokio-rs#455
Part of tokio-rs#922

tracing-core/src/dispatcher.rs

@@ -66,7 +66,7 @@
 //! // no default subscriber
 //!
 //! # #[cfg(feature = "std")]
-//! dispatcher::with_default(&my_dispatch, || {
+//! dispatcher::with_default(my_dispatch, || {
 //!     // my_subscriber is the default
 //! });
 //!
@@ -227,7 +227,7 @@ pub struct DefaultGuard(Option<Dispatch>);
 /// [`set_global_default`]: ../fn.set_global_default.html
 #[cfg(feature = "std")]
 #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
-pub fn with_default<T>(dispatcher: &Dispatch, f: impl FnOnce() -> T) -> T {
+pub fn with_default<T>(dispatcher: Dispatch, f: impl FnOnce() -> T) -> T {
     // When this guard is dropped, the default dispatcher will be reset to the
     // prior default. Using this (rather than simply resetting after calling
     // `f`) ensures that we always reset to the prior dispatcher even if `f`
@@ -253,7 +253,7 @@ pub fn with_default<T>(dispatcher: &Dispatch, f: impl FnOnce() -> T) -> T {
 #[cfg(feature = "std")]
 #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 #[must_use = "Dropping the guard unregisters the dispatcher."]
-pub fn set_default(dispatcher: &Dispatch) -> DefaultGuard {
+pub fn set_default(dispatcher: Dispatch) -> DefaultGuard {
     // When this guard is dropped, the default dispatcher will be reset to the
     // prior default. Using this ensures that we always reset to the prior
     // dispatcher even if the thread calling this function panics.
@@ -856,7 +856,7 @@ mod test {
             fn exit(&self, _: &span::Id) {}
         }
 
-        with_default(&Dispatch::new(TestSubscriber), || {
+        with_default(Dispatch::new(TestSubscriber), || {
             Event::dispatch(&TEST_META, &TEST_META.fields().value_set(&[]))
         })
     }
@@ -904,7 +904,7 @@ mod test {
             fn exit(&self, _: &span::Id) {}
         }
 
-        with_default(&Dispatch::new(TestSubscriber), mk_span)
+        with_default(Dispatch::new(TestSubscriber), mk_span)
     }
 
     #[test]
@@ -936,7 +936,7 @@ mod test {
 
             fn exit(&self, _: &span::Id) {}
         }
-        let guard = set_default(&Dispatch::new(TestSubscriber));
+        let guard = set_default(Dispatch::new(TestSubscriber));
         let default_dispatcher = Dispatch::default();
         assert!(default_dispatcher.is::<TestSubscriber>());
 

tracing-core/tests/dispatch.rs

@@ -14,7 +14,7 @@ fn set_default_dispatch() {
         )
     });
 
-    let guard = set_default(&Dispatch::new(TestSubscriberB));
+    let guard = set_default(Dispatch::new(TestSubscriberB));
     get_default(|current| assert!(current.is::<TestSubscriberB>(), "set_default get failed"));
 
     // Drop the guard, setting the dispatch back to the global dispatch
@@ -31,15 +31,15 @@ fn set_default_dispatch() {
 #[cfg(feature = "std")]
 #[test]
 fn nested_set_default() {
-    let _guard = set_default(&Dispatch::new(TestSubscriberA));
+    let _guard = set_default(Dispatch::new(TestSubscriberA));
     get_default(|current| {
         assert!(
             current.is::<TestSubscriberA>(),
             "set_default for outer subscriber failed"
         )
     });
 
-    let inner_guard = set_default(&Dispatch::new(TestSubscriberB));
+    let inner_guard = set_default(Dispatch::new(TestSubscriberB));
     get_default(|current| {
         assert!(
             current.is::<TestSubscriberB>(),

tracing-core/tests/global_dispatch.rs

@@ -13,7 +13,7 @@ fn global_dispatch() {
     });
 
     #[cfg(feature = "std")]
-    with_default(&Dispatch::new(TestSubscriberB), || {
+    with_default(Dispatch::new(TestSubscriberB), || {
         get_default(|current| {
             assert!(
                 current.is::<TestSubscriberB>(),

tracing-futures/src/lib.rs

@@ -439,7 +439,7 @@ impl<T: futures_01::Future> futures_01::Future for WithDispatch<T> {
 
     fn poll(&mut self) -> futures_01::Poll<Self::Item, Self::Error> {
         let inner = &mut self.inner;
-        dispatcher::with_default(&self.dispatch, || inner.poll())
+        dispatcher::with_default(self.dispatch.clone(), || inner.poll())
     }
 }
 
@@ -452,7 +452,7 @@ impl<T: crate::stdlib::future::Future> crate::stdlib::future::Future for WithDis
         let this = self.project();
         let dispatch = this.dispatch;
         let future = this.inner;
-        dispatcher::with_default(dispatch, || future.poll(cx))
+        dispatcher::with_default(dispatch.clone(), || future.poll(cx))
     }
 }
 

tracing-subscriber/src/fmt/writer.rs

@@ -213,7 +213,7 @@ mod test {
         };
         let dispatch = Dispatch::from(subscriber);
 
-        dispatcher::with_default(&dispatch, || {
+        dispatcher::with_default(dispatch, || {
             error!("{}", msg);
         });
 

tracing-subscriber/src/registry/sharded.rs

@@ -594,7 +594,7 @@ mod tests {
         // registry.
         let dispatch = dispatcher::Dispatch::new(subscriber);
 
-        dispatcher::with_default(&dispatch, || {
+        dispatcher::with_default(dispatch, || {
             let span = tracing::debug_span!("span1");
             drop(span);
             let span = tracing::info_span!("span2");
@@ -604,8 +604,6 @@ mod tests {
         state.assert_removed("span1");
         state.assert_removed("span2");
 
-        // Ensure the registry itself outlives the span.
-        drop(dispatch);
     }
 
     #[test]
@@ -622,7 +620,7 @@ mod tests {
         // registry.
         let dispatch = dispatcher::Dispatch::new(subscriber);
 
-        let span2 = dispatcher::with_default(&dispatch, || {
+        let span2 = dispatcher::with_default(dispatch, || {
             let span = tracing::debug_span!("span1");
             drop(span);
             let span2 = tracing::info_span!("span2");
@@ -637,8 +635,6 @@ mod tests {
         drop(span2);
         state.assert_removed("span1");
 
-        // Ensure the registry itself outlives the span.
-        drop(dispatch);
     }
 
     #[test]
@@ -655,7 +651,7 @@ mod tests {
         // registry.
         let dispatch = dispatcher::Dispatch::new(subscriber);
 
-        dispatcher::with_default(&dispatch, || {
+        dispatcher::with_default(dispatch, || {
             let span1 = tracing::debug_span!("span1");
             let span2 = tracing::info_span!("span2");
 
@@ -688,7 +684,7 @@ mod tests {
 
         let dispatch = dispatcher::Dispatch::new(subscriber);
 
-        dispatcher::with_default(&dispatch, || {
+        dispatcher::with_default(dispatch, || {
             let span1 = tracing::info_span!("parent");
             let span2 = tracing::info_span!(parent: &span1, "child");
 
@@ -715,7 +711,7 @@ mod tests {
 
         let dispatch = dispatcher::Dispatch::new(subscriber);
 
-        dispatcher::with_default(&dispatch, || {
+        dispatcher::with_default(dispatch, || {
             let span1 = tracing::info_span!("grandparent");
             let span2 = tracing::info_span!(parent: &span1, "parent");
             let span3 = tracing::info_span!(parent: &span2, "child");

tracing-subscriber/src/util.rs

@@ -33,7 +33,7 @@ where
         #[cfg(feature = "tracing-log")]
         let _ = tracing_log::LogTracer::init();
 
-        dispatcher::set_default(&self.into())
+        dispatcher::set_default(self.into())
     }
 
     /// Attempts to set `self` as the [global default subscriber] in the current

tracing-subscriber/tests/reload.rs

@@ -61,7 +61,7 @@ fn reload_handle() {
 
     let subscriber = tracing_core::dispatcher::Dispatch::new(layer.with_subscriber(NopSubscriber));
 
-    tracing_core::dispatcher::with_default(&subscriber, || {
+    tracing_core::dispatcher::with_default(subscriber, || {
         assert_eq!(FILTER1_CALLS.load(Ordering::SeqCst), 0);
         assert_eq!(FILTER2_CALLS.load(Ordering::SeqCst), 0);
 

tracing/src/dispatcher.rs

@@ -66,7 +66,7 @@
 //! // no default subscriber
 //!
 //! # #[cfg(feature = "std")]
-//! dispatcher::with_default(&my_dispatch, || {
+//! dispatcher::with_default(my_dispatch, || {
 //!     // my_subscriber is the default
 //! });
 //!

tracing/src/subscriber.rs

@@ -21,7 +21,7 @@ pub fn with_default<T, S>(subscriber: S, f: impl FnOnce() -> T) -> T
 where
     S: Subscriber + Send + Sync + 'static,
 {
-    crate::dispatcher::with_default(&crate::Dispatch::new(subscriber), f)
+    crate::dispatcher::with_default(crate::Dispatch::new(subscriber), f)
 }
 
 /// Sets this subscriber as the global default for the duration of the entire program.
@@ -62,7 +62,7 @@ pub fn set_default<S>(subscriber: S) -> DefaultGuard
 where
     S: Subscriber + Send + Sync + 'static,
 {
-    crate::dispatcher::set_default(&crate::Dispatch::new(subscriber))
+    crate::dispatcher::set_default(crate::Dispatch::new(subscriber))
 }
 
 pub use tracing_core::dispatcher::SetGlobalDefaultError;

tracing/tests/multiple_max_level_hints.rs

@@ -61,10 +61,10 @@ fn multiple_max_level_hints() {
 
     let dispatch1 = tracing::Dispatch::new(subscriber1);
 
-    tracing::dispatcher::with_default(&dispatch1, do_events);
+    tracing::dispatcher::with_default(dispatch1, do_events);
     handle1.assert_finished();
 
     let dispatch2 = tracing::Dispatch::new(subscriber2);
-    tracing::dispatcher::with_default(&dispatch2, do_events);
+    tracing::dispatcher::with_default(dispatch2, do_events);
     handle2.assert_finished();
 }