task: wake LocalSet on spawn_local (#3369)

tokio/src/task/local.rs

@@ -283,6 +283,7 @@ impl LocalSet {
         let future = crate::util::trace::task(future, "local");
         let (task, handle) = unsafe { task::joinable_local(future) };
         self.context.tasks.borrow_mut().queue.push_back(task);
+        self.context.shared.waker.wake();
         handle
     }
 

tokio/tests/task_local_set.rs

@@ -1,6 +1,11 @@
 #![warn(rust_2018_idioms)]
 #![cfg(feature = "full")]
 
+use futures::{
+    future::{pending, ready},
+    FutureExt,
+};
+
 use tokio::runtime::{self, Runtime};
 use tokio::sync::{mpsc, oneshot};
 use tokio::task::{self, LocalSet};
@@ -486,6 +491,15 @@ async fn acquire_mutex_in_drop() {
     drop(local);
 }
 
+#[tokio::test]
+async fn spawn_wakes_localset() {
+    let local = LocalSet::new();
+    futures::select! {
+        _ = local.run_until(pending::<()>()).fuse() => unreachable!(),
+        ret = async { local.spawn_local(ready(())).await.unwrap()}.fuse() => ret
+    }
+}
+
 fn rt() -> Runtime {
     tokio::runtime::Builder::new_current_thread()
         .enable_all()