Fetch messages when joining a channel

gpui/src/app.rs

@@ -14,7 +14,7 @@ use keymap::MatchResult;
 use parking_lot::{Mutex, RwLock};
 use pathfinder_geometry::{rect::RectF, vector::vec2f};
 use platform::Event;
-use postage::{mpsc, sink::Sink as _, stream::Stream as _};
+use postage::{mpsc, oneshot, sink::Sink as _, stream::Stream as _};
 use smol::prelude::*;
 use std::{
     any::{type_name, Any, TypeId},
@@ -2310,6 +2310,24 @@ impl<T: Entity> ModelHandle<T> {
         cx.update_model(self, update)
     }
 
+    pub fn next_notification(&self, cx: &TestAppContext) -> impl Future<Output = ()> {
+        let (tx, mut rx) = oneshot::channel();
+        let mut tx = Some(tx);
+
+        let mut cx = cx.cx.borrow_mut();
+        self.update(&mut *cx, |_, cx| {
+            cx.observe(self, move |_, _, _| {
+                if let Some(mut tx) = tx.take() {
+                    tx.blocking_send(()).ok();
+                }
+            });
+        });
+
+        async move {
+            rx.recv().await;
+        }
+    }
+
     pub fn condition(
         &self,
         cx: &TestAppContext,