Fix race condition when UpdateChannel message is received while fetching participants for previous update

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/collab/src/rpc.rs

@@ -1156,7 +1156,6 @@ async fn rejoin_room(
         channel_members = mem::take(&mut rejoined_room.channel_members);
     }
 
-    //TODO: move this into the room guard
     if let Some(channel_id) = channel_id {
         channel_updated(
             channel_id,
@@ -2453,9 +2452,6 @@ async fn join_channel(
         joined_room.clone()
     };
 
-    // TODO - do this while still holding the room guard,
-    // currently there's a possible race condition if someone joins the channel
-    // after we've dropped the lock but before we finish sending these updates
     channel_updated(
         channel_id,
         &joined_room.room,
@@ -2748,7 +2744,6 @@ async fn leave_room_for_session(session: &Session) -> Result<()> {
         return Ok(());
     }
 
-    // TODO - do this while holding the room guard.
     if let Some(channel_id) = channel_id {
         channel_updated(
             channel_id,

crates/collab/src/tests/channel_tests.rs

@@ -290,6 +290,7 @@ async fn test_core_channels(
     );
 }
 
+#[track_caller]
 fn assert_participants_eq(participants: &[Arc<User>], expected_partitipants: &[u64]) {
     assert_eq!(
         participants.iter().map(|p| p.id).collect::<Vec<_>>(),
@@ -297,6 +298,7 @@ fn assert_participants_eq(participants: &[Arc<User>], expected_partitipants: &[u
     );
 }
 
+#[track_caller]
 fn assert_members_eq(
     members: &[ChannelMembership],
     expected_members: &[(u64, bool, proto::channel_member::Kind)],