feat(ui): RoomListService::subscribe_to_rooms calls LatestEvents::listen_to_room.

This patch updates `RoomListService::subscribe_to_rooms` to call
`LatestEvents::listen_to_room` automatically. This method becomes async,
which propagates to a couple of callers.

The idea is that when one is interested by a specific room, a
subscription will be applied. This is an opportunity to also “activate”
the computation of the `LatestEvent` for this specific room, so that the
user doesn't have to do that manually (except if room subscription is
never used).

bindings/matrix-sdk-ffi/src/room_list.rs

@@ -121,7 +121,7 @@ impl RoomListService {
         })))
     }
 
-    fn subscribe_to_rooms(&self, room_ids: Vec<String>) -> Result<(), RoomListError> {
+    async fn subscribe_to_rooms(&self, room_ids: Vec<String>) -> Result<(), RoomListError> {
         let room_ids = room_ids
             .into_iter()
             .map(|room_id| {
@@ -129,7 +129,9 @@ impl RoomListService {
             })
             .collect::<Result<Vec<_>, _>>()?;
 
-        self.inner.subscribe_to_rooms(&room_ids.iter().map(AsRef::as_ref).collect::<Vec<_>>());
+        self.inner
+            .subscribe_to_rooms(&room_ids.iter().map(AsRef::as_ref).collect::<Vec<_>>())
+            .await;
 
         Ok(())
     }

crates/matrix-sdk-ui/src/room_list_service/mod.rs

@@ -72,7 +72,7 @@ use ruma::{
 };
 pub use state::*;
 use thiserror::Error;
-use tracing::debug;
+use tracing::{debug, error};
 
 /// The default `required_state` constant value for sliding sync lists and
 /// sliding sync room subscriptions.
@@ -393,7 +393,15 @@ impl RoomListService {
     ///
     /// It means that all events from these rooms will be received every time,
     /// no matter how the `RoomList` is configured.
-    pub fn subscribe_to_rooms(&self, room_ids: &[&RoomId]) {
+    ///
+    /// [`LatestEvents::listen_to_room`][listen_to_room] will be called for each
+    /// room in `room_ids`, so that the [`LatestEventValue`] will automatically
+    /// be calculated and updated for these rooms, for free.
+    ///
+    /// [listen_to_room]: matrix_sdk::latest_events::LatestEvents::listen_to_room
+    /// [`LatestEventValue`]: matrix_sdk::latest_events::LatestEventValue
+    pub async fn subscribe_to_rooms(&self, room_ids: &[&RoomId]) {
+        // Calculate the settings for the room subscriptions.
         let settings = assign!(http::request::RoomSubscription::default(), {
             required_state: DEFAULT_REQUIRED_STATE.iter().map(|(state_event, value)| {
                 (state_event.clone(), (*value).to_owned())
@@ -407,6 +415,7 @@ impl RoomListService {
             timeline_limit: UInt::from(DEFAULT_ROOM_SUBSCRIPTION_TIMELINE_LIMIT),
         });
 
+        // Decide whether the in-flight request (if any) should be cancelled if needed.
         let cancel_in_flight_request = match self.state_machine.get() {
             State::Init | State::Recovering | State::Error { .. } | State::Terminated { .. } => {
                 false
@@ -414,6 +423,19 @@ impl RoomListService {
             State::SettingUp | State::Running => true,
         };
 
+        // Before subscribing, let's listen these rooms to calculate their latest
+        // events.
+        let latest_events = self.client.latest_events().await;
+
+        for room_id in room_ids {
+            if let Err(error) = latest_events.listen_to_room(room_id).await {
+                // Let's not fail the room subscription. Instead, emit a log because it's very
+                // unlikely to happen.
+                error!(?error, ?room_id, "Failed to listen to the latest event for this room");
+            }
+        }
+
+        // Subscribe to the rooms.
         self.sliding_sync.subscribe_to_rooms(room_ids, Some(settings), cancel_in_flight_request)
     }
 

crates/matrix-sdk-ui/tests/integration/room_list_service.rs

@@ -2247,7 +2247,7 @@ async fn test_room_subscription() -> Result<(), Error> {
 
     // Subscribe.
 
-    room_list.subscribe_to_rooms(&[room_id_1]);
+    room_list.subscribe_to_rooms(&[room_id_1]).await;
 
     sync_then_assert_request_and_fake_response! {
         [server, room_list, sync]
@@ -2290,7 +2290,7 @@ async fn test_room_subscription() -> Result<(), Error> {
 
     // Subscribe to another room.
 
-    room_list.subscribe_to_rooms(&[room_id_2]);
+    room_list.subscribe_to_rooms(&[room_id_2]).await;
 
     sync_then_assert_request_and_fake_response! {
         [server, room_list, sync]
@@ -2333,7 +2333,7 @@ async fn test_room_subscription() -> Result<(), Error> {
 
     // Subscribe to an already subscribed room. Nothing happens.
 
-    room_list.subscribe_to_rooms(&[room_id_1]);
+    room_list.subscribe_to_rooms(&[room_id_1]).await;
 
     sync_then_assert_request_and_fake_response! {
         [server, room_list, sync]

labs/multiverse/src/main.rs

@@ -325,7 +325,7 @@ impl App {
                 modifiers: KeyModifiers::CONTROL,
                 ..
             }) => {
-                self.room_list.next_room();
+                self.room_list.next_room().await;
                 let room_id = self.room_list.get_selected_room_id();
                 self.room_view.set_selected_room(room_id);
             }
@@ -333,7 +333,7 @@ impl App {
             Event::Key(KeyEvent {
                 code: Char('k') | Up, modifiers: KeyModifiers::CONTROL, ..
             }) => {
-                self.room_list.previous_room();
+                self.room_list.previous_room().await;
                 let room_id = self.room_list.get_selected_room_id();
                 self.room_view.set_selected_room(room_id);
             }

labs/multiverse/src/widgets/room_list.rs

@@ -68,7 +68,7 @@ impl RoomList {
     /// Focus the list on the next item, wraps around if needs be.
     ///
     /// Returns the index only if there was a meaningful change.
-    pub fn next_room(&mut self) {
+    pub async fn next_room(&mut self) {
         let num_items = self.rooms.lock().len();
 
         // If there's no item to select, leave early.
@@ -83,14 +83,14 @@ impl RoomList {
 
         if prev != Some(new) {
             self.state.select(Some(new));
-            self.subscribe_to_room(new);
+            self.subscribe_to_room(new).await;
         }
     }
 
     /// Focus the list on the previous item, wraps around if needs be.
     ///
     /// Returns the index only if there was a meaningful change.
-    pub fn previous_room(&mut self) {
+    pub async fn previous_room(&mut self) {
         let num_items = self.rooms.lock().len();
 
         // If there's no item to select, leave early.
@@ -105,7 +105,7 @@ impl RoomList {
 
         if prev != Some(new) {
             self.state.select(Some(new));
-            self.subscribe_to_room(new);
+            self.subscribe_to_room(new).await;
         }
     }
 
@@ -121,7 +121,7 @@ impl RoomList {
     }
 
     /// Subscribe to room that is shown at the given `index`.
-    fn subscribe_to_room(&mut self, index: usize) {
+    async fn subscribe_to_room(&mut self, index: usize) {
         // Cancel the subscription to the previous room, if any.
         self.current_room_subscription.take();
 
@@ -129,7 +129,7 @@ impl RoomList {
         if let Some(room) =
             self.get_room_id_of_entry(index).and_then(|room_id| self.client.get_room(&room_id))
         {
-            self.sync_service.room_list_service().subscribe_to_rooms(&[room.room_id()]);
+            self.sync_service.room_list_service().subscribe_to_rooms(&[room.room_id()]).await;
             self.current_room_subscription = Some(room);
         }
     }