fix(sliding_sync): avoid resubscribing existing subscriptions

Signed-off-by: Johannes Marbach <n0-0ne+github@mailbox.org>

Author: Johennes

crates/matrix-sdk/src/sliding_sync/mod.rs

@@ -186,15 +186,27 @@ impl SlidingSync {
         cancel_in_flight_request: bool,
     ) {
         let mut room_subscriptions = self.inner.room_subscriptions.write().unwrap();
-        room_subscriptions.clear();
+
+        // Remove rooms that are no longer subscribed.
+        let to_remove: Vec<_> = room_ids
+            .iter()
+            .filter(|room_id| room_subscriptions.contains_key(*room_id.to_owned()))
+            .collect();
+        let mut any_removed = false;
+        for room_id in to_remove {
+            if room_subscriptions.remove(*room_id).is_some() {
+                any_removed = true;
+            }
+        }
 
         if subscribe_to_rooms(
             room_subscriptions,
             &self.inner.client,
             room_ids,
             settings,
             cancel_in_flight_request,
-        ) {
+        ) || any_removed
+        {
             self.inner.internal_channel_send_if_possible(
                 SlidingSyncInternalMessage::SyncLoopSkipOverCurrentIteration,
             );