fixup! lets deal with propagate_changes and updates drain

Author: Hywan

crates/matrix-sdk/src/event_cache/pagination.rs

@@ -131,7 +131,16 @@ impl RoomPagination {
 
             // Try to load one chunk backwards. If it returns `Some(_)`, it means new events
             // have been inserted. No need to reach the network!
-            if let Some((events, reached_start)) = state.load_one_chunk_backwards().await? {
+            if let Some(((events, reached_start), sync_timeline_events_diffs)) =
+                state.load_one_chunk_backwards().await?
+            {
+                if !sync_timeline_events_diffs.is_empty() {
+                    let _ = self.inner.sender.send(RoomEventCacheUpdate::UpdateTimelineEvents {
+                        diffs: sync_timeline_events_diffs,
+                        origin: EventsOrigin::Pagination,
+                    });
+                }
+
                 return Ok(Some(BackPaginationOutcome { reached_start, events }));
             }
         }

crates/matrix-sdk/src/event_cache/room/mod.rs

@@ -747,9 +747,16 @@ mod private {
         /// Return `Ok(Some(events, reached_start))` if events have been
         /// inserted, `Ok(None)` if a gap has been inserted or if the
         /// store is disabled.
+        #[must_use = "Updates as `VectorDiff` must probably be propagated via `RoomEventCacheUpdate`"]
         pub async fn load_one_chunk_backwards(
             &mut self,
-        ) -> Result<Option<(Vec<TimelineEvent>, bool)>, EventCacheError> {
+        ) -> Result<
+            Option<((Vec<TimelineEvent>, bool), Vec<VectorDiff<TimelineEvent>>)>,
+            EventCacheError,
+        > {
+            // ⚠️ Propagate all pending updates before we do anything.
+            self.propagate_changes().await?;
+
             let Some(store) = self.store.get() else {
                 // No store: no events to insert.
                 return Ok(None);
@@ -788,7 +795,15 @@ mod private {
 
             self.events.insert_new_chunk_as_first(new_first_chunk);
 
-            Ok(result)
+            // ⚠️ Let's not propagate the updates to the store! We already have these data
+            // in the store! Let's drain them.
+            let _ = self.events.updates().take();
+
+            // However, we want to get updates as `VectorDiff`s.
+            let updates_as_vector_diffs = self.events.updates_as_vector_diffs();
+
+            Ok(result
+                .map(|(events, reached_start)| ((events, reached_start), updates_as_vector_diffs)))
         }
     }
 }