Merge pull request #3550 from Hywan/fix-ui-timeline-duplicated-events

fix(ui): Change the behaviour when a duplicated event is received by the `Timeline`

crates/matrix-sdk-ui/src/timeline/inner/state.rs

@@ -501,7 +501,9 @@ impl TimelineInnerStateTransaction<'_> {
                         timestamp: Some(event.origin_server_ts()),
                         visible: false,
                     };
-                    self.add_event(event_meta, position, room_data_provider, settings).await;
+                    let _event_added_or_updated = self
+                        .add_or_update_event(event_meta, position, room_data_provider, settings)
+                        .await;
 
                     return HandleEventResult::default();
                 }
@@ -526,7 +528,9 @@ impl TimelineInnerStateTransaction<'_> {
                             timestamp,
                             visible: false,
                         };
-                        self.add_event(event_meta, position, room_data_provider, settings).await;
+                        let _event_added_or_updated = self
+                            .add_or_update_event(event_meta, position, room_data_provider, settings)
+                            .await;
                     }
 
                     return HandleEventResult::default();
@@ -543,7 +547,15 @@ impl TimelineInnerStateTransaction<'_> {
             timestamp: Some(timestamp),
             visible: should_add,
         };
-        self.add_event(event_meta, position, room_data_provider, settings).await;
+
+        let event_added_or_updated =
+            self.add_or_update_event(event_meta, position, room_data_provider, settings).await;
+
+        // If the event has not been added or updated, it's because it's a duplicated
+        // event. Let's return early.
+        if !event_added_or_updated {
+            return HandleEventResult::default();
+        }
 
         let sender_profile = room_data_provider.profile_from_user_id(&sender).await;
         let ctx = TimelineEventContext {
@@ -637,23 +649,37 @@ impl TimelineInnerStateTransaction<'_> {
         items.commit();
     }
 
-    async fn add_event<P: RoomDataProvider>(
+    /// Add or update an event in the [`TimelineInnerMeta::all_events`]
+    /// collection.
+    ///
+    /// This method also adjusts read receipt if needed.
+    ///
+    /// It returns `true` if the event has been added or updated, `false`
+    /// otherwise. The latter happens if the event already exists, i.e. if
+    /// an existing event is requested to be added.
+    async fn add_or_update_event<P: RoomDataProvider>(
         &mut self,
         event_meta: FullEventMeta<'_>,
         position: TimelineItemPosition,
         room_data_provider: &P,
         settings: &TimelineInnerSettings,
-    ) {
+    ) -> bool {
+        // Detect if an event already exists in [`TimelineInnerMeta::all_events`]
+        fn event_already_exists(new_event_id: &EventId, all_events: &VecDeque<EventMeta>) -> bool {
+            all_events.iter().any(|EventMeta { event_id, .. }| event_id == new_event_id)
+        }
+
         match position {
             TimelineItemPosition::Start { .. } => {
+                if event_already_exists(event_meta.event_id, &self.meta.all_events) {
+                    return false;
+                }
+
                 self.meta.all_events.push_front(event_meta.base_meta())
             }
             TimelineItemPosition::End { .. } => {
-                // Handle duplicated event.
-                if let Some(pos) =
-                    self.meta.all_events.iter().position(|ev| ev.event_id == event_meta.event_id)
-                {
-                    self.meta.all_events.remove(pos);
+                if event_already_exists(event_meta.event_id, &self.meta.all_events) {
+                    return false;
                 }
 
                 self.meta.all_events.push_back(event_meta.base_meta());
@@ -686,6 +712,8 @@ impl TimelineInnerStateTransaction<'_> {
 
             self.maybe_add_implicit_read_receipt(event_meta);
         }
+
+        true
     }
 
     fn adjust_day_dividers(&mut self, mut adjuster: DayDividerAdjuster) {

crates/matrix-sdk-ui/tests/integration/timeline/sliding_sync.rs

@@ -416,10 +416,6 @@ async fn test_timeline_duplicated_events() -> Result<()> {
         assert_timeline_stream! {
             [timeline_stream]
             update[3] "$x3:bar.org";
-            update[1] "$x1:bar.org";
-            remove[1];
-            append    "$x1:bar.org";
-            update[3] "$x1:bar.org";
             append    "$x4:bar.org";
         };
     }