chore: Performance improvement on read receipts.

Author: pixlwave

crates/matrix-sdk-ui/src/timeline/controller/read_receipts.rs

@@ -288,33 +288,6 @@ impl ReadReceipts {
         timeline_items: &mut ObservableItemsTransaction<'_>,
         at_end: bool,
     ) -> IndexMap<OwnedUserId, Receipt> {
-        // We only need to compute receipts for the visible events that will show them.
-        if !timeline_items
-            .all_remote_events()
-            .iter()
-            .find(|meta| meta.event_id == event_id)
-            .map(|meta| meta.visible && meta.can_show_read_receipts)
-            .unwrap_or(false)
-        {
-            return Default::default();
-        }
-
-        let mut all_receipts = self.get_event_receipts(event_id).cloned().unwrap_or_default();
-
-        if at_end {
-            // No need to search for extra receipts, there are no events after.
-            trace!(
-                "early return because @end, retrieved receipts: {}",
-                all_receipts.iter().map(|(u, _)| u.as_str()).collect::<Vec<_>>().join(", ")
-            );
-            return all_receipts;
-        }
-
-        trace!(
-            "loaded receipts: {}",
-            all_receipts.iter().map(|(u, _)| u.as_str()).collect::<Vec<_>>().join(", ")
-        );
-
         // We are going to add receipts for hidden events to this item.
         //
         // However: since we may be inserting an event at a random position, the
@@ -330,13 +303,32 @@ impl ReadReceipts {
 
         for meta in events_iter.by_ref() {
             if meta.event_id == event_id {
-                break;
+                // We only need to compute receipts for the visible events that will show them.
+                if !meta.visible || !meta.can_show_read_receipts {
+                    return Default::default();
+                }
             }
             if let Some(item_index) = meta.timeline_item_index {
                 prev_event_and_item_index = Some((meta.event_id.clone(), item_index));
             }
         }
 
+        let mut all_receipts = self.get_event_receipts(event_id).cloned().unwrap_or_default();
+
+        if at_end {
+            // No need to search for extra receipts, there are no events after.
+            trace!(
+                "early return because @end, retrieved receipts: {}",
+                all_receipts.iter().map(|(u, _)| u.as_str()).collect::<Vec<_>>().join(", ")
+            );
+            return all_receipts;
+        }
+
+        trace!(
+            "loaded receipts: {}",
+            all_receipts.iter().map(|(u, _)| u.as_str()).collect::<Vec<_>>().join(", ")
+        );
+
         // Include receipts from all the following events that are hidden or can't show
         // read receipts.
         let mut hidden = Vec::new();