refactor(timeline): no need to look at the receipt timestamp

I was wrong in a previous commit: both receipts are on the same event
anyways, so we can safely override the keys in the read receipts map
(overriding would mean both receipts point to the same event, which is
fine, as we're displaying only one of those).

Author: bnjbvr

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

@@ -561,45 +561,36 @@ impl<P: RoomDataProvider> TimelineStateTransaction<'_, P> {
 
         let receipt_thread = self.focus.receipt_thread();
 
-        let mut read_receipts;
-
-        if matches!(receipt_thread, ReceiptThread::Unthreaded | ReceiptThread::Main) {
+        let receipts = if matches!(receipt_thread, ReceiptThread::Unthreaded | ReceiptThread::Main)
+        {
             // If the requested receipt thread is unthreaded or main, we maintain maximal
             // compatibility with clients using either unthreaded or main-thread read
             // receipts by allowing both here.
 
             // First, load the main receipts.
-            read_receipts =
+            let mut main_receipts =
                 room_data_provider.load_event_receipts(event_id, ReceiptThread::Main).await;
 
             // Then, load the unthreaded receipts.
             let unthreaded_receipts =
                 room_data_provider.load_event_receipts(event_id, ReceiptThread::Unthreaded).await;
 
-            // Only insert unthreaded receipts that are more recent. Ideally we'd compare
-            // the receipted event position, but we don't have access to that
-            // here.
-            for (user_id, unthreaded_receipt) in unthreaded_receipts {
-                if let Some(main_receipt) = read_receipts.get(&user_id) {
-                    if unthreaded_receipt.ts > main_receipt.ts {
-                        read_receipts.insert(user_id, unthreaded_receipt);
-                    }
-                } else {
-                    read_receipts.insert(user_id, unthreaded_receipt);
-                }
-            }
+            // We can safely extend both here: if a key is already set, then that means that
+            // the user has the unthreaded and main receipt on the main event,
+            // which is fine, and something we display as the one user receipt.
+            main_receipts.extend(unthreaded_receipts);
+            main_receipts
         } else {
             // In all other cases, return what's requested, and only that (threaded
             // receipts).
-            read_receipts =
-                room_data_provider.load_event_receipts(event_id, receipt_thread.clone()).await
-        }
+            room_data_provider.load_event_receipts(event_id, receipt_thread.clone()).await
+        };
 
         let own_user_id = room_data_provider.own_user_id();
 
         // Since they are explicit read receipts, we need to check if they are
         // superseded by implicit read receipts.
-        for (user_id, receipt) in read_receipts {
+        for (user_id, receipt) in receipts {
             let full_receipt = FullReceipt {
                 event_id,
                 user_id: &user_id,