refactor(event cache): only send a thread summary update when a thread has changed

Author: bnjbvr

crates/matrix-sdk-common/src/deserialized_responses.rs

@@ -370,7 +370,7 @@ impl<'de> Deserialize<'de> for EncryptionInfo {
 /// - the number of replies to the thread,
 /// - the full event of the latest reply to the thread,
 /// - whether the user participated or not to this thread.
-#[derive(Clone, Debug, Serialize, Deserialize)]
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
 pub struct ThreadSummary {
     /// The number of replies to the thread.
     ///
@@ -381,7 +381,7 @@ pub struct ThreadSummary {
 }
 
 /// The status of a thread summary.
-#[derive(Clone, Debug, Default, Serialize, Deserialize)]
+#[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq)]
 pub enum ThreadSummaryStatus {
     /// We don't know if the event has a thread summary.
     #[default]

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

@@ -1224,8 +1224,17 @@ mod private {
                 related_thread_events.len()
             };
 
-            target_event.thread_summary = ThreadSummaryStatus::Some(ThreadSummary { num_replies });
+            let new_summary = ThreadSummary { num_replies };
 
+            if let ThreadSummaryStatus::Some(existing) = &target_event.thread_summary {
+                if existing == &new_summary {
+                    trace!("thread summary is already up-to-date");
+                    return Ok(());
+                }
+            }
+
+            // Cause an update to observers.
+            target_event.thread_summary = ThreadSummaryStatus::Some(new_summary);
             self.replace_event_at(location, target_event).await?;
 
             Ok(())