doc: Improve doc comments

Also move `EventMeta::thread_root_id` next to `event_id`

Author: jmartinesp

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

@@ -512,6 +512,10 @@ pub(in crate::timeline) struct EventMeta {
     /// The ID of the event.
     pub event_id: OwnedEventId,
 
+    /// If this event is part of a thread, this will contain its thread root
+    /// event id.
+    pub thread_root_id: Option<OwnedEventId>,
+
     /// Whether the event is among the timeline items.
     pub visible: bool,
 
@@ -577,8 +581,6 @@ pub(in crate::timeline) struct EventMeta {
     /// Note that the #2 timeline item (the day divider) doesn't map to any
     /// remote event, but if it moves, it has an impact on this mapping.
     pub timeline_item_index: Option<usize>,
-
-    pub thread_root_id: Option<OwnedEventId>,
 }
 
 impl EventMeta {
@@ -587,6 +589,6 @@ impl EventMeta {
         visible: bool,
         thread_root_id: Option<OwnedEventId>,
     ) -> Self {
-        Self { event_id, visible, timeline_item_index: None, thread_root_id }
+        Self { event_id, thread_root_id, visible, timeline_item_index: None }
     }
 }

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

@@ -1769,6 +1769,11 @@ impl TimelineController {
             }
             _ => true,
         };
+
+        // In some timelines, threaded events are added to the `AllRemoteEvents`
+        // collection since they need to be taken into account to calculate read
+        // receipts, but we don't want to actually take them into account for returning
+        // the latest event id since they're not visibly in the timeline
         state
             .items
             .all_remote_events()

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

@@ -798,9 +798,9 @@ mod observable_items_tests {
     fn event_meta(event_id: &str) -> EventMeta {
         EventMeta {
             event_id: event_id.parse().unwrap(),
+            thread_root_id: None,
             timeline_item_index: None,
             visible: false,
-            thread_root_id: None,
         }
     }
 
@@ -2062,9 +2062,9 @@ mod all_remote_events_tests {
     fn event_meta(event_id: &str, timeline_item_index: Option<usize>) -> EventMeta {
         EventMeta {
             event_id: event_id.parse().unwrap(),
+            thread_root_id: None,
             timeline_item_index,
             visible: false,
-            thread_root_id: None,
         }
     }
 

crates/matrix-sdk-ui/src/timeline/mod.rs

@@ -268,7 +268,7 @@ impl Timeline {
         }
     }
 
-    /// Get the latest of the timeline's event ids.
+    /// Get the latest of the timeline's remote event ids.
     pub async fn latest_event_id(&self) -> Option<OwnedEventId> {
         self.controller.latest_event_id().await
     }