feat(sdk): Remove SlidingSyncRoom::prev_batch.

A `SlidingSyncRoom` receives an Ruma
`api::client::sync::sync_events::v4:SlidingSyncRoom`. This value is
stored in the `SlidingSyncRoom::inner` field. From here, some getters
like `name()`, `is_dm()` etc. are using the `inner` field to compute a
result. There was one exception though: `prev_batch`. This value is part
of `v4::SlidingSyncRoom` but it was copied and updated in its own field:
`SlidingSyncRoom::prev_batch`.

I was wondering why. Turns out, there is no reason. Its getter
`prev_batch()` is public, but it's not used by the FFI bindings, so
basically nobody uses it (as this project is experimental as the time of
writing, we know our users).

This patch removes the `SlidingSyncRoom::prev_batch` field.

This patch also removes the `SlidingSyncRoom::prev_batch()` getter.

This patch finally removes the `FrozenSlidingSyncRoom::prev_batch` field
too.

crates/matrix-sdk/src/sliding_sync/list/frozen.rs

@@ -72,7 +72,6 @@ mod tests {
                         FrozenSlidingSyncRoom {
                             room_id: room_id!("!foo:bar.org").to_owned(),
                             inner: v4::SlidingSyncRoom::default(),
-                            prev_batch: Some("let it go!".to_owned()),
                             timeline_queue: vector![TimelineEvent::new(
                                 Raw::new(&json!({
                                     "content": RoomMessageEventContent::text_plain("let it gooo!"),
@@ -100,7 +99,6 @@ mod tests {
                     "!foo:bar.org": {
                         "room_id": "!foo:bar.org",
                         "inner": {},
-                        "prev_batch": "let it go!",
                         "timeline": [
                             {
                                 "event": {

crates/matrix-sdk/src/sliding_sync/room.rs

@@ -7,7 +7,6 @@ use std::{
     },
 };
 
-use eyeball::unique::Observable;
 use eyeball_im::ObservableVector;
 use imbl::Vector;
 use matrix_sdk_base::deserialized_responses::SyncTimelineEvent;
@@ -45,12 +44,6 @@ pub struct SlidingSyncRoom {
     /// Whether the room has been loaded from the cache only.
     is_cold: Arc<AtomicBool>,
 
-    /// The `prev_batch` data.
-    ///
-    /// It's extracted from `Self::inner`. Why this one is extracted and not the
-    /// others? Maybe it can be simplified.
-    prev_batch: Arc<StdRwLock<Observable<Option<String>>>>,
-
     /// A queue of received events, used to build a
     /// [`Timeline`][crate::Timeline].
     timeline_queue: Arc<StdRwLock<ObservableVector<SyncTimelineEvent>>>,
@@ -70,7 +63,6 @@ impl SlidingSyncRoom {
             client,
             room_id,
             is_cold: Arc::new(AtomicBool::new(false)),
-            prev_batch: Arc::new(StdRwLock::new(Observable::new(inner.prev_batch.clone()))),
             timeline_queue: Arc::new(StdRwLock::new(timeline_queue)),
             inner,
         }
@@ -81,11 +73,6 @@ impl SlidingSyncRoom {
         &self.room_id
     }
 
-    /// The `prev_batch` key to fetch more timeline events for this room.
-    pub fn prev_batch(&self) -> Option<String> {
-        self.prev_batch.read().unwrap().clone()
-    }
-
     /// `Timeline` of this room
     pub async fn timeline(&self) -> Option<Timeline> {
         Some(self.timeline_builder()?.track_read_marker_and_receipts().build().await)
@@ -93,10 +80,12 @@ impl SlidingSyncRoom {
 
     fn timeline_builder(&self) -> Option<TimelineBuilder> {
         if let Some(room) = self.client.get_room(&self.room_id) {
-            Some(Timeline::builder(&room).events(
-                self.prev_batch.read().unwrap().clone(),
-                self.timeline_queue.read().unwrap().clone(),
-            ))
+            Some(
+                Timeline::builder(&room).events(
+                    self.inner.prev_batch.clone(),
+                    self.timeline_queue.read().unwrap().clone(),
+                ),
+            )
         } else if let Some(invited_room) = self.client.get_invited_room(&self.room_id) {
             Some(Timeline::builder(&invited_room).events(None, Vector::new()))
         } else {
@@ -192,7 +181,7 @@ impl SlidingSyncRoom {
         }
 
         if prev_batch.is_some() {
-            Observable::set(&mut self.prev_batch.write().unwrap(), prev_batch);
+            self.inner.prev_batch = prev_batch;
         }
 
         // There is timeline updates.
@@ -238,7 +227,7 @@ impl SlidingSyncRoom {
     }
 
     pub(super) fn from_frozen(frozen_room: FrozenSlidingSyncRoom, client: Client) -> Self {
-        let FrozenSlidingSyncRoom { room_id, inner, prev_batch, timeline_queue } = frozen_room;
+        let FrozenSlidingSyncRoom { room_id, inner, timeline_queue } = frozen_room;
 
         let mut timeline_queue_ob = ObservableVector::new();
         timeline_queue_ob.append(timeline_queue);
@@ -248,7 +237,6 @@ impl SlidingSyncRoom {
             room_id,
             inner,
             is_cold: Arc::new(AtomicBool::new(true)),
-            prev_batch: Arc::new(StdRwLock::new(Observable::new(prev_batch))),
             timeline_queue: Arc::new(StdRwLock::new(timeline_queue_ob)),
         }
     }
@@ -260,7 +248,6 @@ impl SlidingSyncRoom {
 pub(super) struct FrozenSlidingSyncRoom {
     pub(super) room_id: OwnedRoomId,
     pub(super) inner: v4::SlidingSyncRoom,
-    pub(super) prev_batch: Option<String>,
     #[serde(rename = "timeline")]
     pub(super) timeline_queue: Vector<SyncTimelineEvent>,
 }
@@ -270,23 +257,21 @@ impl From<&SlidingSyncRoom> for FrozenSlidingSyncRoom {
         let timeline = value.timeline_queue.read().unwrap();
         let timeline_length = timeline.len();
 
+        let mut inner = value.inner.clone();
+
         // To not overflow the database, we only freeze the newest 10 items. On doing
         // so, we must drop the `prev_batch` key however, as we'd otherwise
         // create a gap between what we have loaded and where the
         // prev_batch-key will start loading when paginating backwards.
-        let (prev_batch, timeline) = if timeline_length > 10 {
+        let timeline = if timeline_length > 10 {
             let pos = timeline_length - 10;
-            (None, timeline.iter().skip(pos).cloned().collect())
+            inner.prev_batch = None;
+            timeline.iter().skip(pos).cloned().collect()
         } else {
-            (value.prev_batch.read().unwrap().clone(), timeline.clone())
+            timeline.clone()
         };
 
-        Self {
-            prev_batch,
-            timeline_queue: timeline,
-            room_id: value.room_id.clone(),
-            inner: value.inner.clone(),
-        }
+        Self { timeline_queue: timeline, room_id: value.room_id.clone(), inner }
     }
 }
 
@@ -304,7 +289,6 @@ mod tests {
         let frozen_sliding_sync_room = FrozenSlidingSyncRoom {
             room_id: room_id!("!29fhd83h92h0:example.com").to_owned(),
             inner: v4::SlidingSyncRoom::default(),
-            prev_batch: Some("let it go!".to_owned()),
             timeline_queue: vector![TimelineEvent::new(
                 Raw::new(&json! ({
                     "content": RoomMessageEventContent::text_plain("let it gooo!"),
@@ -322,7 +306,7 @@ mod tests {
 
         assert_eq!(
             serde_json::to_string(&frozen_sliding_sync_room).unwrap(),
-            r#"{"room_id":"!29fhd83h92h0:example.com","inner":{},"prev_batch":"let it go!","timeline":[{"event":{"content":{"body":"let it gooo!","msgtype":"m.text"},"event_id":"$xxxxx:example.org","origin_server_ts":2189,"room_id":"!someroom:example.com","sender":"@bob:example.com","type":"m.room.message"},"encryption_info":null}]}"#,
+            r#"{"room_id":"!29fhd83h92h0:example.com","inner":{},"timeline":[{"event":{"content":{"body":"let it gooo!","msgtype":"m.text"},"event_id":"$xxxxx:example.org","origin_server_ts":2189,"room_id":"!someroom:example.com","sender":"@bob:example.com","type":"m.room.message"},"encryption_info":null}]}"#,
         );
     }
 }