fix(event cache): get the *most recent* pagination token, not the *ol…

…dest* one

crates/matrix-sdk/src/event_cache/pagination.rs

@@ -245,8 +245,8 @@ impl RoomPagination {
     /// Otherwise, it will immediately skip.
     #[doc(hidden)]
     pub async fn get_or_wait_for_token(&self, wait_time: Option<Duration>) -> Option<String> {
-        fn get_oldest(events: &RoomEvents) -> Option<String> {
-            events.chunks().find_map(|chunk| match chunk.content() {
+        fn get_latest(events: &RoomEvents) -> Option<String> {
+            events.rchunks().find_map(|chunk| match chunk.content() {
                 ChunkContent::Gap(gap) => Some(gap.prev_token.clone()),
                 ChunkContent::Items(..) => None,
             })
@@ -256,7 +256,7 @@ impl RoomPagination {
             // Scope for the lock guard.
             let state = self.inner.state.read().await;
             // Fast-path: we do have a previous-batch token already.
-            if let Some(found) = get_oldest(state.events()) {
+            if let Some(found) = get_latest(state.events()) {
                 return Some(found);
             }
             // If we've already waited for an initial previous-batch token before,
@@ -275,7 +275,7 @@ impl RoomPagination {
         let _ = timeout(wait_time, self.inner.pagination_batch_token_notifier.notified()).await;
 
         let mut state = self.inner.state.write().await;
-        let token = get_oldest(state.events());
+        let token = get_latest(state.events());
         state.waited_for_initial_prev_token = true;
         token
     }

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

@@ -18,10 +18,10 @@ use eyeball_im::VectorDiff;
 pub use matrix_sdk_base::event_cache::{Event, Gap};
 use matrix_sdk_base::{
     event_cache::store::DEFAULT_CHUNK_CAPACITY,
-    linked_chunk::{AsVector, ObservableUpdates},
+    linked_chunk::{AsVector, IterBackward, ObservableUpdates},
 };
 use matrix_sdk_common::linked_chunk::{
-    Chunk, ChunkIdentifier, EmptyChunk, Error, Iter, LinkedChunk, Position,
+    Chunk, ChunkIdentifier, EmptyChunk, Error, LinkedChunk, Position,
 };
 use ruma::OwnedEventId;
 use tracing::{debug, error, warn};
@@ -172,10 +172,20 @@ impl RoomEvents {
     /// Iterate over the chunks, forward.
     ///
     /// The oldest chunk comes first.
-    pub fn chunks(&self) -> Iter<'_, DEFAULT_CHUNK_CAPACITY, Event, Gap> {
+    #[cfg(test)]
+    pub fn chunks(
+        &self,
+    ) -> matrix_sdk_common::linked_chunk::Iter<'_, DEFAULT_CHUNK_CAPACITY, Event, Gap> {
         self.chunks.chunks()
     }
 
+    /// Iterate over the chunks, backward.
+    ///
+    /// The most recent chunk comes first.
+    pub fn rchunks(&self) -> IterBackward<'_, DEFAULT_CHUNK_CAPACITY, Event, Gap> {
+        self.chunks.rchunks()
+    }
+
     /// Iterate over the events, backward.
     ///
     /// The most recent event comes first.