feat(event cache): include the lazy previous chunk in the debug string, if available

Author: bnjbvr

crates/matrix-sdk-common/src/linked_chunk/mod.rs

@@ -1270,6 +1270,14 @@ impl<const CAPACITY: usize, Item, Gap> Chunk<CAPACITY, Item, Gap> {
         self.next.is_none()
     }
 
+    /// Return the link to the previous chunk, if it was loaded lazily.
+    ///
+    /// Doc hidden because this is mostly for internal debugging purposes.
+    #[doc(hidden)]
+    pub fn lazy_previous(&self) -> Option<ChunkIdentifier> {
+        self.lazy_previous
+    }
+
     /// Get the unique identifier of the chunk.
     pub fn identifier(&self) -> ChunkIdentifier {
         self.identifier

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

@@ -341,7 +341,12 @@ impl RoomEvents {
 
         for chunk in self.chunks() {
             let content = chunk_debug_string(chunk.content());
-            let line = format!("chunk #{}: {content}", chunk.identifier().index());
+            let lazy_previous = if let Some(cid) = chunk.lazy_previous() {
+                format!(" (lazy previous = {})", cid.index())
+            } else {
+                "".to_owned()
+            };
+            let line = format!("chunk #{}{lazy_previous}: {content}", chunk.identifier().index());
 
             result.push(line);
         }