fix: Properly sync newly joined rooms

src/api/client/sync/v3/joined.rs

@@ -87,8 +87,11 @@ pub(super) async fn load_joined_room(
 		filter,
 	} = sync_context;
 
-	let mut device_list_updates = DeviceListUpdates::new();
+	// the global count as of the end of the last sync.
+	// this will be None if we are doing an initial sync.
+	let previous_sync_end_count = since.map(PduCount::Normal);
 	let next_batchcount = PduCount::Normal(next_batch);
+	let mut device_list_updates = DeviceListUpdates::new();
 
 	// the room state right now
 	let current_shortstatehash = services
@@ -97,29 +100,27 @@ pub(super) async fn load_joined_room(
 		.get_room_shortstatehash(room_id)
 		.map_err(|_| err!(Database(error!("Room {room_id} has no state"))));
 
-	// the global count and room state as of the end of the last sync.
-	// this will be None if we are doing an initial sync.
-	let previous_sync_end = OptionFuture::from(since.map(|since| async move {
-		let previous_sync_end_count = PduCount::Normal(since);
-
-		let previous_sync_end_shortstatehash = services
+	// the room state as of the end of the last sync.
+	// this will be None if we are doing an initial sync or if we just joined this
+	// room.
+	let previous_sync_end_shortstatehash = OptionFuture::from(since.map(|since| {
+		services
 			.rooms
 			.user
 			.get_token_shortstatehash(room_id, since)
-			.await?;
-
-		Ok((previous_sync_end_count, previous_sync_end_shortstatehash))
+			.ok()
 	}))
-	.map(Option::transpose);
+	.map(Option::flatten)
+	.map(Ok);
 
-	let (current_shortstatehash, previous_sync_end) =
-		try_join(current_shortstatehash, previous_sync_end).await?;
+	let (current_shortstatehash, previous_sync_end_shortstatehash) =
+		try_join(current_shortstatehash, previous_sync_end_shortstatehash).await?;
 
 	let timeline = load_timeline(
 		services,
 		sender_user,
 		room_id,
-		previous_sync_end.map(at!(0)),
+		previous_sync_end_count,
 		Some(next_batchcount),
 		10_usize,
 	);
@@ -167,9 +168,9 @@ pub(super) async fn load_joined_room(
 		})
 		.into();
 
-	// the syncing user's membership event during the last sync
-	let membership_during_previous_sync: OptionFuture<_> = previous_sync_end
-		.map(at!(1))
+	// the syncing user's membership event during the last sync.
+	// this will be None if `previous_sync_end_shortstatehash` is None.
+	let membership_during_previous_sync: OptionFuture<_> = previous_sync_end_shortstatehash
 		.map(|shortstatehash| {
 			services
 				.rooms
@@ -244,7 +245,7 @@ pub(super) async fn load_joined_room(
 	.await;
 
 	// reset lazy loading state on initial sync
-	if previous_sync_end.is_none() {
+	if previous_sync_end_count.is_none() {
 		services
 			.rooms
 			.lazy_loading
@@ -252,48 +253,51 @@ pub(super) async fn load_joined_room(
 			.await;
 	}
 
-	let mut state_events =
-		if let Some((previous_sync_end_count, previous_sync_end_shortstatehash)) =
-			previous_sync_end
-			&& !full_state
-		{
-			let state_incremental = calculate_state_incremental(
-				services,
-				sender_user,
-				room_id,
-				previous_sync_end_count,
-				previous_sync_end_shortstatehash,
-				timeline_start_shortstatehash,
-				current_shortstatehash,
-				&timeline,
-				lazily_loaded_members.as_ref(),
-			)
-			.boxed()
-			.await?;
+	/*
+	compute the state delta between the previous sync and this sync. if this is an initial sync
+	*or* we just joined this room, `calculate_state_initial` will be used, otherwise `calculate_state_incremental`
+	will be used.
+	*/
+	let mut state_events = if let Some(previous_sync_end_count) = previous_sync_end_count
+		&& let Some(previous_sync_end_shortstatehash) = previous_sync_end_shortstatehash
+		&& !full_state
+	{
+		calculate_state_incremental(
+			services,
+			sender_user,
+			room_id,
+			previous_sync_end_count,
+			previous_sync_end_shortstatehash,
+			timeline_start_shortstatehash,
+			current_shortstatehash,
+			&timeline,
+			lazily_loaded_members.as_ref(),
+		)
+		.boxed()
+		.await?
+	} else {
+		calculate_state_initial(
+			services,
+			sender_user,
+			timeline_start_shortstatehash,
+			lazily_loaded_members.as_ref(),
+		)
+		.boxed()
+		.await?
+	};
 
-			if is_encrypted_room {
-				calculate_device_list_updates(
-					services,
-					sync_context,
-					room_id,
-					&mut device_list_updates,
-					&state_incremental,
-					joined_since_last_sync,
-				)
-				.await;
-			}
-
-			state_incremental
-		} else {
-			calculate_state_initial(
-				services,
-				sender_user,
-				timeline_start_shortstatehash,
-				lazily_loaded_members.as_ref(),
-			)
-			.boxed()
-			.await?
-		};
+	// for incremental syncs, calculate updates to E2EE device lists
+	if previous_sync_end_count.is_some() && is_encrypted_room {
+		calculate_device_list_updates(
+			services,
+			sync_context,
+			room_id,
+			&mut device_list_updates,
+			&state_events,
+			joined_since_last_sync,
+		)
+		.await;
+	}
 
 	// only compute room counts and heroes (aka the summary) if the room's members
 	// changed since the last sync