fix: Correctly sync newly created rooms

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

@@ -381,21 +381,25 @@ async fn fetch_shortstatehashes(
 				| Some((_, pdu_after_last_sync_end)) => {
 					trace!(?pdu_after_last_sync_end.event_id, "pdu at last sync end");
 
-					services
-						.rooms
-						.state_accessor
-						.pdu_shortstatehash(&pdu_after_last_sync_end.event_id)
-						.await
-						.map_err(|err| err!("Last sync end PDU has no shortstatehash: {err}"))
+					Some(
+						services
+							.rooms
+							.state_accessor
+							.pdu_shortstatehash(&pdu_after_last_sync_end.event_id)
+							.await
+							.map_err(|err| {
+								err!("Last sync end PDU has no shortstatehash: {err}")
+							}),
+					)
 				},
 				| None => {
-					// No events have been sent since the last sync, or we just joined this room,
-					// so the state then is the same as the state now
-					Ok(current_shortstatehash)
+					// No events have been sent since the last sync, or we just joined this room
+					None
 				},
 			}
 		}))
 		.await
+		.flatten()
 		.transpose()?;
 
 	Ok(ShortStateHashes {
@@ -464,23 +468,10 @@ async fn build_state_events(
 		last_sync_end_shortstatehash,
 	} = shortstatehashes;
 
-	let timeline_start_shortstatehash = if let Some((count, pdu)) = timeline.pdus.front() {
-		if matches!(count, PduCount::Backfilled(_)) {
-			// We don't have shortstatehashes for backfilled PDUs, the best we can
-			// do is to use the current state
-			current_shortstatehash
-		} else {
-			services
-				.rooms
-				.state_accessor
-				.pdu_shortstatehash(&pdu.event_id)
-				.await
-				.map_err(|err| err!("Timeline start has no shortstatehash: {err}"))?
-		}
-	} else {
-		// if the timeline is empty there can't possibly be any changes to the state
+	if timeline.pdus.is_empty() {
+		// If the timeline is empty there can't possibly be any changes to the state
 		return Ok(vec![]);
-	};
+	}
 
 	// the user IDs of members whose membership needs to be sent to the client, if
 	// lazy-loading is enabled.
@@ -499,7 +490,6 @@ async fn build_state_events(
 				services,
 				syncing_user,
 				last_sync_end_shortstatehash,
-				timeline_start_shortstatehash,
 				current_shortstatehash,
 				timeline,
 				use_state_after,
@@ -516,8 +506,8 @@ async fn build_state_events(
 			build_state_initial(
 				services,
 				syncing_user,
-				timeline_start_shortstatehash,
 				current_shortstatehash,
+				timeline,
 				use_state_after,
 				lazily_loaded_members.as_ref(),
 			)

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

@@ -4,7 +4,7 @@ use conduwuit::{
 	trace,
 	utils::{self, IterStream, future::ReadyEqExt, stream::WidebandExt as _},
 };
-use futures::{StreamExt, future::join};
+use futures::StreamExt;
 use ruma::{
 	EventId, OwnedRoomId, RoomId,
 	api::client::sync::sync_events::v3::{
@@ -240,29 +240,8 @@ async fn build_left_state_and_timeline(
 	)
 	.await?;
 
-	let timeline_start_shortstatehash = async {
-		if let Some((_, pdu)) = timeline.pdus.front() {
-			if let Ok(shortstatehash) = services
-				.rooms
-				.state_accessor
-				.pdu_shortstatehash(&pdu.event_id)
-				.await
-			{
-				return shortstatehash;
-			}
-		}
-
-		// the timeline generally should not be empty (see the TODO further down),
-		// but in case it is we use `leave_shortstatehash` as the state to
-		// send
-		leave_shortstatehash
-	};
-
 	let lazily_loaded_members =
-		prepare_lazily_loaded_members(services, sync_context, room_id, timeline.senders());
-
-	let (timeline_start_shortstatehash, lazily_loaded_members) =
-		join(timeline_start_shortstatehash, lazily_loaded_members).await;
+		prepare_lazily_loaded_members(services, sync_context, room_id, timeline.senders()).await;
 
 	// TODO: calculate incremental state for incremental syncs.
 	// always calculating initial state _works_ but returns more data and does
@@ -270,8 +249,8 @@ async fn build_left_state_and_timeline(
 	let mut state = build_state_initial(
 		services,
 		syncing_user,
-		timeline_start_shortstatehash,
 		leave_shortstatehash,
+		&timeline,
 		sync_context.use_state_after,
 		lazily_loaded_members.as_ref(),
 	)

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

@@ -33,19 +33,21 @@ use crate::client::TimelinePdus;
 pub(super) async fn build_state_initial(
 	services: &Services,
 	sender_user: &UserId,
-	timeline_start_shortstatehash: ShortStateHash,
 	timeline_end_shortstatehash: ShortStateHash,
+	timeline: &TimelinePdus,
 	use_state_after: bool,
 	lazily_loaded_members: Option<&MemberSet>,
 ) -> Result<Vec<PduEvent>> {
+	let event_ids_in_timeline: HashSet<_> =
+		timeline.pdus.iter().map(|pdu| &pdu.1.event_id).collect();
+
 	// load the keys and event IDs of the state events at the start of the timeline
 	let (shortstatekeys, event_ids): (Vec<_>, Vec<_>) = services
 		.rooms
 		.state_accessor
-		.state_full_ids(if use_state_after {
-			timeline_end_shortstatehash
-		} else {
-			timeline_start_shortstatehash
+		.state_full_ids(timeline_end_shortstatehash)
+		.ready_filter(|(_, event_id)| {
+			use_state_after || !event_ids_in_timeline.contains(event_id)
 		})
 		.unzip()
 		.await;
@@ -94,7 +96,6 @@ pub(super) async fn build_state_incremental<'a>(
 	services: &Services,
 	sender_user: &'a UserId,
 	last_sync_end_shortstatehash: ShortStateHash,
-	timeline_start_shortstatehash: ShortStateHash,
 	timeline_end_shortstatehash: ShortStateHash,
 	timeline: &TimelinePdus,
 	use_state_after: bool,
@@ -105,7 +106,6 @@ pub(super) async fn build_state_incremental<'a>(
 	trace!(
 		%use_state_after,
 		%last_sync_end_shortstatehash,
-		%timeline_start_shortstatehash,
 		%timeline_end_shortstatehash,
 		"computing state for incremental sync"
 	);
@@ -132,7 +132,7 @@ pub(super) async fn build_state_incremental<'a>(
 							.rooms
 							.state_accessor
 							.state_get_shortid(
-								timeline_start_shortstatehash,
+								timeline_end_shortstatehash,
 								&StateEventType::RoomMember,
 								user_id.as_str(),
 							)