feat: Typing notifications in simplified sliding sync

What's missing? Being able to use separate rooms & lists for typing
indicators.
At the moment, we use the same ones as we use for the timeline, as
todo_rooms is quite intertwined. We need to disentangle this to get that
functionality, although I'm not sure if clients use it.

src/api/client/sync/v3.rs

@@ -808,7 +808,7 @@ async fn load_joined_room(
 			let typings = services
 				.rooms
 				.typing
-				.typings_all(room_id, sender_user)
+				.typings_event_for_user(room_id, sender_user)
 				.await?;
 
 			Ok(vec![serde_json::from_str(&serde_json::to_string(&typings)?)?])

src/api/client/sync/v5.rs

@@ -33,6 +33,7 @@ use ruma::{
 	events::{
 		AnyRawAccountDataEvent, AnySyncEphemeralRoomEvent, StateEventType, TimelineEventType,
 		room::member::{MembershipState, RoomMemberEventContent},
+		typing::TypingEventContent,
 	},
 	serde::Raw,
 	uint,
@@ -205,6 +206,9 @@ pub(crate) async fn sync_events_v5_route(
 		_ = tokio::time::timeout(duration, watcher).await;
 	}
 
+	let typing = collect_typing_events(services, sender_user, &body, &todo_rooms).await?;
+	response.extensions.typing = typing;
+
 	trace!(
 		rooms = ?response.rooms.len(),
 		account_data = ?response.extensions.account_data.rooms.len(),
@@ -288,6 +292,8 @@ where
 	Rooms: Iterator<Item = &'a RoomId> + Clone + Send + 'a,
 	AllRooms: Iterator<Item = &'a RoomId> + Clone + Send + 'a,
 {
+	// TODO MSC4186: Implement remaining list filters: is_dm, is_encrypted,
+	// room_types.
 	for (list_id, list) in &body.lists {
 		let active_rooms: Vec<_> = match list.filters.as_ref().and_then(|f| f.is_invite) {
 			| None => all_rooms.clone().collect(),
@@ -665,6 +671,62 @@ where
 	}
 	Ok(rooms)
 }
+
+async fn collect_typing_events(
+	services: &Services,
+	sender_user: &UserId,
+	body: &sync_events::v5::Request,
+	todo_rooms: &TodoRooms,
+) -> Result<sync_events::v5::response::Typing> {
+	if !body.extensions.typing.enabled.unwrap_or(false) {
+		return Ok(sync_events::v5::response::Typing::default());
+	}
+	let rooms: Vec<_> = body.extensions.typing.rooms.clone().unwrap_or_else(|| {
+		body.room_subscriptions
+			.keys()
+			.map(ToOwned::to_owned)
+			.collect()
+	});
+	let lists: Vec<_> = body
+		.extensions
+		.typing
+		.lists
+		.clone()
+		.unwrap_or_else(|| body.lists.keys().map(ToOwned::to_owned).collect::<Vec<_>>());
+
+	if rooms.is_empty() && lists.is_empty() {
+		return Ok(sync_events::v5::response::Typing::default());
+	}
+
+	let mut typing_response = sync_events::v5::response::Typing::default();
+	for (room_id, (required_state_request, timeline_limit, roomsince)) in todo_rooms {
+		if services.rooms.typing.last_typing_update(room_id).await? <= *roomsince {
+			continue;
+		}
+
+		match services
+			.rooms
+			.typing
+			.typing_users_for_user(room_id, sender_user)
+			.await
+		{
+			| Ok(typing_users) => {
+				typing_response.rooms.insert(
+					room_id.to_owned(), // Already OwnedRoomId
+					Raw::new(&sync_events::v5::response::SyncTypingEvent {
+						content: TypingEventContent::new(typing_users),
+					})?,
+				);
+			},
+			| Err(e) => {
+				warn!(%room_id, "Failed to get typing events for room: {}", e);
+			},
+		}
+	}
+
+	Ok(typing_response)
+}
+
 async fn collect_account_data(
 	services: &Services,
 	(sender_user, _, globalsince, body): (&UserId, &DeviceId, u64, &sync_events::v5::Request),