workaround synapse bug that would make broken PLs

d2m/actions/create-room.js

@@ -95,6 +95,11 @@ async function channelToKState(channel, guild) {
 				type: "m.room_membership",
 				room_id: spaceID
 			}]
+		},
+		"m.room.power_levels/": {
+			events: {
+				"m.room.avatar": 0
+			}
 		}
 	}
 
@@ -114,6 +119,7 @@ async function createRoom(channel, guild, spaceID, kstate) {
 	if (channel.type === DiscordTypes.ChannelType.PublicThread) threadParent = channel.parent_id
 	const invite = threadParent ? [] : ["@cadence:cadence.moe"] // TODO
 
+	const roomID = await postApplyPowerLevels(kstate, async kstate => {
 		const [convertedName, convertedTopic] = convertNameAndTopic(channel, guild, null)
 		const roomID = await api.createRoom({
 			name: convertedName,
@@ -126,12 +132,43 @@ async function createRoom(channel, guild, spaceID, kstate) {
 
 		db.prepare("INSERT INTO channel_room (channel_id, room_id, name, nick, thread_parent) VALUES (?, ?, ?, NULL, ?)").run(channel.id, roomID, channel.name, threadParent)
 
-	// Put the newly created child into the space
+		return roomID
+	})
+
+	// Put the newly created child into the space, no need to await this
 	_syncSpaceMember(channel, spaceID, roomID)
 
 	return roomID
 }
 
+/**
+ * Handling power levels separately. The spec doesn't specify what happens, Dendrite differs,
+ * and Synapse does an absolutely insane *shallow merge* of what I provide on top of what it creates.
+ * We don't want the `events` key to be overridden completely.
+ * https://github.com/matrix-org/synapse/blob/develop/synapse/handlers/room.py#L1170-L1210
+ * https://github.com/matrix-org/matrix-spec/issues/492
+ * @param {any} kstate
+ * @param {(_: any) => Promise<string>} callback must return room ID
+ * @returns {Promise<string>} room ID
+ */
+async function postApplyPowerLevels(kstate, callback) {
+	const powerLevelContent = kstate["m.room.power_levels/"]
+	const kstateWithoutPowerLevels = {...kstate}
+	delete kstateWithoutPowerLevels["m.room.power_levels/"]
+
+	/** @type {string} */
+	const roomID = await callback(kstateWithoutPowerLevels)
+
+	// Now *really* apply the power level overrides on top of what Synapse *really* set
+	if (powerLevelContent) {
+		const newRoomKState = await roomToKState(roomID)
+		const newRoomPowerLevelsDiff = ks.diffKState(newRoomKState, {"m.room.power_levels/": powerLevelContent})
+		await applyKStateDiffToRoom(roomID, newRoomPowerLevelsDiff)
+	}
+
+	return roomID
+}
+
 /**
  * @param {DiscordTypes.APIGuildChannel} channel
  */
@@ -290,5 +327,6 @@ module.exports.createAllForGuild = createAllForGuild
 module.exports.channelToKState = channelToKState
 module.exports.roomToKState = roomToKState
 module.exports.applyKStateDiffToRoom = applyKStateDiffToRoom
+module.exports.postApplyPowerLevels = postApplyPowerLevels
 module.exports._convertNameAndTopic = convertNameAndTopic
 module.exports._unbridgeRoom = _unbridgeRoom

d2m/actions/create-space.js

@@ -21,10 +21,10 @@ const ks = sync.require("../../matrix/kstate")
 async function createSpace(guild, kstate) {
 	const name = kstate["m.room.name/"].name
 	const topic = kstate["m.room.topic/"]?.topic || undefined
-
 	assert(name)
 
-	const roomID = await api.createRoom({
+	const roomID = await createRoom.postApplyPowerLevels(kstate, async kstate => {
+		return api.createRoom({
 			name,
 			preset: "private_chat", // cannot join space unless invited
 			visibility: "private",
@@ -39,6 +39,7 @@ async function createSpace(guild, kstate) {
 			},
 			initial_state: ks.kstateToState(kstate)
 		})
+	})
 	db.prepare("INSERT INTO guild_space (guild_id, space_id) VALUES (?, ?)").run(guild.id, roomID)
 	return roomID
 }

matrix/kstate.js

@@ -47,10 +47,8 @@ function diffKState(actual, target) {
 
 		if (key === "m.room.power_levels/") {
 			// Special handling for power levels, we want to deep merge the actual and target into the final state.
-			console.log(actual[key])
+			if (!(key in actual)) throw new Error(`want to apply a power levels diff, but original power level data is missing\nstarted with:  ${JSON.stringify(actual)}\nwant to apply: ${JSON.stringify(target)}`)
 			const temp = mixin({}, actual[key], target[key])
-			console.log(actual[key])
-			console.log(temp)
 			try {
 				assert.deepEqual(actual[key], temp)
 			} catch (e) {

test/data.js

@@ -27,7 +27,7 @@ module.exports = {
 			"m.room.guest_access/": {guest_access: "can_join"},
 			"m.room.history_visibility/": {history_visibility: "invited"},
 			"m.space.parent/!jjWAGMeQdNrVZSSfvz:cadence.moe": {
-				via: ["cadence.moe"], // TODO: put the proper server here
+				via: ["cadence.moe"],
 				canonical: true
 			},
 			"m.room.join_rules/": {
@@ -40,6 +40,11 @@ module.exports = {
 			"m.room.avatar/": {
 				discord_path: "/icons/112760669178241024/a_f83622e09ead74f0c5c527fe241f8f8c.png?size=1024",
 				url: "mxc://cadence.moe/zKXGZhmImMHuGQZWJEFKJbsF"
+			},
+			"m.room.power_levels/": {
+				events: {
+					"m.room.avatar": 0
+				}
 			}
 		}
 	},