Fix topic diffing from original creation

src/matrix/kstate.js

@@ -109,6 +109,14 @@ function diffKState(actual, target) {
 		} else if (key === "m.room.create/") {
 			// can't be modified - only for kstateToCreationContent
 
+		} else if (key === "m.room.topic/") {
+			// synapse generates different m.room.topic events on original creation
+			// https://github.com/element-hq/synapse/blob/0f2b29511fd88d1dc2278f41fd6e4e2f2989fcb7/synapse/handlers/room.py#L1729
+			// diff the `topic` to determine change
+			if (!(key in actual) || actual[key].topic !== target[key].topic) {
+				diff[key] = target[key]
+			}
+
 		} else if (key in actual) {
 			// diff
 			if (!isDeepStrictEqual(actual[key], target[key])) {

src/matrix/kstate.test.js

@@ -235,30 +235,38 @@ test("diffKState: kstate keys must contain a slash separator", t => {
 	t.pass()
 })
 
-test("diffKState: don't add hide_ui when not present", t => {
-	test("diffKState: detects new properties", t => {
-		t.deepEqual(
-			diffKState({
-			}, {
-				"chat.schildi.hide_ui/read_receipts/": {}
-			}),
-			{
+test("diffKState: topic does not change if the topic key has not changed", t => {
+	t.deepEqual(diffKState({
+		"m.room.topic/": {
+			topic: "hello",
+			"m.topic": {
+				"m.text": "hello"
 			}
-		)
-	})
+		}
+	}, {
+		"m.room.topic/": {
+			topic: "hello"
+		}
+	}),
+	{})
 })
 
-test("diffKState: overwriten hide_ui when present", t => {
-	test("diffKState: detects new properties", t => {
-		t.deepEqual(
-			diffKState({
-				"chat.schildi.hide_ui/read_receipts/": {hidden: true}
-			}, {
-				"chat.schildi.hide_ui/read_receipts/": {}
-			}),
-			{
-				"chat.schildi.hide_ui/read_receipts/": {}
+test("diffKState: topic changes if the topic key has changed", t => {
+	t.deepEqual(diffKState({
+		"m.room.topic/": {
+			topic: "hello",
+			"m.topic": {
+				"m.text": "hello"
 			}
-		)
+		}
+	}, {
+		"m.room.topic/": {
+			topic: "hello you"
+		}
+	}),
+	{
+		"m.room.topic/": {
+			topic: "hello you"
+		}
 	})
 })