Fix invisible power levels tile when showing hidden events (#9162)

* Fix invisible power levels tile when showing hidden events

* Add regression test

src/TextForEvent.tsx

@@ -434,29 +434,29 @@ function textForHistoryVisibilityEvent(event: MatrixEvent): () => string | null
 // Currently will only display a change if a user's power level is changed
 function textForPowerEvent(event: MatrixEvent): () => string | null {
     const senderName = getSenderName(event);
-    if (!event.getPrevContent() || !event.getPrevContent().users ||
-        !event.getContent() || !event.getContent().users) {
+    if (!event.getPrevContent()?.users || !event.getContent()?.users) {
         return null;
     }
-    const previousUserDefault = event.getPrevContent().users_default || 0;
-    const currentUserDefault = event.getContent().users_default || 0;
+    const previousUserDefault: number = event.getPrevContent().users_default || 0;
+    const currentUserDefault: number = event.getContent().users_default || 0;
     // Construct set of userIds
-    const users = [];
-    Object.keys(event.getContent().users).forEach(
-        (userId) => {
+    const users: string[] = [];
+    Object.keys(event.getContent().users).forEach((userId) => {
         if (users.indexOf(userId) === -1) users.push(userId);
-        },
-    );
-    Object.keys(event.getPrevContent().users).forEach(
-        (userId) => {
+    });
+    Object.keys(event.getPrevContent().users).forEach((userId) => {
         if (users.indexOf(userId) === -1) users.push(userId);
-        },
-    );
+    });
 
-    const diffs = [];
+    const diffs: {
+        userId: string;
+        name: string;
+        from: number;
+        to: number;
+    }[] = [];
     users.forEach((userId) => {
         // Previous power level
-        let from = event.getPrevContent().users[userId];
+        let from: number = event.getPrevContent().users[userId];
         if (!Number.isInteger(from)) {
             from = previousUserDefault;
         }

src/events/EventTileFactory.tsx

@@ -225,6 +225,10 @@ export function pickFactory(
             return noEventFactoryFactory(); // improper event type to render
         }
 
+        if (STATE_EVENT_TILE_TYPES[evType] === TextualEventFactory && !hasText(mxEvent, showHiddenEvents)) {
+            return noEventFactoryFactory();
+        }
+
         return STATE_EVENT_TILE_TYPES[evType] ?? noEventFactoryFactory();
     }
 

test/events/EventTileFactory-test.ts

@@ -0,0 +1,36 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { EventType, MatrixEvent } from "matrix-js-sdk/src/matrix";
+
+import { JSONEventFactory, pickFactory } from "../../src/events/EventTileFactory";
+import { createTestClient } from "../test-utils";
+
+const roomId = "!room:example.com";
+
+describe("pickFactory", () => {
+    it("should return JSONEventFactory for a no-op m.room.power_levels event", () => {
+        const cli = createTestClient();
+        const event = new MatrixEvent({
+            type: EventType.RoomPowerLevels,
+            state_key: "",
+            content: {},
+            sender: cli.getUserId(),
+            room_id: roomId,
+        });
+        expect(pickFactory(event, cli, true)).toBe(JSONEventFactory);
+    });
+});