Do not show membership/profile/topic events in public rooms

apps/web/src/shouldHideEvent.ts

@@ -4,12 +4,20 @@
 
 SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE files in the repository root for full details.
- */
-
-import { type MatrixEvent, EventType, RelationType, M_POLL_END } from "matrix-js-sdk/src/matrix";
+*/
+
+import {
+    type MatrixEvent,
+    type MatrixClient,
+    EventType,
+    RelationType,
+    JoinRule,
+    M_POLL_END,
+} from "matrix-js-sdk/src/matrix";
 import { KnownMembership } from "matrix-js-sdk/src/types";
 
 import SettingsStore from "./settings/SettingsStore";
+import { MatrixClientPeg } from "./MatrixClientPeg";
 import { type IRoomState } from "./components/structures/RoomView";
 import { type SettingKey } from "./settings/Settings.tsx";
 
@@ -43,16 +51,26 @@
     return diff;
 }
 
+function isPublicRoom(ev: MatrixEvent, client?: MatrixClient): boolean {
+    const mxClient = client ?? MatrixClientPeg.get();
+    const room = mxClient?.getRoom(ev.getRoomId());
+    return room?.getJoinRule() === JoinRule.Public;
+}
+
 /**
  * Determines whether the given event should be hidden from timelines.
  * @param ev The event
  * @param ctx An optional RoomContext to pull cached settings values from to avoid
  *     hitting the settings store
+ * @param client An optional MatrixClient to use instead of MatrixClientPeg
+ * @returns True if the event should be hidden
  */
-export default function shouldHideEvent(ev: MatrixEvent, ctx?: IRoomState): boolean {
+export default function shouldHideEvent(ev: MatrixEvent, ctx?: IRoomState, client?: MatrixClient): boolean {
     // Hide all poll end events
     if (M_POLL_END.matches(ev.getType())) return true;
 
+    if (ev.getType() === EventType.RoomTopic && isPublicRoom(ev, client)) return true;
+
     // Accessing the settings store directly can be expensive if done frequently,
     // so we should prefer using cached values if a RoomContext is available
     const isEnabled = ctx
@@ -70,6 +88,8 @@
     const eventDiff = memberEventDiff(ev);
 
     if (eventDiff.isMemberEvent) {
+        if (isPublicRoom(ev, client)) return true;
+
         if ((eventDiff.isJoin || eventDiff.isPart) && !isEnabled("showJoinLeaves")) return true;
         if (eventDiff.isAvatarChange && !isEnabled("showAvatarChanges")) return true;
         if (eventDiff.isDisplaynameChange && !isEnabled("showDisplaynameChanges")) return true;

apps/web/test/unit-tests/shouldHideEvent-test.ts

@@ -0,0 +1,109 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { EventType, JoinRule, type MatrixClient, type Room, Room as SDKRoom } from "matrix-js-sdk/src/matrix";
+import { KnownMembership } from "matrix-js-sdk/src/types";
+
+import shouldHideEvent from "../../src/shouldHideEvent";
+import { mkEvent } from "../test-utils/test-utils";
+
+describe("shouldHideEvent", () => {
+    let client: MatrixClient;
+    let publicRoom: Room;
+    let privateRoom: Room;
+
+    beforeEach(() => {
+        client = {
+            getRoom: jest.fn().mockImplementation((roomId: string) => {
+                if (roomId === "!public:server") return publicRoom;
+                if (roomId === "!private:server") return privateRoom;
+                return null;
+            }),
+        } as unknown as MatrixClient;
+
+        publicRoom = new SDKRoom("!public:server", client, "@user:server");
+        privateRoom = new SDKRoom("!private:server", client, "@user:server");
+
+        (publicRoom as unknown as { getJoinRule: jest.Mock }).getJoinRule = jest.fn().mockReturnValue(JoinRule.Public);
+        (privateRoom as unknown as { getJoinRule: jest.Mock }).getJoinRule = jest
+            .fn()
+            .mockReturnValue(JoinRule.Private);
+    });
+
+    function makeMemberEvent(
+        roomId: string,
+        membership: KnownMembership,
+        prevMembership?: KnownMembership,
+    ): ReturnType<typeof mkEvent> {
+        return mkEvent({
+            type: EventType.RoomMember,
+            room: roomId,
+            user: "@user:server",
+            content: {
+                membership,
+                displayname: "User",
+                avatar_url: "mxc://avatar",
+            },
+            prev_content:
+                prevMembership !== undefined
+                    ? {
+                          membership: prevMembership,
+                          displayname: "User",
+                          avatar_url: "mxc://avatar",
+                      }
+                    : undefined,
+            event: true,
+        });
+    }
+
+    function makeTopicEvent(roomId: string): ReturnType<typeof mkEvent> {
+        return mkEvent({
+            type: EventType.RoomTopic,
+            room: roomId,
+            user: "@user:server",
+            skey: "",
+            content: {
+                topic: "Test Topic",
+            },
+            event: true,
+        });
+    }
+
+    describe("public room events", () => {
+        it("should hide member join events in public rooms", () => {
+            const event = makeMemberEvent("!public:server", KnownMembership.Join, KnownMembership.Invite);
+            expect(shouldHideEvent(event, undefined, client)).toBe(true);
+        });
+
+        it("should hide member leave events in public rooms", () => {
+            const event = makeMemberEvent("!public:server", KnownMembership.Leave, KnownMembership.Join);
+            expect(shouldHideEvent(event, undefined, client)).toBe(true);
+        });
+
+        it("should hide topic events in public rooms", () => {
+            const event = makeTopicEvent("!public:server");
+            expect(shouldHideEvent(event, undefined, client)).toBe(true);
+        });
+    });
+
+    describe("non-public room events", () => {
+        it("should show member join events in private rooms", () => {
+            const event = makeMemberEvent("!private:server", KnownMembership.Join, KnownMembership.Invite);
+            expect(shouldHideEvent(event, undefined, client)).toBe(false);
+        });
+
+        it("should show member leave events in private rooms", () => {
+            const event = makeMemberEvent("!private:server", KnownMembership.Leave, KnownMembership.Join);
+            expect(shouldHideEvent(event, undefined, client)).toBe(false);
+        });
+
+        it("should show topic events in private rooms", () => {
+            const event = makeTopicEvent("!private:server");
+            expect(shouldHideEvent(event, undefined, client)).toBe(false);
+        });
+    });
+});