Support for creator power level (#4937)

* Support for creator power level

Adds support for infinite power level specified by [MSC4289](https://github.com/matrix-org/matrix-spec-proposals/pull/4289).

* Update unit test

* Hardcode versions

as room versions strings aren't ordered

* Add test for v12 rooms

* Use more compact syntax

Co-authored-by: R Midhun Suresh <hi@midhun.dev>

* Fix doc

Co-authored-by: R Midhun Suresh <hi@midhun.dev>

* Fix additionalCreators from PR edit

* Split out hydra room version check

* Move power level logic into room state

Which already has knowledge of the room create event

* Add docs

* Fix unused bits

* Fix docs

* Fix lying docstring

* Reverse logic for hydra semantics

Assume unknown room versions do use hydra

* Use backticks

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Switch back to hardcoding just the two hydra versions

---------

Co-authored-by: R Midhun Suresh <hi@midhun.dev>
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

spec/unit/room-member.spec.ts

@@ -20,8 +20,8 @@ import * as utils from "../test-utils/test-utils";
 import { RoomMember, RoomMemberEvent } from "../../src/models/room-member";
 import {
     createClient,
-    EventType,
     type MatrixClient,
+    MatrixEvent,
     type RoomState,
     UNSTABLE_MSC2666_MUTUAL_ROOMS,
     UNSTABLE_MSC2666_QUERY_MUTUAL_ROOMS,
@@ -101,158 +101,32 @@ describe("RoomMember", function () {
         });
     });
 
-    describe("setPowerLevelEvent", function () {
+    describe("setPowerLevel", function () {
-        it("should set 'powerLevel' and 'powerLevelNorm'.", function () {
+        it("should set 'powerLevel'.", function () {
-            const event = utils.mkEvent({
+            member.setPowerLevel(0, new MatrixEvent());
-                type: "m.room.power_levels",
-                room: roomId,
-                user: userA,
-                content: {
-                    users_default: 20,
-                    users: {
-                        "@bertha:bar": 200,
-                        "@invalid:user": 10, // shouldn't barf on this.
-                    },
-                },
-                event: true,
-            });
-            member.setPowerLevelEvent(event);
-            expect(member.powerLevel).toEqual(20);
-            expect(member.powerLevelNorm).toEqual(10);
-
-            const memberB = new RoomMember(roomId, userB);
-            memberB.setPowerLevelEvent(event);
-            expect(memberB.powerLevel).toEqual(200);
-            expect(memberB.powerLevelNorm).toEqual(100);
-        });
-
-        it("should emit 'RoomMember.powerLevel' if the power level changes.", function () {
-            const event = utils.mkEvent({
-                type: "m.room.power_levels",
-                room: roomId,
-                user: userA,
-                content: {
-                    users_default: 20,
-                    users: {
-                        "@bertha:bar": 200,
-                        "@invalid:user": 10, // shouldn't barf on this.
-                    },
-                },
-                event: true,
-            });
-            let emitCount = 0;
-
-            member.on(RoomMemberEvent.PowerLevel, function (emitEvent, emitMember) {
-                emitCount += 1;
-                expect(emitMember).toEqual(member);
-                expect(emitEvent).toEqual(event);
-            });
-
-            member.setPowerLevelEvent(event);
-            expect(emitCount).toEqual(1);
-            member.setPowerLevelEvent(event); // no-op
-            expect(emitCount).toEqual(1);
-        });
-
-        it("should honour power levels of zero.", function () {
-            const event = utils.mkEvent({
-                type: "m.room.power_levels",
-                room: roomId,
-                user: userA,
-                content: {
-                    users_default: 20,
-                    users: {
-                        "@alice:bar": 0,
-                    },
-                },
-                event: true,
-            });
-            let emitCount = 0;
-
-            // set the power level to something other than zero or we
-            // won't get an event
-            member.powerLevel = 1;
-            member.on(RoomMemberEvent.PowerLevel, function (emitEvent, emitMember) {
-                emitCount += 1;
-                expect(emitMember.userId).toEqual("@alice:bar");
-                expect(emitMember.powerLevel).toEqual(0);
-                expect(emitEvent).toEqual(event);
-            });
-
-            member.setPowerLevelEvent(event);
             expect(member.powerLevel).toEqual(0);
-            expect(emitCount).toEqual(1);
+            member.setPowerLevel(200, new MatrixEvent());
+            expect(member.powerLevel).toEqual(200);
         });
 
-        it("should not honor string power levels.", function () {
+        it("should emit when power level set", function () {
-            const event = utils.mkEvent({
+            const onEmit = jest.fn();
-                type: "m.room.power_levels",
+            member.on(RoomMemberEvent.PowerLevel, onEmit);
-                room: roomId,
-                user: userA,
-                content: {
-                    users_default: 20,
-                    users: {
-                        "@alice:bar": "5",
-                    },
-                },
-                event: true,
-            });
-            let emitCount = 0;
 
-            member.on(RoomMemberEvent.PowerLevel, function (emitEvent, emitMember) {
+            const aMatrixEvent = new MatrixEvent();
-                emitCount += 1;
+            member.setPowerLevel(10, aMatrixEvent);
-                expect(emitMember.userId).toEqual("@alice:bar");
-                expect(emitMember.powerLevel).toEqual(20);
-                expect(emitEvent).toEqual(event);
-            });
 
-            member.setPowerLevelEvent(event);
+            expect(onEmit).toHaveBeenCalledWith(aMatrixEvent, member);
-            expect(member.powerLevel).toEqual(20);
-            expect(emitCount).toEqual(1);
         });
 
-        it("should no-op if given a non-state or unrelated event", () => {
+        it("should not emit if new power level is the same", function () {
-            const fn = jest.spyOn(member, "emit");
+            const onEmit = jest.fn();
-            expect(fn).not.toHaveBeenCalledWith(RoomMemberEvent.PowerLevel);
+            member.on(RoomMemberEvent.PowerLevel, onEmit);
-            member.setPowerLevelEvent(
+
-                utils.mkEvent({
+            const aMatrixEvent = new MatrixEvent();
-                    type: EventType.RoomPowerLevels,
+            member.setPowerLevel(0, aMatrixEvent);
-                    room: roomId,
+
-                    user: userA,
+            expect(onEmit).not.toHaveBeenCalled();
-                    content: {
-                        users_default: 20,
-                        users: {
-                            "@alice:bar": "5",
-                        },
-                    },
-                    skey: "invalid",
-                    event: true,
-                }),
-            );
-            const nonStateEv = utils.mkEvent({
-                type: EventType.RoomPowerLevels,
-                room: roomId,
-                user: userA,
-                content: {
-                    users_default: 20,
-                    users: {
-                        "@alice:bar": "5",
-                    },
-                },
-                event: true,
-            });
-            delete nonStateEv.event.state_key;
-            member.setPowerLevelEvent(nonStateEv);
-            member.setPowerLevelEvent(
-                utils.mkEvent({
-                    type: EventType.Sticker,
-                    room: roomId,
-                    user: userA,
-                    content: {},
-                    event: true,
-                }),
-            );
-            expect(fn).not.toHaveBeenCalledWith(RoomMemberEvent.PowerLevel);
         });
     });
 

spec/unit/room-state.spec.ts

@@ -20,6 +20,7 @@ import * as utils from "../test-utils/test-utils";
 import { makeBeaconEvent, makeBeaconInfoEvent } from "../test-utils/beacon";
 import { filterEmitCallsByEventType } from "../test-utils/emitter";
 import { RoomState, RoomStateEvent } from "../../src/models/room-state";
+import { RoomMemberEvent } from "../../src/models/room-member";
 import { type Beacon, BeaconEvent, getBeaconInfoIdentifier } from "../../src/models/beacon";
 import { EventType, RelationType, UNSTABLE_MSC2716_MARKER } from "../../src/@types/event";
 import { MatrixEvent, MatrixEventEvent } from "../../src/models/event";
@@ -259,7 +260,7 @@ describe("RoomState", function () {
             expect(emitCount).toEqual(2);
         });
 
-        it("should call setPowerLevelEvent on each RoomMember for m.room.power_levels", function () {
+        it("should call setPowerLevel on each RoomMember for m.room.power_levels", function () {
             const powerLevelEvent = utils.mkEvent({
                 type: "m.room.power_levels",
                 room: roomId,
@@ -273,12 +274,12 @@ describe("RoomState", function () {
             });
 
             // spy on the room members
-            jest.spyOn(state.members[userA], "setPowerLevelEvent");
+            jest.spyOn(state.members[userA], "setPowerLevel");
-            jest.spyOn(state.members[userB], "setPowerLevelEvent");
+            jest.spyOn(state.members[userB], "setPowerLevel");
             state.setStateEvents([powerLevelEvent]);
 
-            expect(state.members[userA].setPowerLevelEvent).toHaveBeenCalledWith(powerLevelEvent);
+            expect(state.members[userA].setPowerLevel).toHaveBeenCalledWith(10, powerLevelEvent);
-            expect(state.members[userB].setPowerLevelEvent).toHaveBeenCalledWith(powerLevelEvent);
+            expect(state.members[userB].setPowerLevel).toHaveBeenCalledWith(10, powerLevelEvent);
         });
 
         it("should call setPowerLevelEvent on a new RoomMember if power levels exist", function () {
@@ -310,6 +311,156 @@ describe("RoomState", function () {
             expect(state.members[userC].powerLevel).toEqual(10);
         });
 
+        it("should calculate power level correctly", function () {
+            const powerLevelEvent = utils.mkEvent({
+                type: "m.room.power_levels",
+                room: roomId,
+                user: userA,
+                content: {
+                    users_default: 20,
+                    users: {
+                        [userB]: 200,
+                        "@invalid:user": 10, // shouldn't barf on this.
+                    },
+                },
+                event: true,
+            });
+            state.setStateEvents([powerLevelEvent]);
+
+            expect(state.getMember(userA)?.powerLevel).toEqual(20);
+            expect(state.getMember(userB)?.powerLevel).toEqual(200);
+        });
+
+        it("should set 'powerLevel' with a v12 room.", function () {
+            const createEventV12 = utils.mkEvent({
+                type: "m.room.create",
+                room: roomId,
+                sender: userA,
+                content: { room_version: "12" },
+                event: true,
+            });
+            const powerLevelEvent = utils.mkEvent({
+                type: "m.room.power_levels",
+                room: roomId,
+                user: userA,
+                content: {
+                    users_default: 20,
+                    users: {
+                        [userB]: 200,
+                        "@invalid:user": 10, // shouldn't barf on this.
+                    },
+                },
+                event: true,
+            });
+            state.setStateEvents([createEventV12, powerLevelEvent]);
+            expect(state.getMember(userA)?.powerLevel).toEqual(Infinity);
+        });
+
+        it("should honour power levels of zero.", function () {
+            const powerLevelEvent = utils.mkEvent({
+                type: "m.room.power_levels",
+                room: roomId,
+                user: userA,
+                content: {
+                    users_default: 20,
+                    users: {
+                        "@alice:bar": 0,
+                    },
+                },
+                event: true,
+            });
+            let emitCount = 0;
+
+            const memberA = state.getMember(userA)!;
+            // set the power level to something other than zero or we
+            // won't get an event
+            memberA.powerLevel = 1;
+            memberA.on(RoomMemberEvent.PowerLevel, function (emitEvent, emitMember) {
+                emitCount += 1;
+                expect(emitMember.userId).toEqual("@alice:bar");
+                expect(emitMember.powerLevel).toEqual(0);
+                expect(emitEvent).toEqual(powerLevelEvent);
+            });
+
+            state.setStateEvents([powerLevelEvent]);
+            expect(memberA.powerLevel).toEqual(0);
+            expect(emitCount).toEqual(1);
+        });
+
+        it("should not honor string power levels.", function () {
+            const powerLevelEvent = utils.mkEvent({
+                type: "m.room.power_levels",
+                room: roomId,
+                user: userA,
+                content: {
+                    users_default: 20,
+                    users: {
+                        "@alice:bar": "5",
+                    },
+                },
+                event: true,
+            });
+            let emitCount = 0;
+
+            const memberA = state.getMember(userA)!;
+            memberA.on(RoomMemberEvent.PowerLevel, function (emitEvent, emitMember) {
+                emitCount += 1;
+                expect(emitMember.userId).toEqual("@alice:bar");
+                expect(emitMember.powerLevel).toEqual(20);
+                expect(emitEvent).toEqual(powerLevelEvent);
+            });
+
+            state.setStateEvents([powerLevelEvent]);
+            expect(memberA.powerLevel).toEqual(20);
+            expect(emitCount).toEqual(1);
+        });
+
+        it("should no-op if given a non-state or unrelated event", () => {
+            const memberA = state.getMember(userA)!;
+            const fn = jest.spyOn(memberA, "emit");
+            expect(fn).not.toHaveBeenCalledWith(RoomMemberEvent.PowerLevel);
+
+            const powerLevelEvent = utils.mkEvent({
+                type: EventType.RoomPowerLevels,
+                room: roomId,
+                user: userA,
+                content: {
+                    users_default: 20,
+                    users: {
+                        "@alice:bar": "5",
+                    },
+                },
+                skey: "invalid",
+                event: true,
+            });
+
+            state.setStateEvents([powerLevelEvent]);
+            const nonStateEv = utils.mkEvent({
+                type: EventType.RoomPowerLevels,
+                room: roomId,
+                user: userA,
+                content: {
+                    users_default: 20,
+                    users: {
+                        "@alice:bar": "5",
+                    },
+                },
+                event: true,
+            });
+            delete nonStateEv.event.state_key;
+            state.setStateEvents([nonStateEv]);
+            state.setStateEvents([
+                utils.mkEvent({
+                    type: EventType.Sticker,
+                    room: roomId,
+                    user: userA,
+                    content: {},
+                    event: true,
+                }),
+            ]);
+            expect(fn).not.toHaveBeenCalledWith(RoomMemberEvent.PowerLevel);
+        });
+
         it("should call setMembershipEvent on the right RoomMember", function () {
             const memberEvent = utils.mkMembership({
                 user: userB,

src/models/room-member.ts

@@ -66,7 +66,6 @@ export type RoomMemberEventHandlerMap = {
      * ```
      * matrixClient.on("RoomMember.powerLevel", function(event, member){
      *   var newPowerLevel = member.powerLevel;
-     *   var newNormPowerLevel = member.powerLevelNorm;
      * });
      * ```
      */
@@ -109,10 +108,6 @@ export class RoomMember extends TypedEventEmitter<RoomMemberEvent, RoomMemberEve
      * The power level for this room member.
      */
     public powerLevel = 0;
-    /**
-     * The normalised power level (0-100) for this room member.
-     */
-    public powerLevelNorm = 0;
     /**
      * The User object for this room member, if one exists.
      */
@@ -226,43 +221,18 @@ export class RoomMember extends TypedEventEmitter<RoomMemberEvent, RoomMemberEve
     }
 
     /**
-     * Update this room member's power level event. May fire
+     * Update this room member's power level event. Will fire
-     * "RoomMember.powerLevel" if this event updates this member's power levels.
+     * "RoomMember.powerLevel" if the new power level is different
-     * @param powerLevelEvent - The `m.room.power_levels` event
+     * @param powerLevel - The power level of the room member.
      *
      * @remarks
      * Fires {@link RoomMemberEvent.PowerLevel}
      */
-    public setPowerLevelEvent(powerLevelEvent: MatrixEvent): void {
+    public setPowerLevel(powerLevel: number, powerLevelEvent: MatrixEvent): void {
-        if (powerLevelEvent.getType() !== EventType.RoomPowerLevels || powerLevelEvent.getStateKey() !== "") {
-            return;
-        }
-
-        const evContent = powerLevelEvent.getDirectionalContent();
-
-        let maxLevel = evContent.users_default || 0;
-        const users: { [userId: string]: number } = evContent.users || {};
-        Object.values(users).forEach((lvl: number) => {
-            maxLevel = Math.max(maxLevel, lvl);
-        });
         const oldPowerLevel = this.powerLevel;
-        const oldPowerLevelNorm = this.powerLevelNorm;
+        this.powerLevel = powerLevel;
 
-        if (users[this.userId] !== undefined && Number.isInteger(users[this.userId])) {
+        if (oldPowerLevel !== this.powerLevel) {
-            this.powerLevel = users[this.userId];
-        } else if (evContent.users_default !== undefined) {
-            this.powerLevel = evContent.users_default;
-        } else {
-            this.powerLevel = 0;
-        }
-        this.powerLevelNorm = 0;
-        if (maxLevel > 0) {
-            this.powerLevelNorm = (this.powerLevel * 100) / maxLevel;
-        }
-
-        // emit for changes in powerLevelNorm as well (since the app will need to
-        // redraw everyone's level if the max has changed)
-        if (oldPowerLevel !== this.powerLevel || oldPowerLevelNorm !== this.powerLevelNorm) {
             this.updateModifiedTime();
             this.emit(RoomMemberEvent.PowerLevel, powerLevelEvent, this);
         }

src/models/room-state.ts

@@ -33,6 +33,7 @@ import { TypedReEmitter } from "../ReEmitter.ts";
 import { M_BEACON, M_BEACON_INFO } from "../@types/beacon.ts";
 import { KnownMembership } from "../@types/membership.ts";
 import { type RoomJoinRulesEventContent } from "../@types/state_events.ts";
+import { shouldUseHydraForRoomVersion } from "../utils/roomVersion.ts";
 
 export interface IMarkerFoundOptions {
     /** Whether the timeline was empty before the marker event arrived in the
@@ -173,6 +174,9 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
     public readonly beacons = new Map<BeaconIdentifier, Beacon>();
     private _liveBeaconIds: BeaconIdentifier[] = [];
 
+    // We only wants to print warnings about bad room state once.
+    private getVersionWarning = false;
+
     /**
      * Construct room state.
      *
@@ -209,6 +213,22 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
         this.updateModifiedTime();
     }
 
+    /**
+     * Gets the version of the room
+     * @returns The version of the room
+     */
+    public getRoomVersion(): string {
+        const createEvent = this.getStateEvents(EventType.RoomCreate, "");
+        if (!createEvent) {
+            if (!this.getVersionWarning) {
+                logger.warn("[getVersion] Room " + this.roomId + " does not have an m.room.create event");
+                this.getVersionWarning = true;
+            }
+            return "1";
+        }
+        return createEvent.getContent()["room_version"] ?? "1";
+    }
+
     /**
      * Returns the number of joined members in this room
      * This method caches the result.
@@ -468,12 +488,20 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
                     return;
                 }
                 const members = Object.values(this.members);
+
+                const createEvent = this.getStateEvents(EventType.RoomCreate, "");
+                const creators = getCreators(this.getRoomVersion(), createEvent);
+
                 members.forEach((member) => {
                     // We only propagate `RoomState.members` event if the
                     // power levels has been changed
                     // large room suffer from large re-rendering especially when not needed
                     const oldLastModified = member.getLastModifiedTime();
-                    member.setPowerLevelEvent(event);
+
+                    if (createEvent) {
+                        const pl = powerLevelForUserId(member.userId, event, creators);
+                        member.setPowerLevel(pl, event);
+                    }
                     if (oldLastModified !== member.getLastModifiedTime()) {
                         this.emit(RoomStateEvent.Members, event, this, member);
                     }
@@ -625,9 +653,16 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
 
     private updateMember(member: RoomMember): void {
         // this member may have a power level already, so set it.
+        const createEvent = this.getStateEvents(EventType.RoomCreate, "");
         const pwrLvlEvent = this.getStateEvents(EventType.RoomPowerLevels, "");
-        if (pwrLvlEvent) {
+        if (pwrLvlEvent && createEvent) {
-            member.setPowerLevelEvent(pwrLvlEvent);
+            const powerLevel = powerLevelForUserId(
+                member.userId,
+                pwrLvlEvent,
+                getCreators(this.getRoomVersion(), createEvent),
+            );
+
+            member.setPowerLevel(powerLevel, pwrLvlEvent);
         }
 
         // blow away the sentinel which is now outdated
@@ -1106,3 +1141,46 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
         }
     }
 }
+
+/**
+ * Get the set of creator user IDs for a room: empty if the room is not a 'hydra' room, otherwise
+ * computed from the sender of the m.room.create event plus the additional_creators field.
+ * @param roomVersion The version of the room
+ * @param roomCreateEvent The m.room.create event for the room
+ * @returns A set of user IDs of the creators of the room.
+ */
+function getCreators(roomVersion: string, roomCreateEvent: MatrixEvent | null): Set<string> {
+    const creators = new Set<string>();
+    if (shouldUseHydraForRoomVersion(roomVersion) && roomCreateEvent) {
+        const roomCreateSender = roomCreateEvent.getSender();
+        if (roomCreateSender) creators.add(roomCreateSender);
+        const additionalCreators = roomCreateEvent.getDirectionalContent().additional_creators;
+        if (Array.isArray(additionalCreators)) additionalCreators.forEach((c) => creators.add(c));
+    }
+    return creators;
+}
+
+/**
+ *
+ * @param userId The user ID to compute the power level for
+ * @param powerLevelEvents The power level event for the room
+ * @param creators The set of creator user IDs for the room if the room is a 'hydra' room, otherwise the empty set.
+ */
+function powerLevelForUserId(userId: string, powerLevelEvent: MatrixEvent, creators: Set<string>): number {
+    if (creators.has(userId)) {
+        // As of "Hydra", If the user is a creator, they always have the highest power level
+        return Infinity;
+    } else {
+        const evContent = powerLevelEvent.getDirectionalContent();
+
+        const users: { [userId: string]: number } = evContent.users || {};
+
+        if (users[userId] !== undefined && Number.isInteger(users[userId])) {
+            return users[userId];
+        } else if (evContent.users_default !== undefined) {
+            return evContent.users_default;
+        } else {
+            return 0;
+        }
+    }
+}

src/models/room.ts

@@ -374,7 +374,6 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
     private heroes: Hero[] | null = null;
     // flags to stop logspam about missing m.room.create events
     private getTypeWarning = false;
-    private getVersionWarning = false;
     private membersPromise?: Promise<boolean>;
 
     // XXX: These should be read-only
@@ -606,18 +605,10 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
 
     /**
      * Gets the version of the room
-     * @returns The version of the room, or null if it could not be determined
+     * @returns The version of the room
      */
     public getVersion(): string {
-        const createEvent = this.currentState.getStateEvents(EventType.RoomCreate, "");
+        return this.currentState.getRoomVersion();
-        if (!createEvent) {
-            if (!this.getVersionWarning) {
-                logger.warn("[getVersion] Room " + this.roomId + " does not have an m.room.create event");
-                this.getVersionWarning = true;
-            }
-            return "1";
-        }
-        return createEvent.getContent()["room_version"] ?? "1";
     }
 
     /**

src/utils/roomVersion.ts

@@ -0,0 +1,40 @@
+/*
+Copyright 2025 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.
+*/
+
+/**
+ * Room versions strings that we know about and do not use hydra semantics.
+ */
+const HYDRA_ROOM_VERSIONS = ["org.matrix.hydra.11", "12"];
+
+/**
+ * Checks if the given room version is one where new "hydra" power level
+ * semantics (ie. room version 12 or later) should be used
+ * (see https://github.com/matrix-org/matrix-spec-proposals/pull/4289).
+ * This will return `true` for versions that are known to the js-sdk and
+ * use hydra: any room versions unknown to the js-sdk (experimental or
+ * otherwise) will cause the function to return `false`.
+ *
+ * @param roomVersion - The version of the room to check.
+ * @returns `true` if hydra semantics should be used for the room version, `false` otherwise.
+ */
+export function shouldUseHydraForRoomVersion(roomVersion: string): boolean {
+    // Future new room versions must obviously be added to the constant above,
+    // otherwise the js-sdk will use the old, pre-hydra semantics. At some point
+    // it would make sense to assume hydra for unknown versions but this will break
+    // any rooms using unknown versions, so at hydra switch time we've agreed all
+    // Element clients will only use hydra for the two specific hydra versions.
+    return HYDRA_ROOM_VERSIONS.includes(roomVersion);
+}