Switch sliding sync support to simplified sliding sync

spec/unit/room.spec.ts

@@ -1239,9 +1239,7 @@ describe("Room", function () {
                 const nameC = "Clarissa Harissa";
                 addMember(userB, KnownMembership.Join, { name: nameB });
                 addMember(userC, KnownMembership.Join, { name: nameC });
-                room.setSummary({
-                    "m.heroes": [{ userId: userB }, { userId: userC }],
-                });
+                room.setMSC4186SummaryData([{ user_id: userB }, { user_id: userC }], undefined, undefined);
                 room.recalculate();
                 expect(room.name).toEqual(`${nameB} and ${nameC}`);
             });

src/models/room-summary.ts

@@ -16,16 +16,23 @@ limitations under the License.
 
 /**
  * A stripped m.room.member event which contains the key renderable fields from the event,
- * sent only in simplified sliding sync (not sync v2).
+ * sent only in simplified sliding sync (not `/v3/sync`).
+ * This is very similar to MSC4186Hero from sliding-sync.ts but an internal format with
+ * camelCase rather than underscores.
  */
 export type Hero = {
     userId: string;
     displayName?: string;
     avatarUrl?: string;
+    /**
+     * If true, the hero is from an MSC4186 summary, in which case `displayName` and `avatarUrl` will
+     * have been set by the server if available. If false, these fields will always be undefined.
+     */
+    fromMSC4186: boolean;
 };
 
 /**
- * High level summary information for a room
+ * High level summary information for a room, as returned by `/v3/sync`.
  */
 export interface IRoomSummary {
     /**
@@ -43,25 +50,6 @@ export interface IRoomSummary {
     "m.invited_member_count"?: number;
 }
 
-/**
- * High level summary information for a room (MSC4186 sliding sync)
- */
-export interface RoomSummaryMSC4186 {
-    /**
-     * The room heroes: a selected set of members that can be used when summarising or
-     * generating a name for a room.
-     */
-    "m.heroes": Hero[];
-    /**
-     * The number of joined members in the room.
-     */
-    "m.joined_member_count"?: number;
-    /**
-     * The number of invited members in the room.
-     */
-    "m.invited_member_count"?: number;
-}
-
 interface IInfo {
     /** The title of the room (e.g. `m.room.name`) */
     title: string;

src/models/room.ts

@@ -35,7 +35,7 @@ import {
 } from "./event.ts";
 import { EventStatus } from "./event-status.ts";
 import { RoomMember } from "./room-member.ts";
-import { type IRoomSummary, type RoomSummaryMSC4186, type Hero, RoomSummary } from "./room-summary.ts";
+import { type IRoomSummary, type Hero, RoomSummary } from "./room-summary.ts";
 import { logger } from "../logger.ts";
 import { TypedReEmitter } from "../ReEmitter.ts";
 import {
@@ -77,6 +77,7 @@ import { compareEventOrdering } from "./compare-event-ordering.ts";
 import * as utils from "../utils.ts";
 import { KnownMembership, type Membership } from "../@types/membership.ts";
 import { type Capabilities, type IRoomVersionsCapability, RoomVersionStability } from "../serverCapabilities.ts";
+import { type MSC4186Hero } from "../sliding-sync.ts";
 
 // These constants are used as sane defaults when the homeserver doesn't support
 // the m.room_versions capability. In practice, KNOWN_SAFE_ROOM_VERSION should be
@@ -362,8 +363,15 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
     // read by megolm via getter; boolean value - null indicates "use global value"
     private blacklistUnverifiedDevices?: boolean;
     private selfMembership?: Membership;
-    // A Hero is a stripped m.room.member event which contains the key renderable fields from the event.
-    // It is used in MSC4186 (Simplified Sliding Sync) as a replacement for the old 'summary' field.
+    /**
+     * A `Hero` is a stripped `m.room.member` event which contains the important renderable fields from the event.
+     *
+     * It is used in MSC4186 (Simplified Sliding Sync) as a replacement for the old `summary` field.
+     *
+     * When we are doing old-style (`/v3/sync`) sync, we simulate the SSS behaviour by constructing
+     * a `Hero` object based on the user id we get from the summary. Obviously, in that case,
+     * the `Hero` will lack a `displayName` or `avatarUrl`.
+     */
     private heroes: Hero[] | null = null;
     // flags to stop logspam about missing m.room.create events
     private getTypeWarning = false;
@@ -949,13 +957,9 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
             // use first hero that has a display name or avatar url, or whose user ID
             // can be looked up as a member of the room
             for (const hero of nonFunctionalHeroes) {
-                // The old form of heroes simply contained the hero's user ID, which forced clients to then look up the
-                // m.room.member event in the current state. This is entirely decoupled in SSS. To ensure this
-                // works in a backwards compatible way, we will A) only set displayName/avatarUrl with server-provided
-                // values, B) always prefer the hero values if they are set, over calling `.getMember`. This means
-                // in SSS mode we will use the heroes if the display name or avatar URL fields are set, but in sync v2
-                // mode these fields will never be set and hence we will always do getMember lookups (at the right time as well).
-                if (!hero.displayName && !hero.avatarUrl) {
+                // If the hero was from a legacy sync (`/v3/sync`), we will need to look the user ID up in the room
+                // the display name and avatar URL will not be set.
+                if (!hero.fromMSC4186) {
                     // attempt to look up renderable fields from the m.room.member event if it exists
                     const member = this.getMember(hero.userId);
                     if (member) {
@@ -1675,15 +1679,12 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
     }
 
     /**
-     * Takes either a legacy or MSC4186 room summary and updates the room with it.
-     * The summary will be converted to a legacy style summary in order to be emitted
-     * in the `RoomEvent.Summary` event.
+     * Takes a legacy room summary (/v3/sync as opposed to MSC4186) and updates the room with it.
      *
      * @param summary - The room summary to update the room with
      */
-    public setSummary(summary: IRoomSummary | RoomSummaryMSC4186): void {
-        // map heroes onto the MSC4186 form as that has more data
-        const heroes = summary["m.heroes"]?.map((h) => (typeof h === "string" ? { userId: h } : h));
+    public setSummary(summary: IRoomSummary): void {
+        const heroes = summary["m.heroes"]?.map((h) => ({ userId: h, fromMSC4186: false }));
         const joinedCount = summary["m.joined_member_count"];
         const invitedCount = summary["m.invited_member_count"];
         if (Number.isInteger(joinedCount)) {
@@ -1699,12 +1700,47 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
             });
         }
 
-        // Convert back to the legacy heroes format for the `RoomEvent.Summary` event.
-        summary["m.heroes"] = heroes?.map((h) => h.userId);
-
         this.emit(RoomEvent.Summary, summary as IRoomSummary);
     }
 
+    /**
+     * Takes information from the MSC4186 room summary and updates the room with it.
+     *
+     * @param heroes
+     * @param joinedCount
+     * @param invitedCount
+     */
+    public setMSC4186SummaryData(
+        heroes: MSC4186Hero[] | undefined,
+        joinedCount: number | undefined,
+        invitedCount: number | undefined,
+    ): void {
+        if (heroes) {
+            this.heroes = heroes
+                .filter((h) => h.user_id !== this.myUserId)
+                .map((h) => ({
+                    userId: h.user_id,
+                    displayName: h.displayname,
+                    avatarUrl: h.avatar_url,
+                    fromMSC4186: true,
+                }));
+        }
+        if (joinedCount !== undefined && Number.isInteger(joinedCount)) {
+            this.currentState.setJoinedMemberCount(joinedCount);
+        }
+        if (invitedCount !== undefined && Number.isInteger(invitedCount)) {
+            this.currentState.setInvitedMemberCount(invitedCount);
+        }
+
+        // Construct a summary object to emit as the event wants the info in a single object
+        // more like old-style (/v3/sync) summaries.
+        this.emit(RoomEvent.Summary, {
+            "m.heroes": this.heroes ? this.heroes.map((h) => h.userId) : [],
+            "m.joined_member_count": joinedCount,
+            "m.invited_member_count": invitedCount,
+        });
+    }
+
     /**
      * Whether to send encrypted messages to devices within this room.
      * @param value - true to blacklist unverified devices, null

src/sliding-sync-sdk.ts

@@ -726,19 +726,7 @@ export class SlidingSyncSdk {
         // synchronous execution prior to emitting SlidingSyncState.Complete
         room.updateMyMembership(KnownMembership.Join);
 
-        room.setSummary({
-            "m.heroes": roomData.heroes
-                ? roomData.heroes.map((h) => {
-                      return {
-                          userId: h.user_id,
-                          avatarUrl: h.avatar_url,
-                          displayName: h.displayname,
-                      };
-                  })
-                : [],
-            "m.invited_member_count": roomData.invited_count,
-            "m.joined_member_count": roomData.joined_count,
-        });
+        room.setMSC4186SummaryData(roomData.heroes, roomData.joined_count, roomData.invited_count);
 
         room.recalculate();
         if (roomData.initial) {

src/sliding-sync.ts

@@ -84,7 +84,9 @@ export interface MSC3575SlidingSyncRequest {
 
 /**
  * New format of hero introduced in MSC4186 with display name and avatar URL
- * in addition to just user_id
+ * in addition to just user_id (as it is on the wire, with underscores)
+ * as opposed to Hero in room-summary.ts which has fields in camelCase
+ * (and also a flag to note what format the hero came from).
  */
 export interface MSC4186Hero {
     user_id: string;