pass memberchanges around instead of members

so we can easily tell how their membership changes, (e.g. join -> left)
which we'll need for device tracking.

Not adding this to RoomMember because RoomMember also needs to be
able to represent a member loaded from storage which doesn't contain
this error. A MemberChange exists only within a sync.

src/matrix/room/Room.js

@@ -51,7 +51,7 @@ export class Room extends EventEmitter {
             membership,
             isInitialSync, isTimelineOpen,
             txn);
-		const {entries, newLiveKey, changedMembers} = await this._syncWriter.writeSync(roomResponse, txn);
+		const {entries, newLiveKey, memberChanges} = await this._syncWriter.writeSync(roomResponse, txn);
         // fetch new members while we have txn open,
         // but don't make any in-memory changes yet
         let heroChanges;
@@ -60,7 +60,7 @@ export class Room extends EventEmitter {
             if (!this._heroes) {
                 this._heroes = new Heroes(this._roomId);
             }
-            heroChanges = await this._heroes.calculateChanges(summaryChanges.heroes, changedMembers, txn);
+            heroChanges = await this._heroes.calculateChanges(summaryChanges.heroes, memberChanges, txn);
         }
         let removedPendingEvents;
         if (roomResponse.timeline && roomResponse.timeline.events) {
@@ -71,22 +71,22 @@ export class Room extends EventEmitter {
             newTimelineEntries: entries,
             newLiveKey,
             removedPendingEvents,
-            changedMembers,
+            memberChanges,
             heroChanges
         };
     }
 
     /** @package */
-    afterSync({summaryChanges, newTimelineEntries, newLiveKey, removedPendingEvents, changedMembers, heroChanges}) {
+    afterSync({summaryChanges, newTimelineEntries, newLiveKey, removedPendingEvents, memberChanges, heroChanges}) {
         this._syncWriter.afterSync(newLiveKey);
-        if (changedMembers.length) {
+        if (memberChanges.size) {
             if (this._changedMembersDuringSync) {
-                for (const member of changedMembers) {
-                    this._changedMembersDuringSync.set(member.userId, member);
+                for (const [userId, memberChange] of memberChanges.entries()) {
+                    this._changedMembersDuringSync.set(userId, memberChange.member);
                 }
             }
             if (this._memberList) {
-                this._memberList.afterSync(changedMembers);
+                this._memberList.afterSync(memberChanges);
             }
         }
         let emitChange = false;

src/matrix/room/members/Heroes.js

@@ -42,11 +42,11 @@ export class Heroes {
 
     /**
      * @param  {string[]} newHeroes      array of user ids
-     * @param  {RoomMember[]} changedMembers array of changed members in this sync
+     * @param  {Map<string, MemberChange>} memberChanges map of changed memberships
      * @param  {Transaction} txn
      * @return {Promise}
      */
-    async calculateChanges(newHeroes, changedMembers, txn) {
+    async calculateChanges(newHeroes, memberChanges, txn) {
         const updatedHeroMembers = new Map();
         const removedUserIds = [];
         // remove non-present members
@@ -56,9 +56,9 @@ export class Heroes {
             }
         }
         // update heroes with synced member changes
-        for (const member of changedMembers) {
-            if (this._members.has(member.userId) || newHeroes.indexOf(member.userId) !== -1) {
-                updatedHeroMembers.set(member.userId, member);
+        for (const [userId, memberChange] of memberChanges.entries()) {
+            if (this._members.has(userId) || newHeroes.indexOf(userId) !== -1) {
+                updatedHeroMembers.set(userId, memberChange.member);
             }
         }
         // load member for new heroes from storage

src/matrix/room/members/MemberList.js

@@ -26,9 +26,9 @@ export class MemberList {
         this._retentionCount = 1;
     }
 
-    afterSync(updatedMembers) {
-        for (const member of updatedMembers) {
-            this._members.add(member.userId, member);
+    afterSync(memberChanges) {
+        for (const [userId, memberChange] of memberChanges.entries()) {
+            this._members.add(userId, memberChange.member);
         }
     }
 

src/matrix/room/members/RoomMember.js

@@ -99,3 +99,30 @@ export class RoomMember {
         return this._data;
     }
 }
+
+export class MemberChange {
+    constructor(roomId, memberEvent) {
+        this._roomId = roomId;
+        this._memberEvent = memberEvent;
+        this._member = null;
+    }
+
+    get member() {
+        if (!this._member) {
+            this._member = RoomMember.fromMemberEvent(this._roomId, this._memberEvent);
+        }
+        return this._member;
+    }
+
+    userId() {
+        return this._memberEvent.state_key;
+    }
+
+    previousMembership() {
+        return this._memberEvent.unsigned?.prev_content?.membership;
+    }
+
+    membership() {
+        return this._memberEvent.content?.membership;
+    }
+}

src/matrix/room/timeline/persistence/SyncWriter.js

@@ -18,7 +18,7 @@ import {EventKey} from "../EventKey.js";
 import {EventEntry} from "../entries/EventEntry.js";
 import {FragmentBoundaryEntry} from "../entries/FragmentBoundaryEntry.js";
 import {createEventEntry} from "./common.js";
-import {RoomMember, EVENT_TYPE as MEMBER_EVENT_TYPE} from "../../members/RoomMember.js";
+import {MemberChange, RoomMember, EVENT_TYPE as MEMBER_EVENT_TYPE} from "../../members/RoomMember.js";
 
 // Synapse bug? where the m.room.create event appears twice in sync response
 // when first syncing the room
@@ -102,13 +102,13 @@ export class SyncWriter {
         if (event.type === MEMBER_EVENT_TYPE) {
             const userId = event.state_key;
             if (userId) {
-                const member = RoomMember.fromMemberEvent(this._roomId, event);
-                if (member) {
+                const memberChange = new MemberChange(this._roomId, event);
+                if (memberChange.member) {
                     // as this is sync, we can just replace the member
                     // if it is there already
-                    txn.roomMembers.set(member.serialize());
+                    txn.roomMembers.set(memberChange.member.serialize());
+                    return memberChange;
                 }
-                return member;
             }
         } else {
             txn.roomState.set(this._roomId, event);
@@ -116,22 +116,22 @@ export class SyncWriter {
     }
 
     _writeStateEvents(roomResponse, txn) {
-        const changedMembers = [];
+        const memberChanges = new Map();
         // persist state
         const {state} = roomResponse;
         if (Array.isArray(state?.events)) {
             for (const event of state.events) {
-                const member = this._writeStateEvent(event, txn);
-                if (member) {
-                    changedMembers.push(member);
+                const memberChange = this._writeStateEvent(event, txn);
+                if (memberChange) {
+                    memberChanges.set(memberChange.userId, memberChange);
                 }
             }
         }
-        return changedMembers;
+        return memberChanges;
     }
 
     async _writeTimeline(entries, timeline, currentKey, txn) {
-        const changedMembers = [];
+        const memberChanges = new Map();
         if (timeline.events) {
             const events = deduplicateEvents(timeline.events);
             for(const event of events) {
@@ -148,14 +148,14 @@ export class SyncWriter {
                 
                 // process live state events first, so new member info is available
                 if (typeof event.state_key === "string") {
-                    const member = this._writeStateEvent(event, txn);
-                    if (member) {
-                        changedMembers.push(member);
+                    const memberChange = this._writeStateEvent(event, txn);
+                    if (memberChange) {
+                        memberChanges.set(memberChange.userId, memberChange);
                     }
                 }
             }
         }
-        return {currentKey, changedMembers};
+        return {currentKey, memberChanges};
     }
 
     async _findMemberData(userId, events, txn) {
@@ -198,12 +198,14 @@ export class SyncWriter {
         }
         // important this happens before _writeTimeline so
         // members are available in the transaction
-        const changedMembers = this._writeStateEvents(roomResponse, txn);
+        const memberChanges = this._writeStateEvents(roomResponse, txn);
         const timelineResult = await this._writeTimeline(entries, timeline, currentKey, txn);
         currentKey = timelineResult.currentKey;
-        changedMembers.push(...timelineResult.changedMembers);
-
-        return {entries, newLiveKey: currentKey, changedMembers};
+        // merge member changes from state and timeline, giving precedence to the latter
+        for (const [userId, memberChange] of timelineResult.memberChanges.entries()) {
+            memberChanges.set(userId, memberChange);
+        }
+        return {entries, newLiveKey: currentKey, memberChanges};
     }
 
     afterSync(newLiveKey) {