Trigger lazy loading when filtering using spaces

so that the filtered DMs are correct

src/stores/SpaceStore.tsx

@@ -525,6 +525,26 @@ export class SpaceStoreClass extends AsyncStoreWithClient<IState> {
         this.notificationStateMap.set(key, state);
         return state;
     }
+
+    // traverse space tree with DFS calling fn on each space including the given root one
+    public traverseSpace(
+        spaceId: string,
+        fn: (roomId: string) => void,
+        includeRooms = false,
+        parentPath?: Set<string>,
+    ) {
+        if (parentPath && parentPath.has(spaceId)) return; // prevent cycles
+
+        fn(spaceId);
+
+        const newPath = new Set(parentPath).add(spaceId);
+        const [childSpaces, childRooms] = partitionSpacesAndRooms(this.getChildren(spaceId));
+
+        if (includeRooms) {
+            childRooms.forEach(r => fn(r.roomId));
+        }
+        childSpaces.forEach(s => this.traverseSpace(s.roomId, fn, includeRooms, newPath));
+    }
 }
 
 export default class SpaceStore {

src/stores/room-list/SpaceWatcher.ts

@@ -28,12 +28,22 @@ export class SpaceWatcher {
     private activeSpace: Room = SpaceStore.instance.activeSpace;
 
     constructor(private store: RoomListStoreClass) {
-        this.filter.updateSpace(this.activeSpace); // get the filter into a consistent state
+        this.updateFilter(); // get the filter into a consistent state
         store.addFilter(this.filter);
         SpaceStore.instance.on(UPDATE_SELECTED_SPACE, this.onSelectedSpaceUpdated);
     }
 
-    private onSelectedSpaceUpdated = (activeSpace) => {
-        this.filter.updateSpace(this.activeSpace = activeSpace);
+    private onSelectedSpaceUpdated = (activeSpace: Room) => {
+        this.activeSpace = activeSpace;
+        this.updateFilter();
+    };
+
+    private updateFilter = () => {
+        if (this.activeSpace) {
+            SpaceStore.instance.traverseSpace(this.activeSpace.roomId, roomId => {
+                this.store.matrixClient?.getRoom(roomId)?.loadMembersIfNeeded();
+            });
+        }
+        this.filter.updateSpace(this.activeSpace);
     };
 }