offer to rejoin archived room from menu

src/domain/session/room/RoomViewModel.js

@@ -148,6 +148,14 @@ export class RoomViewModel extends ViewModel {
         this._room.forget();
     }
 
+    get canRejoin() {
+        return this._room.isArchived;
+    }
+
+    rejoinRoom() {
+        this._room.join();
+    }
+    
     async _sendMessage(message) {
         if (!this._room.isArchived && message) {
             try {

src/matrix/room/ArchivedRoom.js

@@ -162,6 +162,12 @@ export class ArchivedRoom extends BaseRoom {
             this._forgetCallback(this.id);
         });
     }
+
+    join(log = null) {
+        return this._platform.logger.wrapOrRun(log, "rejoin archived room", async log => {
+            await this._hsApi.join(this.id, {log}).response();
+        });
+    }
 }
 
 function findKickDetails(roomResponse, ownUserId) {

src/platform/web/ui/session/room/RoomView.js

@@ -73,6 +73,9 @@ export class RoomView extends TemplateView {
             if (vm.canForget) {
                 options.push(Menu.option(vm.i18n`Forget room`, () => vm.forgetRoom()));
             }
+            if (vm.canRejoin) {
+                options.push(Menu.option(vm.i18n`Rejoin room`, () => vm.rejoinRoom()));
+            }
             if (!options.length) {
                 return;
             }