Fix a few bugs with TagOrderStore:

- Have TagOrderStore listen for MatrixSync actions so that it can initialise
   tag ordering state.
 - Expose an empty list until the client has done its first sync and has
   fetched list of joined groups

src/actions/MatrixActionCreators.js

@@ -14,7 +14,10 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { createMatrixActionCreator } from './actionCreators';
+import {
+    createMatrixActionCreator,
+    createMatrixSyncActionCreator,
+} from './actionCreators';
 
 // Events emitted from the matrixClient that we want to dispatch as actions
 // via MatrixActionCreators. See createMatrixActionCreator.
@@ -30,6 +33,8 @@ export default {
         this.actionCreators = REGISTERED_EVENTS.map((eventId) =>
             createMatrixActionCreator(matrixClient, eventId),
         );
+        this.actionCreators.push(createMatrixSyncActionCreator(matrixClient));
+
         this.actionCreatorsStop = this.actionCreators.map((ac) => ac());
     },
 

src/actions/actionCreators.js

@@ -70,3 +70,36 @@ export function createMatrixActionCreator(matrixClient, eventId) {
         };
     };
 }
+
+// TODO: migrate from sync_state to MatrixSync so that more js-sdk events
+//       become dispatches in the same place.
+/**
+ * Create an action creator that will listen to `sync` events emitted
+ * by matrixClient and dispatch a corresponding MatrixSync action. E.g:
+ *     {
+ *         action: 'MatrixSync',
+ *         state: 'SYNCING',
+ *         prevState: 'PREPARED'
+ *     }
+ * @param {MatrixClient} matrixClient the matrix client with which to register
+ *                                    a listener.
+ * @returns {function} a function that, when called, will begin to listen to
+ *                     dispatches from matrixClient. The result from that
+ *                     function can be called to stop listening.
+ */
+export function createMatrixSyncActionCreator(matrixClient) {
+    const listener = (state, prevState) => {
+        dis.dispatch({
+            action: 'MatrixSync',
+            state,
+            prevState,
+            matrixClient,
+        });
+    };
+    return () => {
+        matrixClient.on('sync', listener);
+        return () => {
+            matrixClient.removeListener('sync', listener);
+        };
+    };
+}