addressing comments #2

Author: wu-hui

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/FirestoreTest.java

@@ -1110,7 +1110,7 @@ public void testWaitForPendingWritesResolves() {
     Task<Void> pendingWrite = documentReference.set(data);
     Task<Void> awaitsPendingWrites2 = firestore.waitForPendingWrites();
 
-    // `awaitsPendingWrites1` is complete immediately because there is no pending writes at
+    // `awaitsPendingWrites1` completes immediately because there are no pending writes at
     // the time it is created.
     waitFor(awaitsPendingWrites1);
     assertTrue(awaitsPendingWrites1.isComplete() && awaitsPendingWrites1.isSuccessful());

firebase-firestore/src/main/java/com/google/firebase/firestore/core/SyncEngine.java

@@ -40,6 +40,7 @@
 import com.google.firebase.firestore.model.NoDocument;
 import com.google.firebase.firestore.model.SnapshotVersion;
 import com.google.firebase.firestore.model.mutation.Mutation;
+import com.google.firebase.firestore.model.mutation.MutationBatch;
 import com.google.firebase.firestore.model.mutation.MutationBatchResult;
 import com.google.firebase.firestore.remote.Datastore;
 import com.google.firebase.firestore.remote.RemoteEvent;
@@ -448,12 +449,13 @@ public void registerPendingWritesTask(TaskCompletionSource<Void> userTask) {
     if (!remoteStore.canUseNetwork()) {
       Logger.debug(
           TAG,
-          "The network is disabled. The task returned by 'awaitPendingWrites()' will not complete until the network is enabled.");
+          "The network is disabled. The task returned by 'awaitPendingWrites()' will not"
+              + " complete until the network is enabled.");
     }
 
     int largestPendingBatchId = localStore.getHighestUnacknowledgedBatchId();
 
-    if (largestPendingBatchId == 0) {
+    if (largestPendingBatchId == MutationBatch.UNKNOWN) {
       // Complete the task right away if there is no pending writes at the moment.
       userTask.setResult(null);
       return;
@@ -623,10 +625,11 @@ public void handleCredentialChange(User user) {
     currentUser = user;
 
     if (userChanged) {
+      // Fails tasks waiting for pending writes requested by previous user.
+      failOutstandingPendingWritesAwaitingTasks();
       // Notify local store and emit any resulting events from swapping out the mutation queue.
       ImmutableSortedMap<DocumentKey, MaybeDocument> changes = localStore.handleUserChange(user);
       emitNewSnapsAndNotifyLocalStore(changes, /*remoteEvent=*/ null);
-      failOutstandingPendingWritesAwaitingTasks();
     }
 
     // Notify remote store so it can restart its streams.

firebase-firestore/src/main/java/com/google/firebase/firestore/local/LocalStore.java

@@ -284,7 +284,7 @@ public ImmutableSortedMap<DocumentKey, MaybeDocument> rejectBatch(int batchId) {
 
   /**
    * Returns the largest (latest) batch id in mutation queue that is pending server response.
-   * Returns 0 if the queue is empty.
+   * Returns {@link MutationBatch#UNKNOWN} if the queue is empty.
    */
   public int getHighestUnacknowledgedBatchId() {
     return mutationQueue.getHighestUnacknowledgedBatchId();

firebase-firestore/src/main/java/com/google/firebase/firestore/local/MemoryMutationQueue.java

@@ -189,7 +189,7 @@ public MutationBatch getNextMutationBatchAfterBatchId(int batchId) {
 
   @Override
   public int getHighestUnacknowledgedBatchId() {
-    return queue.isEmpty() ? 0 : nextBatchId - 1;
+    return queue.isEmpty() ? MutationBatch.UNKNOWN : nextBatchId - 1;
   }
 
   @Override

firebase-firestore/src/main/java/com/google/firebase/firestore/local/MutationQueue.java

@@ -75,7 +75,7 @@ MutationBatch addMutationBatch(
 
   /**
    * @return The largest (latest) batch id in mutation queue for the current user that is pending
-   *     server response, 0 if the queue is empty.
+   *     server response, {@link MutationBatch#UNKNOWN} if the queue is empty.
    */
   int getHighestUnacknowledgedBatchId();
 

firebase-firestore/src/main/java/com/google/firebase/firestore/local/SQLiteMutationQueue.java

@@ -251,8 +251,8 @@ public MutationBatch getNextMutationBatchAfterBatchId(int batchId) {
 
   @Override
   public int getHighestUnacknowledgedBatchId() {
-    return db.query("SELECT IFNULL(MAX(batch_id), 0) FROM mutations WHERE uid = ?")
-        .binding(uid)
+    return db.query("SELECT IFNULL(MAX(batch_id), ?) FROM mutations WHERE uid = ?")
+        .binding(MutationBatch.UNKNOWN, uid)
         .firstValue(row -> row.getInt(0));
   }
 

firebase-firestore/src/test/java/com/google/firebase/firestore/local/LocalStoreTestCase.java

@@ -1146,7 +1146,7 @@ public void testHandlesPatchMutationWithTransformThenRemoteEvent() {
 
   @Test
   public void testGetHighestUnacknowledgedBatchId() {
-    assertEquals(0, localStore.getHighestUnacknowledgedBatchId());
+    assertEquals(-1, localStore.getHighestUnacknowledgedBatchId());
 
     writeMutation(setMutation("foo/bar", map("abc", 123)));
     assertEquals(1, localStore.getHighestUnacknowledgedBatchId());
@@ -1158,6 +1158,6 @@ public void testGetHighestUnacknowledgedBatchId() {
     assertEquals(2, localStore.getHighestUnacknowledgedBatchId());
 
     rejectMutation();
-    assertEquals(0, localStore.getHighestUnacknowledgedBatchId());
+    assertEquals(-1, localStore.getHighestUnacknowledgedBatchId());
   }
 }