Merge "Preserve task when clearing top activities" into tm-dev

services/core/java/com/android/server/wm/Task.java

@@ -1630,12 +1630,16 @@ class Task extends TaskFragment {
     }
 
     ActivityRecord performClearTop(ActivityRecord newR, int launchFlags) {
+        // The task should be preserved for putting new activity in case the last activity is
+        // finished if it is normal launch mode and not single top ("clear-task-top").
+        mReuseTask = true;
         mTaskSupervisor.beginDeferResume();
         final ActivityRecord result;
         try {
             result = clearTopActivities(newR, launchFlags);
         } finally {
             mTaskSupervisor.endDeferResume();
+            mReuseTask = false;
         }
         return result;
     }

services/tests/wmtests/src/com/android/server/wm/TaskTests.java

@@ -258,6 +258,20 @@ public class TaskTests extends WindowTestsBase {
         assertNull(task1.isInTask(activity2));
     }
 
+    @Test
+    public void testPerformClearTop() {
+        final Task task = createTask(mDisplayContent);
+        final ActivityRecord activity1 = new ActivityBuilder(mAtm).setTask(task).build();
+        final ActivityRecord activity2 = new ActivityBuilder(mAtm).setTask(task).build();
+        // Detach from process so the activities can be removed from hierarchy when finishing.
+        activity1.detachFromProcess();
+        activity2.detachFromProcess();
+        assertNull(task.performClearTop(activity1, 0 /* launchFlags */));
+        assertFalse(task.hasChild());
+        // In real case, the task should be preserved for adding new activity.
+        assertTrue(task.isAttached());
+    }
+
     @Test
     public void testRemoveChildForOverlayTask() {
         final Task task = createTask(mDisplayContent);