Ensure return value can't be obtained for failed task

django/tasks/task.py

@@ -224,11 +224,13 @@ class TaskResult:
         If the task didn't succeed, an exception is raised.
         This is to distinguish against the task returning None.
         """
-        if not self.is_finished:
+        if self.status == ResultStatus.SUCCEEDED:
+            return self._return_value
+        elif self.status == ResultStatus.FAILED:
+            raise ValueError("Task failed")
+        else:
             raise ValueError("Task has not finished yet")
 
-        return self._return_value
-
     @property
     def exception_class(self):
         """The exception raised by the task function"""

docs/topics/tasks.txt

@@ -315,7 +315,8 @@ Return values
 If your task function returns something, it can be retrieved from the
 :attr:`django.tasks.TaskResult.return_value` attribute::
 
-    result.return_value  # 42
+    if result.status == ResultStatus.SUCCEEDED:
+        result.return_value  # 42
 
 If the task has not finished executing, or has failed, :exc:`ValueError` is raised.
 

tests/tasks/test_immediate_backend.py

@@ -82,6 +82,8 @@ class ImmediateBackendTestCase(SimpleTestCase):
 
                 # assert result
                 self.assertEqual(result.status, ResultStatus.FAILED)
+                with self.assertRaisesMessage(ValueError, "Task failed"):
+                    result.return_value
                 self.assertTrue(result.is_finished)
                 self.assertIsNotNone(result.started_at)
                 self.assertIsNotNone(result.finished_at)
@@ -111,6 +113,8 @@ class ImmediateBackendTestCase(SimpleTestCase):
             result = test_tasks.complex_exception.enqueue()
 
         self.assertEqual(result.status, ResultStatus.FAILED)
+        with self.assertRaisesMessage(ValueError, "Task failed"):
+            result.return_value
         self.assertIsNotNone(result.started_at)
         self.assertIsNotNone(result.finished_at)
         self.assertGreaterEqual(result.started_at, result.enqueued_at)