Fix calculating task execution result for "with-items"

* The logic of calculating a task result in case of "with-items" was
  overcomplicated and broke encapsulation of a "with-items" task.
  This patch makes it simpler, so that the method doesn't need to
  peek into the internals of a "with-items" task (e.g. runtime_context).

Change-Id: I036193cbae15d7f3c3414b123525ceafa91fdeb1

mistral/engine/policies.py

@@ -377,6 +377,10 @@ class RetryPolicy(base.TaskPolicy):
         # retried as-is, because these tasks can't start without
         # a correct logical state.
         if hasattr(task.task_spec, "get_join") and task.task_spec.get_join():
+            # TODO(rakhmerov): This is an example of broken encapsulation.
+            # The control over such operations should belong to the class Task.
+            # If it's done, from the outside of the class there will be just
+            # one visible operation "continue_task()" or something like that.
             from mistral.engine import task_handler as t_h
 
             task.set_state(

mistral/workflow/data_flow.py

@@ -167,16 +167,9 @@ def get_task_execution_result(task_ex):
         if hasattr(ex, 'output') and ex.accepted
     ]
 
-    task_spec = spec_parser.get_task_spec(task_ex.spec)
-
-    if task_spec.get_with_items():
-        # TODO(rakhmerov): Smell: violation of 'with-items' encapsulation.
-        with_items_ctx = task_ex.runtime_context.get('with_items')
-
-        if with_items_ctx and with_items_ctx.get('count') > 0:
-            return results
-        else:
-            return []
+    # If it's a 'with-items' task we should always return an array.
+    if spec_parser.get_task_spec(task_ex.spec).get_with_items():
+        return results
 
     return results[0] if len(results) == 1 else results