Task publish does not overwrite variable in context Edit

Use dict update instead of recursive merge when published
task output added to workflow context.

Change-Id: I44f99c6d08c6647e4240367be534e9dc1747b857
Closes-Bug: 1616090
Signed-off-by: Istvan Imre <istvan.imre@nokia.com>

mistral/tests/unit/engine/test_dataflow.py

@@ -371,6 +371,58 @@ class DataFlowEngineTest(engine_test_base.EngineTestCase):
             task4.published
         )
 
+    def test_sequential_tasks_publishing_same_structured(self):
+        var_overwrite_wf = """---
+        version: '2.0'
+
+        wf:
+          type: direct
+
+          tasks:
+            task1:
+              publish:
+                greeting: {"a": "b"}
+              on-success:
+                - task2
+
+            task2:
+              publish:
+                greeting: {}
+              on-success:
+                - task3
+
+            task3:
+              publish:
+                result: <% $.greeting %>
+        """
+
+        wf_service.create_workflows(var_overwrite_wf)
+
+        # Start workflow.
+        wf_ex = self.engine.start_workflow(
+            'wf',
+            {},
+            env={'from': 'Neo'}
+        )
+
+        self.await_workflow_success(wf_ex.id)
+
+        # Note: We need to reread execution to access related tasks.
+        wf_ex = db_api.get_workflow_execution(wf_ex.id)
+
+        self.assertEqual(states.SUCCESS, wf_ex.state)
+
+        tasks = wf_ex.task_executions
+
+        task1 = self._assert_single_item(tasks, name='task1')
+        task2 = self._assert_single_item(tasks, name='task2')
+        task3 = self._assert_single_item(tasks, name='task3')
+
+        self.assertEqual(states.SUCCESS, task3.state)
+        self.assertDictEqual({'greeting': {'a': 'b'}}, task1.published)
+        self.assertDictEqual({'greeting': {}}, task2.published)
+        self.assertDictEqual({'result': {}}, task3.published)
+
     def test_linear_dataflow_implicit_publish(self):
         linear_wf = """---
         version: '2.0'

mistral/utils/__init__.py

@@ -148,6 +148,25 @@ def merge_dicts(left, right, overwrite=True):
     return left
 
 
+def update_dict(left, right):
+    """Updates left dict with content from right dict
+
+    :param left: Left dict.
+    :param right: Right dict.
+    :return: the updated left dictionary.
+    """
+
+    if left is None:
+        return right
+
+    if right is None:
+        return left
+
+    left.update(right)
+
+    return left
+
+
 def get_file_list(directory):
     base_path = pkg.resource_filename(
         version.version_info.package,

mistral/workflow/data_flow.py

@@ -116,7 +116,7 @@ def evaluate_task_outbound_context(task_ex):
     in_context = (copy.deepcopy(dict(task_ex.in_context))
                   if task_ex.in_context is not None else {})
 
-    return utils.merge_dicts(in_context, task_ex.published)
+    return utils.update_dict(in_context, task_ex.published)
 
 
 def evaluate_workflow_output(wf_spec, ctx):