prevent parents from overriding children's (falsy) results (#456)

Changelog.md

@@ -6,6 +6,7 @@
 - Feature: Nested enums can now be passed in a dict as `children` with `initial` parameter
 - Bugfix #449: get_triggers/get_transitions did not return nested triggers correctly (thanks @alexandretanem)
 - Feature #452: Improve handling of label attributes in custom diagram states and `TransitionGraphSupport` (thanks @badiku)
+- Bugfix #456: Prevent parents from overriding (falsy) results of their children's events (thanks @alexandretanem)
 
 ## 0.8.2 (June 2020)
 

tests/test_nesting.py

@@ -472,6 +472,15 @@ def on_enter_A_2(self):
         self.assertTrue(enter_mock.called)
         self.assertFalse(parent_mock.called)
 
+    def test_child_condition_persistence(self):
+        # even though the transition is invalid for the parent it is valid for the nested child state
+        # no invalid transition exception should be thrown
+        machine = self.machine_cls(states=[{'name': 'A', 'children': ['1', '2'], 'initial': '1',
+                                            'transitions': [{'trigger': 'go', 'source': '1', 'dest': '2',
+                                                             'conditions': self.stuff.this_fails}]}, 'B'],
+                                   transitions=[['go', 'B', 'A']], initial='A')
+        self.assertFalse(False, machine.go())
+
 
 class TestSeparatorsBase(TestCase):
 

tests/test_nesting_legacy.py

@@ -86,11 +86,14 @@ def test_transitioning(self):
         self.assertEqual(s.state, 'C')
 
     def test_nested_definitions(self):
-        pass
+        pass  # not supported by legacy machine
 
     def test_add_nested_state(self):
         pass  # not supported by legacy machine
 
+    def test_child_condition_persistence(self):
+        pass  # not supported by legacy machine
+
 
 class TestReuseLegacySeparatorDefault(TestReuseSeparatorBase):
 

transitions/extensions/asyncio.py

@@ -442,9 +442,13 @@ async def _trigger_event(self, _model, _trigger, _state_tree, *args, **kwargs):
         for key, value in _state_tree.items():
             if value:
                 with self(key):
-                    res[key] = await self._trigger_event(_model, _trigger, value, *args, **kwargs)
+                    tmp = await self._trigger_event(_model, _trigger, value, *args, **kwargs)
+                    if tmp is not None:
+                        res[key] = tmp
             if not res.get(key, None) and _trigger in self.events:
-                res[key] = await self.events[_trigger].trigger(_model, self, *args, **kwargs)
+                tmp = await self.events[_trigger].trigger(_model, self, *args, **kwargs)
+                if tmp is not None:
+                    res[key] = tmp
         return None if not res or all([v is None for v in res.values()]) else any(res.values())
 
 

transitions/extensions/nesting.py

@@ -903,7 +903,11 @@ def _trigger_event(self, _model, _trigger, _state_tree, *args, **kwargs):
         for key, value in _state_tree.items():
             if value:
                 with self(key):
-                    res[key] = self._trigger_event(_model, _trigger, value, *args, **kwargs)
+                    tmp = self._trigger_event(_model, _trigger, value, *args, **kwargs)
+                    if tmp is not None:
+                        res[key] = tmp
             if not res.get(key, None) and _trigger in self.events:
-                res[key] = self.events[_trigger].trigger(_model, self, *args, **kwargs)
+                tmp = self.events[_trigger].trigger(_model, self, *args, **kwargs)
+                if tmp is not None:
+                    res[key] = tmp
         return None if not res or all(v is None for v in res.values()) else any(res.values())