Support allowed() in workflows.Step

There are cases where we want to display workflow Step conditionally.

Change-Id: I71ae3ed270d9472190430ac5b4a34682ce3b3f29
Closes-Bug: #1683262

horizon/test/tests/workflows.py

@@ -82,6 +82,14 @@ class AdminAction(workflows.Action):
         permissions = ("horizon.test",)
 
 
+class TestDisabledAction(workflows.Action):
+    disabled_id = forms.CharField(label="Disabled")
+
+    class Meta(object):
+        name = "Test Action Disabled"
+        slug = "test_action_disabled"
+
+
 class AdminForbiddenAction(workflows.Action):
     admin_id = forms.CharField(label="Admin forbidden")
 
@@ -121,6 +129,14 @@ class AdminStep(workflows.Step):
     before = TestStepTwo
 
 
+class TestDisabledStep(workflows.Step):
+    action_class = TestDisabledAction
+    contributes = ("disabled_id",)
+
+    def allowed(self, request):
+        return False
+
+
 class AdminForbiddenStep(workflows.Step):
     action_class = AdminForbiddenAction
 
@@ -312,6 +328,15 @@ class WorkflowsTests(test.TestCase):
                                   '<AdminStep: admin_action>',
                                   '<TestStepTwo: test_action_two>'])
 
+    def test_has_allowed(self):
+        TestWorkflow.register(TestDisabledStep)
+        flow = TestWorkflow(self.request)
+        # Check TestDisabledStep is not included
+        # even though TestDisabledStep is registered.
+        self.assertQuerysetEqual(flow.steps,
+                                 ['<TestStepOne: test_action_one>',
+                                  '<TestStepTwo: test_action_two>'])
+
     def test_step_is_hidden_on_policy(self):
         self.policy_patcher.stop()
 

horizon/workflows/base.py

@@ -465,6 +465,16 @@ class Step(object):
         """Returns True if action contains any required fields."""
         return any(field.required for field in self.action.fields.values())
 
+    def allowed(self, request):
+        """Determines whether or not the step is displayed.
+
+        Step instances can override this method to specify conditions under
+        which this tab should not be shown at all by returning ``False``.
+
+        The default behavior is to return ``True`` for all cases.
+        """
+        return True
+
 
 class WorkflowMetaclass(type):
     def __new__(mcs, name, bases, attrs):
@@ -694,7 +704,8 @@ class Workflow(html.HTMLElement):
         for step_class in ordered_step_classes:
             cls = self._registry[step_class]
             if (has_permissions(self.request.user, cls) and
-                    policy.check(cls.policy_rules, self.request)):
+                    policy.check(cls.policy_rules, self.request) and
+                    cls.allowed(self.request)):
                 self._ordered_steps.append(cls)
 
     def _order_steps(self):

releasenotes/notes/workflow-step-allowed-support-d0a770da1d30efb7.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - Horizon workflow Step now support allowed() method to determine
+    the step should be displayed conditionally.
+    The workflow Step class already support policy check and permission
+    mechanism to decide the step should be displayed, but allowed() is used
+    to support more complex or dynamic condition.