Disable nested validation for ResourceGroup with zero count

Some users (TripleO specifically) want to disable features via a
count of zero, which is a problem as we always recurse and validate
the nested stack since c31c34f8df

Instead, we only do validation when the count is non-zero, to
enable, e.g default image names, to be ignored at validation
time (as we'll never use them) instead of rejected by the nested
schema (e.g the server.py properties schema which contains a
custom contraint to always validate the image).

This should still allow us to fail fast (at validation time before
creating anything) when we're actually about to create something,
e.g when the count is non-zero.

This patch also rolls in the fix for the regression this originally
caused on master, Iea454f4201990f65633b644bbefe708e5a216885.

Change-Id: I411ff41a9e0730e9864f5ed4ac54f1d5d0ec02d7
Closes-Bug: #1401929
Closes-Bug: #1404399
(cherry picked from commit 907c0aac79 and 4834443353)

heat/engine/resources/resource_group.py

@@ -146,7 +146,14 @@ class ResourceGroup(stack_resource.StackResource):
         res_class = self.stack.env.get_class(res_def.resource_type)
         res_inst = res_class("%s:resource_def" % self.name, res_def,
                              self.stack)
-        res_inst.validate()
+        # Only validate the resource definition (which may be a
+        # nested template) if count is non-zero, to enable folks
+        # to disable features via a zero count if they wish
+        # Use self._resource_names() to determine if any resources will
+        # be created, not the COUNT property, because this doesn't exist
+        # in the SoftwareDeployments subclass properties schema.
+        if self._resource_names():
+            res_inst.validate()
 
     def _resource_names(self, properties=None):
         p = properties or self.properties

heat/tests/test_software_deployment.py

@@ -917,3 +917,9 @@ class SoftwareDeploymentsTest(HeatTestCase):
             mock.call('deploy_stderr'),
             mock.call('deploy_status_code'),
         ])
+
+    def test_validate(self):
+        stack = utils.parse_stack(self.template)
+        snip = stack.t.resource_definitions(stack)['deploy_mysql']
+        resg = sd.SoftwareDeployments('test', snip, stack)
+        self.assertIsNone(resg.validate())

heat_integrationtests/functional/test_resource_group.py

@@ -0,0 +1,92 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import six
+
+from heatclient import exc
+
+from heat_integrationtests.common import test
+
+
+class ResourceGroupTest(test.HeatIntegrationTest):
+
+    def setUp(self):
+        super(ResourceGroupTest, self).setUp()
+        self.client = self.orchestration_client
+
+    def _group_nested_identifier(self, stack_identifier,
+                                 group_name='random_group'):
+        # Get the nested stack identifier from the group
+        rsrc = self.client.resources.get(stack_identifier, group_name)
+        physical_resource_id = rsrc.physical_resource_id
+
+        nested_stack = self.client.stacks.get(physical_resource_id)
+        nested_identifier = '%s/%s' % (nested_stack.stack_name,
+                                       nested_stack.id)
+        parent_id = stack_identifier.split("/")[-1]
+        self.assertEqual(parent_id, nested_stack.parent)
+        return nested_identifier
+
+    def test_resource_group_zero_novalidate(self):
+        # Nested resources should be validated only when size > 0
+        # This allows features to be disabled via size=0 without
+        # triggering validation of nested resource custom contraints
+        # e.g images etc in the nested schema.
+        nested_template_fail = '''
+heat_template_version: 2013-05-23
+resources:
+  random:
+    type: OS::Heat::RandomString
+    properties:
+        length: BAD
+'''
+
+        template_zero_nested = '''
+heat_template_version: 2013-05-23
+resources:
+  random_group:
+    type: OS::Heat::ResourceGroup
+    properties:
+      count: 0
+      resource_def:
+        type: My::RandomString
+'''
+
+        files = {'provider.yaml': nested_template_fail}
+        env = {'resource_registry':
+               {'My::RandomString': 'provider.yaml'}}
+        stack_identifier = self.stack_create(
+            template=template_zero_nested,
+            files=files,
+            environment=env
+        )
+
+        self.assertEqual({u'random_group': u'OS::Heat::ResourceGroup'},
+                         self.list_resources(stack_identifier))
+
+        # Check we created an empty nested stack
+        nested_identifier = self._group_nested_identifier(stack_identifier)
+        self.assertEqual({}, self.list_resources(nested_identifier))
+
+        # Prove validation works for non-zero create/update
+        template_two_nested = template_zero_nested.replace("count: 0",
+                                                           "count: 2")
+        expected_err = "length Value 'BAD' is not an integer"
+        ex = self.assertRaises(exc.HTTPBadRequest, self.update_stack,
+                               stack_identifier, template_two_nested,
+                               environment=env, files=files)
+        self.assertIn(expected_err, six.text_type(ex))
+
+        ex = self.assertRaises(exc.HTTPBadRequest, self.stack_create,
+                               template=template_two_nested,
+                               environment=env, files=files)
+        self.assertIn(expected_err, six.text_type(ex))