Reusable empty template

Refactored the empty template and added it to template module so that it
can be re-used else where. In convergence it is needed for rolling back
when create fails. Also needed for deleting stack, that is, update the
stack with empty template.

The empty_template method can be passed a template header (version) in
order to get an empty template of that version, otherwise by default, an
empty HOT template is returned.

Change-Id: Ic59bd2d4b9cfed1efd1973af0c4ec9274bcc204a

heat/engine/service.py

@@ -36,7 +36,6 @@ from heat.common.i18n import _LW
 from heat.common import identifier
 from heat.common import messaging as rpc_messaging
 from heat.common import service_utils
-from heat.common import template_format
 from heat.engine import api
 from heat.engine import attributes
 from heat.engine import clients
@@ -950,12 +949,7 @@ class EngineService(service.Service):
         stack = parser.Stack.load(cnxt, stack=st)
 
         if stack.convergence:
-            empty_template = '''
-            heat_template_version: 2013-05-23
-            description: Empty Template
-            '''
-            tmpl = template_format.parse(empty_template)
-            template = templatem.Template(tmpl)
+            template = templatem.Template.create_empty_template()
             stack.converge_stack(template=template, action=stack.DELETE)
             return
 

heat/engine/template.py

@@ -244,6 +244,23 @@ class Template(collections.Mapping):
                             'Found a [%s] instead') % type(res)
                 raise exception.StackValidationFailed(message=message)
 
+    @classmethod
+    def create_empty_template(cls,
+                              version=('heat_template_version', '2015-04-30')):
+        '''Creates an empty template.
+
+        Creates a new empty template with given version. If version is
+        not provided, a new empty HOT template of version "2015-04-30"
+        is returned.
+
+        :param version: A tuple containing version header of the
+        template: version key and value. E.g. ("heat_template_version",
+        "2015-04-30")
+        :returns: A new empty template.
+        '''
+        tmpl = {version[0]: version[1]}
+        return cls(tmpl)
+
 
 def parse(functions, stack, snippet):
     recurse = functools.partial(parse, functions, stack)

heat/tests/test_engine_service.py

@@ -94,11 +94,6 @@ resources:
             salt: {get_param: salt}
 '''
 
-empty_template = '''
-heat_template_version: 2013-05-23
-description: Empty Template
-'''
-
 wp_template_no_default = '''
 {
   "AWSTemplateFormatVersion" : "2010-09-09",
@@ -400,9 +395,8 @@ class StackConvergenceCreateUpdateDeleteTest(common.HeatTestCase):
         stack.converge_stack(template=stack.t, action=stack.CREATE)
 
         # update stack with new template
-        t2 = template_format.parse(empty_template)
-        template2 = templatem.Template(
-            t2, env=environment.Environment({'KeyName2': 'test2'}))
+        template2 = templatem.Template.create_empty_template(
+            version=stack.t.version)
 
         curr_stack_db = stack_object.Stack.get_by_id(stack.context, stack.id)
         curr_stack = parser.Stack.load(curr_stack_db._context,

heat/tests/test_template.py

@@ -872,6 +872,56 @@ Mappings:
 
         self.assertEqual(cfn_tpl['Resources'], empty.t['Resources'])
 
+    def test_create_empty_template_default_version(self):
+        empty_template = template.Template.create_empty_template()
+        self.assertEqual(hot_t.HOTemplate20150430, empty_template.__class__)
+        self.assertEqual({}, empty_template['parameter_groups'])
+        self.assertEqual({}, empty_template['resources'])
+        self.assertEqual({}, empty_template['outputs'])
+
+    def test_create_empty_template_returns_correct_version(self):
+        t = template_format.parse('''
+            AWSTemplateFormatVersion: 2010-09-09
+            Parameters:
+            Resources:
+            Outputs:
+            ''')
+        aws_tmpl = template.Template(t)
+        empty_template = template.Template.create_empty_template(
+            version=aws_tmpl.version)
+        self.assertEqual(aws_tmpl.__class__, empty_template.__class__)
+        self.assertEqual({}, empty_template['Mappings'])
+        self.assertEqual({}, empty_template['Resources'])
+        self.assertEqual({}, empty_template['Outputs'])
+
+        t = template_format.parse('''
+            HeatTemplateFormatVersion: 2012-12-12
+            Parameters:
+            Resources:
+            Outputs:
+            ''')
+        heat_tmpl = template.Template(t)
+        empty_template = template.Template.create_empty_template(
+            version=heat_tmpl.version)
+        self.assertEqual(heat_tmpl.__class__, empty_template.__class__)
+        self.assertEqual({}, empty_template['Mappings'])
+        self.assertEqual({}, empty_template['Resources'])
+        self.assertEqual({}, empty_template['Outputs'])
+
+        t = template_format.parse('''
+            heat_template_version: 2015-04-30
+            parameter_groups:
+            resources:
+            outputs:
+            ''')
+        hot_tmpl = template.Template(t)
+        empty_template = template.Template.create_empty_template(
+            version=hot_tmpl.version)
+        self.assertEqual(hot_tmpl.__class__, empty_template.__class__)
+        self.assertEqual({}, empty_template['parameter_groups'])
+        self.assertEqual({}, empty_template['resources'])
+        self.assertEqual({}, empty_template['outputs'])
+
 
 class TemplateFnErrorTest(common.HeatTestCase):
     scenarios = [