Fix updating from an empty stack

Change-Id: Ic63e1998316b27a431e856fe43b9ad8cc9dd887a
Closes-bug: #1343171

heat/engine/cfn/template.py

@@ -148,5 +148,6 @@ class CfnTemplate(template.Template):
         if len(cfn_tmpl.get(RES_DEPENDS_ON, [])) == 1:
             cfn_tmpl[RES_DEPENDS_ON] = cfn_tmpl[RES_DEPENDS_ON][0]
 
-        self.t.setdefault(self.RESOURCES, {})
+        if self.t.get(self.RESOURCES) is None:
+            self.t[self.RESOURCES] = {}
         self.t[self.RESOURCES][name] = cfn_tmpl

heat/engine/hot/template.py

@@ -222,5 +222,6 @@ class HOTemplate(template.Template):
         if name is None:
             name = definition.name
 
-        self.t.setdefault(self.RESOURCES, {})
+        if self.t.get(self.RESOURCES) is None:
+            self.t[self.RESOURCES] = {}
         self.t[self.RESOURCES][name] = definition.render_hot()

heat/tests/test_empty_stack.py

@@ -25,12 +25,13 @@ class StackTest(common.HeatTestCase):
         self.ctx = utils.dummy_context()
 
     def _assert_can_create(self, templ):
-        stack = parser.Stack(self.ctx, 'update_stack_arn_test',
+        stack = parser.Stack(self.ctx, utils.random_name(),
                              template.Template(templ))
         stack.store()
         stack.create()
         self.assertEqual((parser.Stack.CREATE, parser.Stack.COMPLETE),
                          stack.state)
+        return stack
 
     def test_heat_empty_json(self):
         tmpl = {'HeatTemplateFormatVersion': '2012-12-12',
@@ -73,3 +74,47 @@ resources:
 outputs:
 ''')
         self._assert_can_create(t)
+
+    def test_update_hot_empty_yaml(self):
+        t = template_format.parse('''
+heat_template_version: 2013-05-23
+parameters:
+resources:
+outputs:
+''')
+        ut = template_format.parse('''
+heat_template_version: 2013-05-23
+parameters:
+resources:
+  rand:
+    type: OS::Heat::RandomString
+outputs:
+''')
+        stack = self._assert_can_create(t)
+        updated = parser.Stack(self.ctx, utils.random_name(),
+                               template.Template(ut))
+        stack.update(updated)
+        self.assertEqual((parser.Stack.UPDATE, parser.Stack.COMPLETE),
+                         stack.state)
+
+    def test_update_cfn_empty_yaml(self):
+        t = template_format.parse('''
+AWSTemplateFormatVersion: 2010-09-09
+Parameters:
+Resources:
+Outputs:
+''')
+        ut = template_format.parse('''
+AWSTemplateFormatVersion: 2010-09-09
+Parameters:
+Resources:
+  rand:
+    Type: OS::Heat::RandomString
+Outputs:
+''')
+        stack = self._assert_can_create(t)
+        updated = parser.Stack(self.ctx, utils.random_name(),
+                               template.Template(ut))
+        stack.update(updated)
+        self.assertEqual((parser.Stack.UPDATE, parser.Stack.COMPLETE),
+                         stack.state)