Make template validation uniform

There were two different behaviours during template validation and creation
stack (with template validation). In first case error was raised if
template did not have any resources. However user could create stack
without error using this such kind of template.
This patch make behaviour equal for both variant and gives ability to
create and successfully validate stack with template which does not have
resources.

Change-Id: I4dc30ccdc45e0fa7ff678b434106e056dba5f3b4
Closes-Bug: #1278090

doc/source/template_guide/hot_spec.rst

@@ -80,8 +80,9 @@ parameters
 
 resources
     This section contains the declaration of the single resources of the
-    template. This section is mandatory and at least one resource must be
-    defined in any HOT template.
+    template. This section with at least one resource should be defined in any
+    HOT template, or the template would not really do anything when being
+    instantiated.
 
 outputs
     This section allows for specifying output parameters available to users once

heat/engine/service.py

@@ -600,7 +600,7 @@ class EngineService(service.Service):
 
         # validate overall template
         try:
-            tmpl.validate(allow_empty=False)
+            tmpl.validate()
         except Exception as ex:
             return {'Error': six.text_type(ex)}
 

heat/engine/template.py

@@ -18,7 +18,9 @@ import functools
 from heat.common import exception
 from heat.db import api as db_api
 from heat.engine import plugin_manager
+from heat.openstack.common import log as logging
 
+logger = logging.getLogger(__name__)
 
 __all__ = ['Template']
 
@@ -164,7 +166,7 @@ class Template(collections.Mapping):
     def parse(self, stack, snippet):
         return parse(self.functions(), stack, snippet)
 
-    def validate(self, allow_empty=True):
+    def validate(self):
         '''Validate the template.
 
         Validates the top-level sections of the template as well as syntax
@@ -172,7 +174,6 @@ class Template(collections.Mapping):
         code parts that are responsible for working with the respective
         sections (e.g. parameters are check by parameters schema class).
 
-        :param allow_empty: whether to allow an empty resources section
         '''
 
         # check top-level sections
@@ -182,11 +183,10 @@ class Template(collections.Mapping):
 
         # check resources
         tmpl_resources = self[self.RESOURCES]
-
-        if not allow_empty and not tmpl_resources:
-            message = _('The template is invalid. A Resources section with at '
-                        'least one resource must be defined.')
-            raise exception.StackValidationFailed(message=message)
+        if not tmpl_resources:
+            logger.warn(_('Template does not contain any resources, so '
+                          'the template would not really do anything when '
+                          'being instantiated.'))
 
         for res in tmpl_resources.values():
             try:

heat/tests/test_validate.py

@@ -1076,9 +1076,8 @@ class validateTest(HeatTestCase):
 
         engine = service.EngineService('a', 't')
         res = dict(engine.validate_template(None, hot_tpl, {}))
-        self.assertEqual({'Error': 'The template is invalid. '
-                          'A Resources section with at least one resource '
-                          'must be defined.'}, res)
+        expected = {'Description': 'No description', 'Parameters': {}}
+        self.assertEqual(expected, res)
 
     def test_validate_template_with_invalid_resource_type(self):
         hot_tpl = template_format.parse('''