Handle invalid depends field

Raise a proper error when something wrong is passed in a depends_on
field.

Change-Id: I9d27cc48a7f4c050fcc89ab5d07b19329d228955
Story: 2002544
Task: 22103

heat/engine/template_common.py

@@ -98,6 +98,14 @@ class CommonTemplate(template.Template):
                                              name, data, no_parse)
         if isinstance(depends, six.string_types):
             depends = [depends]
+        elif depends:
+            for dep in depends:
+                if not isinstance(dep, six.string_types):
+                    msg = _('Resource %(name)s %(key)s '
+                            'must be a list of strings') % {
+                                'name': name, 'key': self.RES_DEPENDS_ON}
+                    raise exception.StackValidationFailed(message=msg)
+
         yield 'depends', depends
 
         del_policy = self._parse_resource_field(self.RES_DELETION_POLICY,

heat/tests/test_validate.py

@@ -2105,3 +2105,21 @@ parameters:
                     'NoEcho': 'false',
                     'Type': 'String'}}}
         self.assertEqual(expected, res)
+
+    def test_validate_bad_depends(self):
+        test_template = '''
+        heat_template_version: 2013-05-23
+
+        resources:
+          random_str:
+            type: OS::Heat::RandomString
+            depends_on: [{foo: bar}]
+        '''
+
+        t = template_format.parse(test_template)
+
+        res = dict(self.engine.validate_template(self.ctx, t, {}))
+        self.assertEqual(
+            {'Error': 'Resource random_str depends_on must be '
+                      'a list of strings'},
+            res)