Add VersionPredicate type of field

Any new property which wants to use a list of versions can
use VersionPredicate to say which ranges are good.

NOTE: The new type of field is also proposed for o.vo
here: https://review.openstack.org/204113

Partially-Implements: blueprint request-spec-object

Change-Id: I8b371ec46f8844fce380988e8fdd52146197503b

nova/objects/fields.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 from collections import OrderedDict
+from distutils import versionpredicate
 
 import netaddr
 from oslo_utils import strutils
@@ -362,6 +363,19 @@ class MonitorMetricType(Enum):
             valid_values=MonitorMetricType.ALL)
 
 
+# NOTE(sbauza): Remove this on next release of oslo.versionedobjects
+class VersionPredicate(fields.String):
+    @staticmethod
+    def coerce(obj, attr, value):
+        try:
+            versionpredicate.VersionPredicate('check (%s)' % value)
+        except ValueError:
+            raise ValueError(_('Version %(val)s is not a valid predicate in '
+                               'field %(attr)s') %
+                             {'val': value, 'attr': attr})
+        return value
+
+
 # NOTE(danms): Remove this on next release of oslo.versionedobjects
 class FlexibleBoolean(fields.Boolean):
     @staticmethod
@@ -629,6 +643,11 @@ class MonitorMetricTypeField(BaseEnumField):
     AUTO_TYPE = MonitorMetricType()
 
 
+# FIXME(sbauza): Remove this after oslo.versionedobjects gets it
+class VersionPredicateField(AutoTypedField):
+    AUTO_TYPE = VersionPredicate()
+
+
 # FIXME(danms): Remove this after oslo.versionedobjects gets it
 # This is a flexible interpretation of boolean
 # values using common user friendly semantics for

nova/tests/unit/objects/test_fields.py

@@ -529,6 +529,18 @@ class TestMonitorMetricType(TestField):
         self.assertRaises(ValueError, self.field.stringify, 'cpufrequency')
 
 
+class TestVersionPredicate(TestString):
+    def setUp(self):
+        super(TestVersionPredicate, self).setUp()
+        self.field = fields.VersionPredicateField()
+        self.coerce_good_values = [('>=1.0', '>=1.0'),
+                                   ('==1.1', '==1.1'),
+                                   ('<1.1.0', '<1.1.0')]
+        self.coerce_bad_values = ['1', 'foo', '>1', 1.0, '1.0', '=1.0']
+        self.to_primitive_values = self.coerce_good_values[0:1]
+        self.from_primitive_values = self.coerce_good_values[0:1]
+
+
 class TestInteger(TestField):
     def setUp(self):
         super(TestInteger, self).setUp()