Improve aggregate version check error messages with min_version

The aggregate set/list commands require at least version 1.1 but
if you don't specify any version we default to 1.0 and you get this
unhelpful message:

  Operation or argument is not supported with version 1.0

This change adds a simple min_version kwarg to the version compare
method such that if we fail the version check and the kwarg is passed
we use it to improve the message so the user doesn't have to read
the help of the command to figure out what they did wrong, e.g.:

  Operation or argument is not supported with version 1.0; \
  requires at least version 1.1

This only handles the aggregate set/list commands and could be used
elsewhere but this is just a start.

Change-Id: I28a859918ab78c8aa47e54928cb14339c7c75498
Story: #2005448
Task: #30498

osc_placement/resources/aggregate.py

@@ -62,7 +62,7 @@ class SetAggregate(command.Lister, version.CheckerMixin):
 
         return parser
 
-    @version.check(version.ge('1.1'))
+    @version.check(version.ge('1.1'), min_version='1.1')
     def take_action(self, parsed_args):
         http = self.app.client_manager.placement
 
@@ -106,7 +106,7 @@ class ListAggregate(command.Lister):
 
         return parser
 
-    @version.check(version.ge('1.1'))
+    @version.check(version.ge('1.1'), min_version='1.1')
     def take_action(self, parsed_args):
         http = self.app.client_manager.placement
 

osc_placement/tests/unit/test_version.py

@@ -13,6 +13,7 @@
 import mock
 
 import oslotest.base as base
+import six
 
 from osc_placement import version
 
@@ -42,6 +43,12 @@ class TestVersion(base.BaseTestCase):
             ValueError, version._compare, '1.0', version.le('.0'))
         self.assertRaises(
             ValueError, version._compare, '1', version.le('2'))
+        ex = self.assertRaises(
+            ValueError, version.compare, '1.0', version.ge('1.1'),
+            min_version='1.1')
+        self.assertEqual(
+            'Operation or argument is not supported with version 1.0; '
+            'requires at least version 1.1', six.text_type(ex))
 
     def test_compare_with_exc(self):
         self.assertTrue(version.compare('1.05', version.gt('1.4')))

osc_placement/version.py

@@ -78,17 +78,24 @@ def compare(ver, *predicates, **kwargs):
 
     kwargs['exc'] - boolean whether exception should be raised
     kwargs['op'] - (all, any) how predicates should be checked
+    kwargs['min_version'] - optional; used to aid in the error message that is
+        given, for example, to specify a minimum version to run a command.
 
     Examples:
         compare('1.1', version.gt('1.2'), exc=False) - False
         compare('1.1', version.eq('1.0'), version.eq('1.1'), op=any) - True
+        compare('1.0', version.ge('1.1'), min_version='1.1') - raise ValueError
 
     """
     exc = kwargs.get('exc', True)
     if not _compare(ver, *predicates, **kwargs):
         if exc:
-            raise ValueError(
-                'Operation or argument is not supported with version %s' % ver)
+            msg = ('Operation or argument is not supported with version %s' %
+                   ver)
+            if 'min_version' in kwargs:
+                msg = ('%s; requires at least version %s' %
+                       (msg, kwargs['min_version']))
+            raise ValueError(msg)
         return False
     return True