Emit deprecation warnings when positional args passed

We should try and enforce that all arguments passed to an oslo_context
are passed as keyword arguments. positional is a library maintained by
the openstack community for exactly this.

We can't simply switch over to raising an error, so by setting
enforcement to warn we will issue a deprecation warning whenever
arguments are being passed positionally.

Change-Id: I47456ac65911d4cc4a5acbacfd1d0dae8429684a

oslo_context/context.py

@@ -31,6 +31,8 @@ import itertools
 import threading
 import uuid
 
+from positional import positional
+
 
 _request_store = threading.local()
 
@@ -68,6 +70,7 @@ class RequestContext(object):
 
     user_idt_format = u'{user} {tenant} {domain} {user_domain} {p_domain}'
 
+    @positional(enforcement=positional.WARN)
     def __init__(self, auth_token=None, user=None, tenant=None, domain=None,
                  user_domain=None, project_domain=None, is_admin=False,
                  read_only=False, show_deleted=False, request_id=None,

oslo_context/tests/test_context.py

@@ -14,8 +14,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import fixtures
 import hashlib
 import uuid
+import warnings
 
 from oslotest import base as test_base
 
@@ -27,6 +29,21 @@ def generate_id(name):
     return hashlib.md5(name.encode('utf-8')).hexdigest()
 
 
+class WarningsFixture(fixtures.Fixture):
+
+    def __init__(self, action="always", category=DeprecationWarning):
+        super(WarningsFixture, self).__init__()
+        self.action = action
+        self.category = category
+
+    def setUp(self):
+        super(WarningsFixture, self).setUp()
+        self._w = warnings.catch_warnings(record=True)
+        self.log = self._w.__enter__()
+        self.addCleanup(self._w.__exit__)
+        warnings.simplefilter(self.action, self.category)
+
+
 class Object(object):
     pass
 
@@ -35,6 +52,7 @@ class ContextTest(test_base.BaseTestCase):
 
     def setUp(self):
         super(ContextTest, self).setUp()
+        self.warnings = self.useFixture(WarningsFixture())
         self.useFixture(fixture.ClearRequestContext())
 
     def test_context(self):
@@ -439,3 +457,10 @@ class ContextTest(test_base.BaseTestCase):
                           'roles': roles,
                           'is_admin_project': False},
                          ctx.to_policy_values())
+
+    def test_positional_args(self):
+        context.RequestContext('abc', 'def')
+
+        self.assertEqual(1, len(self.warnings.log))
+        self.assertIn('__init__ takes at most 1 positional',
+                      str(self.warnings.log[0].message))

requirements.txt

@@ -3,3 +3,5 @@
 # process, which may cause wedges in the gate later.
 
 pbr>=1.6 # Apache-2.0
+
+positional>=1.0.1 # Apache-2.0

test-requirements.txt

@@ -2,6 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
+fixtures>=3.0.0  # Apache-2.0/BSD
 hacking<0.11,>=0.10.0
 oslotest>=1.10.0 # Apache-2.0
 coverage>=3.6 # Apache-2.0