Move warnings to their own module

Raising warnings from an exception module can result in a rather
confusing message:

  Running command: '/usr/bin/nova-scheduler '
  /.../sqlalchemy/enginefacade.py:332: NotSupportedWarning: Configuration option(s) ['use_tpool'] not supported
    exception.NotSupportedWarning

For someone not used to Python's 'warning' infrastructure, this can look
worse than it is, as seen at [1].

While this particular warning was resolved in change I4a5f8958c3e, it's
possible that a similar warning could be raised for other options. Best
to move this out of the 'exception' module and into something more
sensible.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1639423

Change-Id: I8e0480fb11123067a111ed6aeda6b47614615645
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

oslo_db/exception.py

@@ -43,10 +43,12 @@ with `try/except` statement. This is required for consistent handling of
 database errors.
 """
 
+from debtcollector import moves
+from oslo_utils.excutils import CausedByException
 import six
 
 from oslo_db._i18n import _
-from oslo_utils.excutils import CausedByException
+from oslo_db import warning
 
 
 class DBError(CausedByException):
@@ -299,27 +301,10 @@ class CantStartEngineError(Exception):
     """Error raised when the enginefacade cannot start up correctly."""
 
 
-class NotSupportedWarning(Warning):
+moves.moved_class(warning.NotSupportedWarning,
-    """Warn that an argument or call that was passed is not supported.
+                  'NotSupportedWarning',
+                  __name__, version='Stein')
 
-    This subclasses Warning so that it can be filtered as a distinct
+moves.moved_class(warning.OsloDBDeprecationWarning,
-    category.
+                  'OsloDBDeprecationWarning',
-
+                  __name__, version='Stein')
-    .. seealso::
-
-        https://docs.python.org/2/library/warnings.html
-
-    """
-
-
-class OsloDBDeprecationWarning(DeprecationWarning):
-    """Issued per usage of a deprecated API.
-
-    This subclasses DeprecationWarning so that it can be filtered as a distinct
-    category.
-
-    .. seealso::
-
-        https://docs.python.org/2/library/warnings.html
-
-    """

oslo_db/sqlalchemy/enginefacade.py

@@ -10,7 +10,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-
 import contextlib
 import functools
 import operator
@@ -28,6 +27,7 @@ from oslo_db import options
 from oslo_db.sqlalchemy import engines
 from oslo_db.sqlalchemy import orm
 from oslo_db.sqlalchemy import utils
+from oslo_db import warning
 
 
 class _symbol(object):
@@ -334,7 +334,7 @@ class _TransactionFactory(object):
             warnings.warn(
                 "Configuration option(s) %r not supported" %
                 sorted(not_supported),
-                exception.NotSupportedWarning
+                warning.NotSupportedWarning
             )
 
     def get_legacy_facade(self):
@@ -1253,7 +1253,7 @@ class LegacyEngineFacade(object):
         warnings.warn(
             "EngineFacade is deprecated; please use "
             "oslo_db.sqlalchemy.enginefacade",
-            exception.OsloDBDeprecationWarning,
+            warning.OsloDBDeprecationWarning,
             stacklevel=2)
         if _factory:
             self._factory = _factory

oslo_db/tests/sqlalchemy/test_enginefacade.py

@@ -37,6 +37,7 @@ from oslo_db.sqlalchemy import enginefacade
 from oslo_db.sqlalchemy import engines as oslo_engines
 from oslo_db.sqlalchemy import orm
 from oslo_db.tests.sqlalchemy import base as test_base
+from oslo_db import warning
 
 
 enginefacade.transaction_context_provider(oslo_context.RequestContext)
@@ -2182,7 +2183,7 @@ class ConfigOptionsTest(oslo_test_base.BaseTestCase):
 
         self.assertEqual(1, len(w))
         self.assertTrue(
-            issubclass(w[-1].category, exception.NotSupportedWarning))
+            issubclass(w[-1].category, warning.NotSupportedWarning))
         self.assertEqual(
             "Configuration option(s) ['fake1', 'wrong2'] not supported",
             str(w[-1].message)

oslo_db/warning.py

@@ -0,0 +1,41 @@
+# Copyright 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+"""Custom warnings."""
+
+
+class NotSupportedWarning(Warning):
+    """Warn that an argument or call that was passed is not supported.
+
+    This subclasses Warning so that it can be filtered as a distinct
+    category.
+
+    .. seealso::
+
+        https://docs.python.org/2/library/warnings.html
+
+    """
+
+
+class OsloDBDeprecationWarning(DeprecationWarning):
+    """Issued per usage of a deprecated API.
+
+    This subclasses DeprecationWarning so that it can be filtered as a distinct
+    category.
+
+    .. seealso::
+
+        https://docs.python.org/2/library/warnings.html
+
+    """