Make sure we don't introduce oslo_* imports during backports

Backports may contain new oslo_* namespace usage, while we should not
allow those in Juno and earlier. There were some cases of incorrect
backports that included wrong imports in other projects [1], so it's
better to be proactive here.

[1]: https://launchpad.net/bugs/1420335

Change-Id: Ie720c43334364d5e988399c35e137fdbfa420f54

HACKING.rst

@@ -12,6 +12,7 @@ Neutron Specific Commandments
 - [N321] Validate that jsonutils module is used instead of json
 - [N322] We do not use @authors tags in source files. We have git to track
   authorship.
+- [N323] Enforce oslo.* namespace imports for oslo libraries
 
 Creating Unit Tests
 -------------------

neutron/hacking/checks.py

@@ -37,6 +37,12 @@ author_tag_re = (re.compile("^\s*#\s*@?(a|A)uthor"),
                  re.compile("^\.\.\s+moduleauthor::"))
 
 
+oslo_namespace_imports_underscore = re.compile(
+    r"import[\s]+oslo_[^\s]+")
+oslo_namespace_imports_from_underscore = re.compile(
+    r"from[\s]+oslo_[^\s]+[\s]+import[\s]+")
+
+
 def validate_log_translations(logical_line, physical_line, filename):
     # Translations are not required in the test directory
     if "neutron/tests" in filename:
@@ -79,7 +85,21 @@ def no_author_tags(physical_line):
             return pos, "N322: Don't use author tags"
 
 
+def check_oslo_namespace_imports(logical_line):
+    if re.match(oslo_namespace_imports_underscore, logical_line):
+        msg = ("N323: '%s' must be used instead of '%s'.") % (
+               logical_line.replace('import', 'from').replace('_', ' import '),
+               logical_line)
+        yield(0, msg)
+    elif re.match(oslo_namespace_imports_from_underscore, logical_line):
+        msg = ("N323: '%s' must be used instead of '%s'.") % (
+               logical_line.replace('_', '.'),
+               logical_line)
+        yield(0, msg)
+
+
 def factory(register):
     register(validate_log_translations)
     register(use_jsonutils)
     register(no_author_tags)
+    register(check_oslo_namespace_imports)

neutron/tests/unit/test_hacking.py

@@ -10,6 +10,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import testtools
+
 from neutron.hacking import checks
 from neutron.tests import base
 
@@ -79,3 +81,18 @@ class HackingTestCase(base.BaseTestCase):
         self.assertEqual(2, checks.no_author_tags("# author: pele")[0])
         self.assertEqual(2, checks.no_author_tags("# Author: pele")[0])
         self.assertEqual(3, checks.no_author_tags(".. moduleauthor:: pele")[0])
+
+    def test_check_oslo_namespace_imports(self):
+        def check(s, fail=True):
+            func = checks.check_oslo_namespace_imports
+            if fail:
+                self.assertIsInstance(next(func(s)), tuple)
+            else:
+                with testtools.ExpectedException(StopIteration):
+                    next(func(s))
+
+        check('from oslo_utils import importutils')
+        check('import oslo_messaging')
+        check('from oslo.utils import importutils', fail=False)
+        check('from oslo import messaging', fail=False)
+        check('import oslo.messaging', fail=False)