hacking: Prevent use of six

Spotted this in a review recently. We don't want people using six
anymore.

Change-Id: Ie107a95bc06390ab519d3b3af9b07103a9a14316
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

nova/hacking/checks.py

@@ -140,6 +140,7 @@ mock_class_as_new_value_in_patching_re = re.compile(
 rwlock_re = re.compile(
     r"(?P<module_part>(oslo_concurrency\.)?(lockutils|fasteners))"
     r"\.ReaderWriterLock\(.*\)")
+six_re = re.compile(r"^(import six(\..*)?|from six(\..*)? import .*)$")
 
 
 class BaseASTChecker(ast.NodeVisitor):
@@ -1030,3 +1031,18 @@ def check_lockutils_rwlocks(logical_line):
             0,
             msg % {'module': match.group('module_part')}
         )
+
+
+@core.flake8ext
+def check_six(logical_line):
+    """Check for use of six
+
+    nova is now Python 3-only so we don't want six. However, people might use
+    it out of habit and it will likely work since six is a transitive
+    dependency.
+
+    N370
+    """
+    match = re.match(six_re, logical_line)
+    if match:
+        yield (0, "N370: Don't use or import six")

nova/tests/unit/test_hacking.py

@@ -1020,3 +1020,13 @@ class HackingTestCase(test.NoDBTestCase):
                     nova_utils.ReaderWriterLock()
                """
         self._assert_has_no_errors(code, checks.check_lockutils_rwlocks)
+
+    def test_check_six(self):
+        code = """
+            import six
+            from six import moves
+            from six.moves import range
+            import six.moves.urllib.parse as urlparse
+        """
+        errors = [(x + 1, 0, 'N370') for x in range(4)]
+        self._assert_has_errors(code, checks.check_six, expected_errors=errors)

tox.ini

@@ -375,6 +375,7 @@ extension =
   N367 = checks:do_not_alias_mock_class
   N368 = checks:do_not_use_mock_class_as_new_mock_value
   N369 = checks:check_lockutils_rwlocks
+  N370 = checks:check_six
 paths =
   ./nova/hacking