Add HACKING check for db session param

Add a HACKING check to enforce that public db/api and db/sqlalchemy/api
methods to not accept a 'session' parameter.

This check is initially disabled, since it is failing ~24 times right
now, but will be enabled once bp/db-session-cleanup is complete.

Change-Id: Ib89eea58555032dd142d4e21e62d66e2726f0d06

HACKING.rst

@@ -9,7 +9,8 @@ Nova Specific Commandments
 ---------------------------
 
 - ``nova.db`` imports are not allowed in ``nova/virt/*``
-
+- [N309] no db session in public API methods (disabled)
+  This enforces a guideline defined in ``nova.openstack.common.db.sqlalchemy.session``
 
 Creating Unit Tests
 -------------------

nova/hacking/checks.py

@@ -13,6 +13,10 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import re
+
+session_check = re.compile("\w*def [a-zA-Z0-9].*[(].*session.*[)]")
+
 
 def import_no_db_in_virt(logical_line, filename):
     """Check for db calls from nova/virt
@@ -50,6 +54,13 @@ def except_python3x_compatible(logical_line, filename):
         yield(0, "N308: Python 3.x incompatible 'except x,y:' construct")
 
 
+def no_db_session_in_public_api(logical_line, filename):
+    if "db/api.py" in filename or "db/sqlalchemy/api.py" in filename:
+        if session_check.match(logical_line):
+            yield (0, "N309: public db api methods may not accept session")
+
+
 def factory(register):
     register(import_no_db_in_virt)
     register(except_python3x_compatible)
+    register(no_db_session_in_public_api)

tox.ini

@@ -39,7 +39,7 @@ commands =
 commands = {posargs}
 
 [flake8]
-ignore = E121,E122,E123,E124,E125,E126,E127,E128,E711,E712,H302,H303,H404,F403,F811,F841
+ignore = E121,E122,E123,E124,E125,E126,E127,E128,E711,E712,H302,H303,H404,F403,F811,F841,N309
 builtins = _
 exclude =  .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build,plugins,tools