Add a tool for reserving migration placeholders during release time

This adds a tool to make it easy to reserve placeholder migrations
after we do a release. This is something we have to do each time we
do a release, and it can be somewhat silly in terms of mechanical
work. This adds a script to make it trivially easy.

Change-Id: I34c11f1aee64ad36887779f1c9ca4491a25580ec

tools/reserve-migrations.py

@@ -0,0 +1,75 @@
+#!/usr/bin/env python
+
+import argparse
+import glob
+import os
+import subprocess
+
+BASE = 'nova/db/sqlalchemy/migrate_repo/versions'.split('/')
+API_BASE = 'nova/db/sqlalchemy/api_migrations/migrate_repo/versions'.split('/')
+
+STUB = """
+#    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.
+
+# This is a placeholder for backports.
+# Do not use this number for new work.  New work starts after
+# all the placeholders.
+#
+# See this for more information:
+# http://lists.openstack.org/pipermail/openstack-dev/2013-March/006827.html
+
+
+def upgrade(migrate_engine):
+    pass
+"""
+
+
+def get_last_migration(base):
+    path = os.path.join(*tuple(base + ['[0-9]*.py']))
+    migrations = sorted([os.path.split(fn)[-1] for fn in glob.glob(path)])
+    return int(migrations[-1].split('_')[0])
+
+
+def reserve_migrations(base, number, git_add):
+    last = get_last_migration(base)
+    for i in range(last + 1, last + number + 1):
+        name = '%03i_placeholder.py' % i
+        path = os.path.join(*tuple(base + [name]))
+        with open(path, 'w') as f:
+            f.write(STUB)
+        print('Created %s' % path)
+        if git_add:
+            subprocess.call('git add %s' % path, shell=True)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-n', '--number', default=10,
+                        type=int,
+                        help='Number of migrations to reserve')
+    parser.add_argument('-g', '--git-add', action='store_const',
+                        const=True, default=False,
+                        help='Automatically git-add new migrations')
+    parser.add_argument('-a', '--api', action='store_const',
+                        const=True, default=False,
+                        help='Reserve migrations for the API database')
+    args = parser.parse_args()
+    if args.api:
+        base = API_BASE
+    else:
+        base = BASE
+    reserve_migrations(base, args.number, args.git_add)
+
+
+if __name__ == '__main__':
+    main()