Fix cinder-manage <category> traceback

Running the cinder-manage command with a category but without an action
will throw a Traceback saying "oslo_config.cfg.NoSuchOptError: no such
option action_fn in group [DEFAULT]"

Example command that triggers this: cinder-manage backup

This patch fixes this by simulating that the user had used the --help
action while still exitting with an error (after all the call was
missing arguments).

New output:

  $ cinder-manage backup

  usage: cinder-manage backup [-h] {list,update_backup_host} ...

  positional arguments:
    {list,update_backup_host}

    optional arguments:
      -h, --help            show this help message and exit

Closes-Bug: #1902852
Change-Id: I6fca54d95b41d189545789c775e23223abb37c1b

cinder/cmd/manage.py

@@ -691,12 +691,20 @@ def methods_of(obj):
     return result
 
 
+def missing_action(help_func):
+    def wrapped():
+        help_func()
+        exit(2)
+    return wrapped
+
+
 def add_command_parsers(subparsers):
     for category in sorted(CATEGORIES):
         command_object = CATEGORIES[category]()
 
         parser = subparsers.add_parser(category)
         parser.set_defaults(command_object=command_object)
+        parser.set_defaults(action_fn=missing_action(parser.print_help))
 
         category_subparsers = parser.add_subparsers(dest='action')
 

cinder/tests/unit/test_cmd.py

@@ -1155,6 +1155,19 @@ class TestCinderManageCmd(test.TestCase):
             self.assertTrue(register_cli_opt.called)
             self.assertEqual(2, exit.code)
 
+    def test_main_missing_action(self):
+        sys.argv = ['cinder-manage', 'backup']
+        cinder_manage.CONF = cfg.ConfigOpts()
+
+        stdout = io.StringIO()
+        with mock.patch('sys.stdout', new=stdout):
+            exit = self.assertRaises(SystemExit, cinder_manage.main)
+            self.assertEqual(2, exit.code)
+
+        stdout.seek(0)
+        output = stdout.read()
+        self.assertTrue(output.startswith('usage: '))
+
     @mock.patch('oslo_config.cfg.ConfigOpts.__call__')
     @mock.patch('oslo_log.log.setup')
     @mock.patch('oslo_config.cfg.ConfigOpts.register_cli_opt')

releasenotes/notes/fix-manage-no-action-46b023476e8cd938.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    `Bug #1902852
+    <https://bugs.launchpad.net/python-cinderclient/+bug/1902852>`_:
+    Fixed throwing Python traceback message when using ``cinder-manage
+    <category>`` without an action for the category.