Add support to cfg for disabling interspersed args

Implements blueprint cfg-disable-interspersed-args

Nova currently relies on cfg being implemented with optparse because it
uses optparse's disable_interspersed_args()

The use case for this is if you do:

  $> nova-manage --verbose create --project foo --user bar

you want invoking ConfigOpts() to return:

  ['create', '--project', 'foo', '--user', 'bar']

as the "extra" args rather than aborting when it doesn't recognize the
--project arg.

This is a reasonable use case for cfg to support and it should just have
{disable,enable}_interspersed_args() methods.

If we ever switch from optparse to argparse, we'll do something like this:

  parser.add_argument('--verbose')
  ...
  parser.add_argument(
    'extra_args',
    nargs=argparse.REMAINDER if disable_interspersed_args else '*')
  ...
  ns = parser.parse_args(...)
  extra_args = ns.extra_args

i.e. we will need an 'extra_args' multi-value positional argument in any
case and we'll just pass nargs=REMAINDER if we want trailing options to
be included in the extra args.

Change-Id: I3ecb7dc18230327cf5aaaa7d832224e64aafa40c

1 files changed, 41 insertions, 0 deletions

diff --git a/openstack/common/cfg.py b/openstack/common/cfg.py
index 891fcbe..eacd180 100644
--- a/openstack/common/cfg.py
+++ b/openstack/common/cfg.py
@@ -193,6 +193,22 @@ Option values may reference other values using PEP 292 string substitution:
     ]
 
 Note that interpolation can be avoided by using '$$'.
+
+For command line utilities that dispatch to other command line utilities, the
+disable_interspersed_args() method is available. If this this method is called,
+then parsing e.g.
+
+  script --verbose cmd --debug /tmp/mything
+
+will no longer return:
+
+  ['cmd', '/tmp/mything']
+
+as the leftover arguments, but will instead return:
+
+  ['cmd', '--debug', '/tmp/mything']
+
+i.e. argument parsing is stopped at the first non-option argument.
 """
 
 import sys
@@ -875,6 +891,31 @@ class ConfigOpts(object):
         opt_info = self._get_opt_info(name, group)
         opt_info['default'] = default
 
+    def disable_interspersed_args(self):
+        """Set parsing to stop on the first non-option.
+
+        If this this method is called, then parsing e.g.
+
+          script --verbose cmd --debug /tmp/mything
+
+        will no longer return:
+
+          ['cmd', '/tmp/mything']
+
+        as the leftover arguments, but will instead return:
+
+          ['cmd', '--debug', '/tmp/mything']
+
+        i.e. argument parsing is stopped at the first non-option argument.
+        """
+        self._oparser.disable_interspersed_args()
+
+    def enable_interspersed_args(self):
+        """Set parsing to not stop on the first non-option.
+
+        This it the default behaviour."""
+        self._oparser.enable_interspersed_args()
+
     def log_opt_values(self, logger, lvl):
         """Log the value of all registered opts.