cfg: automatically create option groups

Implements blueprint cfg-auto-create-groups

Remove the restriction that groups must be explicitly created. Often
you only need a group to have a name (not e.g. a title or help string)
so we can easily just auto-create groups for that case.

Change-Id: I150ab3900e3aad0068b93487c8d396d21d26cfea

1 files changed, 18 insertions, 8 deletions

diff --git a/openstack/common/cfg.py b/openstack/common/cfg.py
index 08efeb7..8237107 100644
--- a/openstack/common/cfg.py
+++ b/openstack/common/cfg.py
@@ -149,6 +149,14 @@ Options can be registered as belonging to a group::
         conf.register_opt(rabbit_host_opt, group=rabbit_group)
         conf.register_opt(rabbit_port_opt, group='rabbit')
 
+If it no group attributes are required other than the group name, the group
+need not be explicitly registered e.g.
+
+    def register_rabbit_opts(conf):
+        # The group will automatically be created, equivalent calling::
+        #   conf.register_group(OptGroup(name='rabbit'))
+        conf.register_opt(rabbit_port_opt, group='rabbit')
+
 If no group is specified, options belong to the 'DEFAULT' section of config
 files::
 
@@ -977,7 +985,7 @@ class ConfigOpts(collections.Mapping):
         :raises: DuplicateOptError
         """
         if group is not None:
-            return self._get_group(group)._register_opt(opt)
+            return self._get_group(group, autocreate=True)._register_opt(opt)
 
         if _is_opt_registered(self._opts, opt):
             return False
@@ -1012,7 +1020,7 @@ class ConfigOpts(collections.Mapping):
             return False
 
         if group is not None:
-            group = self._get_group(group)
+            group = self._get_group(group, autocreate=True)
 
         opt._add_to_cli(self._oparser, group)
 
@@ -1241,7 +1249,7 @@ class ConfigOpts(collections.Mapping):
         else:
             return value
 
-    def _get_group(self, group_or_name):
+    def _get_group(self, group_or_name, autocreate=False):
         """Looks up a OptGroup object.
 
         Helper function to return an OptGroup given a parameter which can
@@ -1252,15 +1260,17 @@ class ConfigOpts(collections.Mapping):
         the API have access to.
 
         :param group_or_name: the group's name or the OptGroup object itself
+        :param autocreate: whether to auto-create the group if it's not found
         :raises: NoSuchGroupError
         """
-        if isinstance(group_or_name, OptGroup):
-            group_name = group_or_name.name
-        else:
-            group_name = group_or_name
+        group = group_or_name if isinstance(group_or_name, OptGroup) else None
+        group_name = group.name if group else group_or_name
 
         if not group_name in self._groups:
-            raise NoSuchGroupError(group_name)
+            if not group is None or not autocreate:
+                raise NoSuchGroupError(group_name)
+
+            self.register_group(OptGroup(name=group_name))
 
         return self._groups[group_name]