config: Pass description and epilog through

We can already pass a usage string through, we should also be able to
pass the description and epilog through. Often some explanatory text
about how to combine the options productively is very useful.

Change-Id: I0cea0a22284ca8338658534c8c300bb9b7c93dd8

oslo_config/cfg.py

@@ -2218,8 +2218,8 @@ class ConfigOpts(collections.Mapping):
         self._cli_opts = collections.deque()
         self._validate_default_values = False
 
-    def _pre_setup(self, project, prog, version, usage, default_config_files,
-                   default_config_dirs):
+    def _pre_setup(self, project, prog, version, usage, description, epilog,
+                   default_config_files, default_config_dirs):
         """Initialize a ConfigCliParser object for option parsing."""
 
         if prog is None:
@@ -2233,7 +2233,8 @@ class ConfigOpts(collections.Mapping):
         if default_config_dirs is None:
             default_config_dirs = find_config_dirs(project, prog)
 
-        self._oparser = _CachedArgumentParser(prog=prog, usage=usage)
+        self._oparser = _CachedArgumentParser(
+            prog=prog, usage=usage, description=description, epilog=epilog)
 
         if version is not None:
             self._oparser.add_parser_argument(self._oparser,
@@ -2300,7 +2301,9 @@ class ConfigOpts(collections.Mapping):
                  usage=None,
                  default_config_files=None,
                  default_config_dirs=None,
-                 validate_default_values=False):
+                 validate_default_values=False,
+                 description=None,
+                 epilog=None):
         """Parse command line arguments and config files.
 
         Calling a ConfigOpts object causes the supplied command line arguments
@@ -2323,6 +2326,8 @@ class ConfigOpts(collections.Mapping):
             basename, without extension .py)
         :param version: the program version (for --version)
         :param usage: a usage string (%prog will be expanded)
+        :param description: A description of what the program does
+        :param epilog: Text following the argument descriptions
         :param default_config_files: config files to use by default
         :param default_config_dirs: config dirs to use by default
         :param validate_default_values: whether to validate the default values
@@ -2335,12 +2340,8 @@ class ConfigOpts(collections.Mapping):
         self._validate_default_values = validate_default_values
 
         prog, default_config_files, default_config_dirs = self._pre_setup(
-            project,
-            prog,
-            version,
-            usage,
-            default_config_files,
-            default_config_dirs)
+            project, prog, version, usage, description, epilog,
+            default_config_files, default_config_dirs)
 
         self._setup(project, prog, version, usage, default_config_files,
                     default_config_dirs)

oslo_config/tests/test_cfg.py

@@ -100,6 +100,8 @@ class BaseTestCase(base.BaseTestCase):
                 prog='test',
                 version='1.0',
                 usage='%(prog)s FOO BAR',
+                description='somedesc',
+                epilog='tepilog',
                 default_config_files=default_config_files,
                 default_config_dirs=default_config_dirs,
                 validate_default_values=True)
@@ -140,6 +142,17 @@ class UsageTestCase(BaseTestCase):
         self.conf([])
         self.conf.print_usage(file=f)
         self.assertIn('usage: test FOO BAR', f.getvalue())
+        self.assertNotIn('somedesc', f.getvalue())
+        self.assertNotIn('tepilog', f.getvalue())
+        self.assertNotIn('optional:', f.getvalue())
+
+    def test_print_help(self):
+        f = moves.StringIO()
+        self.conf([])
+        self.conf.print_help(file=f)
+        self.assertIn('usage: test FOO BAR', f.getvalue())
+        self.assertIn('somedesc', f.getvalue())
+        self.assertIn('tepilog', f.getvalue())
         self.assertNotIn('optional:', f.getvalue())