cli: simplify parsing of arbitrary types

Add the 'constructor' type to IPAOption to allow parsing arbitrary
types.

When using this type, supply the 'constructor' attribute with the
constructor of the type.  The checker for the 'constructor' type
attempts to construct the data, returning if successful else raising
OptionValueError.

The 'knob' interface remains unchanged but now accepts arbitrary
constructors.

This feature subsumes the '_option_callback' mechanism, which has
been refactored away.

This feature also subsumes the "dn" type in IPAOption, but this
refactor is deferred.

Part of: https://pagure.io/freeipa/issue/6858

Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipapython/install/cli.py

@@ -8,7 +8,6 @@ Command line support.
 
 import collections
 import enum
-import functools
 import logging
 import optparse  # pylint: disable=deprecated-module
 import signal
@@ -105,17 +104,6 @@ def uninstall_tool(configurable_class, command_name, log_file_name,
     )
 
 
-def _option_callback(action, option, opt_str, value, parser, opt_type):
-    try:
-        value = opt_type(value)
-    except ValueError as e:
-        raise optparse.OptionValueError(
-            "option {0}: {1}".format(opt_str, e))
-
-    option.take_action(
-        action, option.dest, opt_str, value, parser.values, parser)
-
-
 class ConfigureTool(admintool.AdminTool):
     configurable_class = None
     debug_option = False
@@ -186,24 +174,16 @@ class ConfigureTool(admintool.AdminTool):
                 kwargs['metavar'] = "{{{0}}}".format(
                                                 ",".join(kwargs['choices']))
             else:
-                kwargs['nargs'] = 1
-                kwargs['callback_args'] = (knob_scalar_type,)
+                kwargs['type'] = 'constructor'
+                kwargs['constructor'] = knob_scalar_type
             kwargs['dest'] = name
             if issubclass(knob_type, list):
-                if 'type' not in kwargs:
-                    kwargs['action'] = 'callback'
-                    kwargs['callback'] = (
-                        functools.partial(_option_callback, 'append'))
-                elif kwargs['type'] is None:
+                if kwargs['type'] is None:
                     kwargs['action'] = 'append_const'
                 else:
                     kwargs['action'] = 'append'
             else:
-                if 'type' not in kwargs:
-                    kwargs['action'] = 'callback'
-                    kwargs['callback'] = (
-                        functools.partial(_option_callback, 'store'))
-                elif kwargs['type'] is None:
+                if kwargs['type'] is None:
                     kwargs['action'] = 'store_const'
                 else:
                     kwargs['action'] = 'store'