Bug 1381802 - [mach] Allow subcommands to use the 'parser' argument, r=gps

This allows subcommands to use external argument parsers.

MozReview-Commit-ID: 7TkbTff0Tv8

--HG--
extra : rebase_source : a1c245efa7ac7b28b974534b4cd2727c96f9219d

python/mach/mach/decorators.py

@@ -255,9 +255,9 @@ class SubCommand(object):
 
         description -- A textual description for this sub command.
     """
-    def __init__(self, command, subcommand, description=None):
+    def __init__(self, command, subcommand, description=None, parser=None):
         self._mach_command = _MachCommand(name=command, subcommand=subcommand,
-                                          description=description)
+                                          description=description, parser=parser)
 
     def __call__(self, func):
         if not hasattr(func, '_mach_command'):

python/mach/mach/dispatcher.py

@@ -389,8 +389,9 @@ class CommandAction(argparse.Action):
         subcommand = subcommand.pop()
         subhandler = handler.subcommand_handlers[subcommand]
 
-        c_parser = argparse.ArgumentParser(add_help=False,
-            formatter_class=CommandFormatter)
+        c_parser = subhandler.parser or argparse.ArgumentParser(add_help=False)
+        c_parser.formatter_class = CommandFormatter
+
         group = c_parser.add_argument_group('Sub Command Arguments')
         self._populate_command_group(c_parser, subhandler, group)