python/mach/mach/dispatcher.py
author Josh Aas <joshmoz@gmail.com>
Fri, 11 Oct 2013 13:58:35 -0500
changeset 164350 5dc3c476f55ef746d66d5e0d273961753cc5a82d
parent 164345 6088d4495e46de48b591e6a4c09c42b55bc3525d
child 164634 875ab904cc997337dc16123586f3d2101e9d4764
permissions -rw-r--r--
Bug 925016: Always use method_exchangeImplementations when swizzling methods on OS X. r=smichaud

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

from __future__ import unicode_literals

import argparse
import sys

from operator import itemgetter

from .base import (
    NoCommandError,
    UnknownCommandError,
    UnrecognizedArgumentError,
)


class CommandFormatter(argparse.HelpFormatter):
    """Custom formatter to format just a subcommand."""

    def add_usage(self, *args):
        pass


class CommandAction(argparse.Action):
    """An argparse action that handles mach commands.

    This class is essentially a reimplementation of argparse's sub-parsers
    feature. We first tried to use sub-parsers. However, they were missing
    features like grouping of commands (http://bugs.python.org/issue14037).

    The way this works involves light magic and a partial understanding of how
    argparse works.

    Arguments registered with an argparse.ArgumentParser have an action
    associated with them. An action is essentially a class that when called
    does something with the encountered argument(s). This class is one of those
    action classes.

    An instance of this class is created doing something like:

        parser.add_argument('command', action=CommandAction, registrar=r)

    Note that a mach.registrar.Registrar instance is passed in. The Registrar
    holds information on all the mach commands that have been registered.

    When this argument is registered with the ArgumentParser, an instance of
    this class is instantiated. One of the subtle but important things it does
    is tell the argument parser that it's interested in *all* of the remaining
    program arguments. So, when the ArgumentParser calls this action, we will
    receive the command name plus all of its arguments.

    For more, read the docs in __call__.
    """
    def __init__(self, option_strings, dest, required=True, default=None,
        registrar=None, context=None):
        # A proper API would have **kwargs here. However, since we are a little
        # hacky, we intentionally omit it as a way of detecting potentially
        # breaking changes with argparse's implementation.
        #
        # In a similar vein, default is passed in but is not needed, so we drop
        # it.
        argparse.Action.__init__(self, option_strings, dest, required=required,
            help=argparse.SUPPRESS, nargs=argparse.REMAINDER)

        self._mach_registrar = registrar
        self._context = context

    def __call__(self, parser, namespace, values, option_string=None):
        """This is called when the ArgumentParser has reached our arguments.

        Since we always register ourselves with nargs=argparse.REMAINDER,
        values should be a list of remaining arguments to parse. The first
        argument should be the name of the command to invoke and all remaining
        arguments are arguments for that command.

        The gist of the flow is that we look at the command being invoked. If
        it's *help*, we handle that specially (because argparse's default help
        handler isn't satisfactory). Else, we create a new, independent
        ArgumentParser instance for just the invoked command (based on the
        information contained in the command registrar) and feed the arguments
        into that parser. We then merge the results with the main
        ArgumentParser.
        """
        if not values:
            raise NoCommandError()

        command = values[0].lower()
        args = values[1:]

        if command == 'help':
            if len(args):
                self._handle_subcommand_help(parser, args[0])
            else:
                self._handle_main_help(parser)

            sys.exit(0)

        handler = self._mach_registrar.command_handlers.get(command)

        # FUTURE consider looking for commands with similar names and
        # suggest or run them.
        if not handler:
            raise UnknownCommandError(command, 'run')

        # FUTURE
        # If we wanted to conditionally enable commands based on whether
        # it's possible to run them given the current state of system, here
        # would be a good place to hook that up.

        # We create a new parser, populate it with the command's arguments,
        # then feed all remaining arguments to it, merging the results
        # with ourselves. This is essentially what argparse subparsers
        # do.

        parser_args = {
            'add_help': False,
            'usage': '%(prog)s [global arguments] ' + command +
                ' command arguments]',
        }

        if handler.allow_all_arguments:
            parser_args['prefix_chars'] = '+'

        subparser = argparse.ArgumentParser(**parser_args)

        for arg in handler.arguments:
            subparser.add_argument(*arg[0], **arg[1])

        # We define the command information on the main parser result so as to
        # not interfere with arguments passed to the command.
        setattr(namespace, 'mach_handler', handler)
        setattr(namespace, 'command', command)

        command_namespace, extra = subparser.parse_known_args(args)
        setattr(namespace, 'command_args', command_namespace)

        if extra:
            raise UnrecognizedArgumentError(command, extra)

    def _handle_main_help(self, parser):
        # Since we don't need full sub-parser support for the main help output,
        # we create groups in the ArgumentParser and populate each group with
        # arguments corresponding to command names. This has the side-effect
        # that argparse renders it nicely.
        r = self._mach_registrar
        disabled_commands = []

        cats = [(k, v[2]) for k, v in r.categories.items()]
        sorted_cats = sorted(cats, key=itemgetter(1), reverse=True)
        for category, priority in sorted_cats:
            group = None

            for command in sorted(r.commands_by_category[category]):
                handler = r.command_handlers[command]

                # Instantiate a handler class to see if it should be filtered
                # out for the current context or not. Condition functions can be
                # applied to the command's decorator.
                if handler.conditions:
                    if handler.pass_context:
                        instance = handler.cls(self._context)
                    else:
                        instance = handler.cls()

                    is_filtered = False
                    for c in handler.conditions:
                        if not c(instance):
                            is_filtered = True
                            break
                    if is_filtered:
                        description = handler.description
                        disabled_command = {'command': command, 'description': description}
                        disabled_commands.append(disabled_command)
                        continue

                if group is None:
                    title, description, _priority = r.categories[category]
                    group = parser.add_argument_group(title, description)

                description = handler.description
                group.add_argument(command, help=description,
                    action='store_true')

        if disabled_commands:
            title, description, _priority = r.categories['disabled']
            group = parser.add_argument_group(title, description)
            for c in disabled_commands:
                group.add_argument(c['command'], help=c['description'],
                    action='store_true')

        parser.print_help()

    def _handle_subcommand_help(self, parser, command):
        handler = self._mach_registrar.command_handlers.get(command)

        if not handler:
            raise UnknownCommandError(command, 'query')

        # This code is worth explaining. Because we are doing funky things with
        # argument registration to allow the same option in both global and
        # command arguments, we can't simply put all arguments on the same
        # parser instance because argparse would complain. We can't register an
        # argparse subparser here because it won't properly show help for
        # global arguments. So, we employ a strategy similar to command
        # execution where we construct a 2nd, independent ArgumentParser for
        # just the command data then supplement the main help's output with
        # this 2nd parser's. We use a custom formatter class to ignore some of
        # the help output.
        parser_args = {
            'formatter_class': CommandFormatter,
            'add_help': False,
        }

        if handler.allow_all_arguments:
            parser_args['prefix_chars'] = '+'

        c_parser = argparse.ArgumentParser(**parser_args)

        group = c_parser.add_argument_group('Command Arguments')

        for arg in handler.arguments:
            group.add_argument(*arg[0], **arg[1])

        # This will print the description of the command below the usage.
        description = handler.description
        if description:
            parser.description = description

        parser.usage = '%(prog)s [global arguments] ' + command + \
            ' [command arguments]'
        parser.print_help()
        print('')
        c_parser.print_help()