servo/python/mach/mach/decorators.py

# 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 collections
import inspect
import types

from .base import (
    MachError,
    MethodHandler
)

from .config import ConfigProvider
from .registrar import Registrar


def CommandProvider(cls):
    """Class decorator to denote that it provides subcommands for Mach.

    When this decorator is present, mach looks for commands being defined by
    methods inside the class.
    """

    # The implementation of this decorator relies on the parse-time behavior of
    # decorators. When the module is imported, the method decorators (like
    # @Command and @CommandArgument) are called *before* this class decorator.
    # The side-effect of the method decorators is to store specifically-named
    # attributes on the function types. We just scan over all functions in the
    # class looking for the side-effects of the method decorators.

    # Tell mach driver whether to pass context argument to __init__.
    pass_context = False

    if inspect.ismethod(cls.__init__):
        spec = inspect.getargspec(cls.__init__)

        if len(spec.args) > 2:
            msg = 'Mach @CommandProvider class %s implemented incorrectly. ' + \
                  '__init__() must take 1 or 2 arguments. From %s'
            msg = msg % (cls.__name__, inspect.getsourcefile(cls))
            raise MachError(msg)

        if len(spec.args) == 2:
            pass_context = True

    # We scan __dict__ because we only care about the classes own attributes,
    # not inherited ones. If we did inherited attributes, we could potentially
    # define commands multiple times. We also sort keys so commands defined in
    # the same class are grouped in a sane order.
    for attr in sorted(cls.__dict__.keys()):
        value = cls.__dict__[attr]

        if not isinstance(value, types.FunctionType):
            continue

        command_name, category, description, allow_all, conditions, parser = getattr(
            value, '_mach_command', (None, None, None, None, None, None))

        if command_name is None:
            continue

        if conditions is None and Registrar.require_conditions:
            continue

        msg = 'Mach command \'%s\' implemented incorrectly. ' + \
              'Conditions argument must take a list ' + \
              'of functions. Found %s instead.'

        conditions = conditions or []
        if not isinstance(conditions, collections.Iterable):
            msg = msg % (command_name, type(conditions))
            raise MachError(msg)

        for c in conditions:
            if not hasattr(c, '__call__'):
                msg = msg % (command_name, type(c))
                raise MachError(msg)

        arguments = getattr(value, '_mach_command_args', None)

        handler = MethodHandler(cls, attr, command_name, category=category,
            description=description, allow_all_arguments=allow_all,
            conditions=conditions, parser=parser, arguments=arguments,
            pass_context=pass_context)

        Registrar.register_command_handler(handler)

    return cls


class Command(object):
    """Decorator for functions or methods that provide a mach subcommand.

    The decorator accepts arguments that define basic attributes of the
    command. The following arguments are recognized:

         category -- The string category to which this command belongs. Mach's
             help will group commands by category.

         description -- A brief description of what the command does.

         allow_all_args -- Bool indicating whether to allow unknown arguments
             through to the command.

         parser -- an optional argparse.ArgumentParser instance to use as
             the basis for the command arguments.

    For example:

        @Command('foo', category='misc', description='Run the foo action')
        def foo(self):
            pass
    """
    def __init__(self, name, category=None, description=None,
                 allow_all_args=False, conditions=None, parser=None):
        self._name = name
        self._category = category
        self._description = description
        self._allow_all_args = allow_all_args
        self._conditions = conditions
        self._parser = parser

    def __call__(self, func):
        func._mach_command = (self._name, self._category, self._description,
                              self._allow_all_args, self._conditions, self._parser)

        return func


class CommandArgument(object):
    """Decorator for additional arguments to mach subcommands.

    This decorator should be used to add arguments to mach commands. Arguments
    to the decorator are proxied to ArgumentParser.add_argument().

    For example:

        @Command('foo', help='Run the foo action')
        @CommandArgument('-b', '--bar', action='store_true', default=False,
            help='Enable bar mode.')
        def foo(self):
            pass
    """
    def __init__(self, *args, **kwargs):
        self._command_args = (args, kwargs)

    def __call__(self, func):
        command_args = getattr(func, '_mach_command_args', [])

        command_args.insert(0, self._command_args)

        func._mach_command_args = command_args

        return func


def SettingsProvider(cls):
    """Class decorator to denote that this class provides Mach settings.

    When this decorator is encountered, the underlying class will automatically
    be registered with the Mach registrar and will (likely) be hooked up to the
    mach driver.

    This decorator is only allowed on mach.config.ConfigProvider classes.
    """
    if not issubclass(cls, ConfigProvider):
        raise MachError('@SettingsProvider encountered on class that does ' +
                        'not derived from mach.config.ConfigProvider.')

    Registrar.register_settings_provider(cls)

    return cls