tools/mb/mb.py

#!/usr/bin/env python
# Copyright 2015 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""MB - the Meta-Build wrapper around GYP and GN

MB is a wrapper script for GYP and GN that can be used to generate build files
for sets of canned configurations and analyze them.
"""

# TODO(thomasanderson): Remove this comment.  It is added to
# workaround https://crbug.com/736215 for CL
# https://codereview.chromium.org/2974603002/

from __future__ import print_function

import argparse
import ast
import errno
import json
import os
import pipes
import pprint
import re
import shutil
import sys
import subprocess
import tempfile
import traceback
import urllib2

from collections import OrderedDict

CHROMIUM_SRC_DIR = os.path.dirname(os.path.dirname(os.path.dirname(
    os.path.abspath(__file__))))
sys.path = [os.path.join(CHROMIUM_SRC_DIR, 'build')] + sys.path

import gn_helpers


def main(args):
  mbw = MetaBuildWrapper()
  return mbw.Main(args)


class MetaBuildWrapper(object):
  def __init__(self):
    self.chromium_src_dir = CHROMIUM_SRC_DIR
    self.default_config = os.path.join(self.chromium_src_dir, 'tools', 'mb',
                                       'mb_config.pyl')
    self.default_isolate_map = os.path.join(self.chromium_src_dir, 'testing',
                                            'buildbot', 'gn_isolate_map.pyl')
    self.executable = sys.executable
    self.platform = sys.platform
    self.sep = os.sep
    self.args = argparse.Namespace()
    self.configs = {}
    self.masters = {}
    self.mixins = {}

  def Main(self, args):
    self.ParseArgs(args)
    try:
      ret = self.args.func()
      if ret:
        self.DumpInputFiles()
      return ret
    except KeyboardInterrupt:
      self.Print('interrupted, exiting')
      return 130
    except Exception:
      self.DumpInputFiles()
      s = traceback.format_exc()
      for l in s.splitlines():
        self.Print(l)
      return 1

  def ParseArgs(self, argv):
    def AddCommonOptions(subp):
      subp.add_argument('-b', '--builder',
                        help='builder name to look up config from')
      subp.add_argument('-m', '--master',
                        help='master name to look up config from')
      subp.add_argument('-c', '--config',
                        help='configuration to analyze')
      subp.add_argument('--phase',
                        help='optional phase name (used when builders '
                             'do multiple compiles with different '
                             'arguments in a single build)')
      subp.add_argument('-f', '--config-file', metavar='PATH',
                        default=self.default_config,
                        help='path to config file '
                             '(default is %(default)s)')
      subp.add_argument('-i', '--isolate-map-file', metavar='PATH',
                        default=self.default_isolate_map,
                        help='path to isolate map file '
                             '(default is %(default)s)')
      subp.add_argument('-g', '--goma-dir',
                        help='path to goma directory')
      subp.add_argument('--gyp-script', metavar='PATH',
                        default=self.PathJoin('build', 'gyp_chromium'),
                        help='path to gyp script relative to project root '
                             '(default is %(default)s)')
      subp.add_argument('--android-version-code',
                        help='Sets GN arg android_default_version_code and '
                             'GYP_DEFINE app_manifest_version_code')
      subp.add_argument('--android-version-name',
                        help='Sets GN arg android_default_version_name and '
                             'GYP_DEFINE app_manifest_version_name')
      subp.add_argument('-n', '--dryrun', action='store_true',
                        help='Do a dry run (i.e., do nothing, just print '
                             'the commands that will run)')
      subp.add_argument('-v', '--verbose', action='store_true',
                        help='verbose logging')

    parser = argparse.ArgumentParser(prog='mb')
    subps = parser.add_subparsers()

    subp = subps.add_parser('analyze',
                            help='analyze whether changes to a set of files '
                                 'will cause a set of binaries to be rebuilt.')
    AddCommonOptions(subp)
    subp.add_argument('path', nargs=1,
                      help='path build was generated into.')
    subp.add_argument('input_path', nargs=1,
                      help='path to a file containing the input arguments '
                           'as a JSON object.')
    subp.add_argument('output_path', nargs=1,
                      help='path to a file containing the output arguments '
                           'as a JSON object.')
    subp.set_defaults(func=self.CmdAnalyze)

    subp = subps.add_parser('export',
                            help='print out the expanded configuration for'
                                 'each builder as a JSON object')
    subp.add_argument('-f', '--config-file', metavar='PATH',
                      default=self.default_config,
                      help='path to config file (default is %(default)s)')
    subp.add_argument('-g', '--goma-dir',
                      help='path to goma directory')
    subp.set_defaults(func=self.CmdExport)

    subp = subps.add_parser('gen',
                            help='generate a new set of build files')
    AddCommonOptions(subp)
    subp.add_argument('--swarming-targets-file',
                      help='save runtime dependencies for targets listed '
                           'in file.')
    subp.add_argument('path', nargs=1,
                      help='path to generate build into')
    subp.set_defaults(func=self.CmdGen)

    subp = subps.add_parser('isolate',
                            help='generate the .isolate files for a given'
                                 'binary')
    AddCommonOptions(subp)
    subp.add_argument('path', nargs=1,
                      help='path build was generated into')
    subp.add_argument('target', nargs=1,
                      help='ninja target to generate the isolate for')
    subp.set_defaults(func=self.CmdIsolate)

    subp = subps.add_parser('lookup',
                            help='look up the command for a given config or '
                                 'builder')
    AddCommonOptions(subp)
    subp.set_defaults(func=self.CmdLookup)

    subp = subps.add_parser(
        'run',
        help='build and run the isolated version of a '
             'binary',
        formatter_class=argparse.RawDescriptionHelpFormatter)
    subp.description = (
        'Build, isolate, and run the given binary with the command line\n'
        'listed in the isolate. You may pass extra arguments after the\n'
        'target; use "--" if the extra arguments need to include switches.\n'
        '\n'
        'Examples:\n'
        '\n'
        '  % tools/mb/mb.py run -m chromium.linux -b "Linux Builder" \\\n'
        '    //out/Default content_browsertests\n'
        '\n'
        '  % tools/mb/mb.py run out/Default content_browsertests\n'
        '\n'
        '  % tools/mb/mb.py run out/Default content_browsertests -- \\\n'
        '    --test-launcher-retry-limit=0'
        '\n'
    )

    AddCommonOptions(subp)
    subp.add_argument('-j', '--jobs', dest='jobs', type=int,
                      help='Number of jobs to pass to ninja')
    subp.add_argument('--no-build', dest='build', default=True,
                      action='store_false',
                      help='Do not build, just isolate and run')
    subp.add_argument('path', nargs=1,
                      help=('path to generate build into (or use).'
                            ' This can be either a regular path or a '
                            'GN-style source-relative path like '
                            '//out/Default.'))
    subp.add_argument('target', nargs=1,
                      help='ninja target to build and run')
    subp.add_argument('extra_args', nargs='*',
                      help=('extra args to pass to the isolate to run. Use '
                            '"--" as the first arg if you need to pass '
                            'switches'))
    subp.set_defaults(func=self.CmdRun)

    subp = subps.add_parser('validate',
                            help='validate the config file')
    subp.add_argument('-f', '--config-file', metavar='PATH',
                      default=self.default_config,
                      help='path to config file (default is %(default)s)')
    subp.set_defaults(func=self.CmdValidate)

    subp = subps.add_parser('audit',
                            help='Audit the config file to track progress')
    subp.add_argument('-f', '--config-file', metavar='PATH',
                      default=self.default_config,
                      help='path to config file (default is %(default)s)')
    subp.add_argument('-i', '--internal', action='store_true',
                      help='check internal masters also')
    subp.add_argument('-m', '--master', action='append',
                      help='master to audit (default is all non-internal '
                           'masters in file)')
    subp.add_argument('-u', '--url-template', action='store',
                      default='https://build.chromium.org/p/'
                              '{master}/json/builders',
                      help='URL scheme for JSON APIs to buildbot '
                           '(default: %(default)s) ')
    subp.add_argument('-c', '--check-compile', action='store_true',
                      help='check whether tbd and master-only bots actually'
                           ' do compiles')
    subp.set_defaults(func=self.CmdAudit)

    subp = subps.add_parser('help',
                            help='Get help on a subcommand.')
    subp.add_argument(nargs='?', action='store', dest='subcommand',
                      help='The command to get help for.')
    subp.set_defaults(func=self.CmdHelp)

    self.args = parser.parse_args(argv)

  def DumpInputFiles(self):

    def DumpContentsOfFilePassedTo(arg_name, path):
      if path and self.Exists(path):
        self.Print("\n# To recreate the file passed to %s:" % arg_name)
        self.Print("%% cat > %s <<EOF" % path)
        contents = self.ReadFile(path)
        self.Print(contents)
        self.Print("EOF\n%\n")

    if getattr(self.args, 'input_path', None):
      DumpContentsOfFilePassedTo(
          'argv[0] (input_path)', self.args.input_path[0])
    if getattr(self.args, 'swarming_targets_file', None):
      DumpContentsOfFilePassedTo(
          '--swarming-targets-file', self.args.swarming_targets_file)

  def CmdAnalyze(self):
    vals = self.Lookup()
    self.ClobberIfNeeded(vals)
    if vals['type'] == 'gn':
      return self.RunGNAnalyze(vals)
    else:
      return self.RunGYPAnalyze(vals)

  def CmdExport(self):
    self.ReadConfigFile()
    obj = {}
    for master, builders in self.masters.items():
      obj[master] = {}
      for builder in builders:
        config = self.masters[master][builder]
        if not config:
          continue

        if isinstance(config, dict):
          args = {k: self.FlattenConfig(v)['gn_args']
                  for k, v in config.items()}
        elif config.startswith('//'):
          args = config
        else:
          args = self.FlattenConfig(config)['gn_args']
          if 'error' in args:
            continue

        obj[master][builder] = args

    # Dump object and trim trailing whitespace.
    s = '\n'.join(l.rstrip() for l in
                  json.dumps(obj, sort_keys=True, indent=2).splitlines())
    self.Print(s)
    return 0

  def CmdGen(self):
    vals = self.Lookup()
    self.ClobberIfNeeded(vals)
    if vals['type'] == 'gn':
      return self.RunGNGen(vals)
    else:
      return self.RunGYPGen(vals)

  def CmdHelp(self):
    if self.args.subcommand:
      self.ParseArgs([self.args.subcommand, '--help'])
    else:
      self.ParseArgs(['--help'])

  def CmdIsolate(self):
    vals = self.GetConfig()
    if not vals:
      return 1

    if vals['type'] == 'gn':
      return self.RunGNIsolate(vals)
    else:
      return self.Build('%s_run' % self.args.target[0])

  def CmdLookup(self):
    vals = self.Lookup()
    if vals['type'] == 'gn':
      cmd = self.GNCmd('gen', '_path_')
      gn_args = self.GNArgs(vals)
      self.Print('\nWriting """\\\n%s""" to _path_/args.gn.\n' % gn_args)
      env = None
    else:
      cmd, env = self.GYPCmd('_path_', vals)

    self.PrintCmd(cmd, env)
    return 0

  def CmdRun(self):
    vals = self.GetConfig()
    if not vals:
      return 1

    build_dir = self.args.path[0]
    target = self.args.target[0]

    if vals['type'] == 'gn':
      if self.args.build:
        ret = self.Build(target)
        if ret:
          return ret
      ret = self.RunGNIsolate(vals)
      if ret:
        return ret
    else:
      ret = self.Build('%s_run' % target)
      if ret:
        return ret

    cmd = [
        self.executable,
        self.PathJoin('tools', 'swarming_client', 'isolate.py'),
        'run',
        '-s',
        self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target)),
    ]
    if self.args.extra_args:
        cmd += ['--'] + self.args.extra_args

    ret, _, _ = self.Run(cmd, force_verbose=False, buffer_output=False)

    return ret

  def CmdValidate(self, print_ok=True):
    errs = []

    # Read the file to make sure it parses.
    self.ReadConfigFile()

    # Build a list of all of the configs referenced by builders.
    all_configs = {}
    for master in self.masters:
      for config in self.masters[master].values():
        if isinstance(config, dict):
          for c in config.values():
            all_configs[c] = master
        else:
          all_configs[config] = master

    # Check that every referenced args file or config actually exists.
    for config, loc in all_configs.items():
      if config.startswith('//'):
        if not self.Exists(self.ToAbsPath(config)):
          errs.append('Unknown args file "%s" referenced from "%s".' %
                      (config, loc))
      elif not config in self.configs:
        errs.append('Unknown config "%s" referenced from "%s".' %
                    (config, loc))

    # Check that every actual config is actually referenced.
    for config in self.configs:
      if not config in all_configs:
        errs.append('Unused config "%s".' % config)

    # Figure out the whole list of mixins, and check that every mixin
    # listed by a config or another mixin actually exists.
    referenced_mixins = set()
    for config, mixins in self.configs.items():
      for mixin in mixins:
        if not mixin in self.mixins:
          errs.append('Unknown mixin "%s" referenced by config "%s".' %
                      (mixin, config))
        referenced_mixins.add(mixin)

    for mixin in self.mixins:
      for sub_mixin in self.mixins[mixin].get('mixins', []):
        if not sub_mixin in self.mixins:
          errs.append('Unknown mixin "%s" referenced by mixin "%s".' %
                      (sub_mixin, mixin))
        referenced_mixins.add(sub_mixin)

    # Check that every mixin defined is actually referenced somewhere.
    for mixin in self.mixins:
      if not mixin in referenced_mixins:
        errs.append('Unreferenced mixin "%s".' % mixin)

    # If we're checking the Chromium config, check that the 'chromium' bots
    # which build public artifacts do not include the chrome_with_codecs mixin.
    if self.args.config_file == self.default_config:
      if 'chromium' in self.masters:
        for builder in self.masters['chromium']:
          config = self.masters['chromium'][builder]
          def RecurseMixins(current_mixin):
            if current_mixin == 'chrome_with_codecs':
              errs.append('Public artifact builder "%s" can not contain the '
                          '"chrome_with_codecs" mixin.' % builder)
              return
            if not 'mixins' in self.mixins[current_mixin]:
              return
            for mixin in self.mixins[current_mixin]['mixins']:
              RecurseMixins(mixin)

          for mixin in self.configs[config]:
            RecurseMixins(mixin)
      else:
        errs.append('Missing "chromium" master. Please update this '
                    'proprietary codecs check with the name of the master '
                    'responsible for public build artifacts.')

    if errs:
      raise MBErr(('mb config file %s has problems:' % self.args.config_file) +
                    '\n  ' + '\n  '.join(errs))

    if print_ok:
      self.Print('mb config file %s looks ok.' % self.args.config_file)
    return 0

  def CmdAudit(self):
    """Track the progress of the GYP->GN migration on the bots."""

    # First, make sure the config file is okay, but don't print anything
    # if it is (it will throw an error if it isn't).
    self.CmdValidate(print_ok=False)

    stats = OrderedDict()
    STAT_MASTER_ONLY = 'Master only'
    STAT_CONFIG_ONLY = 'Config only'
    STAT_TBD = 'Still TBD'
    STAT_GYP = 'Still GYP'
    STAT_DONE = 'Done (on GN)'
    stats[STAT_MASTER_ONLY] = 0
    stats[STAT_CONFIG_ONLY] = 0
    stats[STAT_TBD] = 0
    stats[STAT_GYP] = 0
    stats[STAT_DONE] = 0

    def PrintBuilders(heading, builders, notes):
      stats.setdefault(heading, 0)
      stats[heading] += len(builders)
      if builders:
        self.Print('  %s:' % heading)
        for builder in sorted(builders):
          self.Print('    %s%s' % (builder, notes[builder]))

    self.ReadConfigFile()

    masters = self.args.master or self.masters
    for master in sorted(masters):
      url = self.args.url_template.replace('{master}', master)

      self.Print('Auditing %s' % master)

      MASTERS_TO_SKIP = (
        'client.skia',
        'client.v8.fyi',
        'tryserver.v8',
      )
      if master in MASTERS_TO_SKIP:
        # Skip these bots because converting them is the responsibility of
        # those teams and out of scope for the Chromium migration to GN.
        self.Print('  Skipped (out of scope)')
        self.Print('')
        continue

      INTERNAL_MASTERS = ('official.desktop', 'official.desktop.continuous',
                          'internal.client.kitchensync')
      if master in INTERNAL_MASTERS and not self.args.internal:
        # Skip these because the servers aren't accessible by default ...
        self.Print('  Skipped (internal)')
        self.Print('')
        continue

      try:
        # Fetch the /builders contents from the buildbot master. The
        # keys of the dict are the builder names themselves.
        json_contents = self.Fetch(url)
        d = json.loads(json_contents)
      except Exception as e:
        self.Print(str(e))
        return 1

      config_builders = set(self.masters[master])
      master_builders = set(d.keys())
      both = master_builders & config_builders
      master_only = master_builders - config_builders
      config_only = config_builders - master_builders
      tbd = set()
      gyp = set()
      done = set()
      notes = {builder: '' for builder in config_builders | master_builders}

      for builder in both:
        config = self.masters[master][builder]
        if config == 'tbd':
          tbd.add(builder)
        elif isinstance(config, dict):
          vals = self.FlattenConfig(config.values()[0])
          if vals['type'] == 'gyp':
            gyp.add(builder)
          else:
            done.add(builder)
        elif config.startswith('//'):
          done.add(builder)
        else:
          vals = self.FlattenConfig(config)
          if vals['type'] == 'gyp':
            gyp.add(builder)
          else:
            done.add(builder)

      if self.args.check_compile and (tbd or master_only):
        either = tbd | master_only
        for builder in either:
          notes[builder] = ' (' + self.CheckCompile(master, builder) +')'

      if master_only or config_only or tbd or gyp:
        PrintBuilders(STAT_MASTER_ONLY, master_only, notes)
        PrintBuilders(STAT_CONFIG_ONLY, config_only, notes)
        PrintBuilders(STAT_TBD, tbd, notes)
        PrintBuilders(STAT_GYP, gyp, notes)
      else:
        self.Print('  All GN!')

      stats[STAT_DONE] += len(done)

      self.Print('')

    fmt = '{:<27} {:>4}'
    self.Print(fmt.format('Totals', str(sum(int(v) for v in stats.values()))))
    self.Print(fmt.format('-' * 27, '----'))
    for stat, count in stats.items():
      self.Print(fmt.format(stat, str(count)))

    return 0

  def GetConfig(self):
    build_dir = self.args.path[0]

    vals = self.DefaultVals()
    if self.args.builder or self.args.master or self.args.config:
      vals = self.Lookup()
      if vals['type'] == 'gn':
        # Re-run gn gen in order to ensure the config is consistent with the
        # build dir.
        self.RunGNGen(vals)
      return vals

    mb_type_path = self.PathJoin(self.ToAbsPath(build_dir), 'mb_type')
    if not self.Exists(mb_type_path):
      toolchain_path = self.PathJoin(self.ToAbsPath(build_dir),
                                     'toolchain.ninja')
      if not self.Exists(toolchain_path):
        self.Print('Must either specify a path to an existing GN build dir '
                   'or pass in a -m/-b pair or a -c flag to specify the '
                   'configuration')
        return {}
      else:
        mb_type = 'gn'
    else:
      mb_type = self.ReadFile(mb_type_path).strip()

    if mb_type == 'gn':
      vals['gn_args'] = self.GNArgsFromDir(build_dir)
    vals['type'] = mb_type

    return vals

  def GNArgsFromDir(self, build_dir):
    args_contents = ""
    gn_args_path = self.PathJoin(self.ToAbsPath(build_dir), 'args.gn')
    if self.Exists(gn_args_path):
      args_contents = self.ReadFile(gn_args_path)
    gn_args = []
    for l in args_contents.splitlines():
      fields = l.split(' ')
      name = fields[0]
      val = ' '.join(fields[2:])
      gn_args.append('%s=%s' % (name, val))

    return ' '.join(gn_args)

  def Lookup(self):
    vals = self.ReadIOSBotConfig()
    if not vals:
      self.ReadConfigFile()
      config = self.ConfigFromArgs()
      if config.startswith('//'):
        if not self.Exists(self.ToAbsPath(config)):
          raise MBErr('args file "%s" not found' % config)
        vals = self.DefaultVals()
        vals['args_file'] = config
      else:
        if not config in self.configs:
          raise MBErr('Config "%s" not found in %s' %
                      (config, self.args.config_file))
        vals = self.FlattenConfig(config)

    # Do some basic sanity checking on the config so that we
    # don't have to do this in every caller.
    if 'type' not in vals:
        vals['type'] = 'gn'
    assert vals['type'] in ('gn', 'gyp'), (
        'Unknown meta-build type "%s"' % vals['gn_args'])

    return vals

  def ReadIOSBotConfig(self):
    if not self.args.master or not self.args.builder:
      return {}
    path = self.PathJoin(self.chromium_src_dir, 'ios', 'build', 'bots',
                         self.args.master, self.args.builder + '.json')
    if not self.Exists(path):
      return {}

    contents = json.loads(self.ReadFile(path))
    gyp_vals = contents.get('GYP_DEFINES', {})
    if isinstance(gyp_vals, dict):
      gyp_defines = ' '.join('%s=%s' % (k, v) for k, v in gyp_vals.items())
    else:
      gyp_defines = ' '.join(gyp_vals)
    gn_args = ' '.join(contents.get('gn_args', []))

    vals = self.DefaultVals()
    vals['gn_args'] = gn_args
    vals['gyp_defines'] = gyp_defines
    vals['type'] = contents.get('mb_type', 'gn')
    return vals

  def ReadConfigFile(self):
    if not self.Exists(self.args.config_file):
      raise MBErr('config file not found at %s' % self.args.config_file)

    try:
      contents = ast.literal_eval(self.ReadFile(self.args.config_file))
    except SyntaxError as e:
      raise MBErr('Failed to parse config file "%s": %s' %
                 (self.args.config_file, e))

    self.configs = contents['configs']
    self.masters = contents['masters']
    self.mixins = contents['mixins']

  def ReadIsolateMap(self):
    if not self.Exists(self.args.isolate_map_file):
      raise MBErr('isolate map file not found at %s' %
                  self.args.isolate_map_file)
    try:
      return ast.literal_eval(self.ReadFile(self.args.isolate_map_file))
    except SyntaxError as e:
      raise MBErr('Failed to parse isolate map file "%s": %s' %
                  (self.args.isolate_map_file, e))

  def ConfigFromArgs(self):
    if self.args.config:
      if self.args.master or self.args.builder:
        raise MBErr('Can not specific both -c/--config and -m/--master or '
                    '-b/--builder')

      return self.args.config

    if not self.args.master or not self.args.builder:
      raise MBErr('Must specify either -c/--config or '
                  '(-m/--master and -b/--builder)')

    if not self.args.master in self.masters:
      raise MBErr('Master name "%s" not found in "%s"' %
                  (self.args.master, self.args.config_file))

    if not self.args.builder in self.masters[self.args.master]:
      raise MBErr('Builder name "%s"  not found under masters[%s] in "%s"' %
                  (self.args.builder, self.args.master, self.args.config_file))

    config = self.masters[self.args.master][self.args.builder]
    if isinstance(config, dict):
      if self.args.phase is None:
        raise MBErr('Must specify a build --phase for %s on %s' %
                    (self.args.builder, self.args.master))
      phase = str(self.args.phase)
      if phase not in config:
        raise MBErr('Phase %s doesn\'t exist for %s on %s' %
                    (phase, self.args.builder, self.args.master))
      return config[phase]

    if self.args.phase is not None:
      raise MBErr('Must not specify a build --phase for %s on %s' %
                  (self.args.builder, self.args.master))
    return config

  def FlattenConfig(self, config):
    mixins = self.configs[config]
    vals = self.DefaultVals()

    visited = []
    self.FlattenMixins(mixins, vals, visited)
    return vals

  def DefaultVals(self):
    return {
      'args_file': '',
      'cros_passthrough': False,
      'gn_args': '',
      'gyp_defines': '',
      'gyp_crosscompile': False,
      'type': 'gn',
    }

  def FlattenMixins(self, mixins, vals, visited):
    for m in mixins:
      if m not in self.mixins:
        raise MBErr('Unknown mixin "%s"' % m)

      visited.append(m)

      mixin_vals = self.mixins[m]

      if 'cros_passthrough' in mixin_vals:
        vals['cros_passthrough'] = mixin_vals['cros_passthrough']
      if 'args_file' in mixin_vals:
        if vals['args_file']:
            raise MBErr('args_file specified multiple times in mixins '
                        'for %s on %s' % (self.args.builder, self.args.master))
        vals['args_file'] = mixin_vals['args_file']
      if 'gn_args' in mixin_vals:
        if vals['gn_args']:
          vals['gn_args'] += ' ' + mixin_vals['gn_args']
        else:
          vals['gn_args'] = mixin_vals['gn_args']
      if 'gyp_crosscompile' in mixin_vals:
        vals['gyp_crosscompile'] = mixin_vals['gyp_crosscompile']
      if 'gyp_defines' in mixin_vals:
        if vals['gyp_defines']:
          vals['gyp_defines'] += ' ' + mixin_vals['gyp_defines']
        else:
          vals['gyp_defines'] = mixin_vals['gyp_defines']
      if 'type' in mixin_vals:
        vals['type'] = mixin_vals['type']

      if 'mixins' in mixin_vals:
        self.FlattenMixins(mixin_vals['mixins'], vals, visited)
    return vals

  def ClobberIfNeeded(self, vals):
    path = self.args.path[0]
    build_dir = self.ToAbsPath(path)
    mb_type_path = self.PathJoin(build_dir, 'mb_type')
    needs_clobber = False
    new_mb_type = vals['type']
    if self.Exists(build_dir):
      if self.Exists(mb_type_path):
        old_mb_type = self.ReadFile(mb_type_path)
        if old_mb_type != new_mb_type:
          self.Print("Build type mismatch: was %s, will be %s, clobbering %s" %
                     (old_mb_type, new_mb_type, path))
          needs_clobber = True
      else:
        # There is no 'mb_type' file in the build directory, so this probably
        # means that the prior build(s) were not done through mb, and we
        # have no idea if this was a GYP build or a GN build. Clobber it
        # to be safe.
        self.Print("%s/mb_type missing, clobbering to be safe" % path)
        needs_clobber = True

    if self.args.dryrun:
      return

    if needs_clobber:
      self.RemoveDirectory(build_dir)

    self.MaybeMakeDirectory(build_dir)
    self.WriteFile(mb_type_path, new_mb_type)

  def RunGNGen(self, vals, compute_grit_inputs_for_analyze=False):
    build_dir = self.args.path[0]

    cmd = self.GNCmd('gen', build_dir, '--check')
    gn_args = self.GNArgs(vals)
    if compute_grit_inputs_for_analyze:
      gn_args += ' compute_grit_inputs_for_analyze=true'

    # Since GN hasn't run yet, the build directory may not even exist.
    self.MaybeMakeDirectory(self.ToAbsPath(build_dir))

    gn_args_path = self.ToAbsPath(build_dir, 'args.gn')
    self.WriteFile(gn_args_path, gn_args, force_verbose=True)

    swarming_targets = []
    if getattr(self.args, 'swarming_targets_file', None):
      # We need GN to generate the list of runtime dependencies for
      # the compile targets listed (one per line) in the file so
      # we can run them via swarming. We use gn_isolate_map.pyl to convert
      # the compile targets to the matching GN labels.
      path = self.args.swarming_targets_file
      if not self.Exists(path):
        self.WriteFailureAndRaise('"%s" does not exist' % path,
                                  output_path=None)
      contents = self.ReadFile(path)
      swarming_targets = set(contents.splitlines())

      isolate_map = self.ReadIsolateMap()
      err, labels = self.MapTargetsToLabels(isolate_map, swarming_targets)
      if err:
          raise MBErr(err)

      gn_runtime_deps_path = self.ToAbsPath(build_dir, 'runtime_deps')
      self.WriteFile(gn_runtime_deps_path, '\n'.join(labels) + '\n')
      cmd.append('--runtime-deps-list-file=%s' % gn_runtime_deps_path)

    ret, _, _ = self.Run(cmd)
    if ret:
        # If `gn gen` failed, we should exit early rather than trying to
        # generate isolates. Run() will have already logged any error output.
        self.Print('GN gen failed: %d' % ret)
        return ret

    android = 'target_os="android"' in vals['gn_args']
    for target in swarming_targets:
      if android:
        # Android targets may be either android_apk or executable. The former
        # will result in runtime_deps associated with the stamp file, while the
        # latter will result in runtime_deps associated with the executable.
        label = isolate_map[target]['label']
        runtime_deps_targets = [
            target + '.runtime_deps',
            'obj/%s.stamp.runtime_deps' % label.replace(':', '/')]
      elif (isolate_map[target]['type'] == 'script' or
            isolate_map[target].get('label_type') == 'group'):
        # For script targets, the build target is usually a group,
        # for which gn generates the runtime_deps next to the stamp file
        # for the label, which lives under the obj/ directory, but it may
        # also be an executable.
        label = isolate_map[target]['label']
        runtime_deps_targets = [
            'obj/%s.stamp.runtime_deps' % label.replace(':', '/')]
        if self.platform == 'win32':
          runtime_deps_targets += [ target + '.exe.runtime_deps' ]
        else:
          runtime_deps_targets += [ target + '.runtime_deps' ]
      elif self.platform == 'win32':
        runtime_deps_targets = [target + '.exe.runtime_deps']
      else:
        runtime_deps_targets = [target + '.runtime_deps']

      for r in runtime_deps_targets:
        runtime_deps_path = self.ToAbsPath(build_dir, r)
        if self.Exists(runtime_deps_path):
          break
      else:
        raise MBErr('did not generate any of %s' %
                    ', '.join(runtime_deps_targets))

      command, extra_files = self.GetIsolateCommand(target, vals)

      runtime_deps = self.ReadFile(runtime_deps_path).splitlines()

      self.WriteIsolateFiles(build_dir, command, target, runtime_deps,
                             extra_files)

    return 0

  def RunGNIsolate(self, vals):
    target = self.args.target[0]
    isolate_map = self.ReadIsolateMap()
    err, labels = self.MapTargetsToLabels(isolate_map, [target])
    if err:
      raise MBErr(err)
    label = labels[0]

    build_dir = self.args.path[0]
    command, extra_files = self.GetIsolateCommand(target, vals)

    cmd = self.GNCmd('desc', build_dir, label, 'runtime_deps')
    ret, out, _ = self.Call(cmd)
    if ret:
      if out:
        self.Print(out)
      return ret

    runtime_deps = out.splitlines()

    self.WriteIsolateFiles(build_dir, command, target, runtime_deps,
                           extra_files)

    ret, _, _ = self.Run([
        self.executable,
        self.PathJoin('tools', 'swarming_client', 'isolate.py'),
        'check',
        '-i',
        self.ToSrcRelPath('%s/%s.isolate' % (build_dir, target)),
        '-s',
        self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target))],
        buffer_output=False)

    return ret

  def WriteIsolateFiles(self, build_dir, command, target, runtime_deps,
                        extra_files):
    isolate_path = self.ToAbsPath(build_dir, target + '.isolate')
    self.WriteFile(isolate_path,
      pprint.pformat({
        'variables': {
          'command': command,
          'files': sorted(runtime_deps + extra_files),
        }
      }) + '\n')

    self.WriteJSON(
      {
        'args': [
          '--isolated',
          self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target)),
          '--isolate',
          self.ToSrcRelPath('%s/%s.isolate' % (build_dir, target)),
        ],
        'dir': self.chromium_src_dir,
        'version': 1,
      },
      isolate_path + 'd.gen.json',
    )

  def MapTargetsToLabels(self, isolate_map, targets):
    labels = []
    err = ''

    for target in targets:
      if target == 'all':
        labels.append(target)
      elif target.startswith('//'):
        labels.append(target)
      else:
        if target in isolate_map:
          if isolate_map[target]['type'] == 'unknown':
            err += ('test target "%s" type is unknown\n' % target)
          else:
            labels.append(isolate_map[target]['label'])
        else:
          err += ('target "%s" not found in '
                  '//testing/buildbot/gn_isolate_map.pyl\n' % target)

    return err, labels

  def GNCmd(self, subcommand, path, *args):
    if self.platform == 'linux2':
      subdir, exe = 'linux64', 'gn'
    elif self.platform == 'darwin':
      subdir, exe = 'mac', 'gn'
    else:
      subdir, exe = 'win', 'gn.exe'

    gn_path = self.PathJoin(self.chromium_src_dir, 'buildtools', subdir, exe)
    return [gn_path, subcommand, path] + list(args)


  def GNArgs(self, vals):
    if vals['cros_passthrough']:
      if not 'GN_ARGS' in os.environ:
        raise MBErr('MB is expecting GN_ARGS to be in the environment')
      gn_args = os.environ['GN_ARGS']
      if not re.search('target_os.*=.*"chromeos"', gn_args):
        raise MBErr('GN_ARGS is missing target_os = "chromeos": (GN_ARGS=%s)' %
                    gn_args)
    else:
      gn_args = vals['gn_args']

    if self.args.goma_dir:
      gn_args += ' goma_dir="%s"' % self.args.goma_dir

    android_version_code = self.args.android_version_code
    if android_version_code:
      gn_args += ' android_default_version_code="%s"' % android_version_code

    android_version_name = self.args.android_version_name
    if android_version_name:
      gn_args += ' android_default_version_name="%s"' % android_version_name

    # Canonicalize the arg string into a sorted, newline-separated list
    # of key-value pairs, and de-dup the keys if need be so that only
    # the last instance of each arg is listed.
    gn_args = gn_helpers.ToGNString(gn_helpers.FromGNArgs(gn_args))

    args_file = vals.get('args_file', None)
    if args_file:
      gn_args = ('import("%s")\n' % vals['args_file']) + gn_args
    return gn_args

  def RunGYPGen(self, vals):
    path = self.args.path[0]

    output_dir = self.ParseGYPConfigPath(path)
    cmd, env = self.GYPCmd(output_dir, vals)
    ret, _, _ = self.Run(cmd, env=env)
    return ret

  def RunGYPAnalyze(self, vals):
    output_dir = self.ParseGYPConfigPath(self.args.path[0])
    if self.args.verbose:
      inp = self.ReadInputJSON(['files', 'test_targets',
                                'additional_compile_targets'])
      self.Print()
      self.Print('analyze input:')
      self.PrintJSON(inp)
      self.Print()

    cmd, env = self.GYPCmd(output_dir, vals)
    cmd.extend(['-f', 'analyzer',
                '-G', 'config_path=%s' % self.args.input_path[0],
                '-G', 'analyzer_output_path=%s' % self.args.output_path[0]])
    ret, _, _ = self.Run(cmd, env=env)
    if not ret and self.args.verbose:
      outp = json.loads(self.ReadFile(self.args.output_path[0]))
      self.Print()
      self.Print('analyze output:')
      self.PrintJSON(outp)
      self.Print()

    return ret

  def GetIsolateCommand(self, target, vals):
    isolate_map = self.ReadIsolateMap()

    android = 'target_os="android"' in vals['gn_args']

    # This should be true if tests with type='windowed_test_launcher' are
    # expected to run using xvfb. For example, Linux Desktop, X11 CrOS and
    # Ozone CrOS builds. Note that one Ozone build can be used to run differen
    # backends. Currently, tests are executed for the headless and X11 backends
    # and both can run under Xvfb.
    # TODO(tonikitoo,msisov,fwang): Find a way to run tests for the Wayland
    # backend.
    use_xvfb = self.platform == 'linux2' and not android

    asan = 'is_asan=true' in vals['gn_args']
    msan = 'is_msan=true' in vals['gn_args']
    tsan = 'is_tsan=true' in vals['gn_args']
    cfi_diag = 'use_cfi_diag=true' in vals['gn_args']

    test_type = isolate_map[target]['type']

    executable = isolate_map[target].get('executable', target)
    executable_suffix = '.exe' if self.platform == 'win32' else ''

    cmdline = []
    extra_files = []

    if test_type == 'nontest':
      self.WriteFailureAndRaise('We should not be isolating %s.' % target,
                                output_path=None)

    if android and test_type != "script":
      cmdline = [
          '../../build/android/test_wrapper/logdog_wrapper.py',
          '--target', target,
          '--target-devices-file', '${SWARMING_BOT_FILE}',
          '--logdog-bin-cmd', '../../bin/logdog_butler',
          '--logcat-output-file', '${ISOLATED_OUTDIR}/logcats',
          '--store-tombstones']
    elif use_xvfb and test_type == 'windowed_test_launcher':
      extra_files = [
          '../../testing/test_env.py',
          '../../testing/xvfb.py',
      ]
      cmdline = [
        '../../testing/xvfb.py',
        './' + str(executable) + executable_suffix,
        '--brave-new-test-launcher',
        '--test-launcher-bot-mode',
        '--asan=%d' % asan,
        '--msan=%d' % msan,
        '--tsan=%d' % tsan,
        '--cfi-diag=%d' % cfi_diag,
      ]
    elif test_type in ('windowed_test_launcher', 'console_test_launcher'):
      extra_files = [
          '../../testing/test_env.py'
      ]
      cmdline = [
          '../../testing/test_env.py',
          './' + str(executable) + executable_suffix,
          '--brave-new-test-launcher',
          '--test-launcher-bot-mode',
          '--asan=%d' % asan,
          '--msan=%d' % msan,
          '--tsan=%d' % tsan,
          '--cfi-diag=%d' % cfi_diag,
      ]
    elif test_type == 'script':
      extra_files = [
          '../../testing/test_env.py'
      ]
      cmdline = [
          '../../testing/test_env.py',
          '../../' + self.ToSrcRelPath(isolate_map[target]['script'])
      ]
    elif test_type in ('raw'):
      extra_files = []
      cmdline = [
          './' + str(target) + executable_suffix,
      ]

    else:
      self.WriteFailureAndRaise('No command line for %s found (test type %s).'
                                % (target, test_type), output_path=None)

    cmdline += isolate_map[target].get('args', [])

    return cmdline, extra_files

  def ToAbsPath(self, build_path, *comps):
    return self.PathJoin(self.chromium_src_dir,
                         self.ToSrcRelPath(build_path),
                         *comps)

  def ToSrcRelPath(self, path):
    """Returns a relative path from the top of the repo."""
    if path.startswith('//'):
      return path[2:].replace('/', self.sep)
    return self.RelPath(path, self.chromium_src_dir)

  def ParseGYPConfigPath(self, path):
    rpath = self.ToSrcRelPath(path)
    output_dir, _, _ = rpath.rpartition(self.sep)
    return output_dir

  def GYPCmd(self, output_dir, vals):
    if vals['cros_passthrough']:
      if not 'GYP_DEFINES' in os.environ:
        raise MBErr('MB is expecting GYP_DEFINES to be in the environment')
      gyp_defines = os.environ['GYP_DEFINES']
      if not 'chromeos=1' in gyp_defines:
        raise MBErr('GYP_DEFINES is missing chromeos=1: (GYP_DEFINES=%s)' %
                    gyp_defines)
    else:
      gyp_defines = vals['gyp_defines']

    goma_dir = self.args.goma_dir

    # GYP uses shlex.split() to split the gyp defines into separate arguments,
    # so we can support backslashes and and spaces in arguments by quoting
    # them, even on Windows, where this normally wouldn't work.
    if goma_dir and ('\\' in goma_dir or ' ' in goma_dir):
      goma_dir = "'%s'" % goma_dir

    if goma_dir:
      gyp_defines += ' gomadir=%s' % goma_dir

    android_version_code = self.args.android_version_code
    if android_version_code:
      gyp_defines += ' app_manifest_version_code=%s' % android_version_code

    android_version_name = self.args.android_version_name
    if android_version_name:
      gyp_defines += ' app_manifest_version_name=%s' % android_version_name

    cmd = [
        self.executable,
        self.args.gyp_script,
        '-G',
        'output_dir=' + output_dir,
    ]

    # Ensure that we have an environment that only contains
    # the exact values of the GYP variables we need.
    env = os.environ.copy()

    # This is a terrible hack to work around the fact that
    # //tools/clang/scripts/update.py is invoked by GYP and GN but
    # currently relies on an environment variable to figure out
    # what revision to embed in the command line #defines.
    # For GN, we've made this work via a gn arg that will cause update.py
    # to get an additional command line arg, but getting that to work
    # via GYP_DEFINES has proven difficult, so we rewrite the GYP_DEFINES
    # to get rid of the arg and add the old var in, instead.
    # See crbug.com/582737 for more on this. This can hopefully all
    # go away with GYP.
    m = re.search('llvm_force_head_revision=1\s*', gyp_defines)
    if m:
      env['LLVM_FORCE_HEAD_REVISION'] = '1'
      gyp_defines = gyp_defines.replace(m.group(0), '')

    # This is another terrible hack to work around the fact that
    # GYP sets the link concurrency to use via the GYP_LINK_CONCURRENCY
    # environment variable, and not via a proper GYP_DEFINE. See
    # crbug.com/611491 for more on this.
    m = re.search('gyp_link_concurrency=(\d+)(\s*)', gyp_defines)
    if m:
      env['GYP_LINK_CONCURRENCY'] = m.group(1)
      gyp_defines = gyp_defines.replace(m.group(0), '')

    env['GYP_GENERATORS'] = 'ninja'
    if 'GYP_CHROMIUM_NO_ACTION' in env:
      del env['GYP_CHROMIUM_NO_ACTION']
    if 'GYP_CROSSCOMPILE' in env:
      del env['GYP_CROSSCOMPILE']
    env['GYP_DEFINES'] = gyp_defines
    if vals['gyp_crosscompile']:
      env['GYP_CROSSCOMPILE'] = '1'
    return cmd, env

  def RunGNAnalyze(self, vals):
    # Analyze runs before 'gn gen' now, so we need to run gn gen
    # in order to ensure that we have a build directory.
    ret = self.RunGNGen(vals, compute_grit_inputs_for_analyze=True)
    if ret:
      return ret

    build_path = self.args.path[0]
    input_path = self.args.input_path[0]
    gn_input_path = input_path + '.gn'
    output_path = self.args.output_path[0]
    gn_output_path = output_path + '.gn'

    inp = self.ReadInputJSON(['files', 'test_targets',
                              'additional_compile_targets'])
    if self.args.verbose:
      self.Print()
      self.Print('analyze input:')
      self.PrintJSON(inp)
      self.Print()


    # This shouldn't normally happen, but could due to unusual race conditions,
    # like a try job that gets scheduled before a patch lands but runs after
    # the patch has landed.
    if not inp['files']:
      self.Print('Warning: No files modified in patch, bailing out early.')
      self.WriteJSON({
            'status': 'No dependency',
            'compile_targets': [],
            'test_targets': [],
          }, output_path)
      return 0

    gn_inp = {}
    gn_inp['files'] = ['//' + f for f in inp['files'] if not f.startswith('//')]

    isolate_map = self.ReadIsolateMap()
    err, gn_inp['additional_compile_targets'] = self.MapTargetsToLabels(
        isolate_map, inp['additional_compile_targets'])
    if err:
      raise MBErr(err)

    err, gn_inp['test_targets'] = self.MapTargetsToLabels(
        isolate_map, inp['test_targets'])
    if err:
      raise MBErr(err)
    labels_to_targets = {}
    for i, label in enumerate(gn_inp['test_targets']):
      labels_to_targets[label] = inp['test_targets'][i]

    try:
      self.WriteJSON(gn_inp, gn_input_path)
      cmd = self.GNCmd('analyze', build_path, gn_input_path, gn_output_path)
      ret, _, _ = self.Run(cmd, force_verbose=True)
      if ret:
        return ret

      gn_outp_str = self.ReadFile(gn_output_path)
      try:
        gn_outp = json.loads(gn_outp_str)
      except Exception as e:
        self.Print("Failed to parse the JSON string GN returned: %s\n%s"
                   % (repr(gn_outp_str), str(e)))
        raise

      outp = {}
      if 'status' in gn_outp:
        outp['status'] = gn_outp['status']
      if 'error' in gn_outp:
        outp['error'] = gn_outp['error']
      if 'invalid_targets' in gn_outp:
        outp['invalid_targets'] = gn_outp['invalid_targets']
      if 'compile_targets' in gn_outp:
        if 'all' in gn_outp['compile_targets']:
          outp['compile_targets'] = ['all']
        else:
          outp['compile_targets'] = [
              label.replace('//', '') for label in gn_outp['compile_targets']]
      if 'test_targets' in gn_outp:
        outp['test_targets'] = [
          labels_to_targets[label] for label in gn_outp['test_targets']]

      if self.args.verbose:
        self.Print()
        self.Print('analyze output:')
        self.PrintJSON(outp)
        self.Print()

      self.WriteJSON(outp, output_path)

    finally:
      if self.Exists(gn_input_path):
        self.RemoveFile(gn_input_path)
      if self.Exists(gn_output_path):
        self.RemoveFile(gn_output_path)

    return 0

  def ReadInputJSON(self, required_keys):
    path = self.args.input_path[0]
    output_path = self.args.output_path[0]
    if not self.Exists(path):
      self.WriteFailureAndRaise('"%s" does not exist' % path, output_path)

    try:
      inp = json.loads(self.ReadFile(path))
    except Exception as e:
      self.WriteFailureAndRaise('Failed to read JSON input from "%s": %s' %
                                (path, e), output_path)

    for k in required_keys:
      if not k in inp:
        self.WriteFailureAndRaise('input file is missing a "%s" key' % k,
                                  output_path)

    return inp

  def WriteFailureAndRaise(self, msg, output_path):
    if output_path:
      self.WriteJSON({'error': msg}, output_path, force_verbose=True)
    raise MBErr(msg)

  def WriteJSON(self, obj, path, force_verbose=False):
    try:
      self.WriteFile(path, json.dumps(obj, indent=2, sort_keys=True) + '\n',
                     force_verbose=force_verbose)
    except Exception as e:
      raise MBErr('Error %s writing to the output path "%s"' %
                 (e, path))

  def CheckCompile(self, master, builder):
    url_template = self.args.url_template + '/{builder}/builds/_all?as_text=1'
    url = urllib2.quote(url_template.format(master=master, builder=builder),
                        safe=':/()?=')
    try:
      builds = json.loads(self.Fetch(url))
    except Exception as e:
      return str(e)
    successes = sorted(
        [int(x) for x in builds.keys() if "text" in builds[x] and
          cmp(builds[x]["text"][:2], ["build", "successful"]) == 0],
        reverse=True)
    if not successes:
      return "no successful builds"
    build = builds[str(successes[0])]
    step_names = set([step["name"] for step in build["steps"]])
    compile_indicators = set(["compile", "compile (with patch)", "analyze"])
    if compile_indicators & step_names:
      return "compiles"
    return "does not compile"

  def PrintCmd(self, cmd, env):
    if self.platform == 'win32':
      env_prefix = 'set '
      env_quoter = QuoteForSet
      shell_quoter = QuoteForCmd
    else:
      env_prefix = ''
      env_quoter = pipes.quote
      shell_quoter = pipes.quote

    def print_env(var):
      if env and var in env:
        self.Print('%s%s=%s' % (env_prefix, var, env_quoter(env[var])))

    print_env('GYP_CROSSCOMPILE')
    print_env('GYP_DEFINES')
    print_env('GYP_LINK_CONCURRENCY')
    print_env('LLVM_FORCE_HEAD_REVISION')

    if cmd[0] == self.executable:
      cmd = ['python'] + cmd[1:]
    self.Print(*[shell_quoter(arg) for arg in cmd])

  def PrintJSON(self, obj):
    self.Print(json.dumps(obj, indent=2, sort_keys=True))

  def Build(self, target):
    build_dir = self.ToSrcRelPath(self.args.path[0])
    ninja_cmd = ['ninja', '-C', build_dir]
    if self.args.jobs:
      ninja_cmd.extend(['-j', '%d' % self.args.jobs])
    ninja_cmd.append(target)
    ret, _, _ = self.Run(ninja_cmd, force_verbose=False, buffer_output=False)
    return ret

  def Run(self, cmd, env=None, force_verbose=True, buffer_output=True):
    # This function largely exists so it can be overridden for testing.
    if self.args.dryrun or self.args.verbose or force_verbose:
      self.PrintCmd(cmd, env)
    if self.args.dryrun:
      return 0, '', ''

    ret, out, err = self.Call(cmd, env=env, buffer_output=buffer_output)
    if self.args.verbose or force_verbose:
      if ret:
        self.Print('  -> returned %d' % ret)
      if out:
        self.Print(out, end='')
      if err:
        self.Print(err, end='', file=sys.stderr)
    return ret, out, err

  def Call(self, cmd, env=None, buffer_output=True):
    if buffer_output:
      p = subprocess.Popen(cmd, shell=False, cwd=self.chromium_src_dir,
                           stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                           env=env)
      out, err = p.communicate()
    else:
      p = subprocess.Popen(cmd, shell=False, cwd=self.chromium_src_dir,
                           env=env)
      p.wait()
      out = err = ''
    return p.returncode, out, err

  def ExpandUser(self, path):
    # This function largely exists so it can be overridden for testing.
    return os.path.expanduser(path)

  def Exists(self, path):
    # This function largely exists so it can be overridden for testing.
    return os.path.exists(path)

  def Fetch(self, url):
    # This function largely exists so it can be overridden for testing.
    f = urllib2.urlopen(url)
    contents = f.read()
    f.close()
    return contents

  def MaybeMakeDirectory(self, path):
    try:
      os.makedirs(path)
    except OSError, e:
      if e.errno != errno.EEXIST:
        raise

  def PathJoin(self, *comps):
    # This function largely exists so it can be overriden for testing.
    return os.path.join(*comps)

  def Print(self, *args, **kwargs):
    # This function largely exists so it can be overridden for testing.
    print(*args, **kwargs)
    if kwargs.get('stream', sys.stdout) == sys.stdout:
      sys.stdout.flush()

  def ReadFile(self, path):
    # This function largely exists so it can be overriden for testing.
    with open(path) as fp:
      return fp.read()

  def RelPath(self, path, start='.'):
    # This function largely exists so it can be overriden for testing.
    return os.path.relpath(path, start)

  def RemoveFile(self, path):
    # This function largely exists so it can be overriden for testing.
    os.remove(path)

  def RemoveDirectory(self, abs_path):
    if self.platform == 'win32':
      # In other places in chromium, we often have to retry this command
      # because we're worried about other processes still holding on to
      # file handles, but when MB is invoked, it will be early enough in the
      # build that their should be no other processes to interfere. We
      # can change this if need be.
      self.Run(['cmd.exe', '/c', 'rmdir', '/q', '/s', abs_path])
    else:
      shutil.rmtree(abs_path, ignore_errors=True)

  def TempFile(self, mode='w'):
    # This function largely exists so it can be overriden for testing.
    return tempfile.NamedTemporaryFile(mode=mode, delete=False)

  def WriteFile(self, path, contents, force_verbose=False):
    # This function largely exists so it can be overriden for testing.
    if self.args.dryrun or self.args.verbose or force_verbose:
      self.Print('\nWriting """\\\n%s""" to %s.\n' % (contents, path))
    with open(path, 'w') as fp:
      return fp.write(contents)


class MBErr(Exception):
  pass


# See http://goo.gl/l5NPDW and http://goo.gl/4Diozm for the painful
# details of this next section, which handles escaping command lines
# so that they can be copied and pasted into a cmd window.
UNSAFE_FOR_SET = set('^<>&|')
UNSAFE_FOR_CMD = UNSAFE_FOR_SET.union(set('()%'))
ALL_META_CHARS = UNSAFE_FOR_CMD.union(set('"'))


def QuoteForSet(arg):
  if any(a in UNSAFE_FOR_SET for a in arg):
    arg = ''.join('^' + a if a in UNSAFE_FOR_SET else a for a in arg)
  return arg


def QuoteForCmd(arg):
  # First, escape the arg so that CommandLineToArgvW will parse it properly.
  # From //tools/gyp/pylib/gyp/msvs_emulation.py:23.
  if arg == '' or ' ' in arg or '"' in arg:
    quote_re = re.compile(r'(\\*)"')
    arg = '"%s"' % (quote_re.sub(lambda mo: 2 * mo.group(1) + '\\"', arg))

  # Then check to see if the arg contains any metacharacters other than
  # double quotes; if it does, quote everything (including the double
  # quotes) for safety.
  if any(a in UNSAFE_FOR_CMD for a in arg):
    arg = ''.join('^' + a if a in ALL_META_CHARS else a for a in arg)
  return arg


if __name__ == '__main__':
  sys.exit(main(sys.argv[1:]))