Merge latest MB from trunk back to M46.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index f30fc3a1240742a9b01338575205fee309362fb0..12f942dc87cf75056370a3a99fdb76a03a5505ac 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -18,7 +18,7 @@ import json
 import os
 import pipes
 import pprint
-import shlex
+import re
 import shutil
 import sys
 import subprocess
@@ -37,7 +37,9 @@ class MetaBuildWrapper(object):
     self.chromium_src_dir = p.normpath(d(d(d(p.abspath(__file__)))))
     self.default_config = p.join(self.chromium_src_dir, 'tools', 'mb',
                                  'mb_config.pyl')
+    self.executable = sys.executable
     self.platform = sys.platform
+    self.sep = os.sep
     self.args = argparse.Namespace()
     self.configs = {}
     self.masters = {}
@@ -63,11 +65,8 @@ class MetaBuildWrapper(object):
       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('-q', '--quiet', action='store_true',
-                        help='Do not print anything on success, '
-                             'just return an exit code.')
-      subp.add_argument('-v', '--verbose', action='count',
-                        help='verbose logging (may specify multiple times).')
+      subp.add_argument('-v', '--verbose', action='store_true',
+                        help='verbose logging')
 
     parser = argparse.ArgumentParser(prog='mb')
     subps = parser.add_subparsers()
@@ -111,9 +110,6 @@ class MetaBuildWrapper(object):
                       default=self.default_config,
                       help='path to config file '
                           '(default is //tools/mb/mb_config.pyl)')
-    subp.add_argument('-q', '--quiet', action='store_true',
-                      help='Do not print anything on success, '
-                           'just return an exit code.')
     subp.set_defaults(func=self.CmdValidate)
 
     subp = subps.add_parser('help',
@@ -135,6 +131,9 @@ class MetaBuildWrapper(object):
 
   def CmdGen(self):
     vals = self.GetConfig()
+
+    self.ClobberIfNeeded(vals)
+
     if vals['type'] == 'gn':
       return self.RunGNGen(vals)
     if vals['type'] == 'gyp':
@@ -145,15 +144,16 @@ class MetaBuildWrapper(object):
   def CmdLookup(self):
     vals = self.GetConfig()
     if vals['type'] == 'gn':
-      cmd = self.GNCmd('gen', '<path>', vals['gn_args'])
+      cmd = self.GNCmd('gen', '_path_', vals['gn_args'])
+      env = None
     elif vals['type'] == 'gyp':
       if vals['gyp_crosscompile']:
         self.Print('GYP_CROSSCOMPILE=1')
-      cmd = self.GYPCmd('<path>', vals['gyp_defines'], vals['gyp_config'])
+      cmd, env = self.GYPCmd('_path_', vals['gyp_defines'])
     else:
       raise MBErr('Unknown meta-build type "%s"' % vals['type'])
 
-    self.PrintCmd(cmd)
+    self.PrintCmd(cmd, env)
     return 0
 
   def CmdHelp(self):
@@ -232,8 +232,7 @@ class MetaBuildWrapper(object):
       raise MBErr(('mb config file %s has problems:' % self.args.config_file) +
                     '\n  ' + '\n  '.join(errs))
 
-    if not self.args.quiet:
-      self.Print('mb config file %s looks ok.' % self.args.config_file)
+    self.Print('mb config file %s looks ok.' % self.args.config_file)
     return 0
 
   def GetConfig(self):
@@ -289,8 +288,7 @@ class MetaBuildWrapper(object):
     vals = {
       'type': None,
       'gn_args': [],
-      'gyp_config': [],
-      'gyp_defines': [],
+      'gyp_defines': '',
       'gyp_crosscompile': False,
     }
 
@@ -315,8 +313,6 @@ class MetaBuildWrapper(object):
           vals['gn_args'] += ' ' + mixin_vals['gn_args']
         else:
           vals['gn_args'] = mixin_vals['gn_args']
-      if 'gyp_config' in mixin_vals:
-        vals['gyp_config'] = mixin_vals['gyp_config']
       if 'gyp_crosscompile' in mixin_vals:
         vals['gyp_crosscompile'] = mixin_vals['gyp_crosscompile']
       if 'gyp_defines' in mixin_vals:
@@ -328,10 +324,40 @@ class MetaBuildWrapper(object):
         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):
     path = self.args.path[0]
 
-    cmd = self.GNCmd('gen', path, vals['gn_args'])
+    cmd = self.GNCmd('gen', path, vals['gn_args'], extra_args=['--check'])
 
     swarming_targets = []
     if self.args.swarming_targets_file:
@@ -341,7 +367,7 @@ class MetaBuildWrapper(object):
       # the compile targets to the matching GN labels.
       contents = self.ReadFile(self.args.swarming_targets_file)
       swarming_targets = contents.splitlines()
-      gn_isolate_map = ast.literal_eval(self.ReadFile(os.path.join(
+      gn_isolate_map = ast.literal_eval(self.ReadFile(self.PathJoin(
           self.chromium_src_dir, 'testing', 'buildbot', 'gn_isolate_map.pyl')))
       gn_labels = []
       for target in swarming_targets:
@@ -359,13 +385,24 @@ class MetaBuildWrapper(object):
       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
 
     for target in swarming_targets:
       if gn_isolate_map[target]['type'] == 'gpu_browser_test':
         runtime_deps_target = 'browser_tests'
+      elif gn_isolate_map[target]['type'] == 'script':
+        # 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.
+        label = gn_isolate_map[target]['label']
+        runtime_deps_target = 'obj/%s.stamp' % label.replace(':', '/')
       else:
         runtime_deps_target = target
-      if sys.platform == 'win32':
+      if self.platform == 'win32':
         deps_path = self.ToAbsPath(path,
                                    runtime_deps_target + '.exe.runtime_deps')
       else:
@@ -392,9 +429,9 @@ class MetaBuildWrapper(object):
         {
           'args': [
             '--isolated',
-            self.ToSrcRelPath('%s%s%s.isolated' % (path, os.sep, target)),
+            self.ToSrcRelPath('%s%s%s.isolated' % (path, self.sep, target)),
             '--isolate',
-            self.ToSrcRelPath('%s%s%s.isolate' % (path, os.sep, target)),
+            self.ToSrcRelPath('%s%s%s.isolate' % (path, self.sep, target)),
           ],
           'dir': self.chromium_src_dir,
           'version': 1,
@@ -402,50 +439,37 @@ class MetaBuildWrapper(object):
         isolate_path + 'd.gen.json',
       )
 
-
     return ret
 
-  def GNCmd(self, subcommand, path, gn_args=''):
+  def GNCmd(self, subcommand, path, gn_args='', extra_args=None):
     if self.platform == 'linux2':
-      gn_path = os.path.join(self.chromium_src_dir, 'buildtools', 'linux64',
-                             'gn')
+      subdir = 'linux64'
     elif self.platform == 'darwin':
-      gn_path = os.path.join(self.chromium_src_dir, 'buildtools', 'mac',
-                             'gn')
+      subdir = 'mac'
     else:
-      gn_path = os.path.join(self.chromium_src_dir, 'buildtools', 'win',
-                             'gn.exe')
+      subdir = 'win'
+    gn_path = self.PathJoin(self.chromium_src_dir, 'buildtools', subdir, 'gn')
 
     cmd = [gn_path, subcommand, path]
     gn_args = gn_args.replace("$(goma_dir)", self.args.goma_dir)
     if gn_args:
       cmd.append('--args=%s' % gn_args)
+    if extra_args:
+      cmd.extend(extra_args)
     return cmd
 
   def RunGYPGen(self, vals):
     path = self.args.path[0]
 
-    output_dir, gyp_config = self.ParseGYPConfigPath(path)
-    if gyp_config != vals['gyp_config']:
-      raise MBErr('The last component of the path (%s) must match the '
-                  'GYP configuration specified in the config (%s), and '
-                  'it does not.' % (gyp_config, vals['gyp_config']))
-    cmd = self.GYPCmd(output_dir, vals['gyp_defines'], config=gyp_config)
-    env = None
+    output_dir = self.ParseGYPConfigPath(path)
+    cmd, env = self.GYPCmd(output_dir, vals['gyp_defines'])
     if vals['gyp_crosscompile']:
-      if self.args.verbose:
-        self.Print('Setting GYP_CROSSCOMPILE=1 in the environment')
-      env = os.environ.copy()
       env['GYP_CROSSCOMPILE'] = '1'
     ret, _, _ = self.Run(cmd, env=env)
     return ret
 
   def RunGYPAnalyze(self, vals):
-    output_dir, gyp_config = self.ParseGYPConfigPath(self.args.path[0])
-    if gyp_config != vals['gyp_config']:
-      raise MBErr('The last component of the path (%s) must match the '
-                  'GYP configuration specified in the config (%s), and '
-                  'it does not.' % (gyp_config, vals['gyp_config']))
+    output_dir = self.ParseGYPConfigPath(self.args.path[0])
     if self.args.verbose:
       inp = self.ReadInputJSON(['files', 'targets'])
       self.Print()
@@ -453,11 +477,11 @@ class MetaBuildWrapper(object):
       self.PrintJSON(inp)
       self.Print()
 
-    cmd = self.GYPCmd(output_dir, vals['gyp_defines'], config=gyp_config)
+    cmd, env = self.GYPCmd(output_dir, vals['gyp_defines'])
     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)
+    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()
@@ -467,58 +491,11 @@ class MetaBuildWrapper(object):
 
     return ret
 
-  def RunGNIsolate(self, vals):
-    build_path = self.args.path[0]
-    inp = self.ReadInputJSON(['targets'])
-    if self.args.verbose:
-      self.Print()
-      self.Print('isolate input:')
-      self.PrintJSON(inp)
-      self.Print()
-    output_path = self.args.output_path[0]
-
-    for target in inp['targets']:
-      runtime_deps_path = self.ToAbsPath(build_path, target + '.runtime_deps')
-
-      if not self.Exists(runtime_deps_path):
-        self.WriteFailureAndRaise('"%s" does not exist' % runtime_deps_path,
-                                  output_path)
-
-      command, extra_files = self.GetIsolateCommand(target, vals, None)
-
-      runtime_deps = self.ReadFile(runtime_deps_path).splitlines()
-
-
-      isolate_path = self.ToAbsPath(build_path, 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_path, target)),
-            '--isolate',
-            self.ToSrcRelPath('%s/%s.isolate' % (build_path, target)),
-          ],
-          'dir': self.chromium_src_dir,
-          'version': 1,
-        },
-        isolate_path + 'd.gen.json',
-      )
-
-    return 0
-
   def GetIsolateCommand(self, target, vals, gn_isolate_map):
     # This needs to mirror the settings in //build/config/ui.gni:
     # use_x11 = is_linux && !use_ozone.
     # TODO(dpranke): Figure out how to keep this in sync better.
-    use_x11 = (sys.platform == 'linux2' and
+    use_x11 = (self.platform == 'linux2' and
                not 'target_os="android"' in vals['gn_args'] and
                not 'use_ozone=true' in vals['gn_args'])
 
@@ -526,7 +503,7 @@ class MetaBuildWrapper(object):
     msan = 'is_msan=true' in vals['gn_args']
     tsan = 'is_tsan=true' in vals['gn_args']
 
-    executable_suffix = '.exe' if sys.platform == 'win32' else ''
+    executable_suffix = '.exe' if self.platform == 'win32' else ''
 
     test_type = gn_isolate_map[target]['type']
     cmdline = []
@@ -568,12 +545,19 @@ class MetaBuildWrapper(object):
       gtest_filter = gn_isolate_map[target]['gtest_filter']
       cmdline = [
           '../../testing/test_env.py',
-          'browser_tests<(EXECUTABLE_SUFFIX)',
+          './browser_tests' + executable_suffix,
           '--test-launcher-bot-mode',
           '--enable-gpu',
           '--test-launcher-jobs=1',
           '--gtest_filter=%s' % gtest_filter,
       ]
+    elif test_type == 'script':
+      extra_files = [
+          '../../testing/test_env.py'
+      ]
+      cmdline = [
+          '../../testing/test_env.py',
+      ] + ['../../' + self.ToSrcRelPath(gn_isolate_map[target]['script'])]
     elif test_type in ('raw'):
       extra_files = []
       cmdline = [
@@ -587,42 +571,40 @@ class MetaBuildWrapper(object):
     return cmdline, extra_files
 
   def ToAbsPath(self, build_path, *comps):
-    return os.path.join(self.chromium_src_dir,
-                        self.ToSrcRelPath(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."""
     # TODO: Support normal paths in addition to source-absolute paths.
     assert(path.startswith('//'))
-    return path[2:].replace('/', os.sep)
+    return path[2:].replace('/', self.sep)
 
   def ParseGYPConfigPath(self, path):
     rpath = self.ToSrcRelPath(path)
-    output_dir, _, config = rpath.rpartition('/')
-    self.CheckGYPConfigIsSupported(config, path)
-    return output_dir, config
-
-  def CheckGYPConfigIsSupported(self, config, path):
-    if config not in ('Debug', 'Release'):
-      if (sys.platform in ('win32', 'cygwin') and
-          config not in ('Debug_x64', 'Release_x64')):
-        raise MBErr('Unknown or unsupported config type "%s" in "%s"' %
-                    config, path)
-
-  def GYPCmd(self, output_dir, gyp_defines, config):
-    gyp_defines = gyp_defines.replace("$(goma_dir)", self.args.goma_dir)
+    output_dir, _, _ = rpath.rpartition(self.sep)
+    return output_dir
+
+  def GYPCmd(self, output_dir, gyp_defines):
+    goma_dir = self.args.goma_dir
+
+    # GYP uses shlex.split() to split the gyp defines into separate arguments,
+    # so we can support backslashes and and spaces in arguments by quoting
+    # them, even on Windows, where this normally wouldn't work.
+    if '\\' in goma_dir or ' ' in goma_dir:
+      goma_dir = "'%s'" % goma_dir
+    gyp_defines = gyp_defines.replace("$(goma_dir)", goma_dir)
+
     cmd = [
-        sys.executable,
-        os.path.join('build', 'gyp_chromium'),
+        self.executable,
+        self.PathJoin('build', 'gyp_chromium'),
         '-G',
         'output_dir=' + output_dir,
-        '-G',
-        'config=' + config,
     ]
-    for d in shlex.split(gyp_defines):
-      cmd += ['-D', d]
-    return cmd
+    env = os.environ.copy()
+    env['GYP_DEFINES'] = gyp_defines
+    return cmd, env
 
   def RunGNAnalyze(self, vals):
     # analyze runs before 'gn gen' now, so we need to run gn gen
@@ -670,11 +652,11 @@ class MetaBuildWrapper(object):
     try:
       cmd = self.GNCmd('refs', self.args.path[0]) + [
           '@%s' % response_file.name, '--all', '--as=output']
-      ret, out, _ = self.Run(cmd)
+      ret, out, _ = self.Run(cmd, force_verbose=False)
       if ret and not 'The input matches no targets' in out:
         self.WriteFailureAndRaise('gn refs returned %d: %s' % (ret, out),
                                   output_path)
-      build_dir = self.ToSrcRelPath(self.args.path[0]) + os.sep
+      build_dir = self.ToSrcRelPath(self.args.path[0]) + self.sep
       for output in out.splitlines():
         build_output = output.replace(build_dir, '')
         if build_output in inp['targets']:
@@ -682,14 +664,14 @@ class MetaBuildWrapper(object):
 
       cmd = self.GNCmd('refs', self.args.path[0]) + [
           '@%s' % response_file.name, '--all']
-      ret, out, _ = self.Run(cmd)
+      ret, out, _ = self.Run(cmd, force_verbose=False)
       if ret and not 'The input matches no targets' in out:
         self.WriteFailureAndRaise('gn refs returned %d: %s' % (ret, out),
                                   output_path)
       for label in out.splitlines():
         build_target = label[2:]
-        # We want to accept 'chrome/android:chrome_shell_apk' and
-        # just 'chrome_shell_apk'. This may result in too many targets
+        # We want to accept 'chrome/android:chrome_public_apk' and
+        # just 'chrome_public_apk'. This may result in too many targets
         # getting built, but we can adjust that later if need be.
         for input_target in inp['targets']:
           if (input_target == build_target or
@@ -703,15 +685,15 @@ class MetaBuildWrapper(object):
       # and both would be listed in the input, but we would only need
       # to specify target X as a build_target (whereas both X and Y are
       # targets). I'm not sure if that optimization is generally worth it.
-      self.WriteJSON({'targets': sorted(matching_targets),
-                      'build_targets': sorted(matching_targets),
+      self.WriteJSON({'targets': sorted(set(matching_targets)),
+                      'build_targets': sorted(set(matching_targets)),
                       'status': 'Found dependency'}, output_path)
     else:
       self.WriteJSON({'targets': [],
                       'build_targets': [],
                       'status': 'No dependency'}, output_path)
 
-    if not ret and self.args.verbose:
+    if self.args.verbose:
       outp = json.loads(self.ReadFile(output_path))
       self.Print()
       self.Print('analyze output:')
@@ -741,20 +723,37 @@ class MetaBuildWrapper(object):
 
   def WriteFailureAndRaise(self, msg, output_path):
     if output_path:
-      self.WriteJSON({'error': msg}, output_path)
+      self.WriteJSON({'error': msg}, output_path, force_verbose=True)
     raise MBErr(msg)
 
-  def WriteJSON(self, obj, path):
+  def WriteJSON(self, obj, path, force_verbose=False):
     try:
-      self.WriteFile(path, json.dumps(obj, indent=2, sort_keys=True) + '\n')
+      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 PrintCmd(self, cmd):
-    if cmd[0] == sys.executable:
+  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')
+
+    if cmd[0] == self.executable:
       cmd = ['python'] + cmd[1:]
-    self.Print(*[pipes.quote(c) for c in cmd])
+    self.Print(*[shell_quoter(arg) for arg in cmd])
 
   def PrintJSON(self, obj):
     self.Print(json.dumps(obj, indent=2, sort_keys=True))
@@ -763,14 +762,15 @@ class MetaBuildWrapper(object):
     # This function largely exists so it can be overridden for testing.
     print(*args, **kwargs)
 
-  def Run(self, cmd, env=None):
+  def Run(self, cmd, env=None, force_verbose=True):
     # This function largely exists so it can be overridden for testing.
-    if self.args.dryrun or self.args.verbose:
-      self.PrintCmd(cmd)
+    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)
-    if self.args.verbose:
+    if self.args.verbose or force_verbose:
       if out:
         self.Print(out, end='')
       if err:
@@ -799,6 +799,10 @@ class MetaBuildWrapper(object):
       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 ReadFile(self, path):
     # This function largely exists so it can be overriden for testing.
     with open(path) as fp:
@@ -808,13 +812,24 @@ class MetaBuildWrapper(object):
     # 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):
+  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:
+    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)
@@ -824,6 +839,35 @@ 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__':
   try:
     sys.exit(main(sys.argv[1:]))