/front/node_modules/node-gyp/gyp/pylib/gyp/xcode_emulation.py

# Copyright (c) 2012 Google Inc. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""
This module contains classes that help to emulate xcodebuild behavior on top of
other build systems, such as make and ninja.
"""

import copy
import gyp.common
import os
import os.path
import re
import shlex
import subprocess
import sys
import tempfile
from gyp.common import GypError

# Populated lazily by XcodeVersion, for efficiency, and to fix an issue when
# "xcodebuild" is called too quickly (it has been found to return incorrect
# version number).
XCODE_VERSION_CACHE = None

# Populated lazily by GetXcodeArchsDefault, to an |XcodeArchsDefault| instance
# corresponding to the installed version of Xcode.
XCODE_ARCHS_DEFAULT_CACHE = None


def XcodeArchsVariableMapping(archs, archs_including_64_bit=None):
  """Constructs a dictionary with expansion for $(ARCHS_STANDARD) variable,
  and optionally for $(ARCHS_STANDARD_INCLUDING_64_BIT)."""
  mapping = {'$(ARCHS_STANDARD)': archs}
  if archs_including_64_bit:
    mapping['$(ARCHS_STANDARD_INCLUDING_64_BIT)'] = archs_including_64_bit
  return mapping

class XcodeArchsDefault(object):
  """A class to resolve ARCHS variable from xcode_settings, resolving Xcode
  macros and implementing filtering by VALID_ARCHS. The expansion of macros
  depends on the SDKROOT used ("macosx", "iphoneos", "iphonesimulator") and
  on the version of Xcode.
  """

  # Match variable like $(ARCHS_STANDARD).
  variable_pattern = re.compile(r'\$\([a-zA-Z_][a-zA-Z0-9_]*\)$')

  def __init__(self, default, mac, iphonesimulator, iphoneos):
    self._default = (default,)
    self._archs = {'mac': mac, 'ios': iphoneos, 'iossim': iphonesimulator}

  def _VariableMapping(self, sdkroot):
    """Returns the dictionary of variable mapping depending on the SDKROOT."""
    sdkroot = sdkroot.lower()
    if 'iphoneos' in sdkroot:
      return self._archs['ios']
    elif 'iphonesimulator' in sdkroot:
      return self._archs['iossim']
    else:
      return self._archs['mac']

  def _ExpandArchs(self, archs, sdkroot):
    """Expands variables references in ARCHS, and remove duplicates."""
    variable_mapping = self._VariableMapping(sdkroot)
    expanded_archs = []
    for arch in archs:
      if self.variable_pattern.match(arch):
        variable = arch
        try:
          variable_expansion = variable_mapping[variable]
          for arch in variable_expansion:
            if arch not in expanded_archs:
              expanded_archs.append(arch)
        except KeyError as e:
          print 'Warning: Ignoring unsupported variable "%s".' % variable
      elif arch not in expanded_archs:
        expanded_archs.append(arch)
    return expanded_archs

  def ActiveArchs(self, archs, valid_archs, sdkroot):
    """Expands variables references in ARCHS, and filter by VALID_ARCHS if it
    is defined (if not set, Xcode accept any value in ARCHS, otherwise, only
    values present in VALID_ARCHS are kept)."""
    expanded_archs = self._ExpandArchs(archs or self._default, sdkroot or '')
    if valid_archs:
      filtered_archs = []
      for arch in expanded_archs:
        if arch in valid_archs:
          filtered_archs.append(arch)
      expanded_archs = filtered_archs
    return expanded_archs


def GetXcodeArchsDefault():
  """Returns the |XcodeArchsDefault| object to use to expand ARCHS for the
  installed version of Xcode. The default values used by Xcode for ARCHS
  and the expansion of the variables depends on the version of Xcode used.

  For all version anterior to Xcode 5.0 or posterior to Xcode 5.1 included
  uses $(ARCHS_STANDARD) if ARCHS is unset, while Xcode 5.0 to 5.0.2 uses
  $(ARCHS_STANDARD_INCLUDING_64_BIT). This variable was added to Xcode 5.0
  and deprecated with Xcode 5.1.

  For "macosx" SDKROOT, all version starting with Xcode 5.0 includes 64-bit
  architecture as part of $(ARCHS_STANDARD) and default to only building it.

  For "iphoneos" and "iphonesimulator" SDKROOT, 64-bit architectures are part
  of $(ARCHS_STANDARD_INCLUDING_64_BIT) from Xcode 5.0. From Xcode 5.1, they
  are also part of $(ARCHS_STANDARD).

  All thoses rules are coded in the construction of the |XcodeArchsDefault|
  object to use depending on the version of Xcode detected. The object is
  for performance reason."""
  global XCODE_ARCHS_DEFAULT_CACHE
  if XCODE_ARCHS_DEFAULT_CACHE:
    return XCODE_ARCHS_DEFAULT_CACHE
  xcode_version, _ = XcodeVersion()
  if xcode_version < '0500':
    XCODE_ARCHS_DEFAULT_CACHE = XcodeArchsDefault(
        '$(ARCHS_STANDARD)',
        XcodeArchsVariableMapping(['i386']),
        XcodeArchsVariableMapping(['i386']),
        XcodeArchsVariableMapping(['armv7']))
  elif xcode_version < '0510':
    XCODE_ARCHS_DEFAULT_CACHE = XcodeArchsDefault(
        '$(ARCHS_STANDARD_INCLUDING_64_BIT)',
        XcodeArchsVariableMapping(['x86_64'], ['x86_64']),
        XcodeArchsVariableMapping(['i386'], ['i386', 'x86_64']),
        XcodeArchsVariableMapping(
            ['armv7', 'armv7s'],
            ['armv7', 'armv7s', 'arm64']))
  else:
    XCODE_ARCHS_DEFAULT_CACHE = XcodeArchsDefault(
        '$(ARCHS_STANDARD)',
        XcodeArchsVariableMapping(['x86_64'], ['x86_64']),
        XcodeArchsVariableMapping(['i386', 'x86_64'], ['i386', 'x86_64']),
        XcodeArchsVariableMapping(
            ['armv7', 'armv7s', 'arm64'],
            ['armv7', 'armv7s', 'arm64']))
  return XCODE_ARCHS_DEFAULT_CACHE


class XcodeSettings(object):
  """A class that understands the gyp 'xcode_settings' object."""

  # Populated lazily by _SdkPath(). Shared by all XcodeSettings, so cached
  # at class-level for efficiency.
  _sdk_path_cache = {}
  _sdk_root_cache = {}

  # Populated lazily by GetExtraPlistItems(). Shared by all XcodeSettings, so
  # cached at class-level for efficiency.
  _plist_cache = {}

  # Populated lazily by GetIOSPostbuilds.  Shared by all XcodeSettings, so
  # cached at class-level for efficiency.
  _codesigning_key_cache = {}

  def __init__(self, spec):
    self.spec = spec

    self.isIOS = False

    # Per-target 'xcode_settings' are pushed down into configs earlier by gyp.
    # This means self.xcode_settings[config] always contains all settings
    # for that config -- the per-target settings as well. Settings that are
    # the same for all configs are implicitly per-target settings.
    self.xcode_settings = {}
    configs = spec['configurations']
    for configname, config in configs.iteritems():
      self.xcode_settings[configname] = config.get('xcode_settings', {})
      self._ConvertConditionalKeys(configname)
      if self.xcode_settings[configname].get('IPHONEOS_DEPLOYMENT_TARGET',
                                             None):
        self.isIOS = True

    # This is only non-None temporarily during the execution of some methods.
    self.configname = None

    # Used by _AdjustLibrary to match .a and .dylib entries in libraries.
    self.library_re = re.compile(r'^lib([^/]+)\.(a|dylib)$')

  def _ConvertConditionalKeys(self, configname):
    """Converts or warns on conditional keys.  Xcode supports conditional keys,
    such as CODE_SIGN_IDENTITY[sdk=iphoneos*].  This is a partial implementation
    with some keys converted while the rest force a warning."""
    settings = self.xcode_settings[configname]
    conditional_keys = [key for key in settings if key.endswith(']')]
    for key in conditional_keys:
      # If you need more, speak up at http://crbug.com/122592
      if key.endswith("[sdk=iphoneos*]"):
        if configname.endswith("iphoneos"):
          new_key = key.split("[")[0]
          settings[new_key] = settings[key]
      else:
        print 'Warning: Conditional keys not implemented, ignoring:', \
              ' '.join(conditional_keys)
      del settings[key]

  def _Settings(self):
    assert self.configname
    return self.xcode_settings[self.configname]

  def _Test(self, test_key, cond_key, default):
    return self._Settings().get(test_key, default) == cond_key

  def _Appendf(self, lst, test_key, format_str, default=None):
    if test_key in self._Settings():
      lst.append(format_str % str(self._Settings()[test_key]))
    elif default:
      lst.append(format_str % str(default))

  def _WarnUnimplemented(self, test_key):
    if test_key in self._Settings():
      print 'Warning: Ignoring not yet implemented key "%s".' % test_key

  def IsBinaryOutputFormat(self, configname):
    default = "binary" if self.isIOS else "xml"
    format = self.xcode_settings[configname].get('INFOPLIST_OUTPUT_FORMAT',
                                                 default)
    return format == "binary"

  def _IsBundle(self):
    return int(self.spec.get('mac_bundle', 0)) != 0

  def _IsIosAppExtension(self):
    return int(self.spec.get('ios_app_extension', 0)) != 0

  def _IsIosWatchKitExtension(self):
    return int(self.spec.get('ios_watchkit_extension', 0)) != 0

  def _IsIosWatchApp(self):
    return int(self.spec.get('ios_watch_app', 0)) != 0

  def GetFrameworkVersion(self):
    """Returns the framework version of the current target. Only valid for
    bundles."""
    assert self._IsBundle()
    return self.GetPerTargetSetting('FRAMEWORK_VERSION', default='A')

  def GetWrapperExtension(self):
    """Returns the bundle extension (.app, .framework, .plugin, etc).  Only
    valid for bundles."""
    assert self._IsBundle()
    if self.spec['type'] in ('loadable_module', 'shared_library'):
      default_wrapper_extension = {
        'loadable_module': 'bundle',
        'shared_library': 'framework',
      }[self.spec['type']]
      wrapper_extension = self.GetPerTargetSetting(
          'WRAPPER_EXTENSION', default=default_wrapper_extension)
      return '.' + self.spec.get('product_extension', wrapper_extension)
    elif self.spec['type'] == 'executable':
      if self._IsIosAppExtension() or self._IsIosWatchKitExtension():
        return '.' + self.spec.get('product_extension', 'appex')
      else:
        return '.' + self.spec.get('product_extension', 'app')
    else:
      assert False, "Don't know extension for '%s', target '%s'" % (
          self.spec['type'], self.spec['target_name'])

  def GetProductName(self):
    """Returns PRODUCT_NAME."""
    return self.spec.get('product_name', self.spec['target_name'])

  def GetFullProductName(self):
    """Returns FULL_PRODUCT_NAME."""
    if self._IsBundle():
      return self.GetWrapperName()
    else:
      return self._GetStandaloneBinaryPath()

  def GetWrapperName(self):
    """Returns the directory name of the bundle represented by this target.
    Only valid for bundles."""
    assert self._IsBundle()
    return self.GetProductName() + self.GetWrapperExtension()

  def GetBundleContentsFolderPath(self):
    """Returns the qualified path to the bundle's contents folder. E.g.
    Chromium.app/Contents or Foo.bundle/Versions/A. Only valid for bundles."""
    if self.isIOS:
      return self.GetWrapperName()
    assert self._IsBundle()
    if self.spec['type'] == 'shared_library':
      return os.path.join(
          self.GetWrapperName(), 'Versions', self.GetFrameworkVersion())
    else:
      # loadable_modules have a 'Contents' folder like executables.
      return os.path.join(self.GetWrapperName(), 'Contents')

  def GetBundleResourceFolder(self):
    """Returns the qualified path to the bundle's resource folder. E.g.
    Chromium.app/Contents/Resources. Only valid for bundles."""
    assert self._IsBundle()
    if self.isIOS:
      return self.GetBundleContentsFolderPath()
    return os.path.join(self.GetBundleContentsFolderPath(), 'Resources')

  def GetBundlePlistPath(self):
    """Returns the qualified path to the bundle's plist file. E.g.
    Chromium.app/Contents/Info.plist. Only valid for bundles."""
    assert self._IsBundle()
    if self.spec['type'] in ('executable', 'loadable_module'):
      return os.path.join(self.GetBundleContentsFolderPath(), 'Info.plist')
    else:
      return os.path.join(self.GetBundleContentsFolderPath(),
                          'Resources', 'Info.plist')

  def GetProductType(self):
    """Returns the PRODUCT_TYPE of this target."""
    if self._IsIosAppExtension():
      assert self._IsBundle(), ('ios_app_extension flag requires mac_bundle '
          '(target %s)' % self.spec['target_name'])
      return 'com.apple.product-type.app-extension'
    if self._IsIosWatchKitExtension():
      assert self._IsBundle(), ('ios_watchkit_extension flag requires '
          'mac_bundle (target %s)' % self.spec['target_name'])
      return 'com.apple.product-type.watchkit-extension'
    if self._IsIosWatchApp():
      assert self._IsBundle(), ('ios_watch_app flag requires mac_bundle '
          '(target %s)' % self.spec['target_name'])
      return 'com.apple.product-type.application.watchapp'
    if self._IsBundle():
      return {
        'executable': 'com.apple.product-type.application',
        'loadable_module': 'com.apple.product-type.bundle',
        'shared_library': 'com.apple.product-type.framework',
      }[self.spec['type']]
    else:
      return {
        'executable': 'com.apple.product-type.tool',
        'loadable_module': 'com.apple.product-type.library.dynamic',
        'shared_library': 'com.apple.product-type.library.dynamic',
        'static_library': 'com.apple.product-type.library.static',
      }[self.spec['type']]

  def GetMachOType(self):
    """Returns the MACH_O_TYPE of this target."""
    # Weird, but matches Xcode.
    if not self._IsBundle() and self.spec['type'] == 'executable':
      return ''
    return {
      'executable': 'mh_execute',
      'static_library': 'staticlib',
      'shared_library': 'mh_dylib',
      'loadable_module': 'mh_bundle',
    }[self.spec['type']]

  def _GetBundleBinaryPath(self):
    """Returns the name of the bundle binary of by this target.
    E.g. Chromium.app/Contents/MacOS/Chromium. Only valid for bundles."""
    assert self._IsBundle()
    if self.spec['type'] in ('shared_library') or self.isIOS:
      path = self.GetBundleContentsFolderPath()
    elif self.spec['type'] in ('executable', 'loadable_module'):
      path = os.path.join(self.GetBundleContentsFolderPath(), 'MacOS')
    return os.path.join(path, self.GetExecutableName())

  def _GetStandaloneExecutableSuffix(self):
    if 'product_extension' in self.spec:
      return '.' + self.spec['product_extension']
    return {
      'executable': '',
      'static_library': '.a',
      'shared_library': '.dylib',
      'loadable_module': '.so',
    }[self.spec['type']]

  def _GetStandaloneExecutablePrefix(self):
    return self.spec.get('product_prefix', {
      'executable': '',
      'static_library': 'lib',
      'shared_library': 'lib',
      # Non-bundled loadable_modules are called foo.so for some reason
      # (that is, .so and no prefix) with the xcode build -- match that.
      'loadable_module': '',
    }[self.spec['type']])

  def _GetStandaloneBinaryPath(self):
    """Returns the name of the non-bundle binary represented by this target.
    E.g. hello_world. Only valid for non-bundles."""
    assert not self._IsBundle()
    assert self.spec['type'] in (
        'executable', 'shared_library', 'static_library', 'loadable_module'), (
        'Unexpected type %s' % self.spec['type'])
    target = self.spec['target_name']
    if self.spec['type'] == 'static_library':
      if target[:3] == 'lib':
        target = target[3:]
    elif self.spec['type'] in ('loadable_module', 'shared_library'):
      if target[:3] == 'lib':
        target = target[3:]

    target_prefix = self._GetStandaloneExecutablePrefix()
    target = self.spec.get('product_name', target)
    target_ext = self._GetStandaloneExecutableSuffix()
    return target_prefix + target + target_ext

  def GetExecutableName(self):
    """Returns the executable name of the bundle represented by this target.
    E.g. Chromium."""
    if self._IsBundle():
      return self.spec.get('product_name', self.spec['target_name'])
    else:
      return self._GetStandaloneBinaryPath()

  def GetExecutablePath(self):
    """Returns the directory name of the bundle represented by this target. E.g.
    Chromium.app/Contents/MacOS/Chromium."""
    if self._IsBundle():
      return self._GetBundleBinaryPath()
    else:
      return self._GetStandaloneBinaryPath()

  def GetActiveArchs(self, configname):
    """Returns the architectures this target should be built for."""
    config_settings = self.xcode_settings[configname]
    xcode_archs_default = GetXcodeArchsDefault()
    return xcode_archs_default.ActiveArchs(
        config_settings.get('ARCHS'),
        config_settings.get('VALID_ARCHS'),
        config_settings.get('SDKROOT'))

  def _GetSdkVersionInfoItem(self, sdk, infoitem):
    # xcodebuild requires Xcode and can't run on Command Line Tools-only
    # systems from 10.7 onward.
    # Since the CLT has no SDK paths anyway, returning None is the
    # most sensible route and should still do the right thing.
    try:
      return GetStdout(['xcodebuild', '-version', '-sdk', sdk, infoitem])
    except:
      pass

  def _SdkRoot(self, configname):
    if configname is None:
      configname = self.configname
    return self.GetPerConfigSetting('SDKROOT', configname, default='')

  def _SdkPath(self, configname=None):
    sdk_root = self._SdkRoot(configname)
    if sdk_root.startswith('/'):
      return sdk_root
    return self._XcodeSdkPath(sdk_root)

  def _XcodeSdkPath(self, sdk_root):
    if sdk_root not in XcodeSettings._sdk_path_cache:
      sdk_path = self._GetSdkVersionInfoItem(sdk_root, 'Path')
      XcodeSettings._sdk_path_cache[sdk_root] = sdk_path
      if sdk_root:
        XcodeSettings._sdk_root_cache[sdk_path] = sdk_root
    return XcodeSettings._sdk_path_cache[sdk_root]

  def _AppendPlatformVersionMinFlags(self, lst):
    self._Appendf(lst, 'MACOSX_DEPLOYMENT_TARGET', '-mmacosx-version-min=%s')
    if 'IPHONEOS_DEPLOYMENT_TARGET' in self._Settings():
      # TODO: Implement this better?
      sdk_path_basename = os.path.basename(self._SdkPath())
      if sdk_path_basename.lower().startswith('iphonesimulator'):
        self._Appendf(lst, 'IPHONEOS_DEPLOYMENT_TARGET',
                      '-mios-simulator-version-min=%s')
      else:
        self._Appendf(lst, 'IPHONEOS_DEPLOYMENT_TARGET',
                      '-miphoneos-version-min=%s')

  def GetCflags(self, configname, arch=None):
    """Returns flags that need to be added to .c, .cc, .m, and .mm
    compilations."""
    # This functions (and the similar ones below) do not offer complete
    # emulation of all xcode_settings keys. They're implemented on demand.

    self.configname = configname
    cflags = []

    sdk_root = self._SdkPath()
    if 'SDKROOT' in self._Settings() and sdk_root:
      cflags.append('-isysroot %s' % sdk_root)

    if self._Test('CLANG_WARN_CONSTANT_CONVERSION', 'YES', default='NO'):
      cflags.append('-Wconstant-conversion')

    if self._Test('GCC_CHAR_IS_UNSIGNED_CHAR', 'YES', default='NO'):
      cflags.append('-funsigned-char')

    if self._Test('GCC_CW_ASM_SYNTAX', 'YES', default='YES'):
      cflags.append('-fasm-blocks')

    if 'GCC_DYNAMIC_NO_PIC' in self._Settings():
      if self._Settings()['GCC_DYNAMIC_NO_PIC'] == 'YES':
        cflags.append('-mdynamic-no-pic')
    else:
      pass
      # TODO: In this case, it depends on the target. xcode passes
      # mdynamic-no-pic by default for executable and possibly static lib
      # according to mento

    if self._Test('GCC_ENABLE_PASCAL_STRINGS', 'YES', default='YES'):
      cflags.append('-mpascal-strings')

    self._Appendf(cflags, 'GCC_OPTIMIZATION_LEVEL', '-O%s', default='s')

    if self._Test('GCC_GENERATE_DEBUGGING_SYMBOLS', 'YES', default='YES'):
      dbg_format = self._Settings().get('DEBUG_INFORMATION_FORMAT', 'dwarf')
      if dbg_format == 'dwarf':
        cflags.append('-gdwarf-2')
      elif dbg_format == 'stabs':
        raise NotImplementedError('stabs debug format is not supported yet.')
      elif dbg_format == 'dwarf-with-dsym':
        cflags.append('-gdwarf-2')
      else:
        raise NotImplementedError('Unknown debug format %s' % dbg_format)

    if self._Settings().get('GCC_STRICT_ALIASING') == 'YES':
      cflags.append('-fstrict-aliasing')
    elif self._Settings().get('GCC_STRICT_ALIASING') == 'NO':
      cflags.append('-fno-strict-aliasing')

    if self._Test('GCC_SYMBOLS_PRIVATE_EXTERN', 'YES', default='NO'):
      cflags.append('-fvisibility=hidden')

    if self._Test('GCC_TREAT_WARNINGS_AS_ERRORS', 'YES', default='NO'):
      cflags.append('-Werror')

    if self._Test('GCC_WARN_ABOUT_MISSING_NEWLINE', 'YES', default='NO'):
      cflags.append('-Wnewline-eof')

    # In Xcode, this is only activated when GCC_COMPILER_VERSION is clang or
    # llvm-gcc. It also requires a fairly recent libtool, and
    # if the system clang isn't used, DYLD_LIBRARY_PATH needs to contain the
    # path to the libLTO.dylib that matches the used clang.
    if self._Test('LLVM_LTO', 'YES', default='NO'):
      cflags.append('-flto')

    self._AppendPlatformVersionMinFlags(cflags)

    # TODO:
    if self._Test('COPY_PHASE_STRIP', 'YES', default='NO'):
      self._WarnUnimplemented('COPY_PHASE_STRIP')
    self._WarnUnimplemented('GCC_DEBUGGING_SYMBOLS')
    self._WarnUnimplemented('GCC_ENABLE_OBJC_EXCEPTIONS')

    # TODO: This is exported correctly, but assigning to it is not supported.
    self._WarnUnimplemented('MACH_O_TYPE')
    self._WarnUnimplemented('PRODUCT_TYPE')

    if arch is not None:
      archs = [arch]
    else:
      assert self.configname
      archs = self.GetActiveArchs(self.configname)
    if len(archs) != 1:
      # TODO: Supporting fat binaries will be annoying.
      self._WarnUnimplemented('ARCHS')
      archs = ['i386']
    cflags.append('-arch ' + archs[0])

    if archs[0] in ('i386', 'x86_64'):
      if self._Test('GCC_ENABLE_SSE3_EXTENSIONS', 'YES', default='NO'):
        cflags.append('-msse3')
      if self._Test('GCC_ENABLE_SUPPLEMENTAL_SSE3_INSTRUCTIONS', 'YES',
                    default='NO'):
        cflags.append('-mssse3')  # Note 3rd 's'.
      if self._Test('GCC_ENABLE_SSE41_EXTENSIONS', 'YES', default='NO'):
        cflags.append('-msse4.1')
      if self._Test('GCC_ENABLE_SSE42_EXTENSIONS', 'YES', default='NO'):
        cflags.append('-msse4.2')

    cflags += self._Settings().get('WARNING_CFLAGS', [])

    if sdk_root:
      framework_root = sdk_root
    else:
      framework_root = ''
    config = self.spec['configurations'][self.configname]
    framework_dirs = config.get('mac_framework_dirs', [])
    for directory in framework_dirs:
      cflags.append('-F' + directory.replace('$(SDKROOT)', framework_root))

    self.configname = None
    return cflags

  def GetCflagsC(self, configname):
    """Returns flags that need to be added to .c, and .m compilations."""
    self.configname = configname
    cflags_c = []
    if self._Settings().get('GCC_C_LANGUAGE_STANDARD', '') == 'ansi':
      cflags_c.append('-ansi')
    else:
      self._Appendf(cflags_c, 'GCC_C_LANGUAGE_STANDARD', '-std=%s')
    cflags_c += self._Settings().get('OTHER_CFLAGS', [])
    self.configname = None
    return cflags_c

  def GetCflagsCC(self, configname):
    """Returns flags that need to be added to .cc, and .mm compilations."""
    self.configname = configname
    cflags_cc = []

    clang_cxx_language_standard = self._Settings().get(
        'CLANG_CXX_LANGUAGE_STANDARD')
    # Note: Don't make c++0x to c++11 so that c++0x can be used with older
    # clangs that don't understand c++11 yet (like Xcode 4.2's).
    if clang_cxx_language_standard:
      cflags_cc.append('-std=%s' % clang_cxx_language_standard)

    self._Appendf(cflags_cc, 'CLANG_CXX_LIBRARY', '-stdlib=%s')

    if self._Test('GCC_ENABLE_CPP_RTTI', 'NO', default='YES'):
      cflags_cc.append('-fno-rtti')
    if self._Test('GCC_ENABLE_CPP_EXCEPTIONS', 'NO', default='YES'):
      cflags_cc.append('-fno-exceptions')
    if self._Test('GCC_INLINES_ARE_PRIVATE_EXTERN', 'YES', default='NO'):
      cflags_cc.append('-fvisibility-inlines-hidden')
    if self._Test('GCC_THREADSAFE_STATICS', 'NO', default='YES'):
      cflags_cc.append('-fno-threadsafe-statics')
    # Note: This flag is a no-op for clang, it only has an effect for gcc.
    if self._Test('GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO', 'NO', default='YES'):
      cflags_cc.append('-Wno-invalid-offsetof')

    other_ccflags = []

    for flag in self._Settings().get('OTHER_CPLUSPLUSFLAGS', ['$(inherited)']):
      # TODO: More general variable expansion. Missing in many other places too.
      if flag in ('$inherited', '$(inherited)', '${inherited}'):
        flag = '$OTHER_CFLAGS'
      if flag in ('$OTHER_CFLAGS', '$(OTHER_CFLAGS)', '${OTHER_CFLAGS}'):
        other_ccflags += self._Settings().get('OTHER_CFLAGS', [])
      else:
        other_ccflags.append(flag)
    cflags_cc += other_ccflags

    self.configname = None
    return cflags_cc

  def _AddObjectiveCGarbageCollectionFlags(self, flags):
    gc_policy = self._Settings().get('GCC_ENABLE_OBJC_GC', 'unsupported')
    if gc_policy == 'supported':
      flags.append('-fobjc-gc')
    elif gc_policy == 'required':
      flags.append('-fobjc-gc-only')

  def _AddObjectiveCARCFlags(self, flags):
    if self._Test('CLANG_ENABLE_OBJC_ARC', 'YES', default='NO'):
      flags.append('-fobjc-arc')

  def _AddObjectiveCMissingPropertySynthesisFlags(self, flags):
    if self._Test('CLANG_WARN_OBJC_MISSING_PROPERTY_SYNTHESIS',
                  'YES', default='NO'):
      flags.append('-Wobjc-missing-property-synthesis')

  def GetCflagsObjC(self, configname):
    """Returns flags that need to be added to .m compilations."""
    self.configname = configname
    cflags_objc = []
    self._AddObjectiveCGarbageCollectionFlags(cflags_objc)
    self._AddObjectiveCARCFlags(cflags_objc)
    self._AddObjectiveCMissingPropertySynthesisFlags(cflags_objc)
    self.configname = None
    return cflags_objc

  def GetCflagsObjCC(self, configname):
    """Returns flags that need to be added to .mm compilations."""
    self.configname = configname
    cflags_objcc = []
    self._AddObjectiveCGarbageCollectionFlags(cflags_objcc)
    self._AddObjectiveCARCFlags(cflags_objcc)
    self._AddObjectiveCMissingPropertySynthesisFlags(cflags_objcc)
    if self._Test('GCC_OBJC_CALL_CXX_CDTORS', 'YES', default='NO'):
      cflags_objcc.append('-fobjc-call-cxx-cdtors')
    self.configname = None
    return cflags_objcc

  def GetInstallNameBase(self):
    """Return DYLIB_INSTALL_NAME_BASE for this target."""
    # Xcode sets this for shared_libraries, and for nonbundled loadable_modules.
    if (self.spec['type'] != 'shared_library' and
        (self.spec['type'] != 'loadable_module' or self._IsBundle())):
      return None
    install_base = self.GetPerTargetSetting(
        'DYLIB_INSTALL_NAME_BASE',
        default='/Library/Frameworks' if self._IsBundle() else '/usr/local/lib')
    return install_base

  def _StandardizePath(self, path):
    """Do :standardizepath processing for path."""
    # I'm not quite sure what :standardizepath does. Just call normpath(),
    # but don't let @executable_path/../foo collapse to foo.
    if '/' in path:
      prefix, rest = '', path
      if path.startswith('@'):
        prefix, rest = path.split('/', 1)
      rest = os.path.normpath(rest)  # :standardizepath
      path = os.path.join(prefix, rest)
    return path

  def GetInstallName(self):
    """Return LD_DYLIB_INSTALL_NAME for this target."""
    # Xcode sets this for shared_libraries, and for nonbundled loadable_modules.
    if (self.spec['type'] != 'shared_library' and
        (self.spec['type'] != 'loadable_module' or self._IsBundle())):
      return None

    default_install_name = \
        '$(DYLIB_INSTALL_NAME_BASE:standardizepath)/$(EXECUTABLE_PATH)'
    install_name = self.GetPerTargetSetting(
        'LD_DYLIB_INSTALL_NAME', default=default_install_name)

    # Hardcode support for the variables used in chromium for now, to
    # unblock people using the make build.
    if '$' in install_name:
      assert install_name in ('$(DYLIB_INSTALL_NAME_BASE:standardizepath)/'
          '$(WRAPPER_NAME)/$(PRODUCT_NAME)', default_install_name), (
          'Variables in LD_DYLIB_INSTALL_NAME are not generally supported '
          'yet in target \'%s\' (got \'%s\')' %
              (self.spec['target_name'], install_name))

      install_name = install_name.replace(
          '$(DYLIB_INSTALL_NAME_BASE:standardizepath)',
          self._StandardizePath(self.GetInstallNameBase()))
      if self._IsBundle():
        # These are only valid for bundles, hence the |if|.
        install_name = install_name.replace(
            '$(WRAPPER_NAME)', self.GetWrapperName())
        install_name = install_name.replace(
            '$(PRODUCT_NAME)', self.GetProductName())
      else:
        assert '$(WRAPPER_NAME)' not in install_name
        assert '$(PRODUCT_NAME)' not in install_name

      install_name = install_name.replace(
          '$(EXECUTABLE_PATH)', self.GetExecutablePath())
    return install_name

  def _MapLinkerFlagFilename(self, ldflag, gyp_to_build_path):
    """Checks if ldflag contains a filename and if so remaps it from
    gyp-directory-relative to build-directory-relative."""
    # This list is expanded on demand.
    # They get matched as:
    #   -exported_symbols_list file
    #   -Wl,exported_symbols_list file
    #   -Wl,exported_symbols_list,file
    LINKER_FILE = r'(\S+)'
    WORD = r'\S+'
    linker_flags = [
      ['-exported_symbols_list', LINKER_FILE],    # Needed for NaCl.
      ['-unexported_symbols_list', LINKER_FILE],
      ['-reexported_symbols_list', LINKER_FILE],
      ['-sectcreate', WORD, WORD, LINKER_FILE],   # Needed for remoting.
    ]
    for flag_pattern in linker_flags:
      regex = re.compile('(?:-Wl,)?' + '[ ,]'.join(flag_pattern))
      m = regex.match(ldflag)
      if m:
        ldflag = ldflag[:m.start(1)] + gyp_to_build_path(m.group(1)) + \
                 ldflag[m.end(1):]
    # Required for ffmpeg (no idea why they don't use LIBRARY_SEARCH_PATHS,
    # TODO(thakis): Update ffmpeg.gyp):
    if ldflag.startswith('-L'):
      ldflag = '-L' + gyp_to_build_path(ldflag[len('-L'):])
    return ldflag

  def GetLdflags(self, configname, product_dir, gyp_to_build_path, arch=None):
    """Returns flags that need to be passed to the linker.

    Args:
        configname: The name of the configuration to get ld flags for.
        product_dir: The directory where products such static and dynamic
            libraries are placed. This is added to the library search path.
        gyp_to_build_path: A function that converts paths relative to the
            current gyp file to paths relative to the build direcotry.
    """
    self.configname = configname
    ldflags = []

    # The xcode build is relative to a gyp file's directory, and OTHER_LDFLAGS
    # can contain entries that depend on this. Explicitly absolutify these.
    for ldflag in self._Settings().get('OTHER_LDFLAGS', []):
      ldflags.append(self._MapLinkerFlagFilename(ldflag, gyp_to_build_path))

    if self._Test('DEAD_CODE_STRIPPING', 'YES', default='NO'):
      ldflags.append('-Wl,-dead_strip')

    if self._Test('PREBINDING', 'YES', default='NO'):
      ldflags.append('-Wl,-prebind')

    self._Appendf(
        ldflags, 'DYLIB_COMPATIBILITY_VERSION', '-compatibility_version %s')
    self._Appendf(
        ldflags, 'DYLIB_CURRENT_VERSION', '-current_version %s')

    self._AppendPlatformVersionMinFlags(ldflags)

    if 'SDKROOT' in self._Settings() and self._SdkPath():
      ldflags.append('-isysroot ' + self._SdkPath())

    for library_path in self._Settings().get('LIBRARY_SEARCH_PATHS', []):
      ldflags.append('-L' + gyp_to_build_path(library_path))

    if 'ORDER_FILE' in self._Settings():
      ldflags.append('-Wl,-order_file ' +
                     '-Wl,' + gyp_to_build_path(
                                  self._Settings()['ORDER_FILE']))

    if arch is not None:
      archs = [arch]
    else:
      assert self.configname
      archs = self.GetActiveArchs(self.configname)
    if len(archs) != 1:
      # TODO: Supporting fat binaries will be annoying.
      self._WarnUnimplemented('ARCHS')
      archs = ['i386']
    ldflags.append('-arch ' + archs[0])

    # Xcode adds the product directory by default.
    ldflags.append('-L' + product_dir)

    install_name = self.GetInstallName()
    if install_name and self.spec['type'] != 'loadable_module':
      ldflags.append('-install_name ' + install_name.replace(' ', r'\ '))

    for rpath in self._Settings().get('LD_RUNPATH_SEARCH_PATHS', []):
      ldflags.append('-Wl,-rpath,' + rpath)

    sdk_root = self._SdkPath()
    if not sdk_root:
      sdk_root = ''
    config = self.spec['configurations'][self.configname]
    framework_dirs = config.get('mac_framework_dirs', [])
    for directory in framework_dirs:
      ldflags.append('-F' + directory.replace('$(SDKROOT)', sdk_root))

    is_extension = self._IsIosAppExtension() or self._IsIosWatchKitExtension()
    if sdk_root and is_extension:
      # Adds the link flags for extensions. These flags are common for all
      # extensions and provide loader and main function.
      # These flags reflect the compilation options used by xcode to compile
      # extensions.
      ldflags.append('-lpkstart')
      if XcodeVersion() < '0900':
        ldflags.append(sdk_root +
            '/System/Library/PrivateFrameworks/PlugInKit.framework/PlugInKit')
      ldflags.append('-fapplication-extension')
      ldflags.append('-Xlinker -rpath '
          '-Xlinker @executable_path/../../Frameworks')

    self._Appendf(ldflags, 'CLANG_CXX_LIBRARY', '-stdlib=%s')

    self.configname = None
    return ldflags

  def GetLibtoolflags(self, configname):
    """Returns flags that need to be passed to the static linker.

    Args:
        configname: The name of the configuration to get ld flags for.
    """
    self.configname = configname
    libtoolflags = []

    for libtoolflag in self._Settings().get('OTHER_LDFLAGS', []):
      libtoolflags.append(libtoolflag)
    # TODO(thakis): ARCHS?

    self.configname = None
    return libtoolflags

  def GetPerTargetSettings(self):
    """Gets a list of all the per-target settings. This will only fetch keys
    whose values are the same across all configurations."""
    first_pass = True
    result = {}
    for configname in sorted(self.xcode_settings.keys()):
      if first_pass:
        result = dict(self.xcode_settings[configname])
        first_pass = False
      else:
        for key, value in self.xcode_settings[configname].iteritems():
          if key not in result:
            continue
          elif result[key] != value:
            del result[key]
    return result

  def GetPerConfigSetting(self, setting, configname, default=None):
    if configname in self.xcode_settings:
      return self.xcode_settings[configname].get(setting, default)
    else:
      return self.GetPerTargetSetting(setting, default)

  def GetPerTargetSetting(self, setting, default=None):
    """Tries to get xcode_settings.setting from spec. Assumes that the setting
       has the same value in all configurations and throws otherwise."""
    is_first_pass = True
    result = None
    for configname in sorted(self.xcode_settings.keys()):
      if is_first_pass:
        result = self.xcode_settings[configname].get(setting, None)
        is_first_pass = False
      else:
        assert result == self.xcode_settings[configname].get(setting, None), (
            "Expected per-target setting for '%s', got per-config setting "
            "(target %s)" % (setting, self.spec['target_name']))
    if result is None:
      return default
    return result

  def _GetStripPostbuilds(self, configname, output_binary, quiet):
    """Returns a list of shell commands that contain the shell commands
    neccessary to strip this target's binary. These should be run as postbuilds
    before the actual postbuilds run."""
    self.configname = configname

    result = []
    if (self._Test('DEPLOYMENT_POSTPROCESSING', 'YES', default='NO') and
        self._Test('STRIP_INSTALLED_PRODUCT', 'YES', default='NO')):

      default_strip_style = 'debugging'
      if self.spec['type'] == 'loadable_module' and self._IsBundle():
        default_strip_style = 'non-global'
      elif self.spec['type'] == 'executable':
        default_strip_style = 'all'

      strip_style = self._Settings().get('STRIP_STYLE', default_strip_style)
      strip_flags = {
        'all': '',
        'non-global': '-x',
        'debugging': '-S',
      }[strip_style]

      explicit_strip_flags = self._Settings().get('STRIPFLAGS', '')
      if explicit_strip_flags:
        strip_flags += ' ' + _NormalizeEnvVarReferences(explicit_strip_flags)

      if not quiet:
        result.append('echo STRIP\\(%s\\)' % self.spec['target_name'])
      result.append('strip %s %s' % (strip_flags, output_binary))

    self.configname = None
    return result

  def _GetDebugInfoPostbuilds(self, configname, output, output_binary, quiet):
    """Returns a list of shell commands that contain the shell commands
    neccessary to massage this target's debug information. These should be run
    as postbuilds before the actual postbuilds run."""
    self.configname = configname

    # For static libraries, no dSYMs are created.
    result = []
    if (self._Test('GCC_GENERATE_DEBUGGING_SYMBOLS', 'YES', default='YES') and
        self._Test(
            'DEBUG_INFORMATION_FORMAT', 'dwarf-with-dsym', default='dwarf') and
        self.spec['type'] != 'static_library'):
      if not quiet:
        result.append('echo DSYMUTIL\\(%s\\)' % self.spec['target_name'])
      result.append('dsymutil %s -o %s' % (output_binary, output + '.dSYM'))

    self.configname = None
    return result

  def _GetTargetPostbuilds(self, configname, output, output_binary,
                           quiet=False):
    """Returns a list of shell commands that contain the shell commands
    to run as postbuilds for this target, before the actual postbuilds."""
    # dSYMs need to build before stripping happens.
    return (
        self._GetDebugInfoPostbuilds(configname, output, output_binary, quiet) +
        self._GetStripPostbuilds(configname, output_binary, quiet))

  def _GetIOSPostbuilds(self, configname, output_binary):
    """Return a shell command to codesign the iOS output binary so it can
    be deployed to a device.  This should be run as the very last step of the
    build."""
    if not (self.isIOS and self.spec['type'] == 'executable'):
      return []

    settings = self.xcode_settings[configname]
    key = self._GetIOSCodeSignIdentityKey(settings)
    if not key:
      return []

    # Warn for any unimplemented signing xcode keys.
    unimpl = ['OTHER_CODE_SIGN_FLAGS']
    unimpl = set(unimpl) & set(self.xcode_settings[configname].keys())
    if unimpl:
      print 'Warning: Some codesign keys not implemented, ignoring: %s' % (
          ', '.join(sorted(unimpl)))

    return ['%s code-sign-bundle "%s" "%s" "%s" "%s"' % (
        os.path.join('${TARGET_BUILD_DIR}', 'gyp-mac-tool'), key,
        settings.get('CODE_SIGN_RESOURCE_RULES_PATH', ''),
        settings.get('CODE_SIGN_ENTITLEMENTS', ''),
        settings.get('PROVISIONING_PROFILE', ''))
    ]

  def _GetIOSCodeSignIdentityKey(self, settings):
    identity = settings.get('CODE_SIGN_IDENTITY')
    if not identity:
      return None
    if identity not in XcodeSettings._codesigning_key_cache:
      output = subprocess.check_output(
          ['security', 'find-identity', '-p', 'codesigning', '-v'])
      for line in output.splitlines():
        if identity in line:
          fingerprint = line.split()[1]
          cache = XcodeSettings._codesigning_key_cache
          assert identity not in cache or fingerprint == cache[identity], (
              "Multiple codesigning fingerprints for identity: %s" % identity)
          XcodeSettings._codesigning_key_cache[identity] = fingerprint
    return XcodeSettings._codesigning_key_cache.get(identity, '')

  def AddImplicitPostbuilds(self, configname, output, output_binary,
                            postbuilds=[], quiet=False):
    """Returns a list of shell commands that should run before and after
    |postbuilds|."""
    assert output_binary is not None
    pre = self._GetTargetPostbuilds(configname, output, output_binary, quiet)
    post = self._GetIOSPostbuilds(configname, output_binary)
    return pre + postbuilds + post

  def _AdjustLibrary(self, library, config_name=None):
    if library.endswith('.framework'):
      l = '-framework ' + os.path.splitext(os.path.basename(library))[0]
    else:
      m = self.library_re.match(library)
      if m:
        l = '-l' + m.group(1)
      else:
        l = library

    sdk_root = self._SdkPath(config_name)
    if not sdk_root:
      sdk_root = ''
    # Xcode 7 started shipping with ".tbd" (text based stubs) files instead of
    # ".dylib" without providing a real support for them. What it does, for
    # "/usr/lib" libraries, is do "-L/usr/lib -lname" which is dependent on the
    # library order and cause collision when building Chrome.
    #
    # Instead substitude ".tbd" to ".dylib" in the generated project when the
    # following conditions are both true:
    # - library is referenced in the gyp file as "$(SDKROOT)/**/*.dylib",
    # - the ".dylib" file does not exists but a ".tbd" file do.
    library = l.replace('$(SDKROOT)', sdk_root)
    if l.startswith('$(SDKROOT)'):
      basename, ext = os.path.splitext(library)
      if ext == '.dylib' and not os.path.exists(library):
        tbd_library = basename + '.tbd'
        if os.path.exists(tbd_library):
          library = tbd_library
    return library

  def AdjustLibraries(self, libraries, config_name=None):
    """Transforms entries like 'Cocoa.framework' in libraries into entries like
    '-framework Cocoa', 'libcrypto.dylib' into '-lcrypto', etc.
    """
    libraries = [self._AdjustLibrary(library, config_name)
                 for library in libraries]
    return libraries

  def _BuildMachineOSBuild(self):
    return GetStdout(['sw_vers', '-buildVersion'])

  def _XcodeIOSDeviceFamily(self, configname):
    family = self.xcode_settings[configname].get('TARGETED_DEVICE_FAMILY', '1')
    return [int(x) for x in family.split(',')]

  def GetExtraPlistItems(self, configname=None):
    """Returns a dictionary with extra items to insert into Info.plist."""
    if configname not in XcodeSettings._plist_cache:
      cache = {}
      cache['BuildMachineOSBuild'] = self._BuildMachineOSBuild()

      xcode, xcode_build = XcodeVersion()
      cache['DTXcode'] = xcode
      cache['DTXcodeBuild'] = xcode_build

      sdk_root = self._SdkRoot(configname)
      if not sdk_root:
        sdk_root = self._DefaultSdkRoot()
      cache['DTSDKName'] = sdk_root
      if xcode >= '0430':
        cache['DTSDKBuild'] = self._GetSdkVersionInfoItem(
            sdk_root, 'ProductBuildVersion')
      else:
        cache['DTSDKBuild'] = cache['BuildMachineOSBuild']

      if self.isIOS:
        cache['DTPlatformName'] = cache['DTSDKName']
        if configname.endswith("iphoneos"):
          cache['DTPlatformVersion'] = self._GetSdkVersionInfoItem(
              sdk_root, 'ProductVersion')
          cache['CFBundleSupportedPlatforms'] = ['iPhoneOS']
        else:
          cache['CFBundleSupportedPlatforms'] = ['iPhoneSimulator']
      XcodeSettings._plist_cache[configname] = cache

    # Include extra plist items that are per-target, not per global
    # XcodeSettings.
    items = dict(XcodeSettings._plist_cache[configname])
    if self.isIOS:
      items['UIDeviceFamily'] = self._XcodeIOSDeviceFamily(configname)
    return items

  def _DefaultSdkRoot(self):
    """Returns the default SDKROOT to use.

    Prior to version 5.0.0, if SDKROOT was not explicitly set in the Xcode
    project, then the environment variable was empty. Starting with this
    version, Xcode uses the name of the newest SDK installed.
    """
    xcode_version, xcode_build = XcodeVersion()
    if xcode_version < '0500':
      return ''
    default_sdk_path = self._XcodeSdkPath('')
    default_sdk_root = XcodeSettings._sdk_root_cache.get(default_sdk_path)
    if default_sdk_root:
      return default_sdk_root
    try:
      all_sdks = GetStdout(['xcodebuild', '-showsdks'])
    except:
      # If xcodebuild fails, there will be no valid SDKs
      return ''
    for line in all_sdks.splitlines():
      items = line.split()
      if len(items) >= 3 and items[-2] == '-sdk':
        sdk_root = items[-1]
        sdk_path = self._XcodeSdkPath(sdk_root)
        if sdk_path == default_sdk_path:
          return sdk_root
    return ''


class MacPrefixHeader(object):
  """A class that helps with emulating Xcode's GCC_PREFIX_HEADER feature.

  This feature consists of several pieces:
  * If GCC_PREFIX_HEADER is present, all compilations in that project get an
    additional |-include path_to_prefix_header| cflag.
  * If GCC_PRECOMPILE_PREFIX_HEADER is present too, then the prefix header is
    instead compiled, and all other compilations in the project get an
    additional |-include path_to_compiled_header| instead.
    + Compiled prefix headers have the extension gch. There is one gch file for
      every language used in the project (c, cc, m, mm), since gch files for
      different languages aren't compatible.
    + gch files themselves are built with the target's normal cflags, but they
      obviously don't get the |-include| flag. Instead, they need a -x flag that
      describes their language.
    + All o files in the target need to depend on the gch file, to make sure
      it's built before any o file is built.

  This class helps with some of these tasks, but it needs help from the build
  system for writing dependencies to the gch files, for writing build commands
  for the gch files, and for figuring out the location of the gch files.
  """
  def __init__(self, xcode_settings,
               gyp_path_to_build_path, gyp_path_to_build_output):
    """If xcode_settings is None, all methods on this class are no-ops.

    Args:
        gyp_path_to_build_path: A function that takes a gyp-relative path,
            and returns a path relative to the build directory.
        gyp_path_to_build_output: A function that takes a gyp-relative path and
            a language code ('c', 'cc', 'm', or 'mm'), and that returns a path
            to where the output of precompiling that path for that language
            should be placed (without the trailing '.gch').
    """
    # This doesn't support per-configuration prefix headers. Good enough
    # for now.
    self.header = None
    self.compile_headers = False
    if xcode_settings:
      self.header = xcode_settings.GetPerTargetSetting('GCC_PREFIX_HEADER')
      self.compile_headers = xcode_settings.GetPerTargetSetting(
          'GCC_PRECOMPILE_PREFIX_HEADER', default='NO') != 'NO'
    self.compiled_headers = {}
    if self.header:
      if self.compile_headers:
        for lang in ['c', 'cc', 'm', 'mm']:
          self.compiled_headers[lang] = gyp_path_to_build_output(
              self.header, lang)
      self.header = gyp_path_to_build_path(self.header)

  def _CompiledHeader(self, lang, arch):
    assert self.compile_headers
    h = self.compiled_headers[lang]
    if arch:
      h += '.' + arch
    return h

  def GetInclude(self, lang, arch=None):
    """Gets the cflags to include the prefix header for language |lang|."""
    if self.compile_headers and lang in self.compiled_headers:
      return '-include %s' % self._CompiledHeader(lang, arch)
    elif self.header:
      return '-include %s' % self.header
    else:
      return ''

  def _Gch(self, lang, arch):
    """Returns the actual file name of the prefix header for language |lang|."""
    assert self.compile_headers
    return self._CompiledHeader(lang, arch) + '.gch'

  def GetObjDependencies(self, sources, objs, arch=None):
    """Given a list of source files and the corresponding object files, returns
    a list of (source, object, gch) tuples, where |gch| is the build-directory
    relative path to the gch file each object file depends on.  |compilable[i]|
    has to be the source file belonging to |objs[i]|."""
    if not self.header or not self.compile_headers:
      return []

    result = []
    for source, obj in zip(sources, objs):
      ext = os.path.splitext(source)[1]
      lang = {
        '.c': 'c',
        '.cpp': 'cc', '.cc': 'cc', '.cxx': 'cc',
        '.m': 'm',
        '.mm': 'mm',
      }.get(ext, None)
      if lang:
        result.append((source, obj, self._Gch(lang, arch)))
    return result

  def GetPchBuildCommands(self, arch=None):
    """Returns [(path_to_gch, language_flag, language, header)].
    |path_to_gch| and |header| are relative to the build directory.
    """
    if not self.header or not self.compile_headers:
      return []
    return [
      (self._Gch('c', arch), '-x c-header', 'c', self.header),
      (self._Gch('cc', arch), '-x c++-header', 'cc', self.header),
      (self._Gch('m', arch), '-x objective-c-header', 'm', self.header),
      (self._Gch('mm', arch), '-x objective-c++-header', 'mm', self.header),
    ]


def XcodeVersion():
  """Returns a tuple of version and build version of installed Xcode."""
  # `xcodebuild -version` output looks like
  #    Xcode 4.6.3
  #    Build version 4H1503
  # or like
  #    Xcode 3.2.6
  #    Component versions: DevToolsCore-1809.0; DevToolsSupport-1806.0
  #    BuildVersion: 10M2518
  # Convert that to '0463', '4H1503'.
  global XCODE_VERSION_CACHE
  if XCODE_VERSION_CACHE:
    return XCODE_VERSION_CACHE
  try:
    version_list = GetStdout(['xcodebuild', '-version']).splitlines()
    # In some circumstances xcodebuild exits 0 but doesn't return
    # the