path: root/tools/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.path
import re
import shlex
import subprocess
import sys
from gyp.common import GypError

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 = {}

  # 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 _IsBundle(self):
    return int(self.spec.get('mac_bundle', 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':
      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._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."""
    # TODO: Look at VALID_ARCHS, ONLY_ACTIVE_ARCH; possibly set
    # CURRENT_ARCH / NATIVE_ARCH env vars?
    return self.xcode_settings[configname].get('ARCHS', ['i386'])

  def _GetStdout(self, cmdlist):
    job = subprocess.Popen(cmdlist, stdout=subprocess.PIPE)
    out = job.communicate()[0]
    if job.returncode != 0:
      sys.stderr.write(out + '\n')
      raise GypError('Error %d running %s' % (job.returncode, cmdlist[0]))
    return out.rstrip('\n')

  def _GetSdkVersionInfoItem(self, sdk, infoitem):
    return self._GetStdout(['xcodebuild', '-version', '-sdk', sdk, infoitem])

  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
    if sdk_root not in XcodeSettings._sdk_path_cache:
      XcodeSettings._sdk_path_cache[sdk_root] = self._GetSdkVersionInfoItem(
          sdk_root, 'Path')
    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():
      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')

    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:
      archs = self._Settings().get('ARCHS', ['i386'])
    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', [])

    config = self.spec['configurations'][self.configname]
    framework_dirs = config.get('mac_framework_dirs', [])
    for directory in framework_dirs:
      cflags.append('-F' + directory.replace('$(SDKROOT)', sdk_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 = '(\S+)'
    WORD = '\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():
      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:
      archs = self._Settings().get('ARCHS', ['i386'])
    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)

    config = self.spec['configurations'][self.configname]
    framework_dirs = config.get('mac_framework_dirs', [])
    for directory in framework_dirs:
      ldflags.append('-F' + directory.replace('$(SDKROOT)', self._SdkPath()))

    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 []

    identity = self.xcode_settings[configname].get('CODE_SIGN_IDENTITY', '')
    if identity == '':
      return []
    if identity not in XcodeSettings._codesigning_key_cache:
      proc = subprocess.Popen(['security', 'find-identity', '-p', 'codesigning',
                               '-v'], stdout=subprocess.PIPE)
      output = proc.communicate()[0].strip()
      key = None
      for item in output.split("\n"):
        if identity in item:
          assert key == None, (
              "Multiple codesigning identities for identity: %s" %
              identity)
          key = item.split(' ')[1]
      XcodeSettings._codesigning_key_cache[identity] = key
    key = XcodeSettings._codesigning_key_cache[identity]
    if key:
      # Warn for any unimplemented signing xcode keys.
      unimpl = ['CODE_SIGN_RESOURCE_RULES_PATH', 'OTHER_CODE_SIGN_FLAGS',
                'CODE_SIGN_ENTITLEMENTS']
      keys = set(self.xcode_settings[configname].keys())
      unimpl = set(unimpl) & keys
      if unimpl:
        print 'Warning: Some codesign keys not implemented, ignoring:', \
            ' '.join(unimpl)
      return ['codesign --force --sign %s %s' % (key, output_binary)]
    return []

  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
    return l.replace('$(SDKROOT)', self._SdkPath(config_name))

  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 self._GetStdout(['sw_vers', '-buildVersion'])

  def _XcodeVersion(self):
    # `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'.
    version_list = self._GetStdout(['xcodebuild', '-version']).splitlines()
    version = version_list[0]
    build = version_list[-1]
    # Be careful to convert "4.2" to "0420":
    version = version.split()[-1].replace('.', '')
    version = (version + '0' * (3 - len(version))).zfill(4)
    build = build.split()[-1]
    return version, build

  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 = self._XcodeVersion()
      cache['DTXcode'] = xcode
      cache['DTXcodeBuild'] = xcode_build

      sdk_root = self._SdkRoot(configname)
      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


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 MergeGlobalXcodeSettingsToSpec(global_dict, spec):
  """Merges the global xcode_settings dictionary into each configuration of the
  target represented by spec. For keys that are both in the global and the local
  xcode_settings dict, the local key gets precendence.
  """
  # The xcode generator special-cases global xcode_settings and does something
  # that amounts to merging in the global xcode_settings into each local
  # xcode_settings dict.
  global_xcode_settings = global_dict.get('xcode_settings', {})
  for config in spec['configurations'].values():
    if 'xcode_settings' in config:
      new_settings = global_xcode_settings.copy()
      new_settings.update(config['xcode_settings'])
      config['xcode_settings'] = new_settings


def IsMacBundle(flavor, spec):
  """Returns if |spec| should be treated as a bundle.

  Bundles are directories with a certain subdirectory structure, instead of
  just a single file. Bundle rules do not produce a binary but also package
  resources into that directory."""
  is_mac_bundle = (int(spec.get('mac_bundle', 0)) != 0 and flavor == 'mac')
  if is_mac_bundle:
    assert spec['type'] != 'none', (
        'mac_bundle targets cannot have type none (target "%s")' %
        spec['target_name'])
  return is_mac_bundle


def GetMacBundleResources(product_dir, xcode_settings, resources):
  """Yields (output, resource) pairs for every resource in |resources|.
  Only call this for mac bundle targets.

  Args:
      product_dir: Path to the directory containing the output bundle,
          relative to the build directory.
      xcode_settings: The XcodeSettings of the current target.
      resources: A list of bundle resources, relative to the build directory.
  """
  dest = os.path.join(product_dir,
                      xcode_settings.GetBundleResourceFolder())
  for res in resources:
    output = dest

    # The make generator doesn't support it, so forbid it everywhere
    # to keep the generators more interchangable.
    assert ' ' not in res, (
      "Spaces in resource filenames not supported (%s)"  % res)

    # Split into (path,file).
    res_parts = os.path.split(res)

    # Now split the path into (prefix,maybe.lproj).
    lproj_parts = os.path.split(res_parts[0])
    # If the resource lives in a .lproj bundle, add that to the destination.
    if lproj_parts[1].endswith('.lproj'):
      output = os.path.join(output, lproj_parts[1])

    output = os.path.join(output, res_parts[1])
    # Compiled XIB files are referred to by .nib.
    if output.endswith('.xib'):
      output = os.path.splitext(output)[0] + '.nib'
    # Compiled storyboard files are referred to by .storyboardc.
    if output.endswith('.storyboard'):
      output = os.path.splitext(output)[0] + '.storyboardc'

    yield output, res


def GetMacInfoPlist(product_dir, xcode_settings, gyp_path_to_build_path):
  """Returns (info_plist, dest_plist, defines, extra_env), where:
  * |info_plist| is the source plist path, relative to the
    build directory,
  * |dest_plist| is the destination plist path, relative to the
    build directory,
  * |defines| is a list of preprocessor defines (empty if the plist
    shouldn't be preprocessed,
  * |extra_env| is a dict of env variables that should be exported when
    invoking |mac_tool copy-info-plist|.

  Only call this for mac bundle targets.

  Args:
      product_dir: Path to the directory containing the output bundle,
          relative to the build directory.
      xcode_settings: The XcodeSettings of the current target.
      gyp_to_build_path: A function that converts paths relative to the
          current gyp file to paths relative to the build direcotry.
  """
  info_plist = xcode_settings.GetPerTargetSetting('INFOPLIST_FILE')
  if not info_plist:
    return None, None, [], {}

  # The make generator doesn't support it, so forbid it everywhere
  # to keep the generators more interchangable.
  assert ' ' not in info_plist, (
    "Spaces in Info.plist filenames not supported (%s)"  % info_plist)

  info_plist = gyp_path_to_build_path(info_plist)

  # If explicitly set to preprocess the plist, invoke the C preprocessor and
  # specify any defines as -D flags.
  if xcode_settings.GetPerTargetSetting(
      'INFOPLIST_PREPROCESS', default='NO') == 'YES':
    # Create an intermediate file based on the path.
    defines = shlex.split(xcode_settings.GetPerTargetSetting(
        'INFOPLIST_PREPROCESSOR_DEFINITIONS', default=''))
  else:
    defines = []

  dest_plist = os.path.join(product_dir, xcode_settings.GetBundlePlistPath())
  extra_env = xcode_settings.GetPerTargetSettings()

  return info_plist, dest_plist, defines, extra_env


def _GetXcodeEnv(xcode_settings, built_products_dir, srcroot, configuration,
                additional_settings=None):
  """Return the environment variables that Xcode would set. See
  http://developer.apple.com/library/mac/#documentation/DeveloperTools/Reference/XcodeBuildSettingRef/1-Build_Setting_Reference/build_setting_ref.html#//apple_ref/doc/uid/TP40003931-CH3-SW153
  for a full list.

  Args:
      xcode_settings: An XcodeSettings object. If this is None, this function
          returns an empty dict.
      built_products_dir: Absolute path to the built products dir.
      srcroot: Absolute path to the source root.
      configuration: The build configuration name.
      additional_settings: An optional dict with more values to add to the
          result.
  """
  if not xcode_settings: return {}

  # This function is considered a friend of XcodeSettings, so let it reach into
  # its implementation details.
  spec = xcode_settings.spec

  # These are filled in on a as-needed basis.
  env = {
    'BUILT_PRODUCTS_DIR' : built_products_dir,
    'CONFIGURATION' : configuration,
    'PRODUCT_NAME' : xcode_settings.GetProductName(),
    # See /Developer/Platforms/MacOSX.platform/Developer/Library/Xcode/Specifications/MacOSX\ Product\ Types.xcspec for FULL_PRODUCT_NAME
    'SRCROOT' : srcroot,
    'SOURCE_ROOT': '${SRCROOT}',
    # This is not true for static libraries, but currently the env is only
    # written for bundles:
    'TARGET_BUILD_DIR' : built_products_dir,
    'TEMP_DIR' : '${TMPDIR}',
  }
  if xcode_settings.GetPerConfigSetting('SDKROOT', configuration):
    env['SDKROOT'] = xcode_settings._SdkPath(configuration)
  else:
    env['SDKROOT'] = ''

  if spec['type'] in (
      'executable', 'static_library', 'shared_library', 'loadable_module'):
    env['EXECUTABLE_NAME'] = xcode_settings.GetExecutableName()
    env['EXECUTABLE_PATH'] = xcode_settings.GetExecutablePath()
    env['FULL_PRODUCT_NAME'] = xcode_settings.GetFullProductName()
    mach_o_type = xcode_settings.GetMachOType()
    if mach_o_type:
      env['MACH_O_TYPE'] = mach_o_type
    env['PRODUCT_TYPE'] = xcode_settings.GetProductType()
  if xcode_settings._IsBundle():
    env['CONTENTS_FOLDER_PATH'] = \
      xcode_settings.GetBundleContentsFolderPath()
    env['UNLOCALIZED_RESOURCES_FOLDER_PATH'] = \
        xcode_settings.GetBundleResourceFolder()
    env['INFOPLIST_PATH'] = xcode_settings.GetBundlePlistPath()
    env['WRAPPER_NAME'] = xcode_settings.GetWrapperName()

  install_name = xcode_settings.GetInstallName()
  if install_name:
    env['LD_DYLIB_INSTALL_NAME'] = install_name
  install_name_base = xcode_settings.GetInstallNameBase()
  if install_name_base:
    env['DYLIB_INSTALL_NAME_BASE'] = install_name_base

  if not additional_settings:
    additional_settings = {}
  else:
    # Flatten lists to strings.
    for k in additional_settings:
      if not isinstance(additional_settings[k], str):
        additional_settings[k] = ' '.join(additional_settings[k])
  additional_settings.update(env)

  for k in additional_settings:
    additional_settings[k] = _NormalizeEnvVarReferences(additional_settings[k])

  return additional_settings


def _NormalizeEnvVarReferences(str):
  """Takes a string containing variable references in the form ${FOO}, $(FOO),
  or $FOO, and returns a string with all variable references in the form ${FOO}.
  """
  # $FOO -> ${FOO}
  str = re.sub(r'\$([a-zA-Z_][a-zA-Z0-9_]*)', r'${\1}', str)

  # $(FOO) -> ${FOO}
  matches = re.findall(r'(\$\(([a-zA-Z0-9\-_]+)\))', str)
  for match in matches:
    to_replace, variable = match
    assert '$(' not in match, '$($(FOO)) variables not supported: ' + match
    str = str.replace(to_replace, '${' + variable + '}')

  return str


def ExpandEnvVars(string, expansions):
  """Expands ${VARIABLES}, $(VARIABLES), and $VARIABLES in string per the
  expansions list. If the variable expands to something that references
  another variable, this variable is expanded as well if it's in env --
  until no variables present in env are left."""
  for k, v in reversed(expansions):
    string = string.replace('${' + k + '}', v)
    string = string.replace('$(' + k + ')', v)
    string = string.replace('$' + k, v)
  return string


def _TopologicallySortedEnvVarKeys(env):
  """Takes a dict |env| whose values are strings that can refer to other keys,
  for example env['foo'] = '$(bar) and $(baz)'. Returns a list L of all keys of
  env such that key2 is after key1 in L if env[key2] refers to env[key1].

  Throws an Exception in case of dependency cycles.
  """
  # Since environment variables can refer to other variables, the evaluation
  # order is important. Below is the logic to compute the dependency graph
  # and sort it.
  regex = re.compile(r'\$\{([a-zA-Z0-9\-_]+)\}')
  def GetEdges(node):
    # Use a definition of edges such that user_of_variable -> used_varible.
    # This happens to be easier in this case, since a variable's
    # definition contains all variables it references in a single string.
    # We can then reverse the result of the topological sort at the end.
    # Since: reverse(topsort(DAG)) = topsort(reverse_edges(DAG))
    matches = set([v for v in regex.findall(env[node]) if v in env])
    for dependee in matches:
      assert '${' not in dependee, 'Nested variables not supported: ' + dependee
    return matches

  try:
    # Topologically sort, and then reverse, because we used an edge definition
    # that's inverted from the expected result of this function (see comment
    # above).
    order = gyp.common.TopologicallySorted(env.keys(), GetEdges)
    order.reverse()
    return order
  except gyp.common.CycleError, e:
    raise GypError(
        'Xcode environment variables are cyclically dependent: ' + str(e.nodes))


def GetSortedXcodeEnv(xcode_settings, built_products_dir, srcroot,
                      configuration, additional_settings=None):
  env = _GetXcodeEnv(xcode_settings, built_products_dir, srcroot, configuration,
                    additional_settings)
  return [(key, env[key]) for key in _TopologicallySortedEnvVarKeys(env)]


def GetSpecPostbuildCommands(spec, quiet=False):
  """Returns the list of postbuilds explicitly defined on |spec|, in a form
  executable by a shell."""
  postbuilds = []
  for postbuild in spec.get('postbuilds', []):
    if not quiet:
      postbuilds.append('echo POSTBUILD\\(%s\\) %s' % (
            spec['target_name'], postbuild['postbuild_name']))
    postbuilds.append(gyp.common.EncodePOSIXShellList(postbuild['action']))
  return postbuilds


def _HasIOSTarget(targets):
  """Returns true if any target contains the iOS specific key
  IPHONEOS_DEPLOYMENT_TARGET."""
  for target_dict in targets.values():
    for config in target_dict['configurations'].values():
      if config.get('xcode_settings', {}).get('IPHONEOS_DEPLOYMENT_TARGET'):
        return True
  return False


def _AddIOSDeviceConfigurations(targets):
  """Clone all targets and append -iphoneos to the name. Configure these targets
  to build for iOS devices."""
  for target_dict in targets.values():
    for config_name in target_dict['configurations'].keys():
      config = target_dict['configurations'][config_name]
      new_config_name = config_name + '-iphoneos'
      new_config_dict = copy.deepcopy(config)
      if target_dict['toolset'] == 'target':
        new_config_dict['xcode_settings']['ARCHS'] = ['armv7']
        new_config_dict['xcode_settings']['SDKROOT'] = 'iphoneos'
      target_dict['configurations'][new_config_name] = new_config_dict
  return targets

def CloneConfigurationForDeviceAndEmulator(target_dicts):
  """If |target_dicts| contains any iOS targets, automatically create -iphoneos
  targets for iOS device builds."""
  if _HasIOSTarget(target_dicts):
    return _AddIOSDeviceConfigurations(target_dicts)
  return target_dicts