text: #!/usr/bin/env python
  # Copyright (c) 2012 The Chromium Authors. All rights reserved.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  """
  This file holds a list of reasons why a particular build needs to be clobbered
  (or a list of 'landmines').
  
  This script runs every build as a hook. If it detects that the build should
  be clobbered, it will touch the file <build_dir>/.landmine_triggered. The
  various build scripts will then check for the presence of this file and clobber
  accordingly. The script will also emit the reasons for the clobber to stdout.
  
  A landmine is tripped when a builder checks out a different revision, and the
  diff between the new landmines and the old ones is non-null. At this point, the
  build is clobbered.
  """
  
  import difflib
  import functools
  import gyp_helper
  import logging
  import optparse
  import os
  import shlex
  import sys
  import time
  
  SRC_DIR = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
  
  def memoize(default=None):
    """This decorator caches the return value of a parameterless pure function"""
    def memoizer(func):
      val = []
      @functools.wraps(func)
      def inner():
        if not val:
          ret = func()
          val.append(ret if ret is not None else default)
          if logging.getLogger().isEnabledFor(logging.INFO):
            print '%s -> %r' % (func.__name__, val[0])
        return val[0]
      return inner
    return memoizer
  
  
  @memoize()
  def IsWindows():
    return sys.platform in ['win32', 'cygwin']
  
  
  @memoize()
  def IsLinux():
    return sys.platform.startswith('linux')
  
  
  @memoize()
  def IsMac():
    return sys.platform == 'darwin'
  
  
  @memoize()
  def gyp_defines():
    """Parses and returns GYP_DEFINES env var as a dictionary."""
    return dict(arg.split('=', 1)
        for arg in shlex.split(os.environ.get('GYP_DEFINES', '')))
  
  
  @memoize()
  def distributor():
    """
    Returns a string which is the distributed build engine in use (if any).
    Possible values: 'goma', 'ib', ''
    """
    if 'goma' in gyp_defines():
      return 'goma'
    elif IsWindows():
      if 'CHROME_HEADLESS' in os.environ:
        return 'ib' # use (win and !goma and headless) as approximation of ib
  
  
  @memoize()
  def platform():
    """
    Returns a string representing the platform this build is targetted for.
    Possible values: 'win', 'mac', 'linux', 'ios', 'android'
    """
    if 'OS' in gyp_defines():
      if 'android' in gyp_defines()['OS']:
        return 'android'
      else:
        return gyp_defines()['OS']
    elif IsWindows():
      return 'win'
    elif IsLinux():
      return 'linux'
    else:
      return 'mac'
  
  
  @memoize()
  def builder():
    """
    Returns a string representing the build engine (not compiler) to use.
    Possible values: 'make', 'ninja', 'xcode', 'msvs', 'scons'
    """
    if 'GYP_GENERATORS' in os.environ:
      # for simplicity, only support the first explicit generator
      generator = os.environ['GYP_GENERATORS'].split(',')[0]
      if generator.endswith('-android'):
        return generator.split('-')[0]
      elif generator.endswith('-ninja'):
        return 'ninja'
      else:
        return generator
    else:
      if platform() == 'android':
        # Good enough for now? Do any android bots use make?
        return 'ninja'
      elif platform() == 'ios':
        return 'xcode'
      elif IsWindows():
        return 'msvs'
      elif IsLinux():
        return 'ninja'
      elif IsMac():
        return 'xcode'
      else:
        assert False, 'Don\'t know what builder we\'re using!'
  
  
  def get_landmines(target):
    """
    ALL LANDMINES ARE DEFINED HERE.
    target is 'Release' or 'Debug'
    """
    landmines = []
    add = lambda item: landmines.append(item + '\n')
  
    if (distributor() == 'goma' and platform() == 'win32' and
        builder() == 'ninja'):
      add('Need to clobber winja goma due to backend cwd cache fix.')
    if platform() == 'android':
      add('Clobber: Resources removed in r195014 require clobber.')
    if platform() == 'win' and builder() == 'ninja':
      add('Compile on cc_unittests fails due to symbols removed in r185063.')
    if platform() == 'linux' and builder() == 'ninja':
      add('Builders switching from make to ninja will clobber on this.')
    if platform() == 'mac':
      add('Switching from bundle to unbundled dylib (issue 14743002).')
  
    return landmines
  
  
  def get_target_build_dir(build_tool, target, is_iphone=False):
    """
    Returns output directory absolute path dependent on build and targets.
    Examples:
      r'c:\b\build\slave\win\build\src\out\Release'
      '/mnt/data/b/build/slave/linux/build/src/out/Debug'
      '/b/build/slave/ios_rel_device/build/src/xcodebuild/Release-iphoneos'
  
    Keep this function in sync with tools/build/scripts/slave/compile.py
    """
    ret = None
    if build_tool == 'xcode':
      ret = os.path.join(SRC_DIR, 'xcodebuild',
          target + ('-iphoneos' if is_iphone else ''))
    elif build_tool in ['make', 'ninja', 'ninja-ios']:  # TODO: Remove ninja-ios.
      ret = os.path.join(SRC_DIR, 'out', target)
    elif build_tool in ['msvs', 'vs', 'ib']:
      ret = os.path.join(SRC_DIR, 'build', target)
    elif build_tool == 'scons':
      ret = os.path.join(SRC_DIR, 'sconsbuild', target)
    else:
      raise NotImplementedError('Unexpected GYP_GENERATORS (%s)' % build_tool)
    return os.path.abspath(ret)
  
  
  def set_up_landmines(target):
    """Does the work of setting, planting, and triggering landmines."""
    out_dir = get_target_build_dir(builder(), target, platform() == 'ios')
  
    landmines_path = os.path.join(out_dir, '.landmines')
    if not os.path.exists(out_dir):
      os.makedirs(out_dir)
  
    new_landmines = get_landmines(target)
  
    if not os.path.exists(landmines_path):
      with open(landmines_path, 'w') as f:
        f.writelines(new_landmines)
    else:
      triggered = os.path.join(out_dir, '.landmines_triggered')
      with open(landmines_path, 'r') as f:
        old_landmines = f.readlines()
      if old_landmines != new_landmines:
        old_date = time.ctime(os.stat(landmines_path).st_ctime)
        diff = difflib.unified_diff(old_landmines, new_landmines,
            fromfile='old_landmines', tofile='new_landmines',
            fromfiledate=old_date, tofiledate=time.ctime(), n=0)
  
        with open(triggered, 'w') as f:
          f.writelines(diff)
      elif os.path.exists(triggered):
        # Remove false triggered landmines.
        os.remove(triggered)
  
  
  def main():
    parser = optparse.OptionParser()
    parser.add_option('-v', '--verbose', action='store_true',
        default=('LANDMINES_VERBOSE' in os.environ),
        help=('Emit some extra debugging information (default off). This option '
            'is also enabled by the presence of a LANDMINES_VERBOSE environment '
            'variable.'))
    options, args = parser.parse_args()
  
    if args:
      parser.error('Unknown arguments %s' % args)
  
    logging.basicConfig(
        level=logging.DEBUG if options.verbose else logging.ERROR)
  
    gyp_helper.apply_chromium_gyp_env()
  
    for target in ('Debug', 'Release', 'Debug_x64', 'Release_x64'):
      set_up_landmines(target)
  
    return 0
  
  
  if __name__ == '__main__':
    sys.exit(main())
  