Locate appropriate "winreg" module under both native Win32 and CygWin.

win_toolchain/get_toolchain_if_necessary.py

 #!/usr/bin/env python
 # Copyright 2013 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.
 
 """Downloads and unpacks a toolchain for building on Windows. The contents are
 matched by sha1 which will be updated when the toolchain is updated.
 
 Having a toolchain script in depot_tools means that it's not versioned
 directly with the source code. That is, if the toolchain is upgraded, but
 you're trying to build an historical version of Chromium from before the
 toolchain upgrade, this will cause you to build with a newer toolchain than
 was available when that code was committed. This is done for a two main
 reasons: 1) it would likely be annoying to have the up-to-date toolchain
 removed and replaced by one without a service pack applied); 2) it would
 require maintaining scripts that can build older not-up-to-date revisions of
 the toolchain. This is likely to be a poorly tested code path that probably
 won't be properly maintained. See http://crbug.com/323300.
 
 This does not extend to major versions of the toolchain however, on the
 assumption that there are more likely to be source incompatibilities between
 major revisions. This script calls a subscript (currently, toolchain2013.py)
 to do the main work. It is expected that toolchain2013.py will always be able
 to acquire/build the most current revision of a VS2013-based toolchain. In the
 future when a hypothetical VS2015 is released, the 2013 script will be
 maintained, and a new 2015 script would be added.
 """
 
-import _winreg
 import hashlib
 import json
 import optparse
 import os
 import platform
 import shutil
 import subprocess
 import sys
 import tempfile
 import time
 import zipfile
 
+# winreg isn't natively available under CygWin
+if sys.platform == "win32":
+  try:
+    import winreg

[brucedawson, 2016/01/21 21:03:22]

Why are you importing winreg? Why not just "import _winreg as winreg"? Python 3
forward compatibility?

+  except ImportError:
+    import _winreg as winreg
+elif sys.platform == "cygwin":
+  try:
+    import cygwinreg as winreg
+  except ImportError:
+    print ''
+    print 'CygWin does not natively support winreg but a replacement exists.'
+    print 'https://pypi.python.org/pypi/cygwinreg/'
+    print ''
+    print 'Try: easy_install cygwinreg'
+    print ''
+    raise
 
 BASEDIR = os.path.dirname(os.path.abspath(__file__))
 DEPOT_TOOLS_PATH = os.path.join(BASEDIR, '..')
 sys.path.append(DEPOT_TOOLS_PATH)
 try:
   import download_from_google_storage
 except ImportError:
   # Allow use of utility functions in this script from package_from_installed
   # on bare VM that doesn't have a full depot_tools.
   pass
@@ skipping 168 matching lines @@
 
 
 def GetInstallerName():
   """Return the name of the Windows 10 Universal C Runtime installer for the
   current platform, or None if installer is not needed or not applicable.
   The registry has to be used instead of sys.getwindowsversion() because
   Python 2.7 is only manifested as being compatible up to Windows 8, so the
   version APIs helpfully return a maximum of 6.2 (Windows 8).
   """
   key_name = r'Software\Microsoft\Windows NT\CurrentVersion'
-  key = _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, key_name)
-  value, keytype = _winreg.QueryValueEx(key, "CurrentVersion")
+  key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, key_name)
+  value, keytype = winreg.QueryValueEx(key, "CurrentVersion")
   key.Close()
-  if keytype != _winreg.REG_SZ:
+  if keytype != winreg.REG_SZ:
     raise Exception("Unexpected type in registry")
   if value == '6.1':
     # Windows 7 and Windows Server 2008 R2
     return 'Windows6.1-KB2999226-x64.msu'
   elif value == '6.2':
     # Windows 8 and Windows Server 2012
     return 'Windows8-RT-KB2999226-x64.msu'
   elif value == '6.3':
     # Windows 8.1, Windows Server 2012 R2, and Windows 10.
     # The Windows 8.1 installer doesn't work on Windows 10, but it will never
@@ skipping 164 matching lines @@
                     options.output_json)
 
   if os.environ.get('GYP_MSVS_VERSION') == '2015':
     InstallUniversalCRTIfNeeded(abs_target_dir)
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())