[NaCl SDK] Use subst to keep path lengths short on the buildbots.

native_client_sdk/src/build_tools/buildbot_run.py

 #!/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.
 
 """Main entry point for the NaCl SDK buildbot.
 
 The entry point used to be build_sdk.py itself, but we want
 to be able to simplify build_sdk (for example separating out
 the test code into test_sdk) and change its default behaviour
 while being able to separately control excactly what the bots
 run.
 """
 
 import buildbot_common
 import os
+import subprocess
 import sys
+
 from buildbot_common import Run
-from build_paths import SDK_SRC_DIR, SCRIPT_DIR
+from build_paths import SRC_DIR, SDK_SRC_DIR, SCRIPT_DIR
+import getos
 
 
 def StepRunUnittests():
   buildbot_common.BuildStep('Run unittests')
 
   # Our tests shouldn't be using the proxy; they should all be connecting to
   # localhost. Some slaves can't route HTTP traffic through the proxy to
   # localhost (we get 504 gateway errors), so we clear it here.
   env = dict(os.environ)
   if 'http_proxy' in env:
     del env['http_proxy']
 
   Run([sys.executable, 'test_all.py'], env=env, cwd=SDK_SRC_DIR)
 
 
 def StepBuildSDK(args):
-  Run([sys.executable, 'build_sdk.py'] + args, cwd=SCRIPT_DIR)
+  is_win = getos.GetPlatform() == 'win'
+
+  # Windows has a path length limit of 255 characters, after joining cwd with a
+  # relative path. Use subst before building to keep the path lengths short.
+  if is_win:
+    subst_drive = 'S:'
+    root_dir = os.path.dirname(SRC_DIR)
+    new_root_dir = subst_drive + '\\'
+    subprocess.check_call(['subst', subst_drive, root_dir])
+    new_script_dir = os.path.join(new_root_dir,
+                                  os.path.relpath(SCRIPT_DIR, root_dir))
+  else:
+    new_script_dir = SCRIPT_DIR
+
+  try:
+    Run([sys.executable, 'build_sdk.py'] + args, cwd=new_script_dir)
+  finally:
+    if is_win:
+      subprocess.check_call(['subst', '/D', subst_drive])
 
 
 def StepTestSDK():
   Run([sys.executable, 'test_sdk.py'], cwd=SCRIPT_DIR)
 
 
 def main(args):
   StepRunUnittests()
   StepBuildSDK(args)
   StepTestSDK()
   return 0
 
 
 if __name__ == '__main__':
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     buildbot_common.ErrorExit('buildbot_run: interrupted')