Error checking to clarify SYSTEMROOT errors

pylib/gyp/msvs_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 helps emulate Visual Studio 2008 behavior on top of other
 build systems, primarily ninja.
 """
 
 import os
@@ skipping 943 matching lines @@
       'include',
       'lib',
       'libpath',
       'path',
       'pathext',
       'systemroot',
       'temp',
       'tmp',
       )
   env = {}
+  # This occasionally happens and leads to misleading SYSTEMROOT error messages
+  # if not caught here.
+  if output_of_set.count('=') == 0:
+    raise Exception('Invalid output_of_set. Value is:\n%s' % output_of_set)
   for line in output_of_set.splitlines():
     for envvar in envvars_to_save:
       if re.match(envvar + '=', line.lower()):
         var, setting = line.split('=', 1)
         if envvar == 'path':
           # Our own rules (for running gyp-win-tool) and other actions in
           # Chromium rely on python being in the path. Add the path to this
           # python here so that if it's not in the path when ninja is run
           # later, python will still be found.
           setting = os.path.dirname(sys.executable) + os.pathsep + setting
@@ skipping 48 matching lines @@
     return cl_paths
   vs = GetVSVersion(generator_flags)
   cl_paths = {}
   for arch in archs:
     # Extract environment variables for subprocesses.
     args = vs.SetupScript(arch)
     args.extend(('&&', 'set'))
     popen = subprocess.Popen(
         args, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     variables, _ = popen.communicate()
+    if popen.returncode != 0:
+      raise Exception('"%s" failed with error %d' % (args, popen.returncode))
     env = _ExtractImportantEnvironment(variables)
 
     # Inject system includes from gyp files into INCLUDE.
     if system_includes:
       system_includes = system_includes | OrderedSet(
                                               env.get('INCLUDE', '').split(';'))
       env['INCLUDE'] = ';'.join(system_includes)
 
     env_block = _FormatAsEnvironmentBlock(env)
     f = open_out(os.path.join(toplevel_build_dir, 'environment.' + arch), 'wb')
@@ skipping 36 matching lines @@
 
   # To determine processor word size on Windows, in addition to checking
   # PROCESSOR_ARCHITECTURE (which reflects the word size of the current
   # process), it is also necessary to check PROCESSOR_ARCHITEW6432 (which
   # contains the actual word size of the system when running thru WOW64).
   if ('64' in os.environ.get('PROCESSOR_ARCHITECTURE', '') or
       '64' in os.environ.get('PROCESSOR_ARCHITEW6432', '')):
     default_variables['MSVS_OS_BITS'] = 64
   else:
     default_variables['MSVS_OS_BITS'] = 32