Windows: Fix custom toolchain args with GN

build/toolchain/win/setup_toolchain.py

 # Copyright (c) 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.
 #
 # Copies the given "win tool" (which the toolchain uses to wrap compiler
 # invocations) and the environment blocks for the 32-bit and 64-bit builds on
 # Windows to the build directory.
 #
 # The arguments are the visual studio install location and the location of the
 # win tool. The script assumes that the root build directory is the current dir
@@ skipping 106 matching lines @@
       script = os.path.normpath(os.path.join(sdk_dir, 'Bin/SetEnv.cmd'))
       assert _ExtractImportantEnvironment(variables) == \
              _ExtractImportantEnvironment(_LoadEnvFromBat([script, '/' + cpu]))
   else:
     if 'GYP_MSVS_OVERRIDE_PATH' not in os.environ:
       os.environ['GYP_MSVS_OVERRIDE_PATH'] = _DetectVisualStudioPath()
     # We only support x64-hosted tools.
     script_path = os.path.normpath(os.path.join(
                                        os.environ['GYP_MSVS_OVERRIDE_PATH'],
                                        'VC/vcvarsall.bat'))
-    if not os.path.exists(script_path):
-      raise Exception('%s is missing - make sure VC++ tools are installed.' %
-                      script_path)
-    args = [script_path, 'amd64_x86' if cpu == 'x86' else 'amd64']
-    variables = _LoadEnvFromBat(args)
+    if os.path.exists(script_path):
+      args = [script_path, 'amd64_x86' if cpu == 'x86' else 'amd64']
+      variables = _LoadEnvFromBat(args)
+    else:
+      variables = []

[brucedawson, 2016/07/07 23:31:38]

My only concern is that this might make some failures more cryptic than before.
That is, what happens if the necessary environment variables aren't set? This
should be detected as early as possible so that a helpful error message can be
shown.

Perhaps require that INCLUDE, LIB, etc. be set and if they aren't then raise an
exception saying what the problem is.

We've had cases in the past where errors propagated too far and it took years to
trace them back.

+      for k in sorted(os.environ.keys()):
+        variables.append('%s=%s' % (str(k), str(os.environ[k])))
+      variables = '\n'.join(variables)
   return _ExtractImportantEnvironment(variables)
 
 
 def _FormatAsEnvironmentBlock(envvar_dict):
   """Format as an 'environment block' directly suitable for CreateProcess.
   Briefly this is a list of key=value\0, terminated by an additional \0. See
   CreateProcess documentation for more details."""
   block = ''
   nul = '\0'
   for key, value in envvar_dict.iteritems():
@@ skipping 80 matching lines @@
 
   assert vc_bin_dir
   assert '"' not in vc_bin_dir
   print 'vc_bin_dir = "%s"' % vc_bin_dir
   assert include
   assert '"' not in include
   print 'include_flags = "%s"' % include
 
 if __name__ == '__main__':
   main()