Windows: Fix custom toolchain args with GN

build/toolchain/win/setup_toolchain.py

Index: build/toolchain/win/setup_toolchain.py
diff --git a/build/toolchain/win/setup_toolchain.py b/build/toolchain/win/setup_toolchain.py
index d58cb8536335647195f2945001993ade05fbd9de..fd608ba69d085a2a2626c0bc9b15d211b02fa313 100644
--- a/build/toolchain/win/setup_toolchain.py
+++ b/build/toolchain/win/setup_toolchain.py
@@ -124,11 +124,14 @@ def _LoadToolchainEnv(cpu, sdk_dir):
     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)