Make Clang's update.py use the Win toolchain under depot_tools if available

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index af3df5aac680307b3721420e6e7a0e49d9a2958d..7bb3c1f7e7c02af76537fae186da90907b022e62 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -6,6 +6,7 @@
 """Windows can't run .sh files, so this is a Python implementation of
 update.sh. This script should replace update.sh on all platforms eventually."""
 
+import json
 import os
 import re
 import shutil
@@ -136,13 +137,24 @@ def AddCMakeToPath():
 vs_version = None
 def GetVSVersion():
   global vs_version
-  if not vs_version:
-    # TODO(hans): Find a less hacky way to find the MSVS installation.
-    sys.path.append(os.path.join(CHROMIUM_DIR, 'tools', 'gyp', 'pylib'))
-    import gyp.MSVSVersion
-    # We request VS 2013 because Clang won't build with 2010, and 2013 will be
-    # the default for Chromium soon anyway.
-    vs_version = gyp.MSVSVersion.SelectVisualStudioVersion('2013')
+  if vs_version:
+    return vs_version
+
+  # Try using the toolchain in depot_tools.
+  json_data_file = os.path.join(CHROMIUM_DIR, 'build', 'win_toolchain.json')

[scottmg, 2014/09/22 18:59:48]

could you import vs_toolchain and call SetEnvironmentAndGetRuntimeDllDirs
instead?

[hans, 2014/09/22 19:52:39]

Done.

+  if os.path.exists(json_data_file):
+    with open(json_data_file, 'r') as tempf:
+      toolchain_data = json.load(tempf)
+    # gyp's MSVSVersion will look at these environment variables.
+    os.environ['GYP_MSVS_OVERRIDE_PATH'] = toolchain_data['path']
+    os.environ['GYP_MSVS_VERSION'] = toolchain_data['version']
+    os.environ['WINDOWSSDKDIR'] = toolchain_data['win8sdk']
+
+  # Use gyp to find the MSVS installation, either in depot_tools as per above,
+  # or a system-wide installation otherwise.
+  sys.path.append(os.path.join(CHROMIUM_DIR, 'tools', 'gyp', 'pylib'))
+  import gyp.MSVSVersion
+  vs_version = gyp.MSVSVersion.SelectVisualStudioVersion('2013')
   return vs_version