Update the toolchain if there's a mismatch between the env and win_toolchain.json

build/vs_toolchain.py

Index: build/vs_toolchain.py
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index 1fd8a11445b275fce2be9029d85aadbcb6d75799..e659645c461f669e7e86701a5b1bebe0ae236cca 100755
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -21,6 +21,10 @@ json_data_file = os.path.join(script_dir, 'win_toolchain.json')
 import gyp
 
 
+# Use MSVS2013 as the default toolchain.
+CURRENT_TOOLCHAIN_VERSION = '2013'

[brucedawson, 2016/01/15 21:10:52]

Should probably be "CURRENT_DEFAULT_TOOLCHAIN_VERSION", to better reflect its
actual usage.

[Sébastien Marchand, 2016/01/15 21:21:39]

Done.

+
+
 def SetEnvironmentAndGetRuntimeDllDirs():
   """Sets up os.environ to use the depot_tools VS toolchain with gyp, and
   returns the location of the VS runtime DLLs so they can be copied into
@@ -33,7 +37,7 @@ def SetEnvironmentAndGetRuntimeDllDirs():
   # been downloaded before (in which case json_data_file will exist).
   if ((sys.platform in ('win32', 'cygwin') or os.path.exists(json_data_file))
       and depot_tools_win_toolchain):
-    if not os.path.exists(json_data_file):
+    if ShouldUpdateToolchain():
       Update()
     with open(json_data_file, 'r') as tempf:
       toolchain_data = json.load(tempf)
@@ -105,8 +109,8 @@ def DetectVisualStudioPath():
   # Note that this code is used from
   # build/toolchain/win/setup_toolchain.py as well.
 
-  # Default to Visual Studio 2013 for now.
-  version_as_year = os.environ.get('GYP_MSVS_VERSION', '2013')
+  version_as_year = os.environ.get('GYP_MSVS_VERSION',
+                                   CURRENT_TOOLCHAIN_VERSION)
   year_to_version = {
       '2013': '12.0',
       '2015': '14.0',
@@ -263,6 +267,21 @@ def _GetDesiredVsToolchainHashes():
     return ['9ff97c632ae1fee0c98bcd53e71770eb3a0d8deb']
 
 
+def ShouldUpdateToolchain():
+  """Check if the toolchain should be upgraded."""
+  if not os.path.exists(json_data_file):
+    return True
+  with open(json_data_file, 'r') as tempf:
+    toolchain_data = json.load(tempf)
+  version = toolchain_data['version']
+  env_version = os.environ.get('GYP_MSVS_VERSION', CURRENT_TOOLCHAIN_VERSION)
+  # If there's a mismatch between the version set in the environment and the one
+  # in the json file then the toolchain should be updated.
+  if version != env_version:

[scottmg, 2016/01/15 21:08:13]

return version != env_version

[Sébastien Marchand, 2016/01/15 21:21:39]

Done.

+    return True
+  return False
+
+
 def Update(force=False):
   """Requests an update of the toolchain to the specific hashes we have at
   this revision. The update outputs a .json of the various configuration