Don't return unfound VS version, raise instead

pylib/gyp/MSVSVersion.py

 # Copyright (c) 2013 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.
 
 """Handle version information related to Visual Stuio."""
 
 import errno
 import os
 import re
 import subprocess
@@ skipping 383 matching lines @@
   override_path = os.environ.get('GYP_MSVS_OVERRIDE_PATH')
   if override_path:
     msvs_version = os.environ.get('GYP_MSVS_VERSION')
     if not msvs_version:
       raise ValueError('GYP_MSVS_OVERRIDE_PATH requires GYP_MSVS_VERSION to be '
                        'set to a particular version (e.g. 2010e).')
     return _CreateVersion(msvs_version, override_path, sdk_based=True)
   version = str(version)
   versions = _DetectVisualStudioVersions(version_map[version], 'e' in version)
   if not versions:
-    if version == 'auto':
-      # Default to 2005 if we couldn't find anything
-      return _CreateVersion('2005', None)
-    else:
-      return _CreateVersion(version, None)
+    raise ValueError('Could not locate Visual Studio installation.')
   return versions[0]