[gn] Detect location of Visual Studio in the registry.

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 36 matching lines @@
           # later, python will still be found.
           setting = os.path.dirname(sys.executable) + os.pathsep + setting
         env[var.upper()] = setting
         break
   for required in ('SYSTEMROOT', 'TEMP', 'TMP'):
     if required not in env:
       raise Exception('Environment variable "%s" '
                       'required to be set to valid path' % required)
   return env
 
+def _RegistryGetValueUsingWinReg(key, value):
+  """Use the _winreg module to obtain the value of a registry key.
+
+  Args:
+    key: The registry key.
+    value: The particular registry value to read.
+  Return:
+    contents of the registry key's value, or None on failure.  Throws
+    ImportError if _winreg is unavailable.
+  """
+  import _winreg
+  try:
+    root, subkey = key.split('\\', 1)
+    assert root == 'HKLM'  # Only need HKLM for now.
+    with _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, subkey) as hkey:
+      return _winreg.QueryValueEx(hkey, value)[0]
+  except WindowsError:
+    return None
+
+
+def _RegistryGetValue(key, value):
+   try:
+       return _RegistryGetValueUsingWinReg(key, value)

[brucedawson, 2016/01/04 21:36:06]

Indented two extra spaces?

+   except ImportError:
+     raise Exception('The python library _winreg not found.')
+
+
+def _DetectVisualStudioPath():
+  """Return path to the GYP_MSVS_VERSION of Visual Studio
+  """
+
+  # Default to 2015 for now.
+  version_as_year = os.environ.get('GYP_MSVS_VERSION', '2015')
+  year_to_version = {
+      '2013': '12.0',
+      '2015': '14.0',
+  }
+  if not version_as_year in year_to_version:
+    raise Exception(('Visual Studio Version %s (from GYP_MSVS_VERSION)'
+                     ' not supported. Supported versions are: %s') % (
+                       version_as_year, ', '.join(year_to_version.keys())))
+  version = year_to_version[version_as_year]
+  keys = [r'HKLM\Software\Microsoft\VisualStudio\%s' % version,
+          r'HKLM\Software\Wow6432Node\Microsoft\VisualStudio\%s' % version]
+  for key in keys:
+    path = _RegistryGetValue(key, 'InstallDir')
+    if not path:
+      continue
+    path = os.path.normpath(os.path.join(path, '..', '..'))
+    return path
+
+  raise Exception(('Visual Studio Version %s (from GYP_MSVS_VERSION)'
+                   ' not found.') % (version_as_year))
+
+
 
 def _SetupScript(target_cpu, sdk_dir):
   """Returns a command (with arguments) to be used to set up the
   environment."""
   # Check if we are running in the SDK command line environment and use
   # the setup script from the SDK if so. |target_cpu| should be either
   # 'x86' or 'x64'.
   assert target_cpu in ('x86', 'x64')
   if bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', 1))) and sdk_dir:
     return [os.path.normpath(os.path.join(sdk_dir, 'Bin/SetEnv.Cmd')),
             '/' + target_cpu]
   else:
+    if not 'GYP_MSVS_OVERRIDE_PATH' in os.environ:
+      os.environ['GYP_MSVS_OVERRIDE_PATH'] = _DetectVisualStudioPath()
     # We only support x64-hosted tools.
-    # TODO(scottmg|dpranke): Non-depot_tools toolchain: need to get Visual
-    # Studio install location from registry.
     return [os.path.normpath(os.path.join(os.environ['GYP_MSVS_OVERRIDE_PATH'],
                                           'VC/vcvarsall.bat')),
             'amd64_x86' if target_cpu == 'x86' else 'amd64']
 
 
 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 = ''
@@ skipping 78 matching lines @@
     env_block = _FormatAsEnvironmentBlock(env)
     with open('environment.winrt_' + cpu, 'wb') as f:
         f.write(env_block)
 
   assert vc_bin_dir
   print 'vc_bin_dir = "%s"' % vc_bin_dir
 
 
 if __name__ == '__main__':
   main()