Win-Clang update.py: implement more principled search for CMake

tools/clang/scripts/update.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """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 os
 import re
@@ skipping 81 matching lines @@
   shutil.copy(src, dst)
   print "Copying %s to %s" % (src, dst)
 
 def Checkout(name, url, dir):
   """Checkout the SVN module at url into dir. Use name for the log message."""
   print "Checking out %s r%s into '%s'" % (name, LLVM_WIN_REVISION, dir)
   RunCommand(['svn', 'checkout', '--force',
               url + '@' + LLVM_WIN_REVISION, dir], tries=2)
 
 
+def AddCMakeToPath():
+  """Look for CMake and add it to PATH if it's not there already."""
+  try:
+    # First check if cmake is already on PATH.
+    subprocess.call(['cmake', '--version'])
+    return
+  except OSError as e:
+    if e.errno != os.errno.ENOENT:
+      raise
+
+  cmake_locations = ['C:\\Program Files (x86)\\CMake\\bin',
+                     'C:\\Program Files (x86)\\CMake 2.8\\bin']
+  for d in cmake_locations:
+    if os.path.isdir(d):
+      os.environ['PATH'] = os.environ.get('PATH', '') + os.pathsep + d
+      return
+  print 'Failed to find CMake!'
+  sys.exit(1)
+
+
 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')
   return vs_version
 
 
 def UpdateClang():
   print 'Updating Clang to %s...' % (LLVM_WIN_REVISION)
   if LLVM_WIN_REVISION != 'HEAD' and ReadStampFile() == LLVM_WIN_REVISION:
     print 'Already up to date.'
     return 0
 
+  AddCMakeToPath()
   ClobberChromiumBuildFiles()
 
   # Reset the stamp file in case the build is unsuccessful.
   WriteStampFile('')
 
   Checkout('LLVM', LLVM_REPO_URL + '/llvm/trunk', LLVM_DIR)
   Checkout('Clang', LLVM_REPO_URL + '/cfe/trunk', CLANG_DIR)
   Checkout('compiler-rt', LLVM_REPO_URL + '/compiler-rt/trunk', COMPILER_RT_DIR)
 
   if not os.path.exists(LLVM_BUILD_DIR):
     os.makedirs(LLVM_BUILD_DIR)
   os.chdir(LLVM_BUILD_DIR)
 
-  if not re.search(r'cmake', os.environ['PATH'], flags=re.IGNORECASE):
-    # If CMake is not on the path, try looking in a standard location.
-    os.environ['PATH'] += os.pathsep + 'C:\\Program Files (x86)\\CMake 2.8\\bin'
-
   RunCommand(GetVSVersion().SetupScript('x64') +
              ['&&', 'cmake', '-GNinja', '-DCMAKE_BUILD_TYPE=Release',
               '-DLLVM_ENABLE_ASSERTIONS=ON', LLVM_DIR])
   RunCommand(GetVSVersion().SetupScript('x64') + ['&&', 'ninja', 'all'])
 
   # Do an x86 build of compiler-rt to get the 32-bit ASan run-time.
   # TODO(hans): Remove once the regular build above produces this.
   if not os.path.exists(COMPILER_RT_BUILD_DIR):
     os.makedirs(COMPILER_RT_BUILD_DIR)
   os.chdir(COMPILER_RT_BUILD_DIR)
@@ skipping 61 matching lines @@
 
   if re.search(r'\b(make_clang_dir)=', os.environ.get('GYP_DEFINES', '')):
     print 'Skipping Clang update (make_clang_dir= was set in GYP_DEFINES).'
     return 0
 
   return UpdateClang()
 
 
 if __name__ == '__main__':
   sys.exit(main())