Fix downloading LLVM Gold plugin in the case, when Clang is up to date.

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 argparse
 import cStringIO
@@ skipping 283 matching lines @@
   # 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
 
 
 def UpdateClang(args):
   print 'Updating Clang to %s...' % PACKAGE_VERSION
+
+  need_gold_plugin = 'LLVM_DOWNLOAD_GOLD_PLUGIN' in os.environ or (
+      sys.platform.startswith('linux') and
+      'buildtype=Official' in os.environ.get('GYP_DEFINES', '') and
+      'branding=Chrome' in os.environ.get('GYP_DEFINES', ''))
+
   if ReadStampFile() == PACKAGE_VERSION:
-    print 'Already up to date.'
-    return 0
+    print 'Clang is already up to date.'

[Adrian Kuegel, 2015/12/03 09:29:26]

I think this early return breaks the case if you want to compile clang tools,
like we do on the Codesearch bots:
https://build.chromium.org/p/chromium.infra.cron/builders/Chromium%20Linux%20...
Look at the "compile translation_unit clang tool" step, it does an early return
while in fact it should compile the clang tool.

+    if not need_gold_plugin or os.path.exists(
+        os.path.join(LLVM_BUILD_DIR, "lib/LLVMgold.so")):
+      return 0
 
   # Reset the stamp file in case the build is unsuccessful.
   WriteStampFile('')
 
   if not args.force_local_build:
     cds_file = "clang-%s.tgz" %  PACKAGE_VERSION
     if sys.platform == 'win32':
       cds_full_url = CDS_URL + '/Win/' + cds_file
     elif sys.platform == 'darwin':
       cds_full_url = CDS_URL + '/Mac/' + cds_file
     else:
       assert sys.platform.startswith('linux')
       cds_full_url = CDS_URL + '/Linux_x64/' + cds_file
 
     # Check if there's a prebuilt binary and if so just fetch that. That's
     # faster, and goma relies on having matching binary hashes on client and
     # server too.
     print 'Trying to download prebuilt clang'
 
     try:
       if os.path.exists(LLVM_BUILD_DIR):
         RmTree(LLVM_BUILD_DIR)
       DownloadAndUnpack(cds_full_url, LLVM_BUILD_DIR)
       print 'clang %s unpacked' % PACKAGE_VERSION
       # Download the gold plugin if requested to by an environment variable.
       # This is used by the CFI ClusterFuzz bot, and it's required for official
       # builds on linux.
-      if 'LLVM_DOWNLOAD_GOLD_PLUGIN' in os.environ or (
-          sys.platform.startswith('linux') and
-          'buildtype=Official' in os.environ.get('GYP_DEFINES', '') and
-          'branding=Chrome' in os.environ.get('GYP_DEFINES', '')):
+      if need_gold_plugin:
         RunCommand(['python', CHROMIUM_DIR+'/build/download_gold_plugin.py'])
       WriteStampFile(PACKAGE_VERSION)
       return 0
     except urllib2.HTTPError:
       print 'Did not find prebuilt clang %s, building locally' % cds_file
 
   if args.with_android and not os.path.exists(ANDROID_NDK_DIR):
     print 'Android NDK not found at ' + ANDROID_NDK_DIR
     print 'The Android NDK is needed to build a Clang whose -fsanitize=address'
     print 'works on Android. See '
@@ skipping 428 matching lines @@
     args.force_local_build = True
     if 'OS=android' not in os.environ.get('GYP_DEFINES', ''):
       # Only build the Android ASan rt on ToT bots when targetting Android.
       args.with_android = False
 
   return UpdateClang(args)
 
 
 if __name__ == '__main__':
   sys.exit(main())