sync-webkit-git: link to wiki, do some of Tony's review comments

tools/sync-webkit-git.py

 #!/usr/bin/python
 # Copyright (c) 2009 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.
 
 """Update third_party/WebKit using git.
 
 Under the assumption third_party/WebKit is a clone of git.webkit.org,
 we can use git commands to make it match the version requested by DEPS.
 
-To use this:
-1) rm -rf third_party/WebKit
-2) git clone git://git.webkit.org/WebKit.git third_party/WebKit
-3) edit your .gclient "custom_deps" section to exclude components underneath
-   third_party/WebKit:
-     "src/third_party/WebKit/LayoutTests": None,
-     "src/third_party/WebKit/JavaScriptCore": None,
-     "src/third_party/WebKit/WebCore": None,
-4) run ./tools/sync-webkit-git.py now, and again whenever you run gclient
-   sync.
-
-FAQ:
-Q. Why not add this functionality to gclient itself?
-A. DEPS actually specifies to only pull some subdirectories of
-   third_party/WebKit.  So even if gclient supported git, we'd still need
-   to special-case this.
+See http://code.google.com/p/chromium/wiki/UsingWebKitGit for details on
+how to use this.
 """
 
 import os
 import subprocess
 import sys
 
 # The name of the magic branch that lets us know that DEPS is managing
 # the update cycle.
 MAGIC_GCLIENT_BRANCH = 'refs/heads/gclient'
 
 def RunGit(command):
   """Run a git subcommand, returning its output."""
   proc = subprocess.Popen(['git'] + command, stdout=subprocess.PIPE)
   return proc.communicate()[0].strip()
 
 def GetWebKitRev():
   """Extract the 'webkit_revision' variable out of DEPS."""
   locals = {'Var': lambda _: ''}
   execfile('DEPS', {}, locals)
   return locals['vars']['webkit_revision']
 
 def FindSVNRev(rev):
   """Map an SVN revision to a git hash.
   Like 'git svn find-rev' but without the git-svn bits."""
-  return RunGit(['rev-list', '-n', '1', '--grep=^git-svn-id: .*@%s' % rev,
+  # We find r123 by grepping for a line with "git-svn-id: blahblahblah@123".
+  return RunGit(['rev-list', '-n', '1', '--grep=^git-svn-id: .*@%s$' % rev,
                  'origin'])
 
 def UpdateGClientBranch(webkit_rev):
   """Update the magic gclient branch to point at |webkit_rev|.
 
   Returns: true if the branch didn't need changes."""
   target = FindSVNRev(webkit_rev)
   if not target:
     print "r%s not available; fetching." % webkit_rev
     subprocess.check_call(['git', 'fetch'])
     target = FindSVNRev(webkit_rev)
   if not target:
     print "ERROR: Couldn't map r%s to a git revision." % webkit_rev
     sys.exit(1)
 
   current = RunGit(['show-ref', '--hash', MAGIC_GCLIENT_BRANCH])
   if current == target:
     return False  # No change necessary.
 
   subprocess.check_call(['git', 'update-ref', '-m', 'gclient sync',
                          MAGIC_GCLIENT_BRANCH, target])
   return True
 
 def UpdateCurrentCheckoutIfAppropriate():
   """Reset the current gclient branch if that's what we have checked out."""
   branch = RunGit(['symbolic-ref', '-q', 'HEAD'])
   if branch != MAGIC_GCLIENT_BRANCH:
-    print "Directory has some other branch ('%s') checked out." % branch
+    print "third_party/WebKit has some other branch ('%s') checked out." % branch

[tony, 2009/09/15 22:42:50]

Nit: 80 cols.

     print "Run 'git checkout gclient' to put this under control of gclient."
     return
 
   if subprocess.call(['git', 'diff-index', '--exit-code', '--shortstat',
                       'HEAD']):
     print "Resetting tree state to new revision."
     subprocess.check_call(['git', 'reset', '--hard'])
 
 def main():
+  if not os.path.exists('third_party/WebKit/.git'):
+    print "ERROR: third_party/WebKit appears to not be under git control."
+    print "See http://code.google.com/p/chromium/wiki/UsingWebKitGit for"
+    print "setup instructions."
+    return
+
   webkit_rev = GetWebKitRev()
   print 'Desired revision: r%s.' % webkit_rev
   os.chdir('third_party/WebKit')
   changed = UpdateGClientBranch(webkit_rev)
   if changed:
     UpdateCurrentCheckoutIfAppropriate()
+  else:
+    print "Already on correct revision."
 
 if __name__ == '__main__':
   main()