Setup git-svn and handle detached HEAD state in auto-rebaseline script.

Tools/Scripts/webkitpy/tool/commands/rebaseline.py

 # Copyright (c) 2010 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 811 matching lines @@
         if self.tree_status() == 'closed':
             _log.info('Cannot proceed. Tree is closed.')
             return
 
         _log.info('Rebaselining %s for r%s by %s.' % (list(tests), revision, author))
 
         test_prefix_list, lines_to_remove = self.get_test_prefix_list(tests)
 
         did_finish = False
         try:
-            old_branch_name = tool.scm().current_branch()

[Xianzhu, 2015/07/14 20:40:04]

What will tool.scm().current_branch() return when HEAD is detached? I think we
can just set old_branch_name to 'master' in the case because git will
automatically create 'master' when it doesn't exist.

I think we should also checkout master and set old_branch_name to master if
old_branch_name is self.AUTO_REBASELINE_BRANCH_NAME.

The right-side code also has a problem that old_branch_name has a '\n' in it and
the later checkout will crash because of it.

The following code should work:
  old_branch_name = tool.scm().current_branch()
  if not old_branch_name or old_branch_name == self.AUTO_REBASELINE_BRANCH_NAME:
    old_branch_name = 'master'
    tool.scm().checkout_branch(old_branch_name)

Perhaps we should make the above code a function because we also save/restore
current branch in RebaselineOMatic.

[joelo, 2015/07/14 23:51:01]

Is it possible to create a branch with '\n' in it's name??

[Xianzhu, 2015/07/15 15:57:12]

Just tried:
$ git checkout -tb 'a
fatal: 'a
' is not a valid branch name.

The right side code misses a strip, so will include the ending '\n' of the git
rev-parse command in old_branch_name. I think we should use scm methods if
possible.

BTW, As jsbell@ said, checking out 'master' might not be the best solution.

+            # Setup git-svn for dcommit if necessary.
+            if tool.executive.run_command(
+                    ['git', 'config', '--local', '--get-regexp', r'^svn-remote\.'],
+                    return_exit_code=True):
+                tool.executive.run_command(['git', 'auto-svn'])
+
+            # Save the current branch name and checkout a clean branch for the patch.
+            old_branch_name = tool.executive.run_command(
+                ["git", "rev-parse", "--symbolic-full-name", "HEAD"])
+            if old_branch_name == "HEAD":
+                # If HEAD is detached use commit SHA instead.
+                old_branch_name = tool.executive.run_command(["git", "rev-parse", "HEAD"])
             tool.scm().delete_branch(self.AUTO_REBASELINE_BRANCH_NAME)
             tool.scm().create_clean_branch(self.AUTO_REBASELINE_BRANCH_NAME)
 
             # If the tests are passing everywhere, then this list will be empty. We don't need
             # to rebaseline, but we'll still need to update TestExpectations.
             if test_prefix_list:
                 self._rebaseline(options, test_prefix_list)
 
             tool.scm().commit_locally_with_message(self.commit_message(author, revision, bugs))
 
@@ skipping 91 matching lines @@
             self._tool.scm().checkout_branch(old_branch_name)
         else:
             self._log_queue.put(self.QUIT_LOG)
         log_thread.join()
 
     def execute(self, options, args, tool):
         self._verbose = options.verbose
         while True:
             self._do_one_rebaseline()
             time.sleep(self.SLEEP_TIME_IN_SECONDS)