Fix resolution of local branch name in scm and rebaseline tools.

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 824 matching lines @@
 
         did_finish = False
         try:
             # 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":
+            old_branch_name = self._tool.scm().current_branch()
+            if not old_branch_name:

[Xianzhu, 2015/07/16 22:01:19]

Why don't use the same method as for rebaseline-o-matic?

[joelo, 2015/07/16 23:00:11]

I'm not quite sure what you mean by this. I changed rebaseline-o-matic to also
use the commit SHA if HEAD is detached, does that work? Keep in mind that
rebaseline-o-matic below is going away as soon as I figure out how to get it
running on buildbot.

[Xianzhu, 2015/07/16 23:21:39]

I was just wondering why rebaseline-o-matic asserts while this function tries to
tolerate detached head. Either way is fine. Anyway this doesn't really matter
because you'll remove rebaseline-o-matic.

                 # If HEAD is detached use commit SHA instead.
-                old_branch_name = tool.executive.run_command(["git", "rev-parse", "HEAD"])
+                old_branch_name = tool.executive.run_command(["git", "rev-parse", "HEAD"]).strip()

[Xianzhu, 2015/07/16 22:01:19]

Should use single quotes to keep consistency.

[joelo, 2015/07/16 23:00:11]

Done. Sorry, this file is not consistent at all.

[Xianzhu, 2015/07/16 23:21:39]

Never mind. I didn't notice the inconsistency.

             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 77 matching lines @@
         while out:
             # FIXME: This should probably batch up lines if they're available and log to the server once.
             out = self._log_line(process.stdout)
 
     def _do_one_rebaseline(self):
         self._log_queue = Queue.Queue(256)
         log_thread = threading.Thread(name='LogToServer', target=self._log_to_server_thread)
         log_thread.start()
         try:
             old_branch_name = self._tool.scm().current_branch()
+            assert old_branch_name, (
+                "Rebaseline-o-matic cannot be run from a branch with a detached HEAD.")

[Xianzhu, 2015/07/16 22:01:19]

Ditto.

             self._run_logged_command(['git', 'pull'])
             rebaseline_command = [self._tool.filesystem.join(self._tool.scm().checkout_root, 'Tools', 'Scripts', 'webkit-patch'), 'auto-rebaseline']
             if self._verbose:
                 rebaseline_command.append('--verbose')
             self._run_logged_command(rebaseline_command)
         except:
             self._log_queue.put(self.QUIT_LOG)
             traceback.print_exc(file=sys.stderr)
             # Sometimes git crashes and leaves us on a detached head.
-            self._tool.scm().checkout_branch(old_branch_name)
+            if old_branch_name:
+                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)