If the destination directory doesn't contain the desired repo, delete it

gclient.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.
 
 """Meta checkout manager supporting both Subversion and GIT."""
 # Files
 #   .gclient      : Current client configuration, written by 'config' command.
 #                   Format is a Python script defining 'solutions', a list whose
 #                   entries each are maps binding the strings "name" and "url"
@@ skipping 623 matching lines @@
           self._used_scm.RunCommand('updatesingle',
               options, args + [parsed_url.GetFilename()], file_list)
       else:
         # Create a shallow copy to mutate revision.
         options = copy.copy(options)
         options.revision = revision_overrides.get(self.name)
         self.maybeGetParentRevision(
             command, options, parsed_url, self.parent.name, revision_overrides)
         self._used_scm = gclient_scm.CreateSCM(
             parsed_url, self.root.root_dir, self.name)
+
+        # When updating, determine whether the destination directory contains a
+        # checkout of the desired repository. If not, avoid conflicts by
+        # deleting the directory before running the update.
+        # TODO(borenet): Only enabling this on a few bots at first.
+        import socket
+        if (command == 'update' and
+            socket.gethostname() in ('vm859-m1', 'build1-m1', 'vm630-m1')):
+          logging.warning('Experimental deletion of mismatching checkouts '
+                          'enabled.')

[borenet, 2013/12/10 18:48:27]

Per Isaac's suggestion, using the hostname to enable on only a few bots at
first.

[Isaac (away), 2013/12/11 03:17:33]

This looks good to me.  To be extra safe, maybe also guard with
os.environ.get('CHROME_HEADLESS')

[borenet, 2013/12/11 20:42:19]

Done.

+          actual_remote_url = self._used_scm.GetRemoteURL(options)
+          url, _ = gclient_utils.SplitUrlRevision(parsed_url)
+          url = url.rstrip('/')
+          dest_dir = os.path.join(self.root.root_dir, self.name) 
+          if os.path.isdir(dest_dir) and actual_remote_url != url:
+            should_delete = options.force or os.environ.get('CHROME_HEADLESS')
+            if sys.__stdout__.isatty() and not should_delete:
+              usr_input = ''
+              while usr_input not in ('y', 'n'):
+                usr_input = raw_input('%s does not contain a checkout of %s. '
+                                      'Do you want to delete the directory? '
+                                      'If not, the update will be canceled '
+                                      '(y/n): ' % (dest_dir, url)).lower()
+              should_delete = (usr_input == 'y')
+            if should_delete:
+              logging.warning('%s does not contain a checkout of %s. Removing '
+                              ' %s' % (dest_dir, url, dest_dir))
+              gclient_utils.rmtree(dest_dir)
+            else:
+              raise gclient_utils.Error('%s does not contain a checkout of %s. '
+                                        'Please fix the solution manually or '
+                                        'run with --force to delete '
+                                        'automatically.' % (dest_dir, url))
+
         self._got_revision = self._used_scm.RunCommand(command, options, args,
                                                        file_list)
         if file_list:
           file_list = [os.path.join(self.name, f.strip()) for f in file_list]
 
       # TODO(phajdan.jr): We should know exactly when the paths are absolute.
       # Convert all absolute paths to relative.
       for i in range(len(file_list or [])):
         # It depends on the command being executed (like runhooks vs sync).
         if not os.path.isabs(file_list[i]):
@@ skipping 1235 matching lines @@
     raise
   except (gclient_utils.Error, subprocess2.CalledProcessError), e:
     print >> sys.stderr, 'Error: %s' % str(e)
     return 1
 
 
 if '__main__' == __name__:
   sys.exit(Main(sys.argv[1:]))
 
 # vim: ts=2:sw=2:tw=80:et: