Re-reland r245404 ("If the destination directory doesn't contain the desired repo, delete it")

gclient.py

Index: gclient.py
diff --git a/gclient.py b/gclient.py
index e2491cef1d39b1a80e6c6fcb3ae25fab676696bc..f68b01ebf2f8acec9a9e6616a39b9bd56f098cdf 100755
--- a/gclient.py
+++ b/gclient.py
@@ -87,6 +87,7 @@ import platform
 import posixpath
 import pprint
 import re
+import socket
 import sys
 import time
 import urllib
@@ -668,6 +669,43 @@ class Dependency(gclient_utils.WorkItem, DependencySettings):
             command, options, parsed_url, self.parent.name, revision_overrides)
         self._used_scm = gclient_scm.CreateSCM(
             parsed_url, self.root.root_dir, self.name)
+
+        def enable_deletion_of_conflicting_checkouts():
+          """Determines whether to enable new checkout deletion behavior.
+
+          Initially, enables the experimental functionality on a small set of
+          bots.
+          """
+          # TODO(borenet): Remove this hack as soon as we've verified that it
+          # doesn't cause the bots to break.
+          if not os.environ.get('CHROME_HEADLESS'):
+            return False
+          hostname = socket.gethostname()
+          logging.warning('Hostname of this machine: %s' % hostname)
+          return hostname in ('vm859-m1', 'build1-m1', 'vm630-m1')
+
+        # 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.
+        if command == 'update' and enable_deletion_of_conflicting_checkouts():
+          logging.warning('Experimental deletion of mismatching checkouts '
+                          'enabled.')
+          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:
+            if options.force:
+              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 '
+                                        '(found %s instead). Please fix the '
+                                        'solution manually or run with --force '
+                                        'to delete automatically.' % (
+                                            dest_dir, url, actual_remote_url))
+
         self._got_revision = self._used_scm.RunCommand(command, options, args,
                                                        file_list)
         if file_list: