Finally implement the code to automatically switch checkout when there is no ...

gclient.py

 #!/usr/bin/python
 #
 # Copyright 2008 Google Inc.  All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #      http://www.apache.org/licenses/LICENSE-2.0
 #
@@ skipping 734 matching lines @@
 
   def update(self, options, args, file_list):
     """Runs SCM to update or transparently checkout the working copy.
 
     All updated files will be appended to file_list.
 
     Raises:
       Error: if can't get URL for relative path.
     """
     # Only update if git is not controlling the directory.
-    git_path = os.path.join(self._root_dir, self.relpath, '.git')
+    checkout_path = os.path.join(self._root_dir, self.relpath)
+    git_path = os.path.join(checkout_path, '.git')
     if options.path_exists(git_path):
       print("________ found .git directory; skipping %s" % self.relpath)
       return
 
     if args:
       raise Error("Unsupported argument(s): %s" % ",".join(args))
 
     url = self.url
     components = url.split("@")
     revision = None
     forced_revision = False
     if options.revision:
       # Override the revision number.
       url = '%s@%s' % (components[0], str(options.revision))
       revision = int(options.revision)
       forced_revision = True
     elif len(components) == 2:
       revision = int(components[1])
       forced_revision = True
 
     rev_str = ""
     if revision:
       rev_str = ' at %d' % revision
 
-    if not options.path_exists(os.path.join(self._root_dir, self.relpath)):
+    if not options.path_exists(checkout_path):
       # We need to checkout.
-      command = ['checkout', url, os.path.join(self._root_dir, self.relpath)]
+      command = ['checkout', url, checkout_path]
       if revision:
         command.extend(['--revision', str(revision)])
       RunSVNAndGetFileList(command, self._root_dir, file_list)
       return
 
     # Get the existing scm url and the revision number of the current checkout.
-    from_info = CaptureSVNInfo(os.path.join(self._root_dir, self.relpath, '.'),
-                               '.')
+    from_info = CaptureSVNInfo(os.path.join(checkout_path, '.'), '.')
 
     if options.manually_grab_svn_rev:
       # Retrieve the current HEAD version because svn is slow at null updates.
       if not revision:
         from_info_live = CaptureSVNInfo(from_info['URL'], '.')
         revision = int(from_info_live['Revision'])
         rev_str = ' at %d' % revision
 
     if from_info['URL'] != components[0]:
       to_info = CaptureSVNInfo(url, '.')
-      if from_info['Repository Root'] != to_info['Repository Root']:
+      can_switch = ((from_info['Repository Root'] != to_info['Repository Root'])
+                    and (from_info['UUID'] == to_info['UUID']))
+      if can_switch:
+        print("\n_____ relocating %s to a new checkout" % self.relpath)
         # We have different roots, so check if we can switch --relocate.
         # Subversion only permits this if the repository UUIDs match.
-        if from_info['UUID'] != to_info['UUID']:
-          raise Error("Can't switch the checkout to %s; UUID don't match. That "
-                      "simply means in theory, gclient should verify you don't "
-                      "have a local change, remove the old checkout and do a "
-                      "fresh new checkout of the new repo. Contributions are "
-                      "welcome." % url)
-
         # Perform the switch --relocate, then rewrite the from_url
         # to reflect where we "are now."  (This is the same way that
         # Subversion itself handles the metadata when switch --relocate
         # is used.)  This makes the checks below for whether we
         # can update to a revision or have to switch to a different
         # branch work as expected.
         # TODO(maruel):  TEST ME !
         command = ["switch", "--relocate",
                    from_info['Repository Root'],
                    to_info['Repository Root'],
                    self.relpath]
         RunSVN(command, self._root_dir)
         from_info['URL'] = from_info['URL'].replace(
             from_info['Repository Root'],
             to_info['Repository Root'])
+      else:
+        if CaptureSVNStatus(checkout_path):
+          raise Error("Can't switch the checkout to %s; UUID don't match and "
+                      "there is local changes in %s. Delete the directory and "
+                      "try again." % (url, checkout_path))
+        # Ok delete it.
+        print("\n_____ switching %s to a new checkout" % self.relpath)
+        RemoveDirectory(checkout_path)
+        # We need to checkout.
+        command = ['checkout', url, checkout_path]
+        if revision:
+          command.extend(['--revision', str(revision)])
+        RunSVNAndGetFileList(command, self._root_dir, file_list)
+        return
+          
 
     # If the provided url has a revision number that matches the revision
     # number of the existing directory, then we don't need to bother updating.
     if not options.force and from_info['Revision'] == revision:
       if options.verbose or not forced_revision:
         print("\n_____ %s%s" % (self.relpath, rev_str))
       return
 
-    command = ["update", os.path.join(self._root_dir, self.relpath)]
+    command = ["update", checkout_path]
     if revision:
       command.extend(['--revision', str(revision)])
     RunSVNAndGetFileList(command, self._root_dir, file_list)
 
   def revert(self, options, args, file_list):
     """Reverts local modifications. Subversion specific.
 
     All reverted files will be appended to file_list, even if Subversion
     doesn't know about them.
     """
@@ skipping 866 matching lines @@
 
 if "__main__" == __name__:
   try:
     result = Main(sys.argv)
   except Error, e:
     print >> sys.stderr, "Error: %s" % str(e)
     result = 1
   sys.exit(result)
 
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