Take 2 at adding --force to svn update and svn checkout....

gclient_scm.py

 # Copyright (c) 2010 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.
 
 """Gclient-specific SCM-specific operations."""
 
 import logging
 import os
 import posixpath
 import re
@@ skipping 722 matching lines @@
       # Override the revision number.
       revision = str(options.revision)
     if revision:
       forced_revision = True
       url = '%s@%s' % (url, revision)
       rev_str = ' at %s' % revision
 
     if not os.path.exists(checkout_path):
       # We need to checkout.
       command = ['checkout', url, checkout_path]
-      if revision:
-        command.extend(['--revision', str(revision).strip()])
+      command = self.AddAdditionalFlags(command, options, revision)
       scm.SVN.RunAndGetFileList(options, command, self._root_dir, file_list)
       return
 
     # Get the existing scm url and the revision number of the current checkout.
     from_info = scm.SVN.CaptureInfo(os.path.join(checkout_path, '.'), '.')
     if not from_info:
       raise gclient_utils.Error("Can't update/checkout %r if an unversioned "
                                 "directory is present. Delete the directory "
                                 "and try again." %
                                 checkout_path)
@@ skipping 36 matching lines @@
         if scm.SVN.CaptureStatus(checkout_path):
           raise gclient_utils.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)
         gclient_utils.RemoveDirectory(checkout_path)
         # We need to checkout.
         command = ['checkout', url, checkout_path]
-        if revision:
-          command.extend(['--revision', str(revision).strip()])
+        command = self.AddAdditionalFlags(command, options, revision)
         scm.SVN.RunAndGetFileList(options, 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 str(from_info['Revision']) == revision:
       if options.verbose or not forced_revision:
         print("\n_____ %s%s" % (self.relpath, rev_str))
       return
 
     command = ["update", checkout_path]
-    if revision:
-      command.extend(['--revision', str(revision).strip()])
+    command = self.AddAdditionalFlags(command, options, revision)
     scm.SVN.RunAndGetFileList(options, command, self._root_dir, file_list)
 
   def updatesingle(self, options, args, file_list):
     checkout_path = os.path.join(self._root_dir, self.relpath)
     filename = args.pop()
     if scm.SVN.AssertVersion("1.5")[0]:
       if not os.path.exists(os.path.join(checkout_path, '.svn')):
         # Create an empty checkout and then update the one file we want.  Future
         # operations will only apply to the one file we checked out.
         command = ["checkout", "--depth", "empty", self.url, checkout_path]
         scm.SVN.Run(command, self._root_dir)
         if os.path.exists(os.path.join(checkout_path, filename)):
           os.remove(os.path.join(checkout_path, filename))
         command = ["update", filename]
         scm.SVN.RunAndGetFileList(options, command, checkout_path, file_list)
       # After the initial checkout, we can use update as if it were any other
       # dep.
       self.update(options, args, file_list)
     else:
       # If the installed version of SVN doesn't support --depth, fallback to
       # just exporting the file.  This has the downside that revision
       # information is not stored next to the file, so we will have to
       # re-export the file every time we sync.
       if not os.path.exists(checkout_path):
         os.makedirs(checkout_path)
       command = ["export", os.path.join(self.url, filename),
                  os.path.join(checkout_path, filename)]
-      if options.revision:
-        command.extend(['--revision', str(options.revision).strip()])
+      command = self.AddAdditionalFlags(command, options, options.revision)
       scm.SVN.Run(command, self._root_dir)
 
   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.
     """
     __pychecker__ = 'unusednames=args'
     path = os.path.join(self._root_dir, self.relpath)
@@ skipping 64 matching lines @@
       print("\n________ couldn't run \'%s\' in \'%s\':\nThe directory "
             "does not exist."
             % (' '.join(command), path))
       # There's no file list to retrieve.
     else:
       scm.SVN.RunAndGetFileList(options, command, path, file_list)
 
   def FullUrlForRelativeUrl(self, url):
     # Find the forth '/' and strip from there. A bit hackish.
     return '/'.join(self.url.split('/')[:4]) + url
+
+  def AddAdditionalFlags(self, command, options, revision):
+    """Add additional flags to command depending on what options are set.
+    command should be a list of strings that represents an svn command.
+
+    This method returns a new list to be used as a command."""
+    new_command = command[:]
+    if revision:
+      new_command.extend(['--revision', str(revision).strip()])
+    # --force was added to 'svn update' in svn 1.5.
+    if options.force and scm.SVN.AssertVersion("1.5")[0]:
+      new_command.append('--force')
+    return new_command