Use %B format instead of %s\n\n%b to get the raw commit message from a hash.

git_cl.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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 2003 matching lines @@
     print "\nDescription is empty. Aborting..."
     return 1
 
   if options.title:
     print "\nPatch titles (-t) are not supported in Gerrit. Aborting..."
     return 1
 
   if options.squash:
     # Try to get the message from a previous upload.
     shadow_branch = 'refs/heads/git_cl_uploads/' + cl.GetBranch()
-    message = RunGitSilent(['show', '--format=%s\n\n%b', '-s', shadow_branch])
+    message = RunGitSilent(['show', '--format=%B', '-s', shadow_branch])
     if not message:
       if not options.force:
         change_desc.prompt()
 
       if CHANGE_ID not in change_desc.description:
         # Run the commit-msg hook without modifying the head commit by writing
         # the commit message to a temporary file and running the hook over it,
         # then reading the file back in.
         commit_msg_hook = os.path.join(settings.GetRoot(), '.git', 'hooks',
                                        'commit-msg')
@@ skipping 36 matching lines @@
       # will create additional CLs when uploading.
       if (RunGitSilent(['rev-parse', upstream_branch + ':']) !=
           RunGitSilent(['rev-parse', parent + ':'])):
         print 'Upload upstream branch ' + upstream_branch + ' first.'
         return 1
     else:
       parent = cl.GetCommonAncestorWithUpstream()
 
     tree = RunGit(['rev-parse', 'HEAD:']).strip()
     ref_to_push = RunGit(['commit-tree', tree, '-p', parent,
                           '-m', message]).strip()

[scottmg, 2016/02/18 18:02:48]

Will message still be multiline? I think this will end up only getting the first
line still.

[Bernhard Bauer, 2016/02/18 20:12:18]

Dunno… is that different on Windows? I could imagine that things are different
now that we are going to have the real commit message, not the one with \n after
the first line. But really… would you mind just testing it? :)

   else:
     if CHANGE_ID not in change_desc.description:
       AddChangeIdToCommitMessage(options, args)
     ref_to_push = 'HEAD'
     parent = '%s/%s' % (gerrit_remote, branch)
 
   commits = RunGitSilent(['rev-list', '%s..%s' % (parent,
                                                   ref_to_push)]).splitlines()
   if len(commits) > 1:
     print('WARNING: This will upload %d commits. Run the following command '
@@ skipping 1668 matching lines @@
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)