Fail noisily when git auto-svn can't authenticate.

git_auto_svn.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """Performs all git-svn setup steps necessary for 'git svn dcommit' to work.
 
 Assumes that trunk of the svn remote maps to master of the git remote.
 
 Example:
@@ skipping 60 matching lines @@
   svn_path = None
   for i in xrange(len(path_components)):
     try:
       maybe_repo = '%s://%s%s' % (
           parsed_svn.scheme, parsed_svn.netloc, '/'.join(path_components[:i+1]))
       print 'Checking ', maybe_repo
       run_svn('info', maybe_repo)
       svn_repo = maybe_repo
       svn_path = '/'.join(path_components[i+1:])
       break
-    except subprocess2.CalledProcessError:
+    except subprocess2.CalledProcessError, e:
+      if 'E170001' in str(e):
+        print 'Authentication failed:'
+        print e
+        print ('Try running "svn ls %s" with the password'
+               ' from https://chromium-access.appspot.com' % maybe_repo)
+        print
       continue
   assert svn_repo is not None, 'Unable to find svn repo for %s' % match.group(1)
   print 'Found upstream svn repo %s and path %s' % (svn_repo, svn_path)
 
   set_config('svn-remote.svn.url', svn_repo)
   set_config('svn-remote.svn.fetch',
              '%s:refs/remotes/%s' % (svn_path, upstream))
   print 'Configured metadata, running "git svn fetch". This may take some time.'
   for line in run_git_stream('svn', 'fetch').xreadlines():
     print line.strip()
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))