Fix multi-solution use case with conflicting custom_deps overrides.

gclient.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.
 
 """Meta checkout manager supporting both Subversion and GIT.
 
 Files
   .gclient      : Current client configuration, written by 'config' command.
                   Format is a Python script defining 'solutions', a list whose
@@ skipping 307 matching lines @@
       raise gclient_utils.Error(
           'The same name "%s" appears multiple times in the deps section' %
               self.name)
     if not self.should_process:
       # Return early, no need to set requirements.
       return True
 
     # This require a full tree traversal with locks.
     siblings = [d for d in self.root.subtree(False) if d.name == self.name]
     for sibling in siblings:
-      if self.url != sibling.url:
+      self_url = self.LateOverride(self.url)
+      sibling_url = sibling.LateOverride(sibling.url)
+      # Allow to have only one to be None or ''.
+      if self_url != sibling_url and bool(self_url) == bool(sibling_url):
         raise gclient_utils.Error(
-            'Dependency %s specified more than once:\n  %s\nvs\n  %s' %
-            (self.name, sibling.hierarchy(), self.hierarchy()))
+            ('Dependency %s specified more than once:\n'
+            '  %s [%s]\n'
+            'vs\n'
+            '  %s [%s]') % (
+              self.name,
+              sibling.hierarchy(),
+              sibling_url,
+              self.hierarchy(),
+              self_url))
       # In theory we could keep it as a shadow of the other one. In
       # practice, simply ignore it.
       logging.warn('Won\'t process duplicate dependency %s' % sibling)
       return False
     return True
 
   def LateOverride(self, url):
     """Resolves the parsed url from url.
 
     Manages From() keyword accordingly. Do not touch self.parsed_url nor
@@ skipping 1281 matching lines @@
   except (gclient_utils.Error, subprocess2.CalledProcessError), e:
     print >> sys.stderr, 'Error: %s' % str(e)
     return 1
 
 
 if '__main__' == __name__:
   fix_encoding.fix_encoding()
   sys.exit(Main(sys.argv[1:]))
 
 # vim: ts=2:sw=2:tw=80:et: