Issue 6945 - Add script to make filter list diffs

abp/filters/renderer.py

 # This file is part of Adblock Plus <https://adblockplus.org/>,
 # Copyright (C) 2006-present eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@@ skipping 199 matching lines @@
     latest_metadata, latest_rules = _split_list_for_diff(latest)
     base_metadata, base_rules = _split_list_for_diff(base)
 
     yield '[Adblock Plus Diff]'
     for key, latest in latest_metadata.items():
         base = base_metadata.get(key)
         if not base or base.value != latest.value:
             yield latest.to_string()
     for key in set(base_metadata) - set(latest_metadata):
         yield '! {}:'.format(base_metadata[key].key)
+    # The removed filters are listed first because, in case a filter is both
+    # removed and added, (and the client processes the diff in order), the
+    # filter will be added.
     for rule in base_rules - latest_rules:
         yield '- {}'.format(rule)
     for rule in latest_rules - base_rules:
         yield '+ {}'.format(rule)