Issue 6945 - Add script to make filter list diffs

abp/filters/diff_script.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 12 matching lines @@
 
 from .renderer import render_diff
 
 __all__ = ['main']
 
 
 def parse_args():
     parser = argparse.ArgumentParser(description='Render a filter list diff.')
     parser.add_argument(
         'base', help='the older filter list that needs to be updated',
         nargs='?')

[Sebastian Noack, 2018/09/24 22:21:09]

Didn't we want to make those arguments mandatory?

[rhowell, 2018/09/25 01:53:45]

Positional arguments are already mandatory (or it will raise a TypeError).
Vasily's suggestion was to remove the `default='-'` arguments. I did that in
patch set 3.

[Sebastian Noack, 2018/09/25 17:00:39]

I see, the documentation seems a little misleading:

  One argument will be consumed from the command line if possible, and
  produced as a single item. If no command-line argument is present,
  the value from default will be produced.

It doesn't specify what happens if no default is specified. I wonder what would
happen if you omit the nargs argument altogether?

     parser.add_argument(
         'latest', help='the most recent version of the filter list',
         nargs='?')
     parser.add_argument(
         'outfile', help='output file for filter list diff',
         default='-', nargs='?')
     return parser.parse_args()
 
 
 def main():
-    """Entry point for the diff rendering script (diffrender)."""
+    """Entry point for the diff rendering script (fldiff)."""
     args = parse_args()
 
     with io.open(args.base, 'r', encoding='utf-8') as base, \
             io.open(args.latest, 'r', encoding='utf-8') as latest:
 
         lines = render_diff(base, latest)
         if args.outfile == '-':
             outfile = io.open(sys.stdout.fileno(), 'w',
                               closefd=False,
                               encoding=sys.stdout.encoding or 'utf-8')
         else:
             outfile = io.open(args.outfile, 'w', encoding='utf-8')
 
         with outfile:
             for line in lines:
                 print(line, file=outfile)