Add a completion script generator for the fish shell

devscripts/fish-completion.in

@@ -0,0 +1,5 @@
+
+{{commands}}
+
+
+complete --command youtube-dl --arguments ":ytfavorites :ytrecommended :ytsubscriptions :ytwatchlater :ythistory"

devscripts/fish-completion.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+from __future__ import unicode_literals
+
+import optparse
+import os
+from os.path import dirname as dirn
+import sys
+
+sys.path.append(dirn(dirn((os.path.abspath(__file__)))))
+import youtube_dl
+from youtube_dl.utils import shell_quote
+
+FISH_COMPLETION_FILE = 'youtube-dl.fish'
+FISH_COMPLETION_TEMPLATE = 'devscripts/fish-completion.in'
+
+EXTRA_ARGS = {
+    'recode-video': ['--arguments', 'mp4 flv ogg webm mkv', '--exclusive'],
+
+    # Options that need a file parameter
+    'download-archive': ['--require-parameter'],
+    'cookies': ['--require-parameter'],
+    'load-info': ['--require-parameter'],
+    'batch-file': ['--require-parameter'],
+}
+
+def build_completion(opt_parser):
+    commands = []
+
+    for group in opt_parser.option_groups:
+        for option in group.option_list:
+            long_option = option.get_opt_string().strip('-')
+            help_msg = shell_quote([option.help])
+            complete_cmd = ['complete', '--command', 'youtube-dl', '--long-option', long_option]
+            if option._short_opts:
+                complete_cmd += ['--short-option', option._short_opts[0].strip('-')]
+            if option.help != optparse.SUPPRESS_HELP:
+                complete_cmd += ['--description', option.help]
+            complete_cmd.extend(EXTRA_ARGS.get(long_option, []))
+            commands.append(shell_quote(complete_cmd))
+
+    with open(FISH_COMPLETION_TEMPLATE) as f:
+        template = f.read()
+    filled_template = template.replace('{{commands}}', '\n'.join(commands))
+    with open(FISH_COMPLETION_FILE, 'w') as f:
+        f.write(filled_template)
+
+parser = youtube_dl.parseOpts()[0]
+build_completion(parser)