add fish shell completion (#2363)

scripts/completion_fish.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+"""Generate fish completion script from gallery-dl's argument parser"""
+
+import util
+from gallery_dl import option
+
+
+TEMPLATE = """complete -c gallery-dl -x
+%(opts)s
+"""
+
+opts = []
+for action in option.build_parser()._actions:
+    if not action.option_strings:
+        continue
+
+    opt = "complete -c gallery-dl"
+
+    if action.metavar:
+        if action.metavar == "FILE":
+            opt += " -r -F"
+        elif action.metavar == "PATH":
+            opt += " -x -a '(__fish_complete_directories)'"
+        else:
+            opt += " -x"
+
+    for optstr in action.option_strings:
+        if optstr.startswith("--"):
+            opt += " -l '" + optstr[2:] + "'"
+        else:
+            opt += " -s '" + optstr[1:] + "'"
+
+    opt += " -d '" + action.help.replace("'", '"') + "'"
+
+    opts.append(opt)
+
+PATH = util.path("data/completion/gallery-dl.fish")
+with open(PATH, "w", encoding="utf-8") as file:
+    file.write(TEMPLATE % {"opts": "\n".join(opts)})