bug#26500: [PATCH] gnu: Add mcomix.

[Arun Isaac <arunisaac@systemreboot.net>]

>> Instead of mentioning p7zip, unrar and mupdf in the description, it
>> would be better if we could make them inputs and patch all references to
>> the executables in the source with their absolute paths. Could you try this?
> I could try that, but mupdf is a pretty heavy dependency. guix size says
> it's self-size is 208MiB and total-size is 491MiB.
> I personally never needed it with mcomix, so I like that it is optional.
> Is there some way to define a package with optional inputs?

As far as I understand, there is no way to specify optional inputs
(yet?). Here are two of many threads discussing this.

https://lists.gnu.org/archive/html/guix-devel/2014-11/msg00549.html
https://lists.gnu.org/archive/html/guix-devel/2015-05/msg00379.html

If mupdf is a heavy dependency and it is not commonly needed, you can
drop it and just package with 7z and rar as dependencies.

> +    (arguments `(#:python ,python-2))
> +    (inputs `(("python2-pygtk" ,python2-pygtk)
> +              ("python2-pillow" ,python2-pillow)))

Sort these inputs alphabetically, as I mentioned in the crawl thread.

LGTM, otherwise! Please send an updated patch. Thanks!