Hey Ludo!

> This can be decomposed in several steps:
>
>   1. We can start using ‘guile-zlib’ as extensions for gexps: in (guix
>      scripts pack), (guix download), etc.  Easy, no risk.

There's an attached patch that should cover this first step. An issue
here is that (guix build download-nar) is built in both "make" and "guix
pull" commands, so I cannot use a bare:

--8<---------------cut here---------------start------------->8---
#:use-module (zlib)
--8<---------------cut here---------------end--------------->8---

so, I used:

--8<---------------cut here---------------start------------->8---
#:autoload   (zlib) (call-with-gzip-input-port)
--8<---------------cut here---------------end--------------->8---

that seems to work but produces a lot of warnings when running
"make". Would it be acceptable as a first step?

>
>   2. Use guile-zlib & co. in Guix itself: (guix scripts substitute),
>      (guix scripts publish), etc.  Keep (guix zlib) and (guix lzlib) in
>      parallel.

I'm not sure how it can work without step 4. For me, including (zlib) in
Guix itself requires that build machinery and (guix self) are updated,
but maybe I'm missing something.

>
>   3. Update ‘guix’ package with these two new dependencies.

Seems fair!

> The rest LGTM.  Thanks a lot for all the work!

Thanks for having a look :)

Mathieu