librsvg & Rust

[Ludovic Courtès]

Hello Guix!

address@hidden skribis:

> mbakke pushed a commit to branch staging
> in repository guix.
>
> commit ec47c07d0690653be35a75b346f3c3548a3e71d4
> Author: Marius Bakke <address@hidden>
> Date:   Wed Oct 24 15:26:10 2018 +0200
>
>     gnu: librsvg: Update to 2.44.12.
>     
>     * gnu/packages/gnome.scm (librsvg): Update to 2.44.12.
>     [arguments]: Replace patching phases with custom variants.  Delete five 
> new
>     tests.
>     [native-inputs]: Add RUST-1.27 and RUST-1.27:CARGO.

This change was bound to happen since upstream switched to Rust, but
it creates a few issues.

First, that adds Rust to the base graphical applications, which
significantly increases build times and size:

--8<---------------cut here---------------start------------->8---
$ guix size librsvg | tail -1
total: 207.2 MiB
$ guix size librsvg rust | tail -1
total: 1052.9 MiB
--8<---------------cut here---------------end--------------->8---

Perhaps the size issue can be somewhat mitigated by adding a “lib”
output to the Rust package, but even then it would probably still be an
issue.

Also, is the new librsvg API-compatible with the old one?  IIUC it still
provides a C API, right?  Does guile-rsvg still work, for example?

What do other distros do?  Debian kept ‘librsvg-c’ around, primarily so
that architectures where Rust isn’t supported yet could still work:
<https://lwn.net/Articles/771355/>.

Anyway, lots of questions!

Thanks,
Ludo’.