Spreading the news

Ludovic Courtès — 2019年11月12日

Like most free software projects, Guix has no shortage of communication channels: there’s this blog, the NEWS file for release notes, a bunch of mailing lists, an IRC channel, there’s also an unofficial sub-Reddit and certainly more. Yet, as developers, we often find it hard to communicate important changes to our users. Starting from a few weeks ago, guix pull --news tells users what’s new, and it already feels very helpful! This post is about our motivations and the implementation of this new feature.

Getting the word out

Developers keep adding crazy features, fixing bugs, and generally improving things. But how good is it if users aren’t aware of these new things? As an example, since June, our build farm has been offering lzip-compressed binaries, which results in better performance when installing software. But to take advantage of that, users need to be aware of its existence, and they need to upgrade their Guix daemon. Likewise, how do we get people to learn about the new guix deploy command that’s now available at their fingertips, about security issues that were fixed, about important infrastructure changes, new options added to existing commands, and so forth?

Our (frustrating!) experience has been that release notes, blog posts, and mailing list announcements aren’t quite enough to get the word out. There’s always people who’ll miss important info and realize when it’s already late, sometimes too late. Hence this simple idea: wouldn’t it be nice if important information would reach users right in their terminal?

guix pull news

Alright, that’s not exactly a novel idea! In Debian for example, apt-listchanges shows news at the level of individual packages, taken from the NEWS.Debian or changelog.Debian files that package maintainers update. In addition, apt dist-upgrade and similar commands typically display dialog boxes and menus when special actions need to be taken when upgrading. That’s more or less what we’re looking for.

The situation in Guix is a little different: all of it lives in a single Git repository that contains the core, the command-line interfaces, as well as package definitions and operating system service definitions. The guix pull command is sort-of equivalent to apt update, except that it updates not only the set of available packages but also the guix tools themselves and all the operating system interfaces. Under the hood, guix pull essentially does git pull and consequently updates all of this. Guix very much follows a “rolling release” model.

For some time already, guix pull has been able to extract information about new and upgraded packages and to present it to the user. Our goal was to complement it with high-level information about important changes written with users in mind. Clearly, showing the Git commit log is not an option: commit logs are meant for developers and there’s roughly a thousand commits per month—way too much information. We needed high-level news entries, explicitly written for users.

The end result is this: guix pull now displays, in addition to a summary of the new and upgraded packages, the headlines of applicable news entries contributed by developers. Users can view the details by running guix pull --news:

Users can no longer miss the news, for the benefit of both users and developers!

Under the hood

How does this all work? There were several goals and constraints. First, like commit logs, our high-level news entries should be anchored in the Git history. Second, unlike commit logs, it should be possible to amend them—to fix typos, provide additional info, and so on. Third, the project has been paying a lot of attention to internationalization, with translations available for user interface messages, for package descriptions, and for the user manual—it’s one of these things that helps free software reach out to more people; thus, we naturally wanted news to be internationalized. Last, since Guix supports third-party “channels”, which are extensions of the official guix channel, why not provide channel authors access to that news feature?

With all these things in mind, we designed a simple news format. In essence, channel authors, including Guix developers, can provide a news file that looks like this:

(channel-news
 (version 0)

 (entry (commit "3e962e59d849e4300e447d94487684102d9d412e")
        (title (en "@command{guix graph} now supports package
transformations")
               (de "@command{guix graph} unterstützt nun Paketumwandlungen"))
        (body
         (en "The @command{guix graph} command now supports the common package
transformation options (see @command{info \"(guix) Package Transformation
Options\"}).  This is useful in particular to see the effect of the
@option{--with-input} dependency graph rewriting option.")
         (de "Der Befehl @command{guix graph} unterstützt nun die mit anderen
Befehlen gemeinsamen Umwandlungsoptionen (siehe @command{info \"(guix.de)
Paketumwandlungsoptionen\"}).  Sie helfen insbesondere dabei, die Wirkung der
Befehlszeilenoption @option{--with-input} zum Umschreiben des
Abhängigkeitsgraphen zu sehen.")))

 (entry (commit "49af34cfac89d384c46269bfd9388b2c73b1220a")
        (title (en "@command{guix pull} now honors
@file{/etc/guix/channels.scm}")
               (es "Ahora @command{guix pull} tiene en cuenta
@file{/etc/guix/channels.scm}"))
        (body
         (en "The @command{guix pull} command will now read the
@file{/etc/guix/channels.scm} file if it exists and if the per-user
@file{~/.config/guix/channels.scm} is not present.  This allows administrators
of multi-user systems to define site-wide defaults.")
         (es "Ahora la orden @command{guix pull} lee el fichero
@file{/etc/guix/channels.scm} si existe y el fichero personalizable
@file{~/.config/guix/channels.scm} no está presente. Esto permite a quienes
administran sistemas con múltiples usuarias definir valores predeterminados
en el sistema."))))

Each news entry refers to a commit, the commit that introduced the change it documents, and it has a title and body. Those can use Texinfo markup for rich formatting, and translations can be provided directly within the news file.

When guix pull --news runs, it determines which news entries are applicable given the user’s previous Guix instance. The (guix channels) module provides a simple programming interface for that:

(use-modules (guix channels) (srfi srfi-1))

(channel-news-for-commit (first %default-channels)
                         "66b707a7d2325daadeed5ca913637eea3a2628e7"
                         "ac19950507e941b6263f62f4ee4e8934c1b1598e")
⇒ (#<<channel-news-entry> commit: "3e962e59d849e4300e447d94487684102d9d412e" tag: #f title: (("en" . "@command{guix graph} now supports package\ntransformations") …) body: …> #<<channel-news-entry> commit: "49af34cfac89d384c46269bfd9388b2c73b1220a" tag: #f title: (("en" . "@command{guix pull} now honors\n@file{/etc/guix/channels.scm}") …) body: …>)

One thing is quite unusual (one might say “weird” :-)) about this news format: it refers to commit IDs “in-band”. In other words, unlike Git commit logs, which are “out-of-band”, the news file is contained inside the repository that it refers to. Technically, it means that before pushing a news entry, one must make sure it refers to the right commit ID (the news format allows you to refer to tags as well, but one may not want to create tags for every “news-worthy” change). Likewise, rebasing might invalidate commit IDs that appear in the news file. So this whole “in-band” log has drawbacks, but the big win is that it allows us to amend news entries to fix typos, add translations, and so on.

In other news…

Since it was applied a bit more than a month ago, we’ve already put the news mechanism to good use on quite a few occasions: giving users instructions on how to deal with locales after the last glibc upgrade, giving them upgrade info for CVE-2019-18192, telling them about new command-line options, and more.

In parallel, given that reading the mailing lists is akin to “drinking from a fire hose” as they say, Christopher Baines has been thinking about how to provide regular development updates to interested users and developers. Chris announced last week a prototype of a “Guix Weekly News” web site that would aggregate information about package updates automatically extracted from the Guix Data Service, along with manually written updates. It would seem that this service could readily grab info from channel news as well.

What about you, what do you expect in terms of news distribution? Join us on the mailing list and on IRC and let us know!

About GNU Guix

GNU Guix is a transactional package manager and an advanced distribution of the GNU system that respects user freedom. Guix can be used on top of any system running the kernel Linux, or it can be used as a standalone operating system distribution for i686, x86_64, ARMv7, and AArch64 machines.

In addition to standard package management features, Guix supports transactional upgrades and roll-backs, unprivileged package management, per-user profiles, and garbage collection. When used as a standalone GNU/Linux distribution, Guix offers a declarative, stateless approach to operating system configuration management. Guix is highly customizable and hackable through Guile programming interfaces and extensions to the Scheme language.