guix
/
guix-artwork
mirror of git://git.savannah.gnu.org/guix/guix-artwork.git
2
0
Fork 0
Code Issues Releases Wiki Activity

website: Add draft about packages as channels. 

* website/drafts/package-channel.md: New file.
This commit is contained in:
Ludovic Courtès 2023-06-01 17:16:02 +02:00
parent 8139a10b65
commit dbc448b94a
No known key found for this signature in database
GPG Key ID: 090B11993D9AEBB5
1 changed files with 584 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

584
website/drafts/package-channel.md Normal file
View File

@ -0,0 +1,584 @@
title: From development environments to continuous integration—the ultimate guide to software development with Guix
alttitle: Continuous integration, continuous delivery, and development environments, all at once
author: Ludovic Courtès
tags: Software development, Continuous integration, Cuirass
date: 2023-06-02 15:00:00
---
Guix is a handy tool for developers; [`guix
shell`](https://guix.gnu.org/manual/en/html_node/Invoking-guix-shell.html),
in particular, gives a standalone development environment for your
package, no matter what language(s) it’s written in. To benefit from
it, you have to initially write a package definition and have it either
in Guix proper, in a channel, or directly upstream as a `guix.scm` file.
This last option is appealing: all developers have to do to get set up
is clone the project's repository and run `guix shell`, with no
arguments—we looked at the rationale for `guix shell` in [an earlier
missive](https://guix.gnu.org/en/blog/2021/from-guix-environment-to-guix-shell/).
Development needs go beyond development environments though. How can
developers perform continuous integration of their code in Guix build
environments? How can they deliver their code straight to adventurous
users? This post describes a set of files and conventions developers
can follow in their repository to set up Guix-based development
environments, continuous integration, and continuous delivery—all at
once.
# Getting started
How do we go about “Guixifying” a repository? The first step, as we’ve
seen, will be to add a `guix.scm` at the root of the repository we’re
interested in. We’ll take [Guile](https://www.gnu.org/software/guile)
as an example in this post: it’s written in Scheme (mostly) and C, and
has a number of dependencies—a C compilation tool chain, C libraries,
Autoconf and its friends, LaTeX, and so on. The resulting `guix.scm` is
looks like the usual [package
definition](https://guix.gnu.org/manual/en/html_node/Defining-Packages.html),
just without the `define-public` bit:
```scheme
;; The ‘guix.scm’ file for Guile, for use by ‘guix shell’.
(use-modules (guix)
(guix build-system gnu)
((guix licenses) #:prefix license:)
(gnu packages autotools)
(gnu packages bash)
(gnu packages bdw-gc)
(gnu packages compression)
(gnu packages flex)
(gnu packages gdb)
(gnu packages gettext)
(gnu packages gperf)
(gnu packages libffi)
(gnu packages libunistring)
(gnu packages linux)
(gnu packages pkg-config)
(gnu packages readline)
(gnu packages tex)
(gnu packages texinfo)
(gnu packages version-control))
(package
(name "guile")
(version "3.0.99-git") ;funky version number
(source #f) ;no source
(build-system gnu-build-system)
(native-inputs
(append (list autoconf
automake
libtool
gnu-gettext
flex
texinfo
texlive-base ;for "make pdf"
texlive-epsf
gperf
git
gdb
strace
readline
lzip
pkg-config)
;; When cross-compiling, a native version of Guile itself is
;; needed.
(if (%current-target-system)
(list this-package)
'())))
(inputs
(list libffi bash-minimal))
(propagated-inputs
(list libunistring libgc))
(native-search-paths
(list (search-path-specification
(variable "GUILE_LOAD_PATH")
(files '("share/guile/site/3.0")))
(search-path-specification
(variable "GUILE_LOAD_COMPILED_PATH")
(files '("lib/guile/3.0/site-ccache")))))
(synopsis "Scheme implementation intended especially for extensions")
(description
"Guile is the GNU Ubiquitous Intelligent Language for Extensions,
and it's actually a full-blown Scheme implementation!")
(home-page "https://www.gnu.org/software/guile/")
(license license:lgpl3+))
```
Quite a bit of boilerplate, but now someone who’d like to hack on Guile
just needs to run:
```
guix shell
```
That gives them a shell containing all the dependencies of Guile: those
listed above, but also _implicit dependencies_ such as the GCC tool
chain, GNU Make, sed, grep, and so on. The chef’s recommendation:
```
guix shell -CP
```
That gives a shell in an isolated container, and all the dependencies
show up in `$HOME/.guix-profile`, which plays well with caches such as
[`config.cache`](https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.70/html_node/Cache-Files.html)
and absolute file names recorded in generated `Makefile`s and the likes.
The fact that the shell runs in a container brings peace of mind:
nothing but the current directory and Guile’s dependencies is visible
inside the container; nothing from the system can possibly interfere
with your development.
# Level 1: Building with Guix
Now that we have a package definition, why not also take advantage of it
so we can build Guile with Guix? We had left the `source` field empty,
because `guix shell` above only cares about the *inputs* of our
package—so it can set up the development environment—not about the
package itself.
To build the package with Guix, we’ll need to fill out the `source`
field, along these lines:
```scheme
(use-modules (guix)
(guix git-download) ;for ‘git-predicate’
…)
(define vcs-file?
;; Return true if the given file is under version control.
(or (git-predicate (current-source-directory))
(const #t))) ;not in a Git checkout
(package
(name "guile")
(version "3.0.99-git") ;funky version number
(source (local-file "." "guile-checkout"
#:recursive? #t
#:select? vcs-file?))
…)
```
Here’s what we changed:
1. We add `(guix git-download)` to our set of imported modules, so we
can use its `git-predicate` procedure.
2. We defined `vcs-file?` as a procedure that returns true when passed
a file that is under version control. For good measure, we add a
fallback case for when we’re not in a Git checkout: always return
true.
3. We set `source` to a
[`local-file`](https://guix.gnu.org/manual/devel/en/html_node/G_002dExpressions.html#index-local_002dfile)—a
recursive copy of the current directory (`"."`), limited to files
under version control (the `#:select?` bit).
From there on, our `guix.scm` file serves a second purpose: it lets us
build the software with Guix. The whole point of building with Guix is
that it’s a “clean” build—you can be sure nothing from your working tree
or system interferes with the build result—and it lets you test a
variety of things. First, you can do a plain native build:
```
guix build -f guix.scm
```
But you can also build for another system (possibly after setting up
[offloading](https://guix.gnu.org/manual/devel/en/html_node/Daemon-Offload-Setup.html)
or [transparent
emulation](https://guix.gnu.org/manual/devel/en/html_node/Virtualization-Services.html#index-emulation)):
```
guix build -f guix.scm -s aarch64-linux -s riscv64-linux
```
… or cross-compile:
```
guix build -f guix.scm --target=x86_64-w64-mingw32
```
You can also use [package transformation
options](https://guix.gnu.org/manual/en/html_node/Package-Transformation-Options.html)
to test package variants:
```
# What if we built with Clang instead of GCC?
guix build -f guix.scm \
--with-c-toolchain=guile@3.0.99-git=clang-toolchain
# What about that under-tested configure flag?
guix build -f guix.scm \
--with-configure-flag=guile@3.0.99-git=--disable-networking
```
Handy!
# Level 2: The repository as a channel
We now have a Git repository containing (among other things) a package
definition. Can’t we turn it into a
[*channel*](https://guix.gnu.org/manual/devel/en/html_node/Channels.html)?
After all, channels are designed to ship package definitions to users,
and that’s exactly what we’re doing with our `guix.scm`. Granted, our
Git repository is one package definition lost in a sea of code—in this
case, Guile—, but still.
Turns out we can indeed turn into a channel, but with one caveat: we
must create a separate directory for the `.scm` file(s) of our channel
so that `guix pull` doesn’t end loading unrelated `.scm` files when
someone pulls the channel—and in Guile, there are lots of them! So
we’ll start like this, keeping a top-level `guix.scm` symlink for the
sake of `guix shell`:
```
mkdir .guix
mv guix.scm .guix/guile-package.scm
ln -s .guix/guile-package.scm guix.scm
```
(In Guile we actually used `build-aux/guix` instead of `.guix`, but the
latter is probably clearer.) To make it usable as part of a channel, we
need to turn our `guix.scm` file into a
[module](https://guix.gnu.org/manual/devel/en/html_node/Package-Modules.html):
we do that by changing the `use-modules` form at the top to a
`define-module` form. We also need to actually *export* a package
variable, with `define-public`, while still returning the package value
at the end of the file so we can still use `guix shell` and `guix build
-f guix.scm`. The end result looks like this (not repeating things that
haven’t changed):
```scheme
(define-module (guile-package)
#:use-module (guix)
#:use-module (guix git-download) ;for ‘git-predicate’
…)
(define-public guile
(package
(name "guile")
(version "3.0.99-git") ;funky version number
…))
;; Return the package object define above at the end of the module.
guile
```
We need one last thing: a [`.guix-channel`
file](https://guix.gnu.org/manual/devel/en/html_node/Package-Modules-in-a-Sub_002ddirectory.html)
so Guix knows where to look for package modules in our repository:
```scheme
;; This file lets us present this repo as a Guix channel.
(channel
(version 0)
(directory ".guix")) ;look for package modules under .guix/
```
To recap, we now have these files:
```
.
├── .guix-channel
├── guix.scm → .guix/guile-package.scm
└── .guix
    └── guile-package.scm
```
And that’s it: we have a channel! (We could do better and support
[*channel
authentication*](https://guix.gnu.org/manual/en/html_node/Specifying-Channel-Authorizations.html)
so users know they’re pulling genuine code. We’ll spare you the details
here but it’s worth considering!) Users can pull from this channel by
[adding it to
`~/.config/guix/channels.scm`](https://guix.gnu.org/manual/devel/en/html_node/Specifying-Additional-Channels.html),
along these lines:
```
(append (list (channel
(name 'guile)
(url "https://git.savannah.gnu.org/git/guile.git")
(branch "main")))
%default-channels)
```
After running `guix pull`, we can see the new package:
```
$ guix describe
Generation 264 May 26 2023 16:00:35 (current)
guile 36fd2b4
repository URL: https://git.savannah.gnu.org/git/guile.git
branch: main
commit: 36fd2b4920ae926c79b936c29e739e71a6dff2bc
guix c5bc698
repository URL: https://git.savannah.gnu.org/git/guix.git
commit: c5bc698e8922d78ed85989985cc2ceb034de2f23
$ guix package -A ^guile$
guile 3.0.99-git out,debug guile-package.scm:51:4
guile 3.0.9 out,debug gnu/packages/guile.scm:317:2
guile 2.2.7 out,debug gnu/packages/guile.scm:258:2
guile 2.2.4 out,debug gnu/packages/guile.scm:304:2
guile 2.0.14 out,debug gnu/packages/guile.scm:148:2
guile 1.8.8 out gnu/packages/guile.scm:77:2
$ guix build guile@3.0.99-git
[…]
/gnu/store/axnzbl89yz7ld78bmx72vpqp802dwsar-guile-3.0.99-git-debug
/gnu/store/r34gsij7f0glg2fbakcmmk0zn4v62s5w-guile-3.0.99-git
```
That’s how, as a developer, you get your software delivered directly in
the hands of users! No intermediaries, yet no loss of transparency and
provenance tracking.
With that in place, it also becomes trivial for anyone to create Docker
images, Deb/RPM packages, or plain tarball of the software with [`guix
pack`](https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix-pack.html):
```
# How about a Docker image of our Guile snapshot?
guix pack -f docker -S /bin=bin guile@3.0.99-git
# And a relocatable RPM?
guix pack -f rpm -R -S /bin=bin guile@3.0.99-git
```
# Bonus: Package variants
We now have an actual channel, but it contains only one package. While
we’re at it, we can [define package
variants](https://guix.gnu.org/manual/devel/en/html_node/Defining-Package-Variants.html)
in our `guile-package.scm` file, variants that we want to be able to
test as Guile developers—similar to what we did above with
transformation options. We can add them like so:
```scheme
;; This is the ‘.guix/guile-package.scm’ file.
(define-module (guile-package)
…)
(define-public guile
…)
(define (package-with-configure-flags p flags)
"Return P with FLAGS as addition 'configure' flags."
(package/inherit p
(arguments
(substitute-keyword-arguments (package-arguments p)
((#:configure-flags original-flags #~'())
#~(append #$original-flags #$flags))))))
(define-public guile-without-threads
(package
(inherit (package-with-configure-flags guile
#~'("--without-threads")))
(name "guile-without-threads")))
(define-public guile-without-networking
(package
(inherit (package-with-configure-flags guile
#~'("--disable-networking")))
(name "guile-without-networking")))
;; Return the package object define above at the end of the module.
guile
```
We can build these variants as regular packages once we’ve pulled the
channel, or, if we have a checkout of Guile, we can run a command like
this one from the top level:
```
guix build -L $PWD/.guix guile-without-threads
```
# Level 3: Setting up continuous integration
This channel becomes even more interesting once we set up [continuous
integration](https://en.wikipedia.org/wiki/Continuous_integration) (CI).
There are several ways to do that.
You can use one of the mainstream continuous integration tools, such as
GitLab-CI. To do that, you need to make sure you run jobs into a Docker
image or virtual machine that has Guix installed. If we were to do that
in the case of Guile, we’d have a job that runs a shell command like
this one:
```
guix build -L $PWD/.guix guile@3.0.99-git
```
Doing this works great and has the advantage of being easy to achieve on
your favorite CI platform.
That said, you’ll really get the most of it by using
[Cuirass](https://guix.gnu.org/en/cuirass), a CI tool designed for and
tightly integrated with Guix. Using it is more work than using a hosted
CI tool because you first need to set it up, but that setup phase is
greatly simplified if you use its Guix System
[service](https://guix.gnu.org/manual/devel/en/html_node/Continuous-Integration.html).
Going back to our example, we give Cuirass a spec file that goes like
this:
```scheme
;; Cuirass spec file to build all the packages of the ‘guile’ channel.
(list (specification
(name "guile")
(build '(channels guile))
(channels
(append (list (channel
(name 'guile)
(url "https://git.savannah.gnu.org/git/guile.git")
(branch "main")))
%default-channels))))
```
It differs from what you’d do with other CI tools in two important ways:
- Cuirass knows it’s tracking *two* channels, `guile` and `guix`.
Indeed, our own `guile` package depends on many packages provided by
the `guix` channel—GCC, the GNU libc, libffi, and so on. Changes to
packages from the `guix` channel can potentially influence our
`guile` build and this is something we’d like to see as soon as
possible as Guile developers.
- Build results are not thrown away: they can be distributed as
[*substitutes*](https://guix.gnu.org/manual/devel/en/html_node/Substitutes.html)
so that users of our `guile` channel transparently get pre-built
binaries!
From a developer’s viewpoint, the end result is this [status
page](https://ci.guix.gnu.org/jobset/guile) listing *evaluations*: each
evaluation is a combination of commits of the `guix` and `guile`
channels providing a number of *jobs*—one job per package defined in
`guile-package.scm` times the number of target architectures.
As for substitutes, they come for free! As an example, our `guile`
jobset being built on ci.guix.gnu.org, one automatically gets
substitutes for it from ci.guix.gnu.org. It’s as simple as this.
# Bonus: Build manifest
The Cuirass spec above is convenient: it builds every package in our
channel, which includes a few variants. However, this might may be
insufficiently expressive in some cases: one might want specific
cross-compilation jobs, transformations, Docker images, RPM/Deb
packages, or even system tests.
To achieve that, you can write a
[*manifest*](https://guix.gnu.org/manual/devel/en/html_node/Writing-Manifests.html).
The one we have for Guile has entries for the package variants we
defined above, as well as additional variants and cross builds:
```scheme
;; This is ‘.guix/manifest.scm’ FIXME: move modules to .guix/modules/.
(use-modules (guix)
(guix profiles)
(guile-package)) ;import our own package module
(define* (package->manifest-entry* package system
#:key target)
"Return a manifest entry for PACKAGE on SYSTEM, optionally cross-compiled to
TARGET."
(manifest-entry
(inherit (package->manifest-entry package))
(name (string-append (package-name package) "." system
(if target
(string-append "." target)
"")))
(item (with-parameters ((%current-system system)
(%current-target-system target))
package))))
(define native-builds
(manifest
(append (map (lambda (system)
(package->manifest-entry* guile system))
'("x86_64-linux" "i686-linux"
"aarch64-linux" "armhf-linux"
"powerpc64le-linux"))
(map (lambda (guile)
(package->manifest-entry* guile "x86_64-linux"))
(cons (package
(inherit (package-with-c-toolchain
guile
`(("clang-toolchain"
,(specification->package
"clang-toolchain")))))
(name "guile-clang"))
(list guile-without-threads
guile-without-networking
guile-debug
guile-strict-typing))))))
(define cross-builds
(manifest
(map (lambda (target)
(package->manifest-entry* guile "x86_64-linux"
#:target target))
'("i586-pc-gnu"
"aarch64-linux-gnu"
"riscv64-linux-gnu"
"i686-w64-mingw32"
"x86_64-linux-gnu"))))
(concatenate-manifests (list native-builds cross-builds))
```
We won’t go into the details of this manifest; suffice to say that it
provides additional flexibility. We now need to tell Cuirass to build
this manifest, which is done with a spec slightly different from the
previous one:
```scheme
;; Cuirass spec file to build all the packages of the ‘guile’ channel.
(list (specification
(name "guile")
(build '(manifest ".guix/manifest.scm"))
(channels
(append (list (channel
(name 'guile)
(url "https://git.savannah.gnu.org/git/guile.git")
(branch "main")))
%default-channels))))
```
This is it!
# Wrapping up
We picked Guile as the running example in this post and you can see the
result here:
- [`.guix-channel`](https://git.savannah.gnu.org/cgit/guile.git/tree/.guix-channel?id=36fd2b4920ae926c79b936c29e739e71a6dff2bc);
- [`.guix/modules/guile-package.scm`](https://git.savannah.gnu.org/cgit/guile.git/tree/build-aux/guix/guile-package.scm?id=36fd2b4920ae926c79b936c29e739e71a6dff2bc)
with the top-level `guix.scm` symlink;
- [`.guix/manifest.scm`](https://git.savannah.gnu.org/cgit/guile.git/tree/build-aux/manifest.scm?id=36fd2b4920ae926c79b936c29e739e71a6dff2bc).
These days, repositories are commonly splattered with dot files for
various tools: `.envrc`, `.gitlab-ci.yml`, `.github/workflows`,
`Dockerfile`, `.buildpacks`, `Aptfile`, `requirements.txt`, and whatnot.
It may sound like we’re proposing a bunch of *additional* files, but in
fact those files are expressive enough to *supersede* most or all of
those listed above.
With a couple of files, we get support for:
- development environments (`guix shell`);
- pristine test builds, including for package variants and for
cross-compilation (`guix build`);
- continuous integration;
- continuous delivery to users (*via* the channel and with pre-built
binaries);
- generation of derivative build artifacts such as Docker images or
Deb/RPM packages (`guix pack`).
At the Guix headquarters, we’re quite happy about the result. We’ve
been building a unified tool set for reproducible software deployment
when all the rage is on specialized tools building on one another;
hopefully this is an illustration of how you as a developer can benefit
from it!