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doc: cookbook: Add “Software Development” chapter. 

* doc/guix-cookbook.texi (Software Development): New chapter.
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@ -22,7 +22,7 @@ Copyright @copyright{} 2020 André Batista@*
Copyright @copyright{} 2020 Christine Lemmer-Webber@*
Copyright @copyright{} 2021 Joshua Branson@*
Copyright @copyright{} 2022, 2023 Maxim Cournoyer@*
Copyright @copyright{} 2023 Ludovic Courtès
Copyright @copyright{} 2023 Ludovic Courtès@*
Copyright @copyright{} 2023 Thomas Ieong
Permission is granted to copy, distribute and/or modify this document
@ -78,6 +78,7 @@ manual}).
* System Configuration:: Customizing the GNU System
* Containers:: Isolated environments and nested systems
* Advanced package management:: Power to the users!
* Software Development:: Environments, continuous integration, etc.
* Environment management:: Control environment
* Installing Guix on a Cluster:: High-performance computing.
@ -4099,6 +4100,654 @@ mkdir -p "$GUIX_EXTRA_PROFILES/my-project"
It's safe to delete the Guix channel profile you've just installed with the
channel specification, the project profile does not depend on it.
@node Software Development
@chapter Software Development
@cindex development, with Guix
@cindex software development, with Guix
Guix is a handy tool for developers; @command{guix shell}, in
particular, gives a standalone development environment for your package,
no matter what language(s) it's written in (@pxref{Invoking guix
shell,,, guix, GNU Guix Reference Manual}). To benefit from it, you
have to initially write a package definition and have it either in Guix
proper, or in a channel, or directly in your project's source tree as a
@file{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
@command{guix shell}, with no arguments.
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 chapter describes a set of files developers can add to their
repository to set up Guix-based development environments, continuous
integration, and continuous delivery---all at once@footnote{This chapter
is adapted from a
@uref{https://guix.gnu.org/en/blog/2023/from-development-environments-to-continuous-integrationthe-ultimate-guide-to-software-development-with-guix/,
blog post} published in June 2023 on the Guix web site.}.
@menu
* Getting Started:: Step 0: using `guix shell'.
* Building with Guix:: Step 1: building your code.
* The Repository as a Channel:: Step 2: turning the repo in a channel.
* Package Variants:: Bonus: Defining variants.
* Setting Up Continuous Integration:: Step 3: continuous integration.
* Build Manifest:: Bonus: Manifest.
* Wrapping Up:: Recap.
@end menu
@node Getting Started
@section Getting Started
How do we go about ``Guixifying'' a repository? The first step, as we've
seen, will be to add a @file{guix.scm} at the root of the repository in
question. We'll take @uref{https://www.gnu.org/software/guile,Guile} as
an example in this chapter: 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
@file{guix.scm} looks like the usual package definition (@pxref{Defining
Packages,,, guix, GNU Guix Reference Manual}), just without the
@code{define-public} bit:
@lisp
;; 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 base)
(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+))
@end lisp
Quite a bit of boilerplate, but now someone who'd like to hack on Guile
now only needs to run:
@lisp
guix shell
@end lisp
That gives them a shell containing all the dependencies of Guile: those
listed above, but also @emph{implicit dependencies} such as the GCC tool
chain, GNU@ Make, sed, grep, and so on. @xref{Invoking guix shell,,,
guix, GNU Guix Reference Manual}, for more info on @command{guix shell}.
@quotation The chef's recommendation
Our suggestion is to create development environments like this:
@example
guix shell --container --link-profile
@end example
@noindent
... or, for short:
@example
guix shell -CP
@end example
That gives a shell in an isolated container, and all the dependencies
show up in @code{$HOME/.guix-profile}, which plays well with caches such
as @file{config.cache} (@pxref{Cache Files,,, autoconf, Autoconf}) and
absolute file names recorded in generated @code{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.
@end quotation
@node Building with Guix
@section Level 1: Building with Guix
Now that we have a package definition (@pxref{Getting Started}), why not
also take advantage of it so we can build Guile with Guix? We had left
the @code{source} field empty, because @command{guix shell} above only
cares about the @emph{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 @code{source}
field, along these lines:
@lisp
(use-modules (guix)
(guix git-download) ;for ‘git-predicate’
@dots{})
(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?))
@dots{})
@end lisp
Here's what we changed compared to the previous section:
@enumerate
@item
We added @code{(guix git-download)} to our set of imported modules, so
we can use its @code{git-predicate} procedure.
@item
We defined @code{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.
@item
We set @code{source} to a
@uref{https://guix.gnu.org/manual/devel/en/html_node/G_002dExpressions.html#index-local_002dfile,@code{local-file}}---a
recursive copy of the current directory (@code{"."}), limited to files
under version control (the @code{#:select?} bit).
@end enumerate
From there on, our @file{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:
@example
guix build -f guix.scm
@end example
But you can also build for another system (possibly after setting up
@pxref{Daemon Offload Setup, offloading,, guix, GNU Guix Reference Manual}
or
@pxref{Virtualization Services, transparent emulation,, guix, GNU Guix
Reference Manual}):
@lisp
guix build -f guix.scm -s aarch64-linux -s riscv64-linux
@end lisp
@noindent
@dots{} or cross-compile:
@lisp
guix build -f guix.scm --target=x86_64-w64-mingw32
@end lisp
You can also use @dfn{package transformations} to test package variants
(@pxref{Package Transformations,,, guix, GNU Guix Reference Manual}):
@example
# 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
@end example
Handy!
@node The Repository as a Channel
@section Level 2: The Repository as a Channel
We now have a Git repository containing (among other things) a package
definition (@pxref{Building with Guix}). Can't we turn it into a
@dfn{channel} (@pxref{Channels,,, guix, GNU Guix Reference Manual})?
After all, channels are designed to ship package definitions to users,
and that's exactly what we're doing with our @file{guix.scm}.
Turns out we can indeed turn it into a channel, but with one caveat: we
must create a separate directory for the @code{.scm} file(s) of our
channel so that @command{guix pull} doesn't load unrelated @code{.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 @file{guix.scm}
symlink for the sake of @command{guix shell}:
@lisp
mkdir -p .guix/modules
mv guix.scm .guix/modules/guile-package.scm
ln -s .guix/modules/guile-package.scm guix.scm
@end lisp
To make it usable as part of a channel, we need to turn our
@file{guix.scm} file into a @dfn{package module} (@pxref{Package
Modules,,, guix, GNU Guix Reference Manual}):
we do that by changing the @code{use-modules} form at the top to a
@code{define-module} form. We also need to actually @emph{export} a
package variable, with @code{define-public}, while still returning the
package value at the end of the file so we can still use
@command{guix shell} and @command{guix build -f guix.scm}. The end result
looks like this (not repeating things that haven't changed):
@lisp
(define-module (guile-package)
#:use-module (guix)
#:use-module (guix git-download) ;for ‘git-predicate’
@dots{})
(define vcs-file?
;; Return true if the given file is under version control.
(or (git-predicate (dirname (dirname (current-source-directory))))
(const #t))) ;not in a Git checkout
(define-public guile
(package
(name "guile")
(version "3.0.99-git") ;funky version number
(source (local-file "../.." "guile-checkout"
#:recursive? #t
#:select? vcs-file?))
@dots{}))
;; Return the package object define above at the end of the module.
guile
@end lisp
We need one last thing: a
@uref{https://guix.gnu.org/manual/devel/en/html_node/Package-Modules-in-a-Sub_002ddirectory.html,@code{.guix-channel}
file} so Guix knows where to look for package modules in our repository:
@lisp
;; This file lets us present this repo as a Guix channel.
(channel
(version 0)
(directory ".guix/modules")) ;look for package modules under .guix/modules/
@end lisp
To recap, we now have these files:
@lisp
.
├── .guix-channel
├── guix.scm → .guix/modules/guile-package.scm
└── .guix
    └── modules
       └── guile-package.scm
@end lisp
And that's it: we have a channel! (We could do better and support
@uref{https://guix.gnu.org/manual/devel/en/html_node/Specifying-Channel-Authorizations.html,@emph{channel
authentication}} 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
@uref{https://guix.gnu.org/manual/devel/en/html_node/Specifying-Additional-Channels.html,adding
it to @code{~/.config/guix/channels.scm}}, along these lines:
@lisp
(append (list (channel
(name 'guile)
(url "https://git.savannah.gnu.org/git/guile.git")
(branch "main")))
%default-channels)
@end lisp
After running @command{guix pull}, we can see the new package:
@example
$ 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
[@dots{}]
/gnu/store/axnzbl89yz7ld78bmx72vpqp802dwsar-guile-3.0.99-git-debug
/gnu/store/r34gsij7f0glg2fbakcmmk0zn4v62s5w-guile-3.0.99-git
@end example
That's how, as a developer, you get your software delivered directly
into 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 a plain tarball with @command{guix pack}
(@pxref{Invoking guix pack,,, guix, GNU Guix Reference Manual}):
@example
# 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
@end example
@node Package Variants
@section Bonus: Package Variants
We now have an actual channel, but it contains only one package
(@pxref{The Repository as a Channel}). While we're at it, we can define
@dfn{package variants} (@pxref{Defining Package Variants,,, guix, GNU
Guix Reference Manual}) in our @file{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:
@lisp
;; This is the ‘.guix/modules/guile-package.scm’ file.
(define-module (guile-package)
@dots{})
(define-public guile
@dots{})
(define (package-with-configure-flags p flags)
"Return P with FLAGS as additional 'configure' flags."
(package/inherit p
(arguments
(substitute-keyword-arguments (package-arguments p)
((#:configure-flags original-flags #~(list))
#~(append #$original-flags #$flags))))))
(define-public guile-without-threads
(package
(inherit (package-with-configure-flags guile
#~(list "--without-threads")))
(name "guile-without-threads")))
(define-public guile-without-networking
(package
(inherit (package-with-configure-flags guile
#~(list "--disable-networking")))
(name "guile-without-networking")))
;; Return the package object defined above at the end of the module.
guile
@end lisp
We can build these variants as regular packages once we've pulled the
channel. Alternatively, from a checkout of Guile, we can run a command
like this one from the top level:
@lisp
guix build -L $PWD/.guix/modules guile-without-threads
@end lisp
@node Setting Up Continuous Integration
@section Level 3: Setting Up Continuous Integration
@cindex continuous integration (CI)
The channel we defined above (@pxref{The Repository as a Channel})
becomes even more interesting once we set up
@uref{https://en.wikipedia.org/wiki/Continuous_integration,
@dfn{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 in 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:
@lisp
guix build -L $PWD/.guix/modules guile@@3.0.99-git
@end lisp
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
@uref{https://guix.gnu.org/en/cuirass,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
(@pxref{Continuous Integration,,, guix, GNU Guix Reference Manual}).
Going back to our example, we give Cuirass a spec file that goes like
this:
@lisp
;; 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))))
@end lisp
It differs from what you'd do with other CI tools in two important ways:
@itemize
@item
Cuirass knows it's tracking @emph{two} channels, @code{guile} and
@code{guix}. Indeed, our own @code{guile} package depends on many
packages provided by the @code{guix} channel---GCC, the GNU libc,
libffi, and so on. Changes to packages from the @code{guix} channel can
potentially influence our @code{guile} build and this is something we'd
like to see as soon as possible as Guile developers.
@item
Build results are not thrown away: they can be distributed as
@dfn{substitutes} so that users of our @code{guile} channel
transparently get pre-built binaries! (@pxref{Substitutes,,, guix, GNU
Guix Reference Manual}, for background info on substitutes.)
@end itemize
From a developer's viewpoint, the end result is this
@uref{https://ci.guix.gnu.org/jobset/guile,status page} listing
@emph{evaluations}: each evaluation is a combination of commits of the
@code{guix} and @code{guile} channels providing a number of
@emph{jobs}---one job per package defined in @file{guile-package.scm}
times the number of target architectures.
As for substitutes, they come for free! As an example, since our
@code{guile} jobset is built on ci.guix.gnu.org, which runs
@command{guix publish} (@pxref{Invoking guix publish,,, guix, GNU Guix
Reference Manual}) in addition to Cuirass, one automatically gets
substitutes for @code{guile} builds from ci.guix.gnu.org; no additional
work is needed for that.
@node Build Manifest
@section Bonus: Build manifest
The Cuirass spec above is convenient: it builds every package in our
channel, which includes a few variants (@pxref{Setting Up Continuous
Integration}). However, this might 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 @dfn{manifest} (@pxref{Writing
Manifests,,, guix, GNU Guix Reference Manual}). The one we have for
Guile has entries for the package variants we defined above, as well as
additional variants and cross builds:
@lisp
;; This is ‘.guix/manifest.scm’.
(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))
@end lisp
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:
@lisp
;; 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))))
@end lisp
We changed the @code{(build @dots{})} part of the spec to
@code{'(manifest ".guix/manifest.scm")} so that it would pick our
manifest, and that's it!
@node Wrapping Up
@section Wrapping Up
We picked Guile as the running example in this chapter and you can see
the result here:
@itemize
@item
@uref{https://git.savannah.gnu.org/cgit/guile.git/tree/.guix-channel?id=cd57379b3df636198d8cd8e76c1bfbc523762e79,@code{.guix-channel}};
@item
@uref{https://git.savannah.gnu.org/cgit/guile.git/tree/.guix/modules/guile-package.scm?id=cd57379b3df636198d8cd8e76c1bfbc523762e79,@code{.guix/modules/guile-package.scm}}
with the top-level @file{guix.scm} symlink;
@item
@uref{https://git.savannah.gnu.org/cgit/guile.git/tree/.guix/manifest.scm?id=cd57379b3df636198d8cd8e76c1bfbc523762e79,@code{.guix/manifest.scm}}.
@end itemize
These days, repositories are commonly peppered with dot files for
various tools: @code{.envrc}, @code{.gitlab-ci.yml},
@code{.github/workflows}, @code{Dockerfile}, @code{.buildpacks},
@code{Aptfile}, @code{requirements.txt}, and whatnot. It may sound like
we're proposing a bunch of @emph{additional} files, but in fact those
files are expressive enough to @emph{supersede} most or all of those
listed above.
With a couple of files, we get support for:
@itemize
@item
development environments (@command{guix shell});
@item
pristine test builds, including for package variants and for
cross-compilation (@command{guix build});
@item
continuous integration (with Cuirass or with some other tool);
@item
continuous delivery to users (@emph{via} the channel and with pre-built
binaries);
@item
generation of derivative build artifacts such as Docker images or
Deb/RPM packages (@command{guix pack}).
@end itemize
This a nice (in our view!) unified tool set for reproducible software
deployment, and an illustration of how you as a developer can benefit
from it!
@c *********************************************************************
@node Environment management
@chapter Environment management