HACKING

   1 -*- mode: org; coding: utf-8; -*-
   2
   3 #+TITLE: Hacking GNU Guix and Its Incredible Distro
   4
   5 Copyright © 2012, 2013, 2014 Ludovic Courtès <ludo@gnu.org>
   6 Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
   7 Copyright © 2014 Pierre-Antoine Rault <par@rigelk.eu>
   8
   9   Copying and distribution of this file, with or without modification,
  10   are permitted in any medium without royalty provided the copyright
  11   notice and this notice are preserved.
  12
  13
  14 * Building from Git
  15
  16 When building Guix from a checkout, the following packages are required in
  17 addition to those mentioned in the installation instructions:
  18
  19   - [[http://www.gnu.org/software/autoconf/][GNU Autoconf]]
  20   - [[http://www.gnu.org/software/automake/][GNU Automake]]
  21   - [[http://www.gnu.org/software/gettext/][GNU Gettext]]
  22   - [[http://www.graphviz.org/][Graphviz]]
  23
  24 Run ‘./bootstrap’ to download the Nix daemon source code and to generate the
  25 build system infrastructure using autoconf.  It reports an error if an
  26 inappropriate version of the above packages is being used.
  27
  28 If you get an error like this one:
  29
  30   configure.ac:46: error: possibly undefined macro: PKG_CHECK_MODULES
  31
  32 it probably means that Autoconf couldn’t find ‘pkg.m4’, which is provided by
  33 pkg-config.  Make sure that ‘pkg.m4’ is available.  For instance, if you
  34 installed Automake in ‘/usr/local’, it wouldn’t look for ‘.m4’ files in
  35 ‘/usr/share’.  So you have to invoke the following command in that case
  36
  37   $ export ACLOCAL_PATH=/usr/share/aclocal
  38
  39 See “info '(automake) Macro Search Path'” for more information.
  40
  41 Then, run ‘./configure’ as usual.
  42
  43 Finally, you have to invoke ‘make check’ to run tests.  If anything fails,
  44 take a look at “info '(guix) Installation'” or send a message to
  45 <guix-devel@gnu.org>.
  46
  47 * Running Guix before it is installed
  48
  49 Command-line tools can be used even if you have not run "make install".
  50 To do that, prefix each command with ‘./pre-inst-env’, as in:
  51
  52   ./pre-inst-env guix build --help
  53
  54 Similarly, for a Guile session using the Guix modules:
  55
  56   ./pre-inst-env guile -c '(use-modules (guix utils)) (pk (%current-system))'
  57
  58 The ‘pre-inst-env’ script sets up all the environment variables
  59 necessary to support this.
  60
  61 * The Perfect Setup
  62
  63 The Perfect Setup to hack on Guix is basically the perfect setup used
  64 for Guile hacking (info "(guile) Using Guile in Emacs").  First, you
  65 need more than an editor, you need [[http://www.gnu.org/software/emacs][Emacs]], empowered by the wonderful
  66 [[http://nongnu.org/geiser/][Geiser]].
  67
  68 Geiser allows for interactive and incremental development from within
  69 Emacs: code compilation and evaluation from within buffers, access to
  70 on-line documentation (docstrings), context-sensitive completion, M-. to
  71 jump to an object definition, a REPL to try out your code, and more.
  72
  73 To actually edit the code, Emacs already has a neat Scheme mode.  But in
  74 addition to that, you must not miss [[http://www.emacswiki.org/emacs/ParEdit][Paredit]].  It provides facilities to
  75 directly operate on the syntax tree, such as raising an s-expression or
  76 wrapping it, swallowing or rejecting the following s-expression, etc.
  77
  78 * Submitting Patches
  79
  80 Development is done using the Git distributed version control system.  Thus,
  81 access to the repository is not strictly necessary.  We welcome contributions
  82 in the form of patches as produced by ‘git format-patch’ sent to
  83 guix-devel@gnu.org.  Please write commit logs in the [[http://www.gnu.org/prep/standards/html_node/Change-Logs.html#Change-Logs][GNU ChangeLog
  84 format]]; you can check the commit history for examples.
  85
  86 Before submitting a patch that adds or modifies a package definition, please
  87 run ‘guix lint PACKAGE’, where PACKAGE is the name of the new or modified
  88 package, and fix any errors it reports.  In addition, please make sure the
  89 package builds on your platform, using ‘guix build’.  You may also want to
  90 check that dependent package (if applicable) are not affected by the change;
  91 ‘guix refresh --list-dependent PACKAGE’ will help you do that.
  92
  93 When posting a patch to the mailing list, use "[PATCH] ..." as a subject.  You
  94 may use your email client or the ‘git send-mail’ command.
  95
  96 As you become a regular contributor, you may find it convenient to have write
  97 access to the repository (see below.)
  98
  99 * Coding Style
 100
 101 In general our code follows the [[info:standards][GNU Coding Standards]] (GCS).  However, the GCS
 102 do not say much about Scheme, so here are some additional rules.
 103
 104 ** Programming Paradigm
 105
 106 Scheme code in Guix is written in a purely functional style.  One exception is
 107 code that involves input/output, and procedures that implement low-level
 108 concepts, such as the ‘memoize’ procedure.
 109
 110 ** Modules
 111
 112 Guile modules that are meant to be used on the builder side must live in the
 113 (guix build …) name space.  They must not refer to other Guix or GNU modules.
 114 However, it is OK for a “host-side” module to use a build-side module.
 115
 116 Modules that deal with the broader GNU system should be in the (gnu …) name
 117 space rather than (guix …).
 118
 119 ** Data Types and Pattern Matching
 120
 121 The tendency in classical Lisp is to use lists to represent everything, and
 122 then to browse them “by hand” using ‘car’, ‘cdr’, ‘cadr’, and co.  There are
 123 several problems with that style, notably the fact that it is hard to read,
 124 error-prone, and a hindrance to proper type error reports.
 125
 126 Guix code should define appropriate data types (for instance, using
 127 ‘define-record-type*’) rather than abuse lists.  In addition, it should use
 128 pattern matching, via Guile’s (ice-9 match) module, especially when matching
 129 lists.
 130
 131 ** Formatting Code
 132
 133 When writing Scheme code, we follow common wisdom among Scheme programmers.
 134 In general, we follow the [[http://mumble.net/~campbell/scheme/style.txt][Riastradh's Lisp Style Rules]].  This document happens
 135 to describe the conventions mostly used in Guile’s code too.  It is very
 136 thoughtful and well written, so please do read it.
 137
 138 Some special forms introduced in Guix, such as the ‘substitute*’ macro, have
 139 special indentation rules.  These are defined in the .dir-locals.el file,
 140 which Emacs automatically uses.  If you do not use Emacs, please make sure to
 141 let your editor know the rules.
 142
 143 We require all top-level procedures to carry a docstring.  This requirement
 144 can be relaxed for simple private procedures in the (guix build …) name space,
 145 though.
 146
 147 Procedures should not have more than four positional parameters.  Use keyword
 148 parameters for procedures that take more than four parameters.
 149
 150 * Commit Access
 151
 152 For frequent contributors, having write access to the repository is
 153 convenient.  When you deem it necessary, feel free to ask for it on the
 154 mailing list.  When you get commit access, please make sure to follow the
 155 policy below (discussions of the policy can take place on guix-devel@gnu.org.)
 156
 157 Non-trivial patches should always be posted to guix-devel@gnu.org (trivial
 158 patches include fixing typos, etc.)
 159
 160 For patches that just add a new package, and a simple one, it’s OK to commit,
 161 if you’re confident (which means you successfully built it in a chroot setup,
 162 and have done a reasonable copyright and license auditing.)  Likewise for
 163 package upgrades, except upgrades that trigger a lot of rebuilds (for example,
 164 upgrading GnuTLS or GLib.)  We have a mailing list for commit notifications
 165 (guix-commits@gnu.org), so people can notice.  Before pushing your changes,
 166 make sure to run ‘git pull --rebase’.
 167
 168 For anything else, please post to guix-devel@gnu.org and leave time for a
 169 review, without committing anything.  If you didn’t receive any reply
 170 after two weeks, and if you’re confident, it’s OK to commit.
 171
 172 That last part is subject to being adjusted, allowing individuals to commit
 173 directly on non-controversial changes on parts they’re familiar with.