HACKING

   1 -*- mode: org; coding: utf-8; -*-
   2
   3 #+TITLE: Hacking GNU Guix and Its Incredible Distro
   4
   5 Copyright © 2012, 2013, 2014, 2015 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 See the same-named section in the manual.
  50
  51 * The Perfect Setup
  52
  53 The Perfect Setup to hack on Guix is basically the perfect setup used
  54 for Guile hacking (info "(guile) Using Guile in Emacs").  First, you
  55 need more than an editor, you need [[http://www.gnu.org/software/emacs][Emacs]], empowered by the wonderful
  56 [[http://nongnu.org/geiser/][Geiser]].
  57
  58 Geiser allows for interactive and incremental development from within
  59 Emacs: code compilation and evaluation from within buffers, access to
  60 on-line documentation (docstrings), context-sensitive completion, M-. to
  61 jump to an object definition, a REPL to try out your code, and more.
  62
  63 To actually edit the code, Emacs already has a neat Scheme mode.  But in
  64 addition to that, you must not miss [[http://www.emacswiki.org/emacs/ParEdit][Paredit]].  It provides facilities to
  65 directly operate on the syntax tree, such as raising an s-expression or
  66 wrapping it, swallowing or rejecting the following s-expression, etc.
  67
  68 * Submitting Patches
  69
  70 Development is done using the Git distributed version control system.  Thus,
  71 access to the repository is not strictly necessary.  We welcome contributions
  72 in the form of patches as produced by ‘git format-patch’ sent to
  73 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
  74 format]]; you can check the commit history for examples.
  75
  76 Before submitting a patch that adds or modifies a package definition, please
  77 run ‘guix lint PACKAGE’, where PACKAGE is the name of the new or modified
  78 package, and fix any errors it reports.  In addition, please make sure the
  79 package builds on your platform, using ‘guix build’.  You may also want to
  80 check that dependent package (if applicable) are not affected by the change;
  81 ‘guix refresh --list-dependent PACKAGE’ will help you do that.
  82
  83 When posting a patch to the mailing list, use "[PATCH] ..." as a subject.  You
  84 may use your email client or the ‘git send-mail’ command.
  85
  86 As you become a regular contributor, you may find it convenient to have write
  87 access to the repository (see below.)
  88
  89 * Coding Style
  90
  91 In general our code follows the [[info:standards][GNU Coding Standards]] (GCS).  However, the GCS
  92 do not say much about Scheme, so here are some additional rules.
  93
  94 ** Programming Paradigm
  95
  96 Scheme code in Guix is written in a purely functional style.  One exception is
  97 code that involves input/output, and procedures that implement low-level
  98 concepts, such as the ‘memoize’ procedure.
  99
 100 ** Modules
 101
 102 Guile modules that are meant to be used on the builder side must live in the
 103 (guix build …) name space.  They must not refer to other Guix or GNU modules.
 104 However, it is OK for a “host-side” module to use a build-side module.
 105
 106 Modules that deal with the broader GNU system should be in the (gnu …) name
 107 space rather than (guix …).
 108
 109 ** Data Types and Pattern Matching
 110
 111 The tendency in classical Lisp is to use lists to represent everything, and
 112 then to browse them “by hand” using ‘car’, ‘cdr’, ‘cadr’, and co.  There are
 113 several problems with that style, notably the fact that it is hard to read,
 114 error-prone, and a hindrance to proper type error reports.
 115
 116 Guix code should define appropriate data types (for instance, using
 117 ‘define-record-type*’) rather than abuse lists.  In addition, it should use
 118 pattern matching, via Guile’s (ice-9 match) module, especially when matching
 119 lists.
 120
 121 ** Formatting Code
 122
 123 When writing Scheme code, we follow common wisdom among Scheme programmers.
 124 In general, we follow the [[http://mumble.net/~campbell/scheme/style.txt][Riastradh's Lisp Style Rules]].  This document happens
 125 to describe the conventions mostly used in Guile’s code too.  It is very
 126 thoughtful and well written, so please do read it.
 127
 128 Some special forms introduced in Guix, such as the ‘substitute*’ macro, have
 129 special indentation rules.  These are defined in the .dir-locals.el file,
 130 which Emacs automatically uses.  If you do not use Emacs, please make sure to
 131 let your editor know the rules.
 132
 133 We require all top-level procedures to carry a docstring.  This requirement
 134 can be relaxed for simple private procedures in the (guix build …) name space,
 135 though.
 136
 137 Procedures should not have more than four positional parameters.  Use keyword
 138 parameters for procedures that take more than four parameters.
 139
 140 * Commit Access
 141
 142 For frequent contributors, having write access to the repository is
 143 convenient.  When you deem it necessary, feel free to ask for it on the
 144 mailing list.  When you get commit access, please make sure to follow the
 145 policy below (discussions of the policy can take place on guix-devel@gnu.org.)
 146
 147 Non-trivial patches should always be posted to guix-devel@gnu.org (trivial
 148 patches include fixing typos, etc.)
 149
 150 For patches that just add a new package, and a simple one, it’s OK to commit,
 151 if you’re confident (which means you successfully built it in a chroot setup,
 152 and have done a reasonable copyright and license auditing.)  Likewise for
 153 package upgrades, except upgrades that trigger a lot of rebuilds (for example,
 154 upgrading GnuTLS or GLib.)  We have a mailing list for commit notifications
 155 (guix-commits@gnu.org), so people can notice.  Before pushing your changes,
 156 make sure to run ‘git pull --rebase’.
 157
 158 For anything else, please post to guix-devel@gnu.org and leave time for a
 159 review, without committing anything.  If you didn’t receive any reply
 160 after two weeks, and if you’re confident, it’s OK to commit.
 161
 162 That last part is subject to being adjusted, allowing individuals to commit
 163 directly on non-controversial changes on parts they’re familiar with.