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   - [[http://www.gnu.org/software/help2man/][GNU Help2man]] (optional)
  24
  25 Run ‘./bootstrap’ to download the Nix daemon source code and to generate the
  26 build system infrastructure using autoconf.  It reports an error if an
  27 inappropriate version of the above packages is being used.
  28
  29 If you get an error like this one:
  30
  31   configure.ac:46: error: possibly undefined macro: PKG_CHECK_MODULES
  32
  33 it probably means that Autoconf couldn’t find ‘pkg.m4’, which is provided by
  34 pkg-config.  Make sure that ‘pkg.m4’ is available.  For instance, if you
  35 installed Automake in ‘/usr/local’, it wouldn’t look for ‘.m4’ files in
  36 ‘/usr/share’.  So you have to invoke the following command in that case
  37
  38   $ export ACLOCAL_PATH=/usr/share/aclocal
  39
  40 See “info '(automake) Macro Search Path'” for more information.
  41
  42 Then, run ‘./configure’ as usual.
  43
  44 Finally, you have to invoke ‘make check’ to run tests.  If anything fails,
  45 take a look at “info '(guix) Installation'” or send a message to
  46 <guix-devel@gnu.org>.
  47
  48 * Running Guix before it is installed
  49
  50 See the same-named section in the manual.
  51
  52 * The Perfect Setup
  53
  54 The Perfect Setup to hack on Guix is basically the perfect setup used
  55 for Guile hacking (info "(guile) Using Guile in Emacs").  First, you
  56 need more than an editor, you need [[http://www.gnu.org/software/emacs][Emacs]], empowered by the wonderful
  57 [[http://nongnu.org/geiser/][Geiser]].
  58
  59 Geiser allows for interactive and incremental development from within
  60 Emacs: code compilation and evaluation from within buffers, access to
  61 on-line documentation (docstrings), context-sensitive completion, M-. to
  62 jump to an object definition, a REPL to try out your code, and more.
  63
  64 To actually edit the code, Emacs already has a neat Scheme mode.  But in
  65 addition to that, you must not miss [[http://www.emacswiki.org/emacs/ParEdit][Paredit]].  It provides facilities to
  66 directly operate on the syntax tree, such as raising an s-expression or
  67 wrapping it, swallowing or rejecting the following s-expression, etc.
  68
  69 * Submitting Patches
  70
  71 Development is done using the Git distributed version control system.  Thus,
  72 access to the repository is not strictly necessary.  We welcome contributions
  73 in the form of patches as produced by ‘git format-patch’ sent to
  74 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
  75 format]]; you can check the commit history for examples.
  76
  77 Before submitting a patch that adds or modifies a package definition, please
  78 run ‘guix lint PACKAGE’, where PACKAGE is the name of the new or modified
  79 package, and fix any errors it reports.  In addition, please make sure the
  80 package builds on your platform, using ‘guix build’.  You may also want to
  81 check that dependent package (if applicable) are not affected by the change;
  82 ‘guix refresh --list-dependent PACKAGE’ will help you do that.
  83
  84 When posting a patch to the mailing list, use "[PATCH] ..." as a subject.  You
  85 may use your email client or the ‘git send-mail’ command.
  86
  87 As you become a regular contributor, you may find it convenient to have write
  88 access to the repository (see below.)
  89
  90 * Coding Style
  91
  92 In general our code follows the [[info:standards][GNU Coding Standards]] (GCS).  However, the GCS
  93 do not say much about Scheme, so here are some additional rules.
  94
  95 ** Programming Paradigm
  96
  97 Scheme code in Guix is written in a purely functional style.  One exception is
  98 code that involves input/output, and procedures that implement low-level
  99 concepts, such as the ‘memoize’ procedure.
 100
 101 ** Modules
 102
 103 Guile modules that are meant to be used on the builder side must live in the
 104 (guix build …) name space.  They must not refer to other Guix or GNU modules.
 105 However, it is OK for a “host-side” module to use a build-side module.
 106
 107 Modules that deal with the broader GNU system should be in the (gnu …) name
 108 space rather than (guix …).
 109
 110 ** Data Types and Pattern Matching
 111
 112 The tendency in classical Lisp is to use lists to represent everything, and
 113 then to browse them “by hand” using ‘car’, ‘cdr’, ‘cadr’, and co.  There are
 114 several problems with that style, notably the fact that it is hard to read,
 115 error-prone, and a hindrance to proper type error reports.
 116
 117 Guix code should define appropriate data types (for instance, using
 118 ‘define-record-type*’) rather than abuse lists.  In addition, it should use
 119 pattern matching, via Guile’s (ice-9 match) module, especially when matching
 120 lists.
 121
 122 ** Formatting Code
 123
 124 When writing Scheme code, we follow common wisdom among Scheme programmers.
 125 In general, we follow the [[http://mumble.net/~campbell/scheme/style.txt][Riastradh's Lisp Style Rules]].  This document happens
 126 to describe the conventions mostly used in Guile’s code too.  It is very
 127 thoughtful and well written, so please do read it.
 128
 129 Some special forms introduced in Guix, such as the ‘substitute*’ macro, have
 130 special indentation rules.  These are defined in the .dir-locals.el file,
 131 which Emacs automatically uses.  If you do not use Emacs, please make sure to
 132 let your editor know the rules.
 133
 134 We require all top-level procedures to carry a docstring.  This requirement
 135 can be relaxed for simple private procedures in the (guix build …) name space,
 136 though.
 137
 138 Procedures should not have more than four positional parameters.  Use keyword
 139 parameters for procedures that take more than four parameters.
 140
 141 * Commit Access
 142
 143 For frequent contributors, having write access to the repository is
 144 convenient.  When you deem it necessary, feel free to ask for it on the
 145 mailing list.  When you get commit access, please make sure to follow the
 146 policy below (discussions of the policy can take place on guix-devel@gnu.org.)
 147
 148 Non-trivial patches should always be posted to guix-devel@gnu.org (trivial
 149 patches include fixing typos, etc.)
 150
 151 For patches that just add a new package, and a simple one, it’s OK to commit,
 152 if you’re confident (which means you successfully built it in a chroot setup,
 153 and have done a reasonable copyright and license auditing.)  Likewise for
 154 package upgrades, except upgrades that trigger a lot of rebuilds (for example,
 155 upgrading GnuTLS or GLib.)  We have a mailing list for commit notifications
 156 (guix-commits@gnu.org), so people can notice.  Before pushing your changes,
 157 make sure to run ‘git pull --rebase’.
 158
 159 For anything else, please post to guix-devel@gnu.org and leave time for a
 160 review, without committing anything.  If you didn’t receive any reply
 161 after two weeks, and if you’re confident, it’s OK to commit.
 162
 163 That last part is subject to being adjusted, allowing individuals to commit
 164 directly on non-controversial changes on parts they’re familiar with.