HACKING

   1 -*- mode: org; coding: utf-8; -*-
   2
   3 #+TITLE: Hacking GNU Guix and Its Incredible Distro
   4
   5 Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
   6 Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
   7
   8   Copying and distribution of this file, with or without modification,
   9   are permitted in any medium without royalty provided the copyright
  10   notice and this notice are preserved.
  11
  12
  13 * Building from Git
  14
  15 When building Guix from a checkout, the following packages are required in
  16 addition to those mentioned in the installation instructions:
  17
  18   - [[http://www.gnu.org/software/autoconf/][GNU Autoconf]]
  19   - [[http://www.gnu.org/software/automake/][GNU Automake]]
  20   - [[http://www.gnu.org/software/gettext/][GNU Gettext]]
  21   - [[http://www.graphviz.org/][Graphviz]]
  22
  23 Run ‘./bootstrap’ to download the Nix daemon source code and to generate the
  24 build system infrastructure using autoconf.  It reports an error if an
  25 inappropriate version of the above packages is being used.
  26
  27 The ‘bootstrap’ script, among other things, invokes ‘git submodule update’; if
  28 you didn’t run it, you may get the following error:
  29
  30   make: *** No rule to make target `nix/libstore/schema.sql', needed by
  31   `nix/libstore/schema.sql.hh'
  32
  33 Then, as always, run ‘./configure’.  If you get an error like this one:
  34
  35   ./configure: line 6755: `PKG_CHECK_MODULES(GUILE, guile-2.0 >= 2.0.5)'
  36
  37 it probably means that Autoconf couldn’t find ‘pkg.m4’, which is provided by
  38 pkg-config.  Make sure that ‘pkg.m4’ is available.  For instance, if you
  39 installed Automake in ‘/usr/local’, it wouldn’t look for ‘.m4’ files in
  40 ‘/usr/share’.  So you have to invoke the following command in that case
  41
  42   $ export ACLOCAL_PATH=/usr/share/aclocal
  43
  44 See “info '(automake) Macro Search Path'” for more information.
  45
  46 Finally, you have to invoke ‘make check’ to run tests.  If anything fails,
  47 take a look at “info '(guix) Installation'” or send a message to
  48 <guix-devel@gnu.org>.
  49
  50 * Running Guix before it is installed
  51
  52 Command-line tools can be used even if you have not run "make install".
  53 To do that, prefix each command with ‘./pre-inst-env’, as in:
  54
  55   ./pre-inst-env guix build --help
  56
  57 Similarly, for a Guile session using the Guix modules:
  58
  59   ./pre-inst-env guile -c '(use-modules (guix utils)) (pk (%current-system))'
  60
  61 The ‘pre-inst-env’ script sets up all the environment variables
  62 necessary to support this.
  63
  64 * The Perfect Setup
  65
  66 The Perfect Setup to hack on Guix is basically the perfect setup used
  67 for Guile hacking (info "(guile) Using Guile in Emacs").  First, you
  68 need more than an editor, you need [[http://www.gnu.org/software/emacs][Emacs]], empowered by the wonderful
  69 [[http://nongnu.org/geiser/][Geiser]].
  70
  71 Geiser allows for interactive and incremental development from within
  72 Emacs: code compilation and evaluation from within buffers, access to
  73 on-line documentation (docstrings), context-sensitive completion, M-. to
  74 jump to an object definition, a REPL to try out your code, and more.
  75
  76 To actually edit the code, Emacs already has a neat Scheme mode.  But in
  77 addition to that, you must not miss [[http://www.emacswiki.org/emacs/ParEdit][Paredit]].  It provides facilities to
  78 directly operate on the syntax tree, such as raising an s-expression or
  79 wrapping it, swallowing or rejecting the following s-expression, etc.
  80
  81 * Submitting Patches
  82
  83 Development is done using the Git distributed version control system.  Thus,
  84 access to the repository is not strictly necessary.  We welcome contributions
  85 in the form of patches as produced by ‘git format-patch’ sent to
  86 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 format]].
  87
  88 As you become a regular contributor, you may find it convenient to have write
  89 access to the repository (see below.)
  90
  91 * Coding Style
  92
  93 In general our code follows the [[info:standards][GNU Coding Standards]] (GCS).  However, the GCS
  94 do not say much about Scheme, so here are some additional rules.
  95
  96 ** Programming Paradigm
  97
  98 Scheme code in Guix is written in a purely functional style.  One exception is
  99 code that involves input/output, and procedures that implement low-level
 100 concepts, such as the ‘memoize’ procedure.
 101
 102 ** Modules
 103
 104 Guile modules that are meant to be used on the builder side must live in the
 105 (guix build …) name space.  They must not refer to other Guix or GNU modules.
 106 However, it is OK for a “host-side” module to use a build-side module.
 107
 108 Modules that deal with the broader GNU system should be in the (gnu …) name
 109 space rather than (guix …).
 110
 111 ** Formatting Code
 112
 113 When writing Scheme code, we follow common wisdom among Scheme programmers.
 114 In general, we follow the [[http://mumble.net/~campbell/scheme/style.txt][Riastradh's Lisp Style Rules]].  This document happens
 115 to describe the conventions mostly used in Guile’s code too.  It is very
 116 thoughtful and well written, so please do read it.
 117
 118 In addition, we require all top-level procedures to carry a docstring.  This
 119 requirement can be relaxed for simple private procedures in the (guix build …)
 120 name space, though.
 121
 122 Procedures should not have more than four positional parameters.  Use keyword
 123 parameters for procedures that take more than four parameters.
 124
 125 * Commit Access
 126
 127 For frequent contributors, having write access to the repository is
 128 convenient.  When you deem it necessary, feel free to ask for it on the
 129 mailing list.  When you get commit access, please make sure to follow the
 130 policy below (discussions of the policy can take place on guix-devel@gnu.org.)
 131
 132 Non-trivial patches should always be posted to guix-devel@gnu.org (trivial
 133 patches include fixing typos, etc.)
 134
 135 For patches that just add a new package, and a simple one, it’s OK to commit,
 136 if you’re confident (which means you successfully built it in a chroot setup,
 137 and have done a reasonable copyright and license auditing.)  Likewise for
 138 package upgrades.  We have a mailing list for commit notifications
 139 (guix-commits@gnu.org), so people can notice.  Before pushing your changes,
 140 make sure to run ‘git pull --rebase’.
 141
 142 For anything else, please post to guix-devel@gnu.org and leave time for a
 143 review, without committing anything.  If you didn’t receive any reply
 144 after two weeks, and if you’re confident, it’s OK to commit.
 145
 146 That last part is subject to being adjusted, allowing individuals to commit
 147 directly on non-controversial changes on parts they’re familiar with.