nixpkgs/doc/quick-start.xml
Matthias Beyer 15be920354 doc: gnu hello is much simpler than cpio
This patch changes the documentation about simple packages. cpio was
listed as simplest possible package, which is not true anymore, gnu
hello is much simpler.
2015-07-17 17:00:20 +02:00

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<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="chap-quick-start">
<title>Quick Start to Adding a Package</title>
<para>To add a package to Nixpkgs:
<orderedlist>
<listitem>
<para>Checkout the Nixpkgs source tree:
<screen>
$ git clone git://github.com/NixOS/nixpkgs.git
$ cd nixpkgs</screen>
</para>
</listitem>
<listitem>
<para>Find a good place in the Nixpkgs tree to add the Nix
expression for your package. For instance, a library package
typically goes into
<filename>pkgs/development/libraries/<replaceable>pkgname</replaceable></filename>,
while a web browser goes into
<filename>pkgs/applications/networking/browsers/<replaceable>pkgname</replaceable></filename>.
See <xref linkend="sec-organisation" /> for some hints on the tree
organisation. Create a directory for your package, e.g.
<screen>
$ mkdir pkgs/development/libraries/libfoo</screen>
</para>
</listitem>
<listitem>
<para>In the package directory, create a Nix expression — a piece
of code that describes how to build the package. In this case, it
should be a <emphasis>function</emphasis> that is called with the
package dependencies as arguments, and returns a build of the
package in the Nix store. The expression should usually be called
<filename>default.nix</filename>.
<screen>
$ emacs pkgs/development/libraries/libfoo/default.nix
$ git add pkgs/development/libraries/libfoo/default.nix</screen>
</para>
<para>You can have a look at the existing Nix expressions under
<filename>pkgs/</filename> to see how its done. Here are some
good ones:
<itemizedlist>
<listitem>
<para>GNU Hello: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/hello/ex-2/default.nix"><filename>pkgs/applications/misc/hello/ex-2/default.nix</filename></link>.
Trivial package, which specifies some <varname>meta</varname>
attributes which is good practice.</para>
</listitem>
<listitem>
<para>GNU cpio: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/archivers/cpio/default.nix"><filename>pkgs/tools/archivers/cpio/default.nix</filename></link>.
Also a simple package. The generic builder in
<varname>stdenv</varname> does everything for you. It has
no dependencies beyond <varname>stdenv</varname>.</para>
</listitem>
<listitem>
<para>GNU Multiple Precision arithmetic library (GMP): <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/gmp/5.1.x.nix"><filename>pkgs/development/libraries/gmp/5.1.x.nix</filename></link>.
Also done by the generic builder, but has a dependency on
<varname>m4</varname>.</para>
</listitem>
<listitem>
<para>Pan, a GTK-based newsreader: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/newsreaders/pan/default.nix"><filename>pkgs/applications/networking/newsreaders/pan/default.nix</filename></link>.
Has an optional dependency on <varname>gtkspell</varname>,
which is only built if <varname>spellCheck</varname> is
<literal>true</literal>.</para>
</listitem>
<listitem>
<para>Apache HTTPD: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/servers/http/apache-httpd/2.4.nix"><filename>pkgs/servers/http/apache-httpd/2.4.nix</filename></link>.
A bunch of optional features, variable substitutions in the
configure flags, a post-install hook, and miscellaneous
hackery.</para>
</listitem>
<listitem>
<para>Thunderbird: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/mailreaders/thunderbird/default.nix"><filename>pkgs/applications/networking/mailreaders/thunderbird/default.nix</filename></link>.
Lots of dependencies.</para>
</listitem>
<listitem>
<para>JDiskReport, a Java utility: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/misc/jdiskreport/default.nix"><filename>pkgs/tools/misc/jdiskreport/default.nix</filename></link>
(and the <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/misc/jdiskreport/builder.sh">builder</link>).
Nixpkgs doesnt have a decent <varname>stdenv</varname> for
Java yet so this is pretty ad-hoc.</para>
</listitem>
<listitem>
<para>XML::Simple, a Perl module: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/perl-packages.nix"><filename>pkgs/top-level/perl-packages.nix</filename></link>
(search for the <varname>XMLSimple</varname> attribute).
Most Perl modules are so simple to build that they are
defined directly in <filename>perl-packages.nix</filename>;
no need to make a separate file for them.</para>
</listitem>
<listitem>
<para>Adobe Reader: <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/adobe-reader/default.nix"><filename>pkgs/applications/misc/adobe-reader/default.nix</filename></link>.
Shows how binary-only packages can be supported. In
particular the <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/adobe-reader/builder.sh">builder</link>
uses <command>patchelf</command> to set the RUNPATH and ELF
interpreter of the executables so that the right libraries
are found at runtime.</para>
</listitem>
</itemizedlist>
</para>
<para>Some notes:
<itemizedlist>
<listitem>
<para>All <varname linkend="chap-meta">meta</varname>
attributes are optional, but its still a good idea to
provide at least the <varname>description</varname>,
<varname>homepage</varname> and <varname
linkend="sec-meta-license">license</varname>.</para>
</listitem>
<listitem>
<para>You can use <command>nix-prefetch-url</command> (or similar nix-prefetch-git, etc)
<replaceable>url</replaceable> to get the SHA-256 hash of
source distributions. There are similar commands as <command>nix-prefetch-git</command> and
<command>nix-prefetch-hg</command> available in <literal>nix-prefetch-scripts</literal> package.</para>
</listitem>
<listitem>
<para>A list of schemes for <literal>mirror://</literal>
URLs can be found in <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/fetchurl/mirrors.nix"><filename>pkgs/build-support/fetchurl/mirrors.nix</filename></link>.</para>
</listitem>
</itemizedlist>
</para>
<para>The exact syntax and semantics of the Nix expression
language, including the built-in function, are described in the
Nix manual in the <link
xlink:href="http://hydra.nixos.org/job/nix/trunk/tarball/latest/download-by-type/doc/manual/#chap-writing-nix-expressions">chapter
on writing Nix expressions</link>.</para>
</listitem>
<listitem>
<para>Add a call to the function defined in the previous step to
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/all-packages.nix"><filename>pkgs/top-level/all-packages.nix</filename></link>
with some descriptive name for the variable,
e.g. <varname>libfoo</varname>.
<screen>
$ emacs pkgs/top-level/all-packages.nix</screen>
</para>
<para>The attributes in that file are sorted by category (like
“Development / Libraries”) that more-or-less correspond to the
directory structure of Nixpkgs, and then by attribute name.</para>
</listitem>
<listitem>
<para>To test whether the package builds, run the following command
from the root of the nixpkgs source tree:
<screen>
$ nix-build -A libfoo</screen>
where <varname>libfoo</varname> should be the variable name
defined in the previous step. You may want to add the flag
<option>-K</option> to keep the temporary build directory in case
something fails. If the build succeeds, a symlink
<filename>./result</filename> to the package in the Nix store is
created.</para>
</listitem>
<listitem>
<para>If you want to install the package into your profile
(optional), do
<screen>
$ nix-env -f . -iA libfoo</screen>
</para>
</listitem>
<listitem>
<para>Optionally commit the new package and open a pull request, or send a patch to
<literal>nix-dev@cs.uu.nl</literal>.</para>
</listitem>
</orderedlist>
</para>
</chapter>