322 lines
12 KiB
XML
322 lines
12 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xml:id="chap-meta">
|
||
|
||
<title>Meta-attributes</title>
|
||
|
||
<para>Nix packages can declare <emphasis>meta-attributes</emphasis>
|
||
that contain information about a package such as a description, its
|
||
homepage, its license, and so on. For instance, the GNU Hello package
|
||
has a <varname>meta</varname> declaration like this:
|
||
|
||
<programlisting>
|
||
meta = {
|
||
description = "A program that produces a familiar, friendly greeting";
|
||
longDescription = ''
|
||
GNU Hello is a program that prints "Hello, world!" when you run it.
|
||
It is fully customizable.
|
||
'';
|
||
homepage = http://www.gnu.org/software/hello/manual/;
|
||
license = stdenv.lib.licenses.gpl3Plus;
|
||
maintainers = [ stdenv.lib.maintainers.eelco ];
|
||
platforms = stdenv.lib.platforms.all;
|
||
};
|
||
</programlisting>
|
||
|
||
</para>
|
||
|
||
<para>Meta-attributes are not passed to the builder of the package.
|
||
Thus, a change to a meta-attribute doesn’t trigger a recompilation of
|
||
the package. The value of a meta-attribute must be a string.</para>
|
||
|
||
<para>The meta-attributes of a package can be queried from the
|
||
command-line using <command>nix-env</command>:
|
||
|
||
<screen>
|
||
$ nix-env -qa hello --json
|
||
{
|
||
"hello": {
|
||
"meta": {
|
||
"description": "A program that produces a familiar, friendly greeting",
|
||
"homepage": "http://www.gnu.org/software/hello/manual/",
|
||
"license": {
|
||
"fullName": "GNU General Public License version 3 or later",
|
||
"shortName": "GPLv3+",
|
||
"url": "http://www.fsf.org/licensing/licenses/gpl.html"
|
||
},
|
||
"longDescription": "GNU Hello is a program that prints \"Hello, world!\" when you run it.\nIt is fully customizable.\n",
|
||
"maintainers": [
|
||
"Ludovic Court\u00e8s <ludo@gnu.org>"
|
||
],
|
||
"platforms": [
|
||
"i686-linux",
|
||
"x86_64-linux",
|
||
"armv5tel-linux",
|
||
"armv7l-linux",
|
||
"mips32-linux",
|
||
"x86_64-darwin",
|
||
"i686-cygwin",
|
||
"i686-freebsd",
|
||
"x86_64-freebsd",
|
||
"i686-openbsd",
|
||
"x86_64-openbsd"
|
||
],
|
||
"position": "/home/user/dev/nixpkgs/pkgs/applications/misc/hello/default.nix:14"
|
||
},
|
||
"name": "hello-2.9",
|
||
"system": "x86_64-linux"
|
||
}
|
||
}
|
||
|
||
|
||
</screen>
|
||
|
||
<command>nix-env</command> knows about the
|
||
<varname>description</varname> field specifically:
|
||
|
||
<screen>
|
||
$ nix-env -qa hello --description
|
||
hello-2.3 A program that produces a familiar, friendly greeting
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
|
||
<section xml:id="sec-standard-meta-attributes"><title>Standard
|
||
meta-attributes</title>
|
||
|
||
<para>It is expected that each meta-attribute is one of the following:</para>
|
||
|
||
<variablelist>
|
||
|
||
<varlistentry>
|
||
<term><varname>description</varname></term>
|
||
<listitem><para>A short (one-line) description of the package.
|
||
This is shown by <command>nix-env -q --description</command> and
|
||
also on the Nixpkgs release pages.</para>
|
||
|
||
<para>Don’t include a period at the end. Don’t include newline
|
||
characters. Capitalise the first character. For brevity, don’t
|
||
repeat the name of package — just describe what it does.</para>
|
||
|
||
<para>Wrong: <literal>"libpng is a library that allows you to decode PNG images."</literal></para>
|
||
|
||
<para>Right: <literal>"A library for decoding PNG images"</literal></para>
|
||
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>longDescription</varname></term>
|
||
<listitem><para>An arbitrarily long description of the
|
||
package.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>branch</varname></term>
|
||
<listitem><para>Release branch. Used to specify that a package is not
|
||
going to receive updates that are not in this branch; for example, Linux
|
||
kernel 3.0 is supposed to be updated to 3.0.X, not 3.1.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>homepage</varname></term>
|
||
<listitem><para>The package’s homepage. Example:
|
||
<literal>http://www.gnu.org/software/hello/manual/</literal></para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>downloadPage</varname></term>
|
||
<listitem><para>The page where a link to the current version can be found. Example:
|
||
<literal>http://ftp.gnu.org/gnu/hello/</literal></para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>license</varname></term>
|
||
<listitem>
|
||
<para>
|
||
The license, or licenses, for the package. One from the attribute set
|
||
defined in <link
|
||
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/licenses.nix">
|
||
<filename>nixpkgs/lib/licenses.nix</filename></link>. At this moment
|
||
using both a list of licenses and a single license is valid. If the
|
||
license field is in the form of a list representation, then it means
|
||
that parts of the package are licensed differently. Each license
|
||
should preferably be referenced by their attribute. The non-list
|
||
attribute value can also be a space delimited string representation of
|
||
the contained attribute shortNames or spdxIds. The following are all valid
|
||
examples:
|
||
<itemizedlist>
|
||
<listitem><para>Single license referenced by attribute (preferred)
|
||
<literal>stdenv.lib.licenses.gpl3</literal>.
|
||
</para></listitem>
|
||
<listitem><para>Single license referenced by its attribute shortName (frowned upon)
|
||
<literal>"gpl3"</literal>.
|
||
</para></listitem>
|
||
<listitem><para>Single license referenced by its attribute spdxId (frowned upon)
|
||
<literal>"GPL-3.0"</literal>.
|
||
</para></listitem>
|
||
<listitem><para>Multiple licenses referenced by attribute (preferred)
|
||
<literal>with stdenv.lib.licenses; [ asl20 free ofl ]</literal>.
|
||
</para></listitem>
|
||
<listitem><para>Multiple licenses referenced as a space delimited string of attribute shortNames (frowned upon)
|
||
<literal>"asl20 free ofl"</literal>.
|
||
</para></listitem>
|
||
</itemizedlist>
|
||
For details, see <xref linkend='sec-meta-license'/>.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>maintainers</varname></term>
|
||
<listitem><para>A list of names and e-mail addresses of the
|
||
maintainers of this Nix expression. If
|
||
you would like to be a maintainer of a package, you may want to add
|
||
yourself to <link
|
||
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/maintainers/maintainer-list.nix"><filename>nixpkgs/maintainers/maintainer-list.nix</filename></link>
|
||
and write something like <literal>[ stdenv.lib.maintainers.alice
|
||
stdenv.lib.maintainers.bob ]</literal>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>priority</varname></term>
|
||
<listitem><para>The <emphasis>priority</emphasis> of the package,
|
||
used by <command>nix-env</command> to resolve file name conflicts
|
||
between packages. See the Nix manual page for
|
||
<command>nix-env</command> for details. Example:
|
||
<literal>"10"</literal> (a low-priority
|
||
package).</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>platforms</varname></term>
|
||
<listitem><para>The list of Nix platform types on which the
|
||
package is supported. Hydra builds packages according to the
|
||
platform specified. If no platform is specified, the package does
|
||
not have prebuilt binaries. An example is:
|
||
|
||
<programlisting>
|
||
meta.platforms = stdenv.lib.platforms.linux;
|
||
</programlisting>
|
||
|
||
Attribute Set <varname>stdenv.lib.platforms</varname> defines
|
||
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/systems/doubles.nix">
|
||
various common lists</link> of platforms types.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>hydraPlatforms</varname></term>
|
||
<listitem><para>The list of Nix platform types for which the Hydra
|
||
instance at <literal>hydra.nixos.org</literal> will build the
|
||
package. (Hydra is the Nix-based continuous build system.) It
|
||
defaults to the value of <varname>meta.platforms</varname>. Thus,
|
||
the only reason to set <varname>meta.hydraPlatforms</varname> is
|
||
if you want <literal>hydra.nixos.org</literal> to build the
|
||
package on a subset of <varname>meta.platforms</varname>, or not
|
||
at all, e.g.
|
||
|
||
<programlisting>
|
||
meta.platforms = stdenv.lib.platforms.linux;
|
||
meta.hydraPlatforms = [];
|
||
</programlisting>
|
||
|
||
</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>broken</varname></term>
|
||
<listitem><para>If set to <literal>true</literal>, the package is
|
||
marked as “broken”, meaning that it won’t show up in
|
||
<literal>nix-env -qa</literal>, and cannot be built or installed.
|
||
Such packages should be removed from Nixpkgs eventually unless
|
||
they are fixed.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>updateWalker</varname></term>
|
||
<listitem><para>If set to <literal>true</literal>, the package is
|
||
tested to be updated correctly by the <literal>update-walker.sh</literal>
|
||
script without additional settings. Such packages have
|
||
<varname>meta.version</varname> set and their homepage (or
|
||
the page specified by <varname>meta.downloadPage</varname>) contains
|
||
a direct link to the package tarball.</para></listitem>
|
||
</varlistentry>
|
||
|
||
</variablelist>
|
||
|
||
|
||
</section>
|
||
|
||
|
||
<section xml:id="sec-meta-license"><title>Licenses</title>
|
||
|
||
<para>The <varname>meta.license</varname> attribute should preferrably contain
|
||
a value from <varname>stdenv.lib.licenses</varname> defined in
|
||
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/licenses.nix">
|
||
<filename>nixpkgs/lib/licenses.nix</filename></link>,
|
||
or in-place license description of the same format if the license is
|
||
unlikely to be useful in another expression.</para>
|
||
|
||
<para>Although it's typically better to indicate the specific license,
|
||
a few generic options are available:
|
||
|
||
<variablelist>
|
||
|
||
<varlistentry>
|
||
<term><varname>stdenv.lib.licenses.free</varname>,
|
||
<varname>"free"</varname></term>
|
||
|
||
<listitem><para>Catch-all for free software licenses not listed
|
||
above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>stdenv.lib.licenses.unfreeRedistributable</varname>,
|
||
<varname>"unfree-redistributable"</varname></term>
|
||
|
||
<listitem><para>Unfree package that can be redistributed in binary
|
||
form. That is, it’s legal to redistribute the
|
||
<emphasis>output</emphasis> of the derivation. This means that
|
||
the package can be included in the Nixpkgs
|
||
channel.</para>
|
||
|
||
<para>Sometimes proprietary software can only be redistributed
|
||
unmodified. Make sure the builder doesn’t actually modify the
|
||
original binaries; otherwise we’re breaking the license. For
|
||
instance, the NVIDIA X11 drivers can be redistributed unmodified,
|
||
but our builder applies <command>patchelf</command> to make them
|
||
work. Thus, its license is <varname>"unfree"</varname> and it
|
||
cannot be included in the Nixpkgs channel.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>stdenv.lib.licenses.unfree</varname>,
|
||
<varname>"unfree"</varname></term>
|
||
|
||
<listitem><para>Unfree package that cannot be redistributed. You
|
||
can build it yourself, but you cannot redistribute the output of
|
||
the derivation. Thus it cannot be included in the Nixpkgs
|
||
channel.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>stdenv.lib.licenses.unfreeRedistributableFirmware</varname>,
|
||
<varname>"unfree-redistributable-firmware"</varname></term>
|
||
|
||
<listitem><para>This package supplies unfree, redistributable
|
||
firmware. This is a separate value from
|
||
<varname>unfree-redistributable</varname> because not everybody
|
||
cares whether firmware is free.</para></listitem>
|
||
</varlistentry>
|
||
|
||
</variablelist>
|
||
|
||
</para>
|
||
|
||
|
||
</section>
|
||
|
||
|
||
</chapter>
|