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* Started documenting the meta attributes, including a first

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(very incomplete) attempt at standardising the license attribute.

svn path=/nixpkgs/trunk/; revision=14028
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Eelco Dolstra 2009-02-10 23:29:42 +00:00
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doc/manual.xml
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<xi:include href="introduction.xml" />
<xi:include href="quick-start.xml" />
<xi:include href="stdenv.xml" />
<xi:include href="meta.xml" />
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<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 = "GPLv3+";
};
</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 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 --meta --xml
&lt;?xml version='1.0' encoding='utf-8'?>
&lt;items>
&lt;item attrPath="hello" name="hello-2.3" system="i686-linux">
&lt;meta name="description" value="A program that produces a familiar, friendly greeting" />
&lt;meta name="homepage" value="http://www.gnu.org/software/hello/manual/" />
&lt;meta name="license" value="GPLv3+" />
&lt;meta name="longDescription" value="GNU Hello is a program that prints &amp;quot;Hello, world!&amp;quot; when you run it.&amp;#xA;It is fully customizable.&amp;#xA;" />
&lt;/item>
&lt;/items>
</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><title>Standard meta-attributes</title>
<para>The following meta-attributes have a standard
interpretation:</para>
<variablelist>
<varlistentry>
<term><varname>description</varname></term>
<listitem><para>A short (one-line) description of the package.
Don’t include a period at the end. This is shown by
<command>nix-env -q --description</command> and also on the
Nixpkgs release pages. Example: <literal>"A program that produces
a familiar, friendly greeting"</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>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>license</varname></term>
<listitem><para>The license for the package. See below for the
allowed values.</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>
</variablelist>
</section>
<section><title>Licenses</title>
<note><para>This is just a first attempt at standardising the license
attribute.</para></note>
<para>The <varname>meta.license</varname> attribute must be one of the
following:
<variablelist>
<varlistentry>
<term><varname>GPL</varname></term>
<listitem><para>GNU General Public License; version not
specified.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>GPLv2</varname></term>
<listitem><para>GNU General Public License, version
2.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>GPLv2+</varname></term>
<listitem><para>GNU General Public License, version
2 or higher.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>GPLv3</varname></term>
<listitem><para>GNU General Public License, version
3.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>GPLv3+</varname></term>
<listitem><para>GNU General Public License, version
3 or higher.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>free</varname></term>
<listitem><para>Catch-all for free software licenses not listed
above.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>free-copyleft</varname></term>
<listitem><para>Catch-all for free, copyleft software licenses not
listed above.</para></listitem>
</varlistentry>
<varlistentry>
<term><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>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>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>