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