mirror of
https://github.com/ilyakooo0/nixpkgs.git
synced 2024-12-27 22:03:54 +03:00
93 lines
3.7 KiB
XML
93 lines
3.7 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xmlns:xi="http://www.w3.org/2001/XInclude"
|
||
version="5.0"
|
||
xml:id="sec-customising-packages">
|
||
|
||
<title>Customising Packages</title>
|
||
|
||
<para>Some packages in Nixpkgs have options to enable or disable
|
||
optional functionality or change other aspects of the package. For
|
||
instance, the Firefox wrapper package (which provides Firefox with a
|
||
set of plugins such as the Adobe Flash player) has an option to enable
|
||
the Google Talk plugin. It can be set in
|
||
<filename>configuration.nix</filename> as follows:
|
||
|
||
<filename>
|
||
nixpkgs.config.firefox.enableGoogleTalkPlugin = true;
|
||
</filename>
|
||
</para>
|
||
|
||
<warning><para>Unfortunately, Nixpkgs currently lacks a way to query
|
||
available configuration options.</para></warning>
|
||
|
||
<para>Apart from high-level options, it’s possible to tweak a package
|
||
in almost arbitrary ways, such as changing or disabling dependencies
|
||
of a package. For instance, the Emacs package in Nixpkgs by default
|
||
has a dependency on GTK+ 2. If you want to build it against GTK+ 3,
|
||
you can specify that as follows:
|
||
|
||
<programlisting>
|
||
environment.systemPackages = [ (pkgs.emacs.override { gtk = pkgs.gtk3; }) ];
|
||
</programlisting>
|
||
|
||
The function <varname>override</varname> performs the call to the Nix
|
||
function that produces Emacs, with the original arguments amended by
|
||
the set of arguments specified by you. So here the function argument
|
||
<varname>gtk</varname> gets the value <literal>pkgs.gtk3</literal>,
|
||
causing Emacs to depend on GTK+ 3. (The parentheses are necessary
|
||
because in Nix, function application binds more weakly than list
|
||
construction, so without them,
|
||
<literal>environment.systemPackages</literal> would be a list with two
|
||
elements.)</para>
|
||
|
||
<para>Even greater customisation is possible using the function
|
||
<varname>overrideDerivation</varname>. While the
|
||
<varname>override</varname> mechanism above overrides the arguments of
|
||
a package function, <varname>overrideDerivation</varname> allows
|
||
changing the <emphasis>result</emphasis> of the function. This
|
||
permits changing any aspect of the package, such as the source code.
|
||
For instance, if you want to override the source code of Emacs, you
|
||
can say:
|
||
|
||
<programlisting>
|
||
environment.systemPackages =
|
||
[ (pkgs.lib.overrideDerivation pkgs.emacs (attrs: {
|
||
name = "emacs-25.0-pre";
|
||
src = /path/to/my/emacs/tree;
|
||
}))
|
||
];
|
||
</programlisting>
|
||
|
||
Here, <varname>overrideDerivation</varname> takes the Nix derivation
|
||
specified by <varname>pkgs.emacs</varname> and produces a new
|
||
derivation in which the original’s <literal>name</literal> and
|
||
<literal>src</literal> attribute have been replaced by the given
|
||
values. The original attributes are accessible via
|
||
<varname>attrs</varname>.</para>
|
||
|
||
<para>The overrides shown above are not global. They do not affect
|
||
the original package; other packages in Nixpkgs continue to depend on
|
||
the original rather than the customised package. This means that if
|
||
another package in your system depends on the original package, you
|
||
end up with two instances of the package. If you want to have
|
||
everything depend on your customised instance, you can apply a
|
||
<emphasis>global</emphasis> override as follows:
|
||
|
||
<screen>
|
||
nixpkgs.config.packageOverrides = pkgs:
|
||
{ emacs = pkgs.emacs.override { gtk = pkgs.gtk3; };
|
||
};
|
||
</screen>
|
||
|
||
The effect of this definition is essentially equivalent to modifying
|
||
the <literal>emacs</literal> attribute in the Nixpkgs source tree.
|
||
Any package in Nixpkgs that depends on <literal>emacs</literal> will
|
||
be passed your customised instance. (However, the value
|
||
<literal>pkgs.emacs</literal> in
|
||
<varname>nixpkgs.config.packageOverrides</varname> refers to the
|
||
original rather than overridden instance, to prevent an infinite
|
||
recursion.)</para>
|
||
|
||
</section>
|