2018-10-02 18:52:21 +01:00
|
|
|
<section xmlns="http://docbook.org/ns/docbook"
|
|
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
|
|
|
xmlns:xi="http://www.w3.org/2001/XInclude"
|
|
|
|
xml:id="sec-overrides">
|
2018-10-02 20:59:59 +01:00
|
|
|
<title>Overriding</title>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
Sometimes one wants to override parts of <literal>nixpkgs</literal>, e.g.
|
2018-10-15 12:47:36 +01:00
|
|
|
derivation attributes, the results of derivations.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
These overriding functions let you focus on one part of Nixpkgs and give you
|
|
|
|
back the requested variation. This is orthogonal but related to overlays and
|
|
|
|
the extending functions. Those also let you make modifications but return the
|
|
|
|
whole package set instead of just what you modified. When used together, the
|
|
|
|
override functions make the changes and overlays or extending functions add
|
|
|
|
those changes to the package sets.
|
2018-10-02 20:59:59 +01:00
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<section xml:id="sec-pkg-override">
|
|
|
|
<title><pkg>.override</title>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
The function <varname>override</varname> is usually available for all the
|
|
|
|
derivations in the nixpkgs expression (<varname>pkgs</varname>).
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
It is used to override the arguments passed to a function.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
Example usages:
|
2018-10-02 18:52:21 +01:00
|
|
|
<programlisting>pkgs.foo.override { arg1 = val1; arg2 = val2; ... }</programlisting>
|
2018-10-15 12:47:36 +01:00
|
|
|
<!-- TODO: move below programlisting to a new section about extending and overlays
|
|
|
|
and reference it
|
|
|
|
-->
|
2018-10-02 18:52:21 +01:00
|
|
|
<programlisting>
|
|
|
|
import pkgs.path { overlays = [ (self: super: {
|
|
|
|
foo = super.foo.override { barSupport = true ; };
|
|
|
|
})]};
|
|
|
|
</programlisting>
|
|
|
|
<programlisting>
|
|
|
|
mypkg = pkgs.callPackage ./mypkg.nix {
|
|
|
|
mydep = pkgs.mydep.override { ... };
|
|
|
|
}
|
|
|
|
</programlisting>
|
2018-10-02 20:59:59 +01:00
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
In the first example, <varname>pkgs.foo</varname> is the result of a
|
|
|
|
function call with some default arguments, usually a derivation. Using
|
|
|
|
<varname>pkgs.foo.override</varname> will call the same function with the
|
|
|
|
given new arguments.
|
|
|
|
</para>
|
|
|
|
</section>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<section xml:id="sec-pkg-overrideAttrs">
|
|
|
|
<title><pkg>.overrideAttrs</title>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
The function <varname>overrideAttrs</varname> allows overriding the
|
|
|
|
attribute set passed to a <varname>stdenv.mkDerivation</varname> call,
|
|
|
|
producing a new derivation based on the original one. This function is
|
|
|
|
available on all derivations produced by the
|
|
|
|
<varname>stdenv.mkDerivation</varname> function, which is most packages in
|
|
|
|
the nixpkgs expression <varname>pkgs</varname>.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
Example usage:
|
2018-10-02 18:52:21 +01:00
|
|
|
<programlisting>
|
|
|
|
helloWithDebug = pkgs.hello.overrideAttrs (oldAttrs: rec {
|
|
|
|
separateDebugInfo = true;
|
|
|
|
});
|
|
|
|
</programlisting>
|
2018-10-02 20:59:59 +01:00
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
In the above example, the <varname>separateDebugInfo</varname> attribute is
|
|
|
|
overridden to be true, thus building debug info for
|
|
|
|
<varname>helloWithDebug</varname>, while all other attributes will be
|
|
|
|
retained from the original <varname>hello</varname> package.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
The argument <varname>oldAttrs</varname> is conventionally used to refer to
|
|
|
|
the attr set originally passed to <varname>stdenv.mkDerivation</varname>.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<note>
|
|
|
|
<para>
|
|
|
|
Note that <varname>separateDebugInfo</varname> is processed only by the
|
|
|
|
<varname>stdenv.mkDerivation</varname> function, not the generated, raw Nix
|
|
|
|
derivation. Thus, using <varname>overrideDerivation</varname> will not work
|
|
|
|
in this case, as it overrides only the attributes of the final derivation.
|
|
|
|
It is for this reason that <varname>overrideAttrs</varname> should be
|
|
|
|
preferred in (almost) all cases to <varname>overrideDerivation</varname>,
|
|
|
|
i.e. to allow using <varname>sdenv.mkDerivation</varname> to process input
|
|
|
|
arguments, as well as the fact that it is easier to use (you can use the
|
|
|
|
same attribute names you see in your Nix code, instead of the ones
|
|
|
|
generated (e.g. <varname>buildInputs</varname> vs
|
|
|
|
<varname>nativeBuildInputs</varname>, and involves less typing.
|
|
|
|
</para>
|
|
|
|
</note>
|
|
|
|
</section>
|
|
|
|
|
|
|
|
<section xml:id="sec-pkg-overrideDerivation">
|
|
|
|
<title><pkg>.overrideDerivation</title>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<warning>
|
2018-10-02 18:52:21 +01:00
|
|
|
<para>
|
2018-10-02 20:59:59 +01:00
|
|
|
You should prefer <varname>overrideAttrs</varname> in almost all cases, see
|
|
|
|
its documentation for the reasons why.
|
|
|
|
<varname>overrideDerivation</varname> is not deprecated and will continue
|
|
|
|
to work, but is less nice to use and does not have as many abilities as
|
|
|
|
<varname>overrideAttrs</varname>.
|
2018-10-02 18:52:21 +01:00
|
|
|
</para>
|
2018-10-02 20:59:59 +01:00
|
|
|
</warning>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<warning>
|
2018-10-02 18:52:21 +01:00
|
|
|
<para>
|
2018-10-02 20:59:59 +01:00
|
|
|
Do not use this function in Nixpkgs as it evaluates a Derivation before
|
|
|
|
modifying it, which breaks package abstraction and removes error-checking
|
|
|
|
of function arguments. In addition, this evaluation-per-function
|
|
|
|
application incurs a performance penalty, which can become a problem if
|
|
|
|
many overrides are used. It is only intended for ad-hoc customisation, such
|
|
|
|
as in <filename>~/.config/nixpkgs/config.nix</filename>.
|
|
|
|
</para>
|
|
|
|
</warning>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
The function <varname>overrideDerivation</varname> creates a new derivation
|
|
|
|
based on an existing one by overriding the original's attributes with the
|
|
|
|
attribute set produced by the specified function. This function is available
|
|
|
|
on all derivations defined using the <varname>makeOverridable</varname>
|
|
|
|
function. Most standard derivation-producing functions, such as
|
|
|
|
<varname>stdenv.mkDerivation</varname>, are defined using this function,
|
|
|
|
which means most packages in the nixpkgs expression,
|
|
|
|
<varname>pkgs</varname>, have this function.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
Example usage:
|
2018-10-02 18:52:21 +01:00
|
|
|
<programlisting>
|
|
|
|
mySed = pkgs.gnused.overrideDerivation (oldAttrs: {
|
|
|
|
name = "sed-4.2.2-pre";
|
|
|
|
src = fetchurl {
|
|
|
|
url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
|
|
|
|
sha256 = "11nq06d131y4wmf3drm0yk502d2xc6n5qy82cg88rb9nqd2lj41k";
|
|
|
|
};
|
|
|
|
patches = [];
|
|
|
|
});
|
|
|
|
</programlisting>
|
2018-10-02 20:59:59 +01:00
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
In the above example, the <varname>name</varname>, <varname>src</varname>,
|
|
|
|
and <varname>patches</varname> of the derivation will be overridden, while
|
|
|
|
all other attributes will be retained from the original derivation.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
The argument <varname>oldAttrs</varname> is used to refer to the attribute
|
|
|
|
set of the original derivation.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<note>
|
2018-10-02 18:52:21 +01:00
|
|
|
<para>
|
2018-10-02 20:59:59 +01:00
|
|
|
A package's attributes are evaluated *before* being modified by the
|
|
|
|
<varname>overrideDerivation</varname> function. For example, the
|
|
|
|
<varname>name</varname> attribute reference in <varname>url =
|
|
|
|
"mirror://gnu/hello/${name}.tar.gz";</varname> is filled-in *before* the
|
|
|
|
<varname>overrideDerivation</varname> function modifies the attribute set.
|
|
|
|
This means that overriding the <varname>name</varname> attribute, in this
|
|
|
|
example, *will not* change the value of the <varname>url</varname>
|
|
|
|
attribute. Instead, we need to override both the <varname>name</varname>
|
|
|
|
*and* <varname>url</varname> attributes.
|
2018-10-02 18:52:21 +01:00
|
|
|
</para>
|
2018-10-02 20:59:59 +01:00
|
|
|
</note>
|
|
|
|
</section>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<section xml:id="sec-lib-makeOverridable">
|
|
|
|
<title>lib.makeOverridable</title>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
The function <varname>lib.makeOverridable</varname> is used to make the
|
|
|
|
result of a function easily customizable. This utility only makes sense for
|
|
|
|
functions that accept an argument set and return an attribute set.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
Example usage:
|
2018-10-02 18:52:21 +01:00
|
|
|
<programlisting>
|
|
|
|
f = { a, b }: { result = a+b; };
|
|
|
|
c = lib.makeOverridable f { a = 1; b = 2; };
|
|
|
|
</programlisting>
|
2018-10-02 20:59:59 +01:00
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
The variable <varname>c</varname> is the value of the <varname>f</varname>
|
|
|
|
function applied with some default arguments. Hence the value of
|
|
|
|
<varname>c.result</varname> is <literal>3</literal>, in this example.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
|
2018-10-02 20:59:59 +01:00
|
|
|
<para>
|
|
|
|
The variable <varname>c</varname> however also has some additional
|
|
|
|
functions, like <link linkend="sec-pkg-override">c.override</link> which can
|
|
|
|
be used to override the default arguments. In this example the value of
|
|
|
|
<varname>(c.override { a = 4; }).result</varname> is 6.
|
|
|
|
</para>
|
2018-10-02 18:52:21 +01:00
|
|
|
</section>
|
2018-10-02 20:59:59 +01:00
|
|
|
</section>
|