nordic-dev.net/nixpkgs
nordic-dev.net/nixpkgs
2
0
Fork 0
mirror of https://github.com/NixOS/nixpkgs.git synced 2024-11-23 07:23:20 +00:00
Code Issues Packages Projects Releases Wiki Activity

nixpkgs docs: move overrides to its own file

Browse Source
This commit is contained in:
Graham Christensen 2018-10-02 13:52:21 -04:00
parent 18b468ed81
commit f200a322c4
No known key found for this signature in database
GPG Key ID: ACA1C1D120C83D5C
2 changed files with 206 additions and 201 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

202
doc/functions.xml
View File

@ -7,208 +7,8 @@
The nixpkgs repository has several utility functions to manipulate Nix
expressions.
</para>
<section xml:id="sec-overrides">
<title>Overriding</title>
<para>
Sometimes one wants to override parts of <literal>nixpkgs</literal>, e.g.
derivation attributes, the results of derivations or even the whole package
set.
</para>
<section xml:id="sec-pkg-override">
<title>&lt;pkg&gt;.override</title>
<para>
The function <varname>override</varname> is usually available for all the
derivations in the nixpkgs expression (<varname>pkgs</varname>).
</para>
<para>
It is used to override the arguments passed to a function.
</para>
<para>
Example usages:
<programlisting>pkgs.foo.override { arg1 = val1; arg2 = val2; ... }</programlisting>
<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>
</para>
<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>
<section xml:id="sec-pkg-overrideAttrs">
<title>&lt;pkg&gt;.overrideAttrs</title>
<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>
<para>
Example usage:
<programlisting>
helloWithDebug = pkgs.hello.overrideAttrs (oldAttrs: rec {
separateDebugInfo = true;
});
</programlisting>
</para>
<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>
<para>
The argument <varname>oldAttrs</varname> is conventionally used to refer to
the attr set originally passed to <varname>stdenv.mkDerivation</varname>.
</para>
<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>&lt;pkg&gt;.overrideDerivation</title>
<warning>
<para>
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>.
</para>
</warning>
<warning>
<para>
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:
<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>
</para>
<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>
<note>
<para>
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.
</para>
</note>
</section>
<section xml:id="sec-lib-makeOverridable">
<title>lib.makeOverridable</title>
<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>
<para>
Example usage:
<programlisting>
f = { a, b }: { result = a+b; };
c = lib.makeOverridable f { a = 1; b = 2; };
</programlisting>
</para>
<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>
<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>
</section>
</section>
<xi:include href="functions/overrides.xml" />
<section xml:id="sec-generators">
<title>Generators</title>

205
doc/functions/overrides.xml Normal file
View File

@ -0,0 +1,205 @@
<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">
<title>Overriding</title>
<para>
Sometimes one wants to override parts of <literal>nixpkgs</literal>, e.g.
derivation attributes, the results of derivations or even the whole package
set.
</para>
<section xml:id="sec-pkg-override">
<title>&lt;pkg&gt;.override</title>
<para>
The function <varname>override</varname> is usually available for all the
derivations in the nixpkgs expression (<varname>pkgs</varname>).
</para>
<para>
It is used to override the arguments passed to a function.
</para>
<para>
Example usages:
<programlisting>pkgs.foo.override { arg1 = val1; arg2 = val2; ... }</programlisting>
<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>
</para>
<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>
<section xml:id="sec-pkg-overrideAttrs">
<title>&lt;pkg&gt;.overrideAttrs</title>
<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>
<para>
Example usage:
<programlisting>
helloWithDebug = pkgs.hello.overrideAttrs (oldAttrs: rec {
separateDebugInfo = true;
});
</programlisting>
</para>
<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>
<para>
The argument <varname>oldAttrs</varname> is conventionally used to refer to
the attr set originally passed to <varname>stdenv.mkDerivation</varname>.
</para>
<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>&lt;pkg&gt;.overrideDerivation</title>
<warning>
<para>
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>.
</para>
</warning>
<warning>
<para>
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:
<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>
</para>
<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>
<note>
<para>
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.
</para>
</note>
</section>
<section xml:id="sec-lib-makeOverridable">
<title>lib.makeOverridable</title>
<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>
<para>
Example usage:
<programlisting>
f = { a, b }: { result = a+b; };
c = lib.makeOverridable f { a = 1; b = 2; };
</programlisting>
</para>
<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>
<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>
</section>
</section>