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Update overlay documentation by following nits from aneeshusa.

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Nicolas B. Pierron 2017-01-15 15:07:29 +00:00 committed by Nicolas B. Pierron
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80
doc/overlays.xml
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@ -4,56 +4,53 @@
<title>Overlays</title>
<para>This chapter describes how to extend and change Nixpkgs content using
overlays. Overlays are used to add layers in the fix-point used by Nixpkgs
to bind the dependencies of all packages.</para>
<para>This chapter describes how to extend and change Nixpkgs packages using
overlays. Overlays are used to add layers in the fix-point used by Nixpkgs
to compose the set of all packages.</para>
<!--============================================================-->
<section xml:id="sec-overlays-install">
<title>Installing Overlays</title>
<para>The set of overlays are looked for in the following order, only the
<para>The set of overlays is looked for in the following places. The
first one present is considered, and all the rest are ignored:
<orderedlist>
<listitem>
<para>As argument of the imported attribute set. When importing Nixpkgs,
<para>As an argument of the imported attribute set. When importing Nixpkgs,
the <varname>overlays</varname> attribute argument can be set to a list of
functions, which would be describe in <xref linkend="sec-overlays-layout"/>.</para>
functions, which is described in <xref linkend="sec-overlays-layout"/>.</para>
</listitem>
<listitem>
<para>As a directory pointed by the environment variable named
<varname>NIXPKGS_OVERLAYS</varname>. This directory can contain symbolic
links to Nix expressions.
<para>In the directory pointed by the environment variable
<varname>NIXPKGS_OVERLAYS</varname>.
</listitem>
<listitem>
<para>As the directory located at
<filename>~/.nixpkgs/overlays/</filename>. This directory can contain
symbolic links to Nix expressions.
<para>In the directory <filename>~/.nixpkgs/overlays/</filename>.
</listitem>
</orderedlist>
</para>
<para>For the second and third option, the directory contains either
directories providing a default.nix expression, or files, or symbolic links
to the entry Nix expression of the overlay. These Nix expressions are
following the syntax described in <xref
linkend="sec-overlays-layout"/>.</para>
<para>For the second and third option, the directory should contain Nix expressions defining the
overlays. Each overlay can be a file, a directory containing a
<filename>default.nix</filename>, or a symlink to one of those. The expressions should follow
the syntax described in <xref linkend="sec-overlays-layout"/>.</para>
<para>To install an overlay, using the last option. Clone the repository of
the overlay, and add a symbolic link to it in the
<filename>~/.nixpkgs/overlays/</filename> directory.</para>
<para>The order of the overlay layers can influence the recipe of packages if multiple layers override
the same recipe. In the case where overlays are loaded from a directory, these are loaded in
alphabetical order.</para>
<para>To install an overlay using the last option, you can clone the overlay's repository and add
a symbolic link to in the <filename>~/.nixpkgs/overlays/</filename> directory.</para>
</section>
@ -62,37 +59,40 @@ the overlay, and add a symbolic link to it in the
<section xml:id="sec-overlays-layout">
<title>Overlays Layout</title>
<para>An overlay is a Nix expression, which is a function which accepts 2
arguments.</para>
<para>Overlays are expressed as Nix functions which accept 2 arguments and return a set of
packages</para>
<programlisting>
self: super:
{
foo = super.foo.override { ... };
bar = import ./pkgs/bar {
inherit (self) stdenv fetchurl;
inherit (self) ninja crawl dwarf-fortress;
boost = super.boost.override {
python = self.python3;
};
rr = super.callPackage ./pkgs/rr {
stdenv = self.stdenv_32bit;
};
}
</programlisting>
<para>The first argument, usualy named <varname>self</varname>, corresponds
to the final package set. You should use this set to inherit all the
dependencies needed by your package expression.</para>
<para>The first argument, usually named <varname>self</varname>, corresponds to the final package
set. You should use this set for the dependencies of all packages specified in your
overlay. For example, all the dependencies of <varname>rr</varname> in the example above come
from <varname>self</varname>, as well as the overriden dependencies used in the
<varname>boost</varname> override.</para>
<para>The second argument, usualy named <varname>super</varname>,
<para>The second argument, usually named <varname>super</varname>,
corresponds to the result of the evaluation of the previous stages of
Nixpkgs, it does not contain any of the packages added by the current
overlay nor any of the following overlays. This set is used in to override
existing packages, either by changing their dependencies or their
recipes.</para>
Nixpkgs. It does not contain any of the packages added by the current
overlay nor any of the following overlays. This set should be used either
to refer to packages you wish to override, or to access functions defined
in Nixpkgs. For example, the original recipe of <varname>boost</varname>
in the above example, comes from <varname>super</varname>, as well as the
<varname>callPackage</varname> function.</para>
<para>The value returned by this function should be a set similar to
<filename>pkgs/top-level/all-packages.nix</filename>, which contains either
extra packages defined by the overlay, or which overwrite Nixpkgs packages
with other custom defaults. This is similar to <xref
linkend="sec-modify-via-packageOverrides"/>.</para>
<filename>pkgs/top-level/all-packages.nix</filename>, which contains
overridden and/or new packages.</para>
</section>

2
nixos/doc/manual/release-notes/rl-1703.xml
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@ -113,7 +113,7 @@ following incompatible changes:</para>
pkgs.overridePackages (self: super: ...)
</programlisting>
Should be replaced by:
should be replaced by:
<programlisting>
let

2
nixos/modules/misc/nixpkgs.nix
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@ -69,7 +69,7 @@ in
openssh = super.openssh.override {
hpnSupport = true;
withKerberos = true;
kerberos = self.libkrb5
kerberos = self.libkrb5;
};
};
) ]