nixpkgs manual: add a section about passthru

This commit is contained in:
Nikolay Amiantov 2016-01-21 19:43:52 +03:00
parent f727f815cb
commit 9c1d8037c0

View File

@ -247,6 +247,39 @@ genericBuild
</variablelist> </variablelist>
<variablelist>
<title>Special variables</title>
<varlistentry>
<term><varname>passthru</varname></term>
<listitem><para>This is an attribute set which can be filled with arbitrary
values. For example:
<programlisting>
passthru = {
foo = "bar";
baz = {
value1 = 4;
value2 = 5;
};
}
</programlisting>
</para>
<para>Values inside it are not passed to the builder, so you can change
them without triggering a rebuild. However, they can be accessed outside of a
derivation directly, as if they were set inside a derivation itself, e.g.
<literal>hello.baz.value1</literal>. We don't specify any usage or
schema of <literal>passthru</literal> - it is meant for values that would be
useful outside the derivation in other parts of a Nix expression (e.g. in other
derivations). An example would be to convey some specific dependency of your
derivation which contains a program with plugins support. Later, others who
make derivations with plugins can use passed-through dependency to ensure that
their plugin would be binary-compatible with built program.</para></listitem>
</varlistentry>
</variablelist>
</section> </section>