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<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-freeform-modules">
<title>Freeform modules</title>
<para>
Freeform modules allow you to define values for option paths that have not been declared explicitly. This can be used to add attribute-specific types to what would otherwise have to be <literal>attrsOf</literal> options in order to accept all attribute names.
</para>
<para>
This feature can be enabled by using the attribute <literal>freeformType</literal> to define a freeform type. By doing this, all assignments without an associated option will be merged using the freeform type and combined into the resulting <literal>config</literal> set. Since this feature nullifies name checking for entire option trees, it is only recommended for use in submodules.
</para>
<example xml:id="ex-freeform-module">
<title>Freeform submodule</title>
<para>
The following shows a submodule assigning a freeform type that allows arbitrary attributes with <literal>str</literal> values below <literal>settings</literal>, but also declares an option for the <literal>settings.port</literal> attribute to have it type-checked and assign a default value. See <xref linkend="ex-settings-typed-attrs"/> for a more complete example.
</para>
<programlisting>
{ lib, config, ... }: {
options.settings = lib.mkOption {
type = lib.types.submodule {
freeformType = with lib.types; attrsOf str;
# We want this attribute to be checked for the correct type
options.port = lib.mkOption {
type = lib.types.port;
# Declaring the option also allows defining a default value
default = 8080;
};
};
};
}
</programlisting>
<para>
And the following shows what such a module then allows
</para>
<programlisting>
{
# Not a declared option, but the freeform type allows this
settings.logLevel = "debug";
# Not allowed because the the freeform type only allows strings
# settings.enable = true;
# Allowed because there is a port option declared
settings.port = 80;
# Not allowed because the port option doesn't allow strings
# settings.port = "443";
}
</programlisting>
</example>
<note>
<para>
Freeform attributes cannot depend on other attributes of the same set without infinite recursion:
<programlisting>
{
# This throws infinite recursion encountered
settings.logLevel = lib.mkIf (config.settings.port == 80) "debug";
}
</programlisting>
To prevent this, declare options for all attributes that need to depend on others. For above example this means to declare <literal>logLevel</literal> to be an option.
</para>
</note>
</section>
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