forked from mirrors/nixpkgs
69 lines
2.7 KiB
XML
69 lines
2.7 KiB
XML
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="sec-freeform-modules">
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<title>Freeform modules</title>
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<para>
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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.
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</para>
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<para>
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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.
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</para>
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<example xml:id="ex-freeform-module">
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<title>Freeform submodule</title>
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<para>
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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.
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</para>
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<programlisting>
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{ lib, config, ... }: {
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options.settings = lib.mkOption {
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type = lib.types.submodule {
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freeformType = with lib.types; attrsOf str;
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# We want this attribute to be checked for the correct type
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options.port = lib.mkOption {
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type = lib.types.port;
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# Declaring the option also allows defining a default value
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default = 8080;
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};
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};
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};
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}
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</programlisting>
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<para>
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And the following shows what such a module then allows
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</para>
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<programlisting>
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{
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# Not a declared option, but the freeform type allows this
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settings.logLevel = "debug";
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# Not allowed because the the freeform type only allows strings
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# settings.enable = true;
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# Allowed because there is a port option declared
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settings.port = 80;
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# Not allowed because the port option doesn't allow strings
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# settings.port = "443";
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}
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</programlisting>
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</example>
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<note>
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<para>
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Freeform attributes cannot depend on other attributes of the same set without infinite recursion:
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<programlisting>
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{
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# This throws infinite recursion encountered
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settings.logLevel = lib.mkIf (config.settings.port == 80) "debug";
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}
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</programlisting>
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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.
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</para>
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</note>
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</section>
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