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nixos: nixos/doc/manual/development/freeform-modules.xml to CommonMark

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79
nixos/doc/manual/development/freeform-modules.section.md Normal file
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# Freeform modules {#sec-freeform-modules}
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 `attrsOf` options in order to
accept all attribute names.
This feature can be enabled by using the attribute `freeformType` 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 `config` set. Since this feature nullifies name
checking for entire option trees, it is only recommended for use in
submodules.
::: {#ex-freeform-module .example}
::: {.title}
**Example: Freeform submodule**
:::
The following shows a submodule assigning a freeform type that allows
arbitrary attributes with `str` values below `settings`, but also
declares an option for the `settings.port` attribute to have it
type-checked and assign a default value. See
[Example: Declaring a type-checked `settings` attribute](#ex-settings-typed-attrs)
for a more complete example.
```nix
{ 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;
};
};
};
}
```
And the following shows what such a module then allows
```nix
{
# 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";
}
```
:::
::: {.note}
Freeform attributes cannot depend on other attributes of the same set
without infinite recursion:
```nix
{
# This throws infinite recursion encountered
settings.logLevel = lib.mkIf (config.settings.port == 80) "debug";
}
```
To prevent this, declare options for all attributes that need to depend
on others. For above example this means to declare `logLevel` to be an
option.
:::

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nixos/doc/manual/development/freeform-modules.xml
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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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nixos/doc/manual/from_md/development/freeform-modules.section.xml Normal file
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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" 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>
<anchor xml:id="ex-freeform-module" />
<para>
<emphasis role="strong">Example: Freeform submodule</emphasis>
</para>
<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
<link linkend="ex-settings-typed-attrs">Example: Declaring a
type-checked <literal>settings</literal> attribute</link> for a more
complete example.
</para>
<programlisting language="bash">
{ 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 language="bash">
{
# Not a declared option, but the freeform type allows this
settings.logLevel = &quot;debug&quot;;
# 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 = &quot;443&quot;;
}
</programlisting>
<note>
<para>
Freeform attributes cannot depend on other attributes of the same
set without infinite recursion:
</para>
<programlisting language="bash">
{
# This throws infinite recursion encountered
settings.logLevel = lib.mkIf (config.settings.port == 80) &quot;debug&quot;;
}
</programlisting>
<para>
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>