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nixos/doc/manual/development/option-types.section.md Normal file
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# Options Types {#sec-option-types}
Option types are a way to put constraints on the values a module option
can take. Types are also responsible of how values are merged in case of
multiple value definitions.
## Basic Types {#sec-option-types-basic}
Basic types are the simplest available types in the module system. Basic
types include multiple string types that mainly differ in how definition
merging is handled.
`types.bool`
: A boolean, its values can be `true` or `false`.
`types.path`
: A filesystem path, defined as anything that when coerced to a string
starts with a slash. Even if derivations can be considered as path,
the more specific `types.package` should be preferred.
`types.package`
: A derivation or a store path.
`types.anything`
: A type that accepts any value and recursively merges attribute sets
together. This type is recommended when the option type is unknown.
::: {#ex-types-anything .example}
::: {.title}
**Example: `types.anything` Example**
:::
Two definitions of this type like
```nix
{
str = lib.mkDefault "foo";
pkg.hello = pkgs.hello;
fun.fun = x: x + 1;
}
```
```nix
{
str = lib.mkIf true "bar";
pkg.gcc = pkgs.gcc;
fun.fun = lib.mkForce (x: x + 2);
}
```
will get merged to
```nix
{
str = "bar";
pkg.gcc = pkgs.gcc;
pkg.hello = pkgs.hello;
fun.fun = x: x + 2;
}
```
:::
`types.attrs`
: A free-form attribute set.
::: {.warning}
This type will be deprecated in the future because it doesn\'t
recurse into attribute sets, silently drops earlier attribute
definitions, and doesn\'t discharge `lib.mkDefault`, `lib.mkIf`
and co. For allowing arbitrary attribute sets, prefer
`types.attrsOf types.anything` instead which doesn\'t have these
problems.
:::
Integer-related types:
`types.int`
: A signed integer.
`types.ints.{s8, s16, s32}`
: Signed integers with a fixed length (8, 16 or 32 bits). They go from
−2^n/2 to
2^n/2−1 respectively (e.g. `−128` to
`127` for 8 bits).
`types.ints.unsigned`
: An unsigned integer (that is >= 0).
`types.ints.{u8, u16, u32}`
: Unsigned integers with a fixed length (8, 16 or 32 bits). They go
from 0 to 2^n−1 respectively (e.g. `0`
to `255` for 8 bits).
`types.ints.positive`
: A positive integer (that is > 0).
`types.port`
: A port number. This type is an alias to
`types.ints.u16`.
String-related types:
`types.str`
: A string. Multiple definitions cannot be merged.
`types.lines`
: A string. Multiple definitions are concatenated with a new line
`"\n"`.
`types.commas`
: A string. Multiple definitions are concatenated with a comma `","`.
`types.envVar`
: A string. Multiple definitions are concatenated with a collon `":"`.
`types.strMatching`
: A string matching a specific regular expression. Multiple
definitions cannot be merged. The regular expression is processed
using `builtins.match`.
## Value Types {#sec-option-types-value}
Value types are types that take a value parameter.
`types.enum` *`l`*
: One element of the list *`l`*, e.g. `types.enum [ "left" "right" ]`.
Multiple definitions cannot be merged.
`types.separatedString` *`sep`*
: A string with a custom separator *`sep`*, e.g.
`types.separatedString "|"`.
`types.ints.between` *`lowest highest`*
: An integer between *`lowest`* and *`highest`* (both inclusive). Useful
for creating types like `types.port`.
`types.submodule` *`o`*
: A set of sub options *`o`*. *`o`* can be an attribute set, a function
returning an attribute set, or a path to a file containing such a
value. Submodules are used in composed types to create modular
options. This is equivalent to
`types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }`.
Submodules are detailed in [Submodule](#section-option-types-submodule).
`types.submoduleWith` { *`modules`*, *`specialArgs`* ? {}, *`shorthandOnlyDefinesConfig`* ? false }
: Like `types.submodule`, but more flexible and with better defaults.
It has parameters
- *`modules`* A list of modules to use by default for this
submodule type. This gets combined with all option definitions
to build the final list of modules that will be included.
::: {.note}
Only options defined with this argument are included in rendered
documentation.
:::
- *`specialArgs`* An attribute set of extra arguments to be passed
to the module functions. The option `_module.args` should be
used instead for most arguments since it allows overriding.
*`specialArgs`* should only be used for arguments that can\'t go
through the module fixed-point, because of infinite recursion or
other problems. An example is overriding the `lib` argument,
because `lib` itself is used to define `_module.args`, which
makes using `_module.args` to define it impossible.
- *`shorthandOnlyDefinesConfig`* Whether definitions of this type
should default to the `config` section of a module (see
[Example: Structure of NixOS Modules](#ex-module-syntax))
if it is an attribute set. Enabling this only has a benefit
when the submodule defines an option named `config` or `options`.
In such a case it would allow the option to be set with
`the-submodule.config = "value"` instead of requiring
`the-submodule.config.config = "value"`. This is because
only when modules *don\'t* set the `config` or `options`
keys, all keys are interpreted as option definitions in the
`config` section. Enabling this option implicitly puts all
attributes in the `config` section.
With this option enabled, defining a non-`config` section
requires using a function:
`the-submodule = { ... }: { options = { ... }; }`.
## Composed Types {#sec-option-types-composed}
Composed types are types that take a type as parameter. `listOf
int` and `either int str` are examples of composed types.
`types.listOf` *`t`*
: A list of *`t`* type, e.g. `types.listOf
int`. Multiple definitions are merged with list concatenation.
`types.attrsOf` *`t`*
: An attribute set of where all the values are of *`t`* type. Multiple
definitions result in the joined attribute set.
::: {.note}
This type is *strict* in its values, which in turn means attributes
cannot depend on other attributes. See `
types.lazyAttrsOf` for a lazy version.
:::
`types.lazyAttrsOf` *`t`*
: An attribute set of where all the values are of *`t`* type. Multiple
definitions result in the joined attribute set. This is the lazy
version of `types.attrsOf
`, allowing attributes to depend on each other.
::: {.warning}
This version does not fully support conditional definitions! With an
option `foo` of this type and a definition
`foo.attr = lib.mkIf false 10`, evaluating `foo ? attr` will return
`true` even though it should be false. Accessing the value will then
throw an error. For types *`t`* that have an `emptyValue` defined,
that value will be returned instead of throwing an error. So if the
type of `foo.attr` was `lazyAttrsOf (nullOr int)`, `null` would be
returned instead for the same `mkIf false` definition.
:::
`types.nullOr` *`t`*
: `null` or type *`t`*. Multiple definitions are merged according to
type *`t`*.
`types.uniq` *`t`*
: Ensures that type *`t`* cannot be merged. It is used to ensure option
definitions are declared only once.
`types.either` *`t1 t2`*
: Type *`t1`* or type *`t2`*, e.g. `with types; either int str`.
Multiple definitions cannot be merged.
`types.oneOf` \[ *`t1 t2`* \... \]
: Type *`t1`* or type *`t2`* and so forth, e.g.
`with types; oneOf [ int str bool ]`. Multiple definitions cannot be
merged.
`types.coercedTo` *`from f to`*
: Type *`to`* or type *`from`* which will be coerced to type *`to`* using
function *`f`* which takes an argument of type *`from`* and return a
value of type *`to`*. Can be used to preserve backwards compatibility
of an option if its type was changed.
## Submodule {#section-option-types-submodule}
`submodule` is a very powerful type that defines a set of sub-options
that are handled like a separate module.
It takes a parameter *`o`*, that should be a set, or a function returning
a set with an `options` key defining the sub-options. Submodule option
definitions are type-checked accordingly to the `options` declarations.
Of course, you can nest submodule option definitons for even higher
modularity.
The option set can be defined directly
([Example: Directly defined submodule](#ex-submodule-direct)) or as reference
([Example: Submodule defined as a reference](#ex-submodule-reference)).
::: {#ex-submodule-direct .example}
::: {.title}
**Example: Directly defined submodule**
:::
```nix
options.mod = mkOption {
description = "submodule example";
type = with types; submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
};
};
```
:::
::: {#ex-submodule-reference .example}
::: {.title}
**Example: Submodule defined as a reference**
:::
```nix
let
modOptions = {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = int;
};
};
};
in
options.mod = mkOption {
description = "submodule example";
type = with types; submodule modOptions;
};
```
:::
The `submodule` type is especially interesting when used with composed
types like `attrsOf` or `listOf`. When composed with `listOf`
([Example: Declaration of a list of submodules](#ex-submodule-listof-declaration)), `submodule` allows
multiple definitions of the submodule option set
([Example: Definition of a list of submodules](#ex-submodule-listof-definition)).
::: {#ex-submodule-listof-declaration .example}
::: {.title}
**Example: Declaration of a list of submodules**
:::
```nix
options.mod = mkOption {
description = "submodule example";
type = with types; listOf (submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
});
};
```
:::
::: {#ex-submodule-listof-definition .example}
::: {.title}
**Example: Definition of a list of submodules**
:::
```nix
config.mod = [
{ foo = 1; bar = "one"; }
{ foo = 2; bar = "two"; }
];
```
:::
When composed with `attrsOf`
([Example: Declaration of attribute sets of submodules](#ex-submodule-attrsof-declaration)), `submodule` allows
multiple named definitions of the submodule option set
([Example: Definition of attribute sets of submodules](#ex-submodule-attrsof-definition)).
::: {#ex-submodule-attrsof-declaration .example}
::: {.title}
**Example: Declaration of attribute sets of submodules**
:::
```nix
options.mod = mkOption {
description = "submodule example";
type = with types; attrsOf (submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
});
};
```
:::
::: {#ex-submodule-attrsof-definition .example}
::: {.title}
**Example: Definition of attribute sets of submodules**
:::
```nix
config.mod.one = { foo = 1; bar = "one"; };
config.mod.two = { foo = 2; bar = "two"; };
```
:::
## Extending types {#sec-option-types-extending}
Types are mainly characterized by their `check` and `merge` functions.
`check`
: The function to type check the value. Takes a value as parameter and
return a boolean. It is possible to extend a type check with the
`addCheck` function ([Example: Adding a type check](#ex-extending-type-check-1)),
or to fully override the check function
([Example: Overriding a type check](#ex-extending-type-check-2)).
::: {#ex-extending-type-check-1 .example}
::: {.title}
**Example: Adding a type check**
:::
```nix
byte = mkOption {
description = "An integer between 0 and 255.";
type = types.addCheck types.int (x: x >= 0 && x <= 255);
};
```
:::
::: {#ex-extending-type-check-2 .example}
::: {.title}
**Example: Overriding a type check**
:::
```nix
nixThings = mkOption {
description = "words that start with 'nix'";
type = types.str // {
check = (x: lib.hasPrefix "nix" x)
};
};
```
:::
`merge`
: Function to merge the options values when multiple values are set.
The function takes two parameters, `loc` the option path as a list
of strings, and `defs` the list of defined values as a list. It is
possible to override a type merge function for custom needs.
## Custom Types {#sec-option-types-custom}
Custom types can be created with the `mkOptionType` function. As type
creation includes some more complex topics such as submodule handling,
it is recommended to get familiar with `types.nix` code before creating
a new type.
The only required parameter is `name`.
`name`
: A string representation of the type function name.
`definition`
: Description of the type used in documentation. Give information of
the type and any of its arguments.
`check`
: A function to type check the definition value. Takes the definition
value as a parameter and returns a boolean indicating the type check
result, `true` for success and `false` for failure.
`merge`
: A function to merge multiple definitions values. Takes two
parameters:
*`loc`*
: The option path as a list of strings, e.g. `["boot" "loader
"grub" "enable"]`.
*`defs`*
: The list of sets of defined `value` and `file` where the value
was defined, e.g. `[ {
file = "/foo.nix"; value = 1; } { file = "/bar.nix"; value = 2 }
]`. The `merge` function should return the merged value
or throw an error in case the values are impossible or not meant
to be merged.
`getSubOptions`
: For composed types that can take a submodule as type parameter, this
function generate sub-options documentation. It takes the current
option prefix as a list and return the set of sub-options. Usually
defined in a recursive manner by adding a term to the prefix, e.g.
`prefix:
elemType.getSubOptions (prefix ++
["prefix"])` where *`"prefix"`* is the newly added prefix.
`getSubModules`
: For composed types that can take a submodule as type parameter, this
function should return the type parameters submodules. If the type
parameter is called `elemType`, the function should just recursively
look into submodules by returning `elemType.getSubModules;`.
`substSubModules`
: For composed types that can take a submodule as type parameter, this
function can be used to substitute the parameter of a submodule
type. It takes a module as parameter and return the type with the
submodule options substituted. It is usually defined as a type
function call with a recursive call to `substSubModules`, e.g for a
type `composedType` that take an `elemtype` type parameter, this
function should be defined as `m:
composedType (elemType.substSubModules m)`.
`typeMerge`
: A function to merge multiple type declarations. Takes the type to
merge `functor` as parameter. A `null` return value means that type
cannot be merged.
*`f`*
: The type to merge `functor`.
Note: There is a generic `defaultTypeMerge` that work with most of
value and composed types.
`functor`
: An attribute set representing the type. It is used for type
operations and has the following keys:
`type`
: The type function.
`wrapped`
: Holds the type parameter for composed types.
`payload`
: Holds the value parameter for value types. The types that have a
`payload` are the `enum`, `separatedString` and `submodule`
types.
`binOp`
: A binary operation that can merge the payloads of two same
types. Defined as a function that take two payloads as
parameters and return the payloads merged.

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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-option-types">
<title>Options Types</title>
<para>
Option types are a way to put constraints on the values a module option can
take. Types are also responsible of how values are merged in case of multiple
value definitions.
</para>
<section xml:id="sec-option-types-basic">
<title>Basic Types</title>
<para>
Basic types are the simplest available types in the module system. Basic
types include multiple string types that mainly differ in how definition
merging is handled.
</para>
<variablelist>
<varlistentry>
<term>
<varname>types.bool</varname>
</term>
<listitem>
<para>
A boolean, its values can be <literal>true</literal> or
<literal>false</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.path</varname>
</term>
<listitem>
<para>
A filesystem path, defined as anything that when coerced to a string
starts with a slash. Even if derivations can be considered as path, the
more specific <literal>types.package</literal> should be preferred.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.package</varname>
</term>
<listitem>
<para>
A derivation or a store path.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.anything</varname>
</term>
<listitem>
<para>
A type that accepts any value and recursively merges attribute sets together.
This type is recommended when the option type is unknown.
<example xml:id="ex-types-anything">
<title><literal>types.anything</literal> Example</title>
<para>
Two definitions of this type like
<programlisting>
{
str = lib.mkDefault "foo";
pkg.hello = pkgs.hello;
fun.fun = x: x + 1;
}
</programlisting>
<programlisting>
{
str = lib.mkIf true "bar";
pkg.gcc = pkgs.gcc;
fun.fun = lib.mkForce (x: x + 2);
}
</programlisting>
will get merged to
<programlisting>
{
str = "bar";
pkg.gcc = pkgs.gcc;
pkg.hello = pkgs.hello;
fun.fun = x: x + 2;
}
</programlisting>
</para>
</example>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.attrs</varname>
</term>
<listitem>
<para>
A free-form attribute set.
<warning><para>
This type will be deprecated in the future because it doesn't recurse
into attribute sets, silently drops earlier attribute definitions, and
doesn't discharge <literal>lib.mkDefault</literal>, <literal>lib.mkIf
</literal> and co. For allowing arbitrary attribute sets, prefer
<literal>types.attrsOf types.anything</literal> instead which doesn't
have these problems.
</para></warning>
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
Integer-related types:
</para>
<variablelist>
<varlistentry>
<term>
<varname>types.int</varname>
</term>
<listitem>
<para>
A signed integer.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.ints.{s8, s16, s32}</varname>
</term>
<listitem>
<para>
Signed integers with a fixed length (8, 16 or 32 bits). They go from
<inlineequation><mathphrase>−2<superscript>n</superscript>/2</mathphrase>
</inlineequation> to <inlineequation>
<mathphrase>2<superscript>n</superscript>/2−1</mathphrase>
</inlineequation> respectively (e.g. <literal>−128</literal> to
<literal>127</literal> for 8 bits).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.ints.unsigned</varname>
</term>
<listitem>
<para>
An unsigned integer (that is >= 0).
</para>
</listitem>
</varlistentry>
<varlistentry xml:id='types.ints.ux'>
<term>
<varname>types.ints.{u8, u16, u32}</varname>
</term>
<listitem>
<para>
Unsigned integers with a fixed length (8, 16 or 32 bits). They go from
<inlineequation><mathphrase>0</mathphrase></inlineequation> to
<inlineequation>
<mathphrase>2<superscript>n</superscript>−1</mathphrase>
</inlineequation> respectively (e.g. <literal>0</literal> to
<literal>255</literal> for 8 bits).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.ints.positive</varname>
</term>
<listitem>
<para>
A positive integer (that is > 0).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.port</varname>
</term>
<listitem>
<para>
A port number. This type is an alias to
<link linkend='types.ints.ux'><varname>types.ints.u16</varname></link>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
String-related types:
</para>
<variablelist>
<varlistentry>
<term>
<varname>types.str</varname>
</term>
<listitem>
<para>
A string. Multiple definitions cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.lines</varname>
</term>
<listitem>
<para>
A string. Multiple definitions are concatenated with a new line
<literal>"\n"</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.commas</varname>
</term>
<listitem>
<para>
A string. Multiple definitions are concatenated with a comma
<literal>","</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.envVar</varname>
</term>
<listitem>
<para>
A string. Multiple definitions are concatenated with a collon
<literal>":"</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.strMatching</varname>
</term>
<listitem>
<para>
A string matching a specific regular expression. Multiple definitions
cannot be merged. The regular expression is processed using
<literal>builtins.match</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-option-types-value">
<title>Value Types</title>
<para>
Value types are types that take a value parameter.
</para>
<variablelist>
<varlistentry>
<term>
<varname>types.enum</varname> <replaceable>l</replaceable>
</term>
<listitem>
<para>
One element of the list <replaceable>l</replaceable>, e.g.
<literal>types.enum [ "left" "right" ]</literal>. Multiple definitions
cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.separatedString</varname> <replaceable>sep</replaceable>
</term>
<listitem>
<para>
A string with a custom separator <replaceable>sep</replaceable>, e.g.
<literal>types.separatedString "|"</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.ints.between</varname> <replaceable>lowest</replaceable> <replaceable>highest</replaceable>
</term>
<listitem>
<para>
An integer between <replaceable>lowest</replaceable> and
<replaceable>highest</replaceable> (both inclusive). Useful for creating
types like <literal>types.port</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.submodule</varname> <replaceable>o</replaceable>
</term>
<listitem>
<para>
A set of sub options <replaceable>o</replaceable>.
<replaceable>o</replaceable> can be an attribute set, a function
returning an attribute set, or a path to a file containing such a value. Submodules are used in
composed types to create modular options. This is equivalent to
<literal>types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }</literal>.
Submodules are detailed in
<xref
linkend='section-option-types-submodule' />.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.submoduleWith</varname> {
<replaceable>modules</replaceable>,
<replaceable>specialArgs</replaceable> ? {},
<replaceable>shorthandOnlyDefinesConfig</replaceable> ? false }
</term>
<listitem>
<para>
Like <varname>types.submodule</varname>, but more flexible and with better defaults.
It has parameters
<itemizedlist>
<listitem><para>
<replaceable>modules</replaceable>
A list of modules to use by default for this submodule type. This gets combined
with all option definitions to build the final list of modules that will be included.
<note><para>
Only options defined with this argument are included in rendered documentation.
</para></note>
</para></listitem>
<listitem><para>
<replaceable>specialArgs</replaceable>
An attribute set of extra arguments to be passed to the module functions.
The option <literal>_module.args</literal> should be used instead
for most arguments since it allows overriding. <replaceable>specialArgs</replaceable> should only be
used for arguments that can&apos;t go through the module fixed-point, because of
infinite recursion or other problems. An example is overriding the
<varname>lib</varname> argument, because <varname>lib</varname> itself is used
to define <literal>_module.args</literal>, which makes using
<literal>_module.args</literal> to define it impossible.
</para></listitem>
<listitem><para>
<replaceable>shorthandOnlyDefinesConfig</replaceable>
Whether definitions of this type should default to the <literal>config</literal>
section of a module (see <xref linkend='ex-module-syntax'/>) if it is an attribute
set. Enabling this only has a benefit when the submodule defines an option named
<literal>config</literal> or <literal>options</literal>. In such a case it would
allow the option to be set with <literal>the-submodule.config = "value"</literal>
instead of requiring <literal>the-submodule.config.config = "value"</literal>.
This is because only when modules <emphasis>don&apos;t</emphasis> set the
<literal>config</literal> or <literal>options</literal> keys, all keys are interpreted
as option definitions in the <literal>config</literal> section. Enabling this option
implicitly puts all attributes in the <literal>config</literal> section.
</para>
<para>
With this option enabled, defining a non-<literal>config</literal> section requires
using a function: <literal>the-submodule = { ... }: { options = { ... }; }</literal>.
</para></listitem>
</itemizedlist>
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-option-types-composed">
<title>Composed Types</title>
<para>
Composed types are types that take a type as parameter. <literal>listOf
int</literal> and <literal>either int str</literal> are examples of composed
types.
</para>
<variablelist>
<varlistentry>
<term>
<varname>types.listOf</varname> <replaceable>t</replaceable>
</term>
<listitem>
<para>
A list of <replaceable>t</replaceable> type, e.g. <literal>types.listOf
int</literal>. Multiple definitions are merged with list concatenation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.attrsOf</varname> <replaceable>t</replaceable>
</term>
<listitem>
<para>
An attribute set of where all the values are of
<replaceable>t</replaceable> type. Multiple definitions result in the
joined attribute set.
<note><para>
This type is <emphasis>strict</emphasis> in its values, which in turn
means attributes cannot depend on other attributes. See <varname>
types.lazyAttrsOf</varname> for a lazy version.
</para></note>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.lazyAttrsOf</varname> <replaceable>t</replaceable>
</term>
<listitem>
<para>
An attribute set of where all the values are of
<replaceable>t</replaceable> type. Multiple definitions result in the
joined attribute set. This is the lazy version of <varname>types.attrsOf
</varname>, allowing attributes to depend on each other.
<warning><para>
This version does not fully support conditional definitions! With an
option <varname>foo</varname> of this type and a definition
<literal>foo.attr = lib.mkIf false 10</literal>, evaluating
<literal>foo ? attr</literal> will return <literal>true</literal>
even though it should be false. Accessing the value will then throw
an error. For types <replaceable>t</replaceable> that have an
<literal>emptyValue</literal> defined, that value will be returned
instead of throwing an error. So if the type of <literal>foo.attr</literal>
was <literal>lazyAttrsOf (nullOr int)</literal>, <literal>null</literal>
would be returned instead for the same <literal>mkIf false</literal> definition.
</para></warning>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.nullOr</varname> <replaceable>t</replaceable>
</term>
<listitem>
<para>
<literal>null</literal> or type <replaceable>t</replaceable>. Multiple
definitions are merged according to type <replaceable>t</replaceable>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.uniq</varname> <replaceable>t</replaceable>
</term>
<listitem>
<para>
Ensures that type <replaceable>t</replaceable> cannot be merged. It is
used to ensure option definitions are declared only once.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.either</varname> <replaceable>t1</replaceable> <replaceable>t2</replaceable>
</term>
<listitem>
<para>
Type <replaceable>t1</replaceable> or type <replaceable>t2</replaceable>,
e.g. <literal>with types; either int str</literal>. Multiple definitions
cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.oneOf</varname> [ <replaceable>t1</replaceable> <replaceable>t2</replaceable> ... ]
</term>
<listitem>
<para>
Type <replaceable>t1</replaceable> or type <replaceable>t2</replaceable> and so forth,
e.g. <literal>with types; oneOf [ int str bool ]</literal>. Multiple definitions
cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>types.coercedTo</varname> <replaceable>from</replaceable> <replaceable>f</replaceable> <replaceable>to</replaceable>
</term>
<listitem>
<para>
Type <replaceable>to</replaceable> or type
<replaceable>from</replaceable> which will be coerced to type
<replaceable>to</replaceable> using function <replaceable>f</replaceable>
which takes an argument of type <replaceable>from</replaceable> and
return a value of type <replaceable>to</replaceable>. Can be used to
preserve backwards compatibility of an option if its type was changed.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id='section-option-types-submodule'>
<title>Submodule</title>
<para>
<literal>submodule</literal> is a very powerful type that defines a set of
sub-options that are handled like a separate module.
</para>
<para>
It takes a parameter <replaceable>o</replaceable>, that should be a set, or
a function returning a set with an <literal>options</literal> key defining
the sub-options. Submodule option definitions are type-checked accordingly
to the <literal>options</literal> declarations. Of course, you can nest
submodule option definitons for even higher modularity.
</para>
<para>
The option set can be defined directly
(<xref linkend='ex-submodule-direct' />) or as reference
(<xref linkend='ex-submodule-reference' />).
</para>
<example xml:id='ex-submodule-direct'>
<title>Directly defined submodule</title>
<screen>
options.mod = mkOption {
description = "submodule example";
type = with types; submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
};
};</screen>
</example>
<example xml:id='ex-submodule-reference'>
<title>Submodule defined as a reference</title>
<screen>
let
modOptions = {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = int;
};
};
};
in
options.mod = mkOption {
description = "submodule example";
type = with types; submodule modOptions;
};</screen>
</example>
<para>
The <literal>submodule</literal> type is especially interesting when used
with composed types like <literal>attrsOf</literal> or
<literal>listOf</literal>. When composed with <literal>listOf</literal>
(<xref linkend='ex-submodule-listof-declaration' />),
<literal>submodule</literal> allows multiple definitions of the submodule
option set (<xref linkend='ex-submodule-listof-definition' />).
</para>
<example xml:id='ex-submodule-listof-declaration'>
<title>Declaration of a list of submodules</title>
<screen>
options.mod = mkOption {
description = "submodule example";
type = with types; listOf (submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
});
};</screen>
</example>
<example xml:id='ex-submodule-listof-definition'>
<title>Definition of a list of submodules</title>
<screen>
config.mod = [
{ foo = 1; bar = "one"; }
{ foo = 2; bar = "two"; }
];</screen>
</example>
<para>
When composed with <literal>attrsOf</literal>
(<xref linkend='ex-submodule-attrsof-declaration' />),
<literal>submodule</literal> allows multiple named definitions of the
submodule option set (<xref linkend='ex-submodule-attrsof-definition' />).
</para>
<example xml:id='ex-submodule-attrsof-declaration'>
<title>Declaration of attribute sets of submodules</title>
<screen>
options.mod = mkOption {
description = "submodule example";
type = with types; attrsOf (submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
});
};</screen>
</example>
<example xml:id='ex-submodule-attrsof-definition'>
<title>Declaration of attribute sets of submodules</title>
<screen>
config.mod.one = { foo = 1; bar = "one"; };
config.mod.two = { foo = 2; bar = "two"; };</screen>
</example>
</section>
<section xml:id="sec-option-types-extending">
<title>Extending types</title>
<para>
Types are mainly characterized by their <literal>check</literal> and
<literal>merge</literal> functions.
</para>
<variablelist>
<varlistentry>
<term>
<varname>check</varname>
</term>
<listitem>
<para>
The function to type check the value. Takes a value as parameter and
return a boolean. It is possible to extend a type check with the
<literal>addCheck</literal> function
(<xref
linkend='ex-extending-type-check-1' />), or to fully
override the check function
(<xref linkend='ex-extending-type-check-2' />).
</para>
<example xml:id='ex-extending-type-check-1'>
<title>Adding a type check</title>
<screen>
byte = mkOption {
description = "An integer between 0 and 255.";
type = types.addCheck types.int (x: x &gt;= 0 &amp;&amp; x &lt;= 255);
};</screen>
</example>
<example xml:id='ex-extending-type-check-2'>
<title>Overriding a type check</title>
<screen>
nixThings = mkOption {
description = "words that start with 'nix'";
type = types.str // {
check = (x: lib.hasPrefix "nix" x)
};
};</screen>
</example>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>merge</varname>
</term>
<listitem>
<para>
Function to merge the options values when multiple values are set. The
function takes two parameters, <literal>loc</literal> the option path as
a list of strings, and <literal>defs</literal> the list of defined values
as a list. It is possible to override a type merge function for custom
needs.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-option-types-custom">
<title>Custom Types</title>
<para>
Custom types can be created with the <literal>mkOptionType</literal>
function. As type creation includes some more complex topics such as
submodule handling, it is recommended to get familiar with
<filename
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/types.nix">types.nix</filename>
code before creating a new type.
</para>
<para>
The only required parameter is <literal>name</literal>.
</para>
<variablelist>
<varlistentry>
<term>
<varname>name</varname>
</term>
<listitem>
<para>
A string representation of the type function name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>definition</varname>
</term>
<listitem>
<para>
Description of the type used in documentation. Give information of the
type and any of its arguments.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>check</varname>
</term>
<listitem>
<para>
A function to type check the definition value. Takes the definition value
as a parameter and returns a boolean indicating the type check result,
<literal>true</literal> for success and <literal>false</literal> for
failure.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>merge</varname>
</term>
<listitem>
<para>
A function to merge multiple definitions values. Takes two parameters:
</para>
<variablelist>
<varlistentry>
<term>
<replaceable>loc</replaceable>
</term>
<listitem>
<para>
The option path as a list of strings, e.g. <literal>["boot" "loader
"grub" "enable"]</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<replaceable>defs</replaceable>
</term>
<listitem>
<para>
The list of sets of defined <literal>value</literal> and
<literal>file</literal> where the value was defined, e.g. <literal>[ {
file = "/foo.nix"; value = 1; } { file = "/bar.nix"; value = 2 }
]</literal>. The <literal>merge</literal> function should return the
merged value or throw an error in case the values are impossible or
not meant to be merged.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>getSubOptions</varname>
</term>
<listitem>
<para>
For composed types that can take a submodule as type parameter, this
function generate sub-options documentation. It takes the current option
prefix as a list and return the set of sub-options. Usually defined in a
recursive manner by adding a term to the prefix, e.g. <literal>prefix:
elemType.getSubOptions (prefix ++
[<replaceable>"prefix"</replaceable>])</literal> where
<replaceable>"prefix"</replaceable> is the newly added prefix.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>getSubModules</varname>
</term>
<listitem>
<para>
For composed types that can take a submodule as type parameter, this
function should return the type parameters submodules. If the type
parameter is called <literal>elemType</literal>, the function should just
recursively look into submodules by returning
<literal>elemType.getSubModules;</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>substSubModules</varname>
</term>
<listitem>
<para>
For composed types that can take a submodule as type parameter, this
function can be used to substitute the parameter of a submodule type. It
takes a module as parameter and return the type with the submodule
options substituted. It is usually defined as a type function call with a
recursive call to <literal>substSubModules</literal>, e.g for a type
<literal>composedType</literal> that take an <literal>elemtype</literal>
type parameter, this function should be defined as <literal>m:
composedType (elemType.substSubModules m)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>typeMerge</varname>
</term>
<listitem>
<para>
A function to merge multiple type declarations. Takes the type to merge
<literal>functor</literal> as parameter. A <literal>null</literal> return
value means that type cannot be merged.
</para>
<variablelist>
<varlistentry>
<term>
<replaceable>f</replaceable>
</term>
<listitem>
<para>
The type to merge <literal>functor</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
Note: There is a generic <literal>defaultTypeMerge</literal> that work
with most of value and composed types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>functor</varname>
</term>
<listitem>
<para>
An attribute set representing the type. It is used for type operations
and has the following keys:
</para>
<variablelist>
<varlistentry>
<term>
<varname>type</varname>
</term>
<listitem>
<para>
The type function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>wrapped</varname>
</term>
<listitem>
<para>
Holds the type parameter for composed types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>payload</varname>
</term>
<listitem>
<para>
Holds the value parameter for value types. The types that have a
<literal>payload</literal> are the <literal>enum</literal>,
<literal>separatedString</literal> and <literal>submodule</literal>
types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>binOp</varname>
</term>
<listitem>
<para>
A binary operation that can merge the payloads of two same types.
Defined as a function that take two payloads as parameters and return
the payloads merged.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>

2
nixos/doc/manual/development/writing-modules.xml
View File

@ -180,7 +180,7 @@ in {
</programlisting>
</example>
<xi:include href="../from_md/development/option-declarations.section.xml" />
<xi:include href="option-types.xml" />
<xi:include href="../from_md/development/option-types.section.xml" />
<xi:include href="option-def.xml" />
<xi:include href="../from_md/development/assertions.section.xml" />
<xi:include href="meta-attributes.xml" />

987
nixos/doc/manual/from_md/development/option-types.section.xml Normal file
View File

@ -0,0 +1,987 @@
<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-option-types">
<title>Options Types</title>
<para>
Option types are a way to put constraints on the values a module
option can take. Types are also responsible of how values are merged
in case of multiple value definitions.
</para>
<section xml:id="sec-option-types-basic">
<title>Basic Types</title>
<para>
Basic types are the simplest available types in the module system.
Basic types include multiple string types that mainly differ in
how definition merging is handled.
</para>
<variablelist>
<varlistentry>
<term>
<literal>types.bool</literal>
</term>
<listitem>
<para>
A boolean, its values can be <literal>true</literal> or
<literal>false</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.path</literal>
</term>
<listitem>
<para>
A filesystem path, defined as anything that when coerced to
a string starts with a slash. Even if derivations can be
considered as path, the more specific
<literal>types.package</literal> should be preferred.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.package</literal>
</term>
<listitem>
<para>
A derivation or a store path.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.anything</literal>
</term>
<listitem>
<para>
A type that accepts any value and recursively merges
attribute sets together. This type is recommended when the
option type is unknown.
</para>
<anchor xml:id="ex-types-anything" />
<para>
<emphasis role="strong">Example:
<literal>types.anything</literal> Example</emphasis>
</para>
<para>
Two definitions of this type like
</para>
<programlisting language="bash">
{
str = lib.mkDefault &quot;foo&quot;;
pkg.hello = pkgs.hello;
fun.fun = x: x + 1;
}
</programlisting>
<programlisting language="bash">
{
str = lib.mkIf true &quot;bar&quot;;
pkg.gcc = pkgs.gcc;
fun.fun = lib.mkForce (x: x + 2);
}
</programlisting>
<para>
will get merged to
</para>
<programlisting language="bash">
{
str = &quot;bar&quot;;
pkg.gcc = pkgs.gcc;
pkg.hello = pkgs.hello;
fun.fun = x: x + 2;
}
</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.attrs</literal>
</term>
<listitem>
<para>
A free-form attribute set.
</para>
<warning>
<para>
This type will be deprecated in the future because it
doesn't recurse into attribute sets, silently drops
earlier attribute definitions, and doesn't discharge
<literal>lib.mkDefault</literal>,
<literal>lib.mkIf</literal> and co. For allowing arbitrary
attribute sets, prefer
<literal>types.attrsOf types.anything</literal> instead
which doesn't have these problems.
</para>
</warning>
</listitem>
</varlistentry>
</variablelist>
<para>
Integer-related types:
</para>
<variablelist>
<varlistentry>
<term>
<literal>types.int</literal>
</term>
<listitem>
<para>
A signed integer.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.ints.{s8, s16, s32}</literal>
</term>
<listitem>
<para>
Signed integers with a fixed length (8, 16 or 32 bits). They
go from −2^n/2 to 2^n/2−1 respectively (e.g.
<literal>−128</literal> to <literal>127</literal> for 8
bits).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.ints.unsigned</literal>
</term>
<listitem>
<para>
An unsigned integer (that is &gt;= 0).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.ints.{u8, u16, u32}</literal>
</term>
<listitem>
<para>
Unsigned integers with a fixed length (8, 16 or 32 bits).
They go from 0 to 2^n−1 respectively (e.g.
<literal>0</literal> to <literal>255</literal> for 8 bits).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.ints.positive</literal>
</term>
<listitem>
<para>
A positive integer (that is &gt; 0).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.port</literal>
</term>
<listitem>
<para>
A port number. This type is an alias to
<literal>types.ints.u16</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
String-related types:
</para>
<variablelist>
<varlistentry>
<term>
<literal>types.str</literal>
</term>
<listitem>
<para>
A string. Multiple definitions cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.lines</literal>
</term>
<listitem>
<para>
A string. Multiple definitions are concatenated with a new
line <literal>&quot;\n&quot;</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.commas</literal>
</term>
<listitem>
<para>
A string. Multiple definitions are concatenated with a comma
<literal>&quot;,&quot;</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.envVar</literal>
</term>
<listitem>
<para>
A string. Multiple definitions are concatenated with a
collon <literal>&quot;:&quot;</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.strMatching</literal>
</term>
<listitem>
<para>
A string matching a specific regular expression. Multiple
definitions cannot be merged. The regular expression is
processed using <literal>builtins.match</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-option-types-value">
<title>Value Types</title>
<para>
Value types are types that take a value parameter.
</para>
<variablelist>
<varlistentry>
<term>
<literal>types.enum</literal>
<emphasis><literal>l</literal></emphasis>
</term>
<listitem>
<para>
One element of the list
<emphasis><literal>l</literal></emphasis>, e.g.
<literal>types.enum [ &quot;left&quot; &quot;right&quot; ]</literal>.
Multiple definitions cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.separatedString</literal>
<emphasis><literal>sep</literal></emphasis>
</term>
<listitem>
<para>
A string with a custom separator
<emphasis><literal>sep</literal></emphasis>, e.g.
<literal>types.separatedString &quot;|&quot;</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.ints.between</literal>
<emphasis><literal>lowest highest</literal></emphasis>
</term>
<listitem>
<para>
An integer between
<emphasis><literal>lowest</literal></emphasis> and
<emphasis><literal>highest</literal></emphasis> (both
inclusive). Useful for creating types like
<literal>types.port</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.submodule</literal>
<emphasis><literal>o</literal></emphasis>
</term>
<listitem>
<para>
A set of sub options
<emphasis><literal>o</literal></emphasis>.
<emphasis><literal>o</literal></emphasis> can be an
attribute set, a function returning an attribute set, or a
path to a file containing such a value. Submodules are used
in composed types to create modular options. This is
equivalent to
<literal>types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }</literal>.
Submodules are detailed in
<link linkend="section-option-types-submodule">Submodule</link>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.submoduleWith</literal> {
<emphasis><literal>modules</literal></emphasis>,
<emphasis><literal>specialArgs</literal></emphasis> ? {},
<emphasis><literal>shorthandOnlyDefinesConfig</literal></emphasis>
? false }
</term>
<listitem>
<para>
Like <literal>types.submodule</literal>, but more flexible
and with better defaults. It has parameters
</para>
<itemizedlist>
<listitem>
<para>
<emphasis><literal>modules</literal></emphasis> A list
of modules to use by default for this submodule type.
This gets combined with all option definitions to build
the final list of modules that will be included.
</para>
<note>
<para>
Only options defined with this argument are included
in rendered documentation.
</para>
</note>
</listitem>
<listitem>
<para>
<emphasis><literal>specialArgs</literal></emphasis> An
attribute set of extra arguments to be passed to the
module functions. The option
<literal>_module.args</literal> should be used instead
for most arguments since it allows overriding.
<emphasis><literal>specialArgs</literal></emphasis>
should only be used for arguments that can't go through
the module fixed-point, because of infinite recursion or
other problems. An example is overriding the
<literal>lib</literal> argument, because
<literal>lib</literal> itself is used to define
<literal>_module.args</literal>, which makes using
<literal>_module.args</literal> to define it impossible.
</para>
</listitem>
<listitem>
<para>
<emphasis><literal>shorthandOnlyDefinesConfig</literal></emphasis>
Whether definitions of this type should default to the
<literal>config</literal> section of a module (see
<link linkend="ex-module-syntax">Example: Structure of
NixOS Modules</link>) if it is an attribute set.
Enabling this only has a benefit when the submodule
defines an option named <literal>config</literal> or
<literal>options</literal>. In such a case it would
allow the option to be set with
<literal>the-submodule.config = &quot;value&quot;</literal>
instead of requiring
<literal>the-submodule.config.config = &quot;value&quot;</literal>.
This is because only when modules
<emphasis>don't</emphasis> set the
<literal>config</literal> or <literal>options</literal>
keys, all keys are interpreted as option definitions in
the <literal>config</literal> section. Enabling this
option implicitly puts all attributes in the
<literal>config</literal> section.
</para>
<para>
With this option enabled, defining a
non-<literal>config</literal> section requires using a
function:
<literal>the-submodule = { ... }: { options = { ... }; }</literal>.
</para>
</listitem>
</itemizedlist>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-option-types-composed">
<title>Composed Types</title>
<para>
Composed types are types that take a type as parameter.
<literal>listOf int</literal> and
<literal>either int str</literal> are examples of composed types.
</para>
<variablelist>
<varlistentry>
<term>
<literal>types.listOf</literal>
<emphasis><literal>t</literal></emphasis>
</term>
<listitem>
<para>
A list of <emphasis><literal>t</literal></emphasis> type,
e.g. <literal>types.listOf int</literal>. Multiple
definitions are merged with list concatenation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.attrsOf</literal>
<emphasis><literal>t</literal></emphasis>
</term>
<listitem>
<para>
An attribute set of where all the values are of
<emphasis><literal>t</literal></emphasis> type. Multiple
definitions result in the joined attribute set.
</para>
<note>
<para>
This type is <emphasis>strict</emphasis> in its values,
which in turn means attributes cannot depend on other
attributes. See <literal> types.lazyAttrsOf</literal> for
a lazy version.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.lazyAttrsOf</literal>
<emphasis><literal>t</literal></emphasis>
</term>
<listitem>
<para>
An attribute set of where all the values are of
<emphasis><literal>t</literal></emphasis> type. Multiple
definitions result in the joined attribute set. This is the
lazy version of <literal>types.attrsOf </literal>, allowing
attributes to depend on each other.
</para>
<warning>
<para>
This version does not fully support conditional
definitions! With an option <literal>foo</literal> of this
type and a definition
<literal>foo.attr = lib.mkIf false 10</literal>,
evaluating <literal>foo ? attr</literal> will return
<literal>true</literal> even though it should be false.
Accessing the value will then throw an error. For types
<emphasis><literal>t</literal></emphasis> that have an
<literal>emptyValue</literal> defined, that value will be
returned instead of throwing an error. So if the type of
<literal>foo.attr</literal> was
<literal>lazyAttrsOf (nullOr int)</literal>,
<literal>null</literal> would be returned instead for the
same <literal>mkIf false</literal> definition.
</para>
</warning>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.nullOr</literal>
<emphasis><literal>t</literal></emphasis>
</term>
<listitem>
<para>
<literal>null</literal> or type
<emphasis><literal>t</literal></emphasis>. Multiple
definitions are merged according to type
<emphasis><literal>t</literal></emphasis>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.uniq</literal>
<emphasis><literal>t</literal></emphasis>
</term>
<listitem>
<para>
Ensures that type <emphasis><literal>t</literal></emphasis>
cannot be merged. It is used to ensure option definitions
are declared only once.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.either</literal>
<emphasis><literal>t1 t2</literal></emphasis>
</term>
<listitem>
<para>
Type <emphasis><literal>t1</literal></emphasis> or type
<emphasis><literal>t2</literal></emphasis>, e.g.
<literal>with types; either int str</literal>. Multiple
definitions cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.oneOf</literal> [
<emphasis><literal>t1 t2</literal></emphasis> ... ]
</term>
<listitem>
<para>
Type <emphasis><literal>t1</literal></emphasis> or type
<emphasis><literal>t2</literal></emphasis> and so forth,
e.g. <literal>with types; oneOf [ int str bool ]</literal>.
Multiple definitions cannot be merged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>types.coercedTo</literal>
<emphasis><literal>from f to</literal></emphasis>
</term>
<listitem>
<para>
Type <emphasis><literal>to</literal></emphasis> or type
<emphasis><literal>from</literal></emphasis> which will be
coerced to type <emphasis><literal>to</literal></emphasis>
using function <emphasis><literal>f</literal></emphasis>
which takes an argument of type
<emphasis><literal>from</literal></emphasis> and return a
value of type <emphasis><literal>to</literal></emphasis>.
Can be used to preserve backwards compatibility of an option
if its type was changed.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="section-option-types-submodule">
<title>Submodule</title>
<para>
<literal>submodule</literal> is a very powerful type that defines
a set of sub-options that are handled like a separate module.
</para>
<para>
It takes a parameter <emphasis><literal>o</literal></emphasis>,
that should be a set, or a function returning a set with an
<literal>options</literal> key defining the sub-options. Submodule
option definitions are type-checked accordingly to the
<literal>options</literal> declarations. Of course, you can nest
submodule option definitons for even higher modularity.
</para>
<para>
The option set can be defined directly
(<link linkend="ex-submodule-direct">Example: Directly defined
submodule</link>) or as reference
(<link linkend="ex-submodule-reference">Example: Submodule defined
as a reference</link>).
</para>
<anchor xml:id="ex-submodule-direct" />
<para>
<emphasis role="strong">Example: Directly defined
submodule</emphasis>
</para>
<programlisting language="bash">
options.mod = mkOption {
description = &quot;submodule example&quot;;
type = with types; submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
};
};
</programlisting>
<anchor xml:id="ex-submodule-reference" />
<para>
<emphasis role="strong">Example: Submodule defined as a
reference</emphasis>
</para>
<programlisting language="bash">
let
modOptions = {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = int;
};
};
};
in
options.mod = mkOption {
description = &quot;submodule example&quot;;
type = with types; submodule modOptions;
};
</programlisting>
<para>
The <literal>submodule</literal> type is especially interesting
when used with composed types like <literal>attrsOf</literal> or
<literal>listOf</literal>. When composed with
<literal>listOf</literal>
(<link linkend="ex-submodule-listof-declaration">Example:
Declaration of a list of submodules</link>),
<literal>submodule</literal> allows multiple definitions of the
submodule option set
(<link linkend="ex-submodule-listof-definition">Example:
Definition of a list of submodules</link>).
</para>
<anchor xml:id="ex-submodule-listof-declaration" />
<para>
<emphasis role="strong">Example: Declaration of a list of
submodules</emphasis>
</para>
<programlisting language="bash">
options.mod = mkOption {
description = &quot;submodule example&quot;;
type = with types; listOf (submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
});
};
</programlisting>
<anchor xml:id="ex-submodule-listof-definition" />
<para>
<emphasis role="strong">Example: Definition of a list of
submodules</emphasis>
</para>
<programlisting language="bash">
config.mod = [
{ foo = 1; bar = &quot;one&quot;; }
{ foo = 2; bar = &quot;two&quot;; }
];
</programlisting>
<para>
When composed with <literal>attrsOf</literal>
(<link linkend="ex-submodule-attrsof-declaration">Example:
Declaration of attribute sets of submodules</link>),
<literal>submodule</literal> allows multiple named definitions of
the submodule option set
(<link linkend="ex-submodule-attrsof-definition">Example:
Definition of attribute sets of submodules</link>).
</para>
<anchor xml:id="ex-submodule-attrsof-declaration" />
<para>
<emphasis role="strong">Example: Declaration of attribute sets of
submodules</emphasis>
</para>
<programlisting language="bash">
options.mod = mkOption {
description = &quot;submodule example&quot;;
type = with types; attrsOf (submodule {
options = {
foo = mkOption {
type = int;
};
bar = mkOption {
type = str;
};
};
});
};
</programlisting>
<anchor xml:id="ex-submodule-attrsof-definition" />
<para>
<emphasis role="strong">Example: Definition of attribute sets of
submodules</emphasis>
</para>
<programlisting language="bash">
config.mod.one = { foo = 1; bar = &quot;one&quot;; };
config.mod.two = { foo = 2; bar = &quot;two&quot;; };
</programlisting>
</section>
<section xml:id="sec-option-types-extending">
<title>Extending types</title>
<para>
Types are mainly characterized by their <literal>check</literal>
and <literal>merge</literal> functions.
</para>
<variablelist>
<varlistentry>
<term>
<literal>check</literal>
</term>
<listitem>
<para>
The function to type check the value. Takes a value as
parameter and return a boolean. It is possible to extend a
type check with the <literal>addCheck</literal> function
(<link linkend="ex-extending-type-check-1">Example: Adding a
type check</link>), or to fully override the check function
(<link linkend="ex-extending-type-check-2">Example:
Overriding a type check</link>).
</para>
<anchor xml:id="ex-extending-type-check-1" />
<para>
<emphasis role="strong">Example: Adding a type
check</emphasis>
</para>
<programlisting language="bash">
byte = mkOption {
description = &quot;An integer between 0 and 255.&quot;;
type = types.addCheck types.int (x: x &gt;= 0 &amp;&amp; x &lt;= 255);
};
</programlisting>
<anchor xml:id="ex-extending-type-check-2" />
<para>
<emphasis role="strong">Example: Overriding a type
check</emphasis>
</para>
<programlisting language="bash">
nixThings = mkOption {
description = &quot;words that start with 'nix'&quot;;
type = types.str // {
check = (x: lib.hasPrefix &quot;nix&quot; x)
};
};
</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>merge</literal>
</term>
<listitem>
<para>
Function to merge the options values when multiple values
are set. The function takes two parameters,
<literal>loc</literal> the option path as a list of strings,
and <literal>defs</literal> the list of defined values as a
list. It is possible to override a type merge function for
custom needs.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-option-types-custom">
<title>Custom Types</title>
<para>
Custom types can be created with the
<literal>mkOptionType</literal> function. As type creation
includes some more complex topics such as submodule handling, it
is recommended to get familiar with <literal>types.nix</literal>
code before creating a new type.
</para>
<para>
The only required parameter is <literal>name</literal>.
</para>
<variablelist>
<varlistentry>
<term>
<literal>name</literal>
</term>
<listitem>
<para>
A string representation of the type function name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>definition</literal>
</term>
<listitem>
<para>
Description of the type used in documentation. Give
information of the type and any of its arguments.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>check</literal>
</term>
<listitem>
<para>
A function to type check the definition value. Takes the
definition value as a parameter and returns a boolean
indicating the type check result, <literal>true</literal>
for success and <literal>false</literal> for failure.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>merge</literal>
</term>
<listitem>
<para>
A function to merge multiple definitions values. Takes two
parameters:
</para>
<variablelist>
<varlistentry>
<term>
<emphasis><literal>loc</literal></emphasis>
</term>
<listitem>
<para>
The option path as a list of strings, e.g.
<literal>[&quot;boot&quot; &quot;loader &quot;grub&quot; &quot;enable&quot;]</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<emphasis><literal>defs</literal></emphasis>
</term>
<listitem>
<para>
The list of sets of defined <literal>value</literal>
and <literal>file</literal> where the value was
defined, e.g.
<literal>[ { file = &quot;/foo.nix&quot;; value = 1; } { file = &quot;/bar.nix&quot;; value = 2 } ]</literal>.
The <literal>merge</literal> function should return
the merged value or throw an error in case the values
are impossible or not meant to be merged.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>getSubOptions</literal>
</term>
<listitem>
<para>
For composed types that can take a submodule as type
parameter, this function generate sub-options documentation.
It takes the current option prefix as a list and return the
set of sub-options. Usually defined in a recursive manner by
adding a term to the prefix, e.g.
<literal>prefix: elemType.getSubOptions (prefix ++ [&quot;prefix&quot;])</literal>
where
<emphasis><literal>&quot;prefix&quot;</literal></emphasis>
is the newly added prefix.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>getSubModules</literal>
</term>
<listitem>
<para>
For composed types that can take a submodule as type
parameter, this function should return the type parameters
submodules. If the type parameter is called
<literal>elemType</literal>, the function should just
recursively look into submodules by returning
<literal>elemType.getSubModules;</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>substSubModules</literal>
</term>
<listitem>
<para>
For composed types that can take a submodule as type
parameter, this function can be used to substitute the
parameter of a submodule type. It takes a module as
parameter and return the type with the submodule options
substituted. It is usually defined as a type function call
with a recursive call to <literal>substSubModules</literal>,
e.g for a type <literal>composedType</literal> that take an
<literal>elemtype</literal> type parameter, this function
should be defined as
<literal>m: composedType (elemType.substSubModules m)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>typeMerge</literal>
</term>
<listitem>
<para>
A function to merge multiple type declarations. Takes the
type to merge <literal>functor</literal> as parameter. A
<literal>null</literal> return value means that type cannot
be merged.
</para>
<variablelist>
<varlistentry>
<term>
<emphasis><literal>f</literal></emphasis>
</term>
<listitem>
<para>
The type to merge <literal>functor</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
Note: There is a generic <literal>defaultTypeMerge</literal>
that work with most of value and composed types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>functor</literal>
</term>
<listitem>
<para>
An attribute set representing the type. It is used for type
operations and has the following keys:
</para>
<variablelist>
<varlistentry>
<term>
<literal>type</literal>
</term>
<listitem>
<para>
The type function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wrapped</literal>
</term>
<listitem>
<para>
Holds the type parameter for composed types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>payload</literal>
</term>
<listitem>
<para>
Holds the value parameter for value types. The types
that have a <literal>payload</literal> are the
<literal>enum</literal>,
<literal>separatedString</literal> and
<literal>submodule</literal> types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>binOp</literal>
</term>
<listitem>
<para>
A binary operation that can merge the payloads of two
same types. Defined as a function that take two
payloads as parameters and return the payloads merged.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>