commit c7d32059b126e2ba61a9d2422a0baf76fbf7101a · pyrox.dev/nixpkgs

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nixos/doc/manual/development/freeform-modules.section.md

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       # Freeform modules {#sec-freeform-modules}

     

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       Freeform modules allow you to define values for option paths that have

     

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       not been declared explicitly. This can be used to add attribute-specific

     

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       types to what would otherwise have to be `attrsOf` options in order to

     

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       accept all attribute names.

     

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       This feature can be enabled by using the attribute `freeformType` to

     

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       define a freeform type. By doing this, all assignments without an

     

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       associated option will be merged using the freeform type and combined

     

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       into the resulting `config` set. Since this feature nullifies name

     

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       checking for entire option trees, it is only recommended for use in

     

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       submodules.

     

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       ::: {#ex-freeform-module .example}

     

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       ::: {.title}

     

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       **Example: Freeform submodule**

     

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       :::

     

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       The following shows a submodule assigning a freeform type that allows

     

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       arbitrary attributes with `str` values below `settings`, but also

     

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       declares an option for the `settings.port` attribute to have it

     

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       type-checked and assign a default value. See

     

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       [Example: Declaring a type-checked `settings` attribute](#ex-settings-typed-attrs)

     

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       for a more complete example.

     

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       ```nix

     

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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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       ```

     

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       And the following shows what such a module then allows

     

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       ```nix

     

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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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       ```

     

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       :::

     

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       ::: {.note}

     

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       Freeform attributes cannot depend on other attributes of the same set

     

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       without infinite recursion:

     

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       ```nix

     

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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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       ```

     

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       To prevent this, declare options for all attributes that need to depend

     

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       on others. For above example this means to declare `logLevel` to be an

     

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       option.

     

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       :::

-68

nixos/doc/manual/development/freeform-modules.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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nixos/doc/manual/development/importing-modules.section.md

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       # Importing Modules {#sec-importing-modules}

     

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       Sometimes NixOS modules need to be used in configuration but exist

     

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       outside of Nixpkgs. These modules can be imported:

     

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       ```nix

     

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       { config, lib, pkgs, ... }:

     

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       {

     

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         imports =

     

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           [ # Use a locally-available module definition in

     

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             # ./example-module/default.nix

     

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               ./example-module

     

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           ];

     

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         services.exampleModule.enable = true;

     

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       }

     

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       ```

     

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       The environment variable `NIXOS_EXTRA_MODULE_PATH` is an absolute path

     

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       to a NixOS module that is included alongside the Nixpkgs NixOS modules.

     

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       Like any NixOS module, this module can import additional modules:

     

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       ```nix

     

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       # ./module-list/default.nix

     

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       [

     

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         ./example-module1

     

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         ./example-module2

     

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       ]

     

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       ```

     

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       ```nix

     

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       # ./extra-module/default.nix

     

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       { imports = import ./module-list.nix; }

     

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       ```

     

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       ```nix

     

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       # NIXOS_EXTRA_MODULE_PATH=/absolute/path/to/extra-module

     

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       { config, lib, pkgs, ... }:

     

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       {

     

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         # No `imports` needed

     

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         services.exampleModule1.enable = true;

     

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       }

     

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       ```

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nixos/doc/manual/development/importing-modules.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-importing-modules">

     

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        <title>Importing Modules</title>

     

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        <para>

     

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         Nixpkgs. These modules can be imported:

     

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        </para>

     

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       { config, lib, pkgs, ... }:

     

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         imports =

     

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             # ./example-module/default.nix

     

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               ./example-module

     

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           ];

     

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         services.exampleModule.enable = true;

     

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       }

     

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       </programlisting>

     

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        <para>

     

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         The environment variable <literal>NIXOS_EXTRA_MODULE_PATH</literal> is an

     

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         absolute path to a NixOS module that is included alongside the Nixpkgs NixOS

     

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         modules. Like any NixOS module, this module can import additional modules:

     

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        </para>

     

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       <programlisting>

     

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       # ./module-list/default.nix

     

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       [

     

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         ./example-module1

     

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         ./example-module2

     

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       ]

     

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       </programlisting>

     

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       <programlisting>

     

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       # ./extra-module/default.nix

     

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       { imports = import ./module-list.nix; }

     

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       </programlisting>

     

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       <programlisting>

     

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       # NIXOS_EXTRA_MODULE_PATH=/absolute/path/to/extra-module

     

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       { config, lib, pkgs, ... }:

     

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       {

     

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         # No `imports` needed

     

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         services.exampleModule1.enable = true;

     

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       }

     

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       </programlisting>

     

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       </section>

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nixos/doc/manual/development/meta-attributes.section.md

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       # Meta Attributes {#sec-meta-attributes}

     

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       Like Nix packages, NixOS modules can declare meta-attributes to provide

     

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       extra information. Module meta attributes are defined in the `meta.nix`

     

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       special module.

     

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       `meta` is a top level attribute like `options` and `config`. Available

     

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       meta-attributes are `maintainers` and `doc`.

     

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       Each of the meta-attributes must be defined at most once per module

     

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       file.

     

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       ```nix

     

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       { config, lib, pkgs, ... }:

     

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       {

     

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         options = {

     

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           ...

     

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         };

     

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         config = {

     

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           ...

     

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         };

     

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         meta = {

     

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           maintainers = with lib.maintainers; [ ericsagnes ];

     

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           doc = ./default.xml;

     

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         };

     

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       }

     

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       ```

     

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       -   `maintainers` contains a list of the module maintainers.

     

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       -   `doc` points to a valid DocBook file containing the module

     

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           documentation. Its contents is automatically added to

     

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           [](#ch-configuration). Changes to a module documentation have to

     

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           be checked to not break building the NixOS manual:

     

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           ```ShellSession

     

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           $ nix-build nixos/release.nix -A manual.x86_64-linux

     

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           ```

-63

nixos/doc/manual/development/meta-attributes.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-meta-attributes">

     

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        <title>Meta Attributes</title>

     

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        <para>

     

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         Like Nix packages, NixOS modules can declare meta-attributes to provide extra

     

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         information. Module meta attributes are defined in the

     

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         <filename

     

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           xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/misc/meta.nix">meta.nix</filename>

     

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         special module.

     

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         <literal>meta</literal> is a top level attribute like

     

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         <literal>options</literal> and <literal>config</literal>. Available

     

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         meta-attributes are <literal>maintainers</literal> and

     

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         <literal>doc</literal>.

     

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        </para>

     

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        <para>

     

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         Each of the meta-attributes must be defined at most once per module file.

     

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        </para>

     

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       { config, lib, pkgs, ... }:

     

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         options = {

     

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           ...

     

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           ...

     

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         };

     

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         meta = {

     

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           maintainers = with lib.maintainers; [ ericsagnes ]; <co

     

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             xml:id='modules-meta-1' />

     

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           doc = ./default.xml; <co xml:id='modules-meta-2' />

     

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         };

     

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       }

     

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       </programlisting>

     

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        <calloutlist>

     

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         <callout arearefs='modules-meta-1'>

     

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          <para>

     

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           <varname>maintainers</varname> contains a list of the module maintainers.

     

       50
       50
       -
          </para>

     

       51
       51
       -
         </callout>

     

       52
       52
       -
         <callout arearefs='modules-meta-2'>

     

       53
       53
       -
          <para>

     

       54
       54
       -
           <varname>doc</varname> points to a valid DocBook file containing the module

     

       55
       55
       -
           documentation. Its contents is automatically added to

     

       56
       56
       -
           <xref

     

       57
       57
       -
             linkend="ch-configuration"/>. Changes to a module documentation

     

       58
       58
       -
           have to be checked to not break building the NixOS manual:

     

       59
       59
       -
          </para>

     

       60
       60
       -
       <screen><prompt>$ </prompt>nix-build nixos/release.nix -A manual.x86_64-linux</screen>

     

       61
       61
       -
         </callout>

     

       62
       62
       -
        </calloutlist>

     

       63
       63
       -
       </section>

+136

nixos/doc/manual/development/option-declarations.section.md

···

       1
       1
       +
       # Option Declarations {#sec-option-declarations}

     

       2
       2
       +
       

     

       3
       3
       +
       An option declaration specifies the name, type and description of a

     

       4
       4
       +
       NixOS configuration option. It is invalid to define an option that

     

       5
       5
       +
       hasn't been declared in any module. An option declaration generally

     

       6
       6
       +
       looks like this:

     

       7
       7
       +
       

     

       8
       8
       +
       ```nix

     

       9
       9
       +
       options = {

     

       10
       10
       +
         name = mkOption {

     

       11
       11
       +
           type = type specification;

     

       12
       12
       +
           default = default value;

     

       13
       13
       +
           example = example value;

     

       14
       14
       +
           description = "Description for use in the NixOS manual.";

     

       15
       15
       +
         };

     

       16
       16
       +
       };

     

       17
       17
       +
       ```

     

       18
       18
       +
       

     

       19
       19
       +
       The attribute names within the `name` attribute path must be camel

     

       20
       20
       +
       cased in general but should, as an exception, match the [ package

     

       21
       21
       +
       attribute name](https://nixos.org/nixpkgs/manual/#sec-package-naming)

     

       22
       22
       +
       when referencing a Nixpkgs package. For example, the option

     

       23
       23
       +
       `services.nix-serve.bindAddress` references the `nix-serve` Nixpkgs

     

       24
       24
       +
       package.

     

       25
       25
       +
       

     

       26
       26
       +
       The function `mkOption` accepts the following arguments.

     

       27
       27
       +
       

     

       28
       28
       +
       `type`

     

       29
       29
       +
       

     

       30
       30
       +
       :   The type of the option (see [](#sec-option-types)). It may be

     

       31
       31
       +
           omitted, but that's not advisable since it may lead to errors that

     

       32
       32
       +
           are hard to diagnose.

     

       33
       33
       +
       

     

       34
       34
       +
       `default`

     

       35
       35
       +
       

     

       36
       36
       +
       :   The default value used if no value is defined by any module. A

     

       37
       37
       +
           default is not required; but if a default is not given, then users

     

       38
       38
       +
           of the module will have to define the value of the option, otherwise

     

       39
       39
       +
           an error will be thrown.

     

       40
       40
       +
       

     

       41
       41
       +
       `example`

     

       42
       42
       +
       

     

       43
       43
       +
       :   An example value that will be shown in the NixOS manual.

     

       44
       44
       +
       

     

       45
       45
       +
       `description`

     

       46
       46
       +
       

     

       47
       47
       +
       :   A textual description of the option, in DocBook format, that will be

     

       48
       48
       +
           included in the NixOS manual.

     

       49
       49
       +
       

     

       50
       50
       +
       ## Extensible Option Types {#sec-option-declarations-eot}

     

       51
       51
       +
       

     

       52
       52
       +
       Extensible option types is a feature that allow to extend certain types

     

       53
       53
       +
       declaration through multiple module files. This feature only work with a

     

       54
       54
       +
       restricted set of types, namely `enum` and `submodules` and any composed

     

       55
       55
       +
       forms of them.

     

       56
       56
       +
       

     

       57
       57
       +
       Extensible option types can be used for `enum` options that affects

     

       58
       58
       +
       multiple modules, or as an alternative to related `enable` options.

     

       59
       59
       +
       

     

       60
       60
       +
       As an example, we will take the case of display managers. There is a

     

       61
       61
       +
       central display manager module for generic display manager options and a

     

       62
       62
       +
       module file per display manager backend (sddm, gdm \...).

     

       63
       63
       +
       

     

       64
       64
       +
       There are two approach to this module structure:

     

       65
       65
       +
       

     

       66
       66
       +
       -   Managing the display managers independently by adding an enable

     

       67
       67
       +
           option to every display manager module backend. (NixOS)

     

       68
       68
       +
       

     

       69
       69
       +
       -   Managing the display managers in the central module by adding an

     

       70
       70
       +
           option to select which display manager backend to use.

     

       71
       71
       +
       

     

       72
       72
       +
       Both approaches have problems.

     

       73
       73
       +
       

     

       74
       74
       +
       Making backends independent can quickly become hard to manage. For

     

       75
       75
       +
       display managers, there can be only one enabled at a time, but the type

     

       76
       76
       +
       system can not enforce this restriction as there is no relation between

     

       77
       77
       +
       each backend `enable` option. As a result, this restriction has to be

     

       78
       78
       +
       done explicitely by adding assertions in each display manager backend

     

       79
       79
       +
       module.

     

       80
       80
       +
       

     

       81
       81
       +
       On the other hand, managing the display managers backends in the central

     

       82
       82
       +
       module will require to change the central module option every time a new

     

       83
       83
       +
       backend is added or removed.

     

       84
       84
       +
       

     

       85
       85
       +
       By using extensible option types, it is possible to create a placeholder

     

       86
       86
       +
       option in the central module

     

       87
       87
       +
       ([Example: Extensible type placeholder in the service module](#ex-option-declaration-eot-service)),

     

       88
       88
       +
       and to extend it in each backend module

     

       89
       89
       +
       ([Example: Extending `services.xserver.displayManager.enable` in the `gdm` module](#ex-option-declaration-eot-backend-gdm),

     

       90
       90
       +
       [Example: Extending `services.xserver.displayManager.enable` in the `sddm` module](#ex-option-declaration-eot-backend-sddm)).

     

       91
       91
       +
       

     

       92
       92
       +
       As a result, `displayManager.enable` option values can be added without

     

       93
       93
       +
       changing the main service module file and the type system automatically

     

       94
       94
       +
       enforce that there can only be a single display manager enabled.

     

       95
       95
       +
       

     

       96
       96
       +
       ::: {#ex-option-declaration-eot-service .example}

     

       97
       97
       +
       ::: {.title}

     

       98
       98
       +
       **Example: Extensible type placeholder in the service module**

     

       99
       99
       +
       :::

     

       100
       100
       +
       ```nix

     

       101
       101
       +
       services.xserver.displayManager.enable = mkOption {

     

       102
       102
       +
         description = "Display manager to use";

     

       103
       103
       +
         type = with types; nullOr (enum [ ]);

     

       104
       104
       +
       };

     

       105
       105
       +
       ```

     

       106
       106
       +
       :::

     

       107
       107
       +
       

     

       108
       108
       +
       ::: {#ex-option-declaration-eot-backend-gdm .example}

     

       109
       109
       +
       ::: {.title}

     

       110
       110
       +
       **Example: Extending `services.xserver.displayManager.enable` in the `gdm` module**

     

       111
       111
       +
       :::

     

       112
       112
       +
       ```nix

     

       113
       113
       +
       services.xserver.displayManager.enable = mkOption {

     

       114
       114
       +
         type = with types; nullOr (enum [ "gdm" ]);

     

       115
       115
       +
       };

     

       116
       116
       +
       ```

     

       117
       117
       +
       :::

     

       118
       118
       +
       

     

       119
       119
       +
       ::: {#ex-option-declaration-eot-backend-sddm .example}

     

       120
       120
       +
       ::: {.title}

     

       121
       121
       +
       **Example: Extending `services.xserver.displayManager.enable` in the `sddm` module**

     

       122
       122
       +
       :::

     

       123
       123
       +
       ```nix

     

       124
       124
       +
       services.xserver.displayManager.enable = mkOption {

     

       125
       125
       +
         type = with types; nullOr (enum [ "sddm" ]);

     

       126
       126
       +
       };

     

       127
       127
       +
       ```

     

       128
       128
       +
       :::

     

       129
       129
       +
       

     

       130
       130
       +
       The placeholder declaration is a standard `mkOption` declaration, but it

     

       131
       131
       +
       is important that extensible option declarations only use the `type`

     

       132
       132
       +
       argument.

     

       133
       133
       +
       

     

       134
       134
       +
       Extensible option types work with any of the composed variants of `enum`

     

       135
       135
       +
       such as `with types; nullOr (enum [ "foo" "bar" ])` or `with types;

     

       136
       136
       +
       listOf (enum [ "foo" "bar" ])`.

-199

nixos/doc/manual/development/option-declarations.xml

···

       1
       1
       -
       <section xmlns="http://docbook.org/ns/docbook"

     

       2
       2
       -
               xmlns:xlink="http://www.w3.org/1999/xlink"

     

       3
       3
       -
               xmlns:xi="http://www.w3.org/2001/XInclude"

     

       4
       4
       -
               version="5.0"

     

       5
       5
       -
               xml:id="sec-option-declarations">

     

       6
       6
       -
        <title>Option Declarations</title>

     

       7
       7
       -
       

     

       8
       8
       -
        <para>

     

       9
       9
       -
         An option declaration specifies the name, type and description of a NixOS

     

       10
       10
       -
         configuration option. It is invalid to define an option that hasn’t been

     

       11
       11
       -
         declared in any module. An option declaration generally looks like this:

     

       12
       12
       -
       <programlisting>

     

       13
       13
       -
       options = {

     

       14
       14
       -
         <replaceable>name</replaceable> = mkOption {

     

       15
       15
       -
           type = <replaceable>type specification</replaceable>;

     

       16
       16
       -
           default = <replaceable>default value</replaceable>;

     

       17
       17
       -
           example = <replaceable>example value</replaceable>;

     

       18
       18
       -
           description = "<replaceable>Description for use in the NixOS manual.</replaceable>";

     

       19
       19
       -
         };

     

       20
       20
       -
       };

     

       21
       21
       -
       </programlisting>

     

       22
       22
       -
         The attribute names within the <replaceable>name</replaceable> attribute path

     

       23
       23
       -
         must be camel cased in general but should, as an exception, match the

     

       24
       24
       -
         <link

     

       25
       25
       -
       xlink:href="https://nixos.org/nixpkgs/manual/#sec-package-naming">

     

       26
       26
       -
         package attribute name</link> when referencing a Nixpkgs package. For

     

       27
       27
       -
         example, the option <varname>services.nix-serve.bindAddress</varname>

     

       28
       28
       -
         references the <varname>nix-serve</varname> Nixpkgs package.

     

       29
       29
       -
        </para>

     

       30
       30
       -
       

     

       31
       31
       -
        <para>

     

       32
       32
       -
         The function <varname>mkOption</varname> accepts the following arguments.

     

       33
       33
       -
         <variablelist>

     

       34
       34
       -
          <varlistentry>

     

       35
       35
       -
           <term>

     

       36
       36
       -
            <varname>type</varname>

     

       37
       37
       -
           </term>

     

       38
       38
       -
           <listitem>

     

       39
       39
       -
            <para>

     

       40
       40
       -
             The type of the option (see <xref linkend='sec-option-types' />). It may

     

       41
       41
       -
             be omitted, but that’s not advisable since it may lead to errors that

     

       42
       42
       -
             are hard to diagnose.

     

       43
       43
       -
            </para>

     

       44
       44
       -
           </listitem>

     

       45
       45
       -
          </varlistentry>

     

       46
       46
       -
          <varlistentry>

     

       47
       47
       -
           <term>

     

       48
       48
       -
            <varname>default</varname>

     

       49
       49
       -
           </term>

     

       50
       50
       -
           <listitem>

     

       51
       51
       -
            <para>

     

       52
       52
       -
             The default value used if no value is defined by any module. A default is

     

       53
       53
       -
             not required; but if a default is not given, then users of the module

     

       54
       54
       -
             will have to define the value of the option, otherwise an error will be

     

       55
       55
       -
             thrown.

     

       56
       56
       -
            </para>

     

       57
       57
       -
           </listitem>

     

       58
       58
       -
          </varlistentry>

     

       59
       59
       -
          <varlistentry>

     

       60
       60
       -
           <term>

     

       61
       61
       -
            <varname>example</varname>

     

       62
       62
       -
           </term>

     

       63
       63
       -
           <listitem>

     

       64
       64
       -
            <para>

     

       65
       65
       -
             An example value that will be shown in the NixOS manual.

     

       66
       66
       -
            </para>

     

       67
       67
       -
           </listitem>

     

       68
       68
       -
          </varlistentry>

     

       69
       69
       -
          <varlistentry>

     

       70
       70
       -
           <term>

     

       71
       71
       -
            <varname>description</varname>

     

       72
       72
       -
           </term>

     

       73
       73
       -
           <listitem>

     

       74
       74
       -
            <para>

     

       75
       75
       -
             A textual description of the option, in DocBook format, that will be

     

       76
       76
       -
             included in the NixOS manual.

     

       77
       77
       -
            </para>

     

       78
       78
       -
           </listitem>

     

       79
       79
       -
          </varlistentry>

     

       80
       80
       -
         </variablelist>

     

       81
       81
       -
        </para>

     

       82
       82
       -
       

     

       83
       83
       -
        <section xml:id="sec-option-declarations-eot">

     

       84
       84
       -
         <title>Extensible Option Types</title>

     

       85
       85
       -
       

     

       86
       86
       -
         <para>

     

       87
       87
       -
          Extensible option types is a feature that allow to extend certain types

     

       88
       88
       -
          declaration through multiple module files. This feature only work with a

     

       89
       89
       -
          restricted set of types, namely <literal>enum</literal> and

     

       90
       90
       -
          <literal>submodules</literal> and any composed forms of them.

     

       91
       91
       -
         </para>

     

       92
       92
       -
       

     

       93
       93
       -
         <para>

     

       94
       94
       -
          Extensible option types can be used for <literal>enum</literal> options that

     

       95
       95
       -
          affects multiple modules, or as an alternative to related

     

       96
       96
       -
          <literal>enable</literal> options.

     

       97
       97
       -
         </para>

     

       98
       98
       -
       

     

       99
       99
       -
         <para>

     

       100
       100
       -
          As an example, we will take the case of display managers. There is a central

     

       101
       101
       -
          display manager module for generic display manager options and a module file

     

       102
       102
       -
          per display manager backend (sddm, gdm ...).

     

       103
       103
       -
         </para>

     

       104
       104
       -
       

     

       105
       105
       -
         <para>

     

       106
       106
       -
          There are two approach to this module structure:

     

       107
       107
       -
          <itemizedlist>

     

       108
       108
       -
           <listitem>

     

       109
       109
       -
            <para>

     

       110
       110
       -
             Managing the display managers independently by adding an enable option to

     

       111
       111
       -
             every display manager module backend. (NixOS)

     

       112
       112
       -
            </para>

     

       113
       113
       -
           </listitem>

     

       114
       114
       -
           <listitem>

     

       115
       115
       -
            <para>

     

       116
       116
       -
             Managing the display managers in the central module by adding an option

     

       117
       117
       -
             to select which display manager backend to use.

     

       118
       118
       -
            </para>

     

       119
       119
       -
           </listitem>

     

       120
       120
       -
          </itemizedlist>

     

       121
       121
       -
         </para>

     

       122
       122
       -
       

     

       123
       123
       -
         <para>

     

       124
       124
       -
          Both approaches have problems.

     

       125
       125
       -
         </para>

     

       126
       126
       -
       

     

       127
       127
       -
         <para>

     

       128
       128
       -
          Making backends independent can quickly become hard to manage. For display

     

       129
       129
       -
          managers, there can be only one enabled at a time, but the type system can

     

       130
       130
       -
          not enforce this restriction as there is no relation between each backend

     

       131
       131
       -
          <literal>enable</literal> option. As a result, this restriction has to be

     

       132
       132
       -
          done explicitely by adding assertions in each display manager backend

     

       133
       133
       -
          module.

     

       134
       134
       -
         </para>

     

       135
       135
       -
       

     

       136
       136
       -
         <para>

     

       137
       137
       -
          On the other hand, managing the display managers backends in the central

     

       138
       138
       -
          module will require to change the central module option every time a new

     

       139
       139
       -
          backend is added or removed.

     

       140
       140
       -
         </para>

     

       141
       141
       -
       

     

       142
       142
       -
         <para>

     

       143
       143
       -
          By using extensible option types, it is possible to create a placeholder

     

       144
       144
       -
          option in the central module

     

       145
       145
       -
          (<xref linkend='ex-option-declaration-eot-service'

     

       146
       146
       -
             />), and to extend

     

       147
       147
       -
          it in each backend module

     

       148
       148
       -
          (<xref

     

       149
       149
       -
             linkend='ex-option-declaration-eot-backend-gdm' />,

     

       150
       150
       -
          <xref

     

       151
       151
       -
             linkend='ex-option-declaration-eot-backend-sddm' />).

     

       152
       152
       -
         </para>

     

       153
       153
       -
       

     

       154
       154
       -
         <para>

     

       155
       155
       -
          As a result, <literal>displayManager.enable</literal> option values can be

     

       156
       156
       -
          added without changing the main service module file and the type system

     

       157
       157
       -
          automatically enforce that there can only be a single display manager

     

       158
       158
       -
          enabled.

     

       159
       159
       -
         </para>

     

       160
       160
       -
       

     

       161
       161
       -
         <example xml:id='ex-option-declaration-eot-service'>

     

       162
       162
       -
          <title>Extensible type placeholder in the service module</title>

     

       163
       163
       -
       <screen>

     

       164
       164
       -
       services.xserver.displayManager.enable = mkOption {

     

       165
       165
       -
         description = "Display manager to use";

     

       166
       166
       -
         type = with types; nullOr (enum [ ]);

     

       167
       167
       -
       };</screen>

     

       168
       168
       -
         </example>

     

       169
       169
       -
       

     

       170
       170
       -
         <example xml:id='ex-option-declaration-eot-backend-gdm'>

     

       171
       171
       -
          <title>Extending <literal>services.xserver.displayManager.enable</literal> in the <literal>gdm</literal> module</title>

     

       172
       172
       -
       <screen>

     

       173
       173
       -
       services.xserver.displayManager.enable = mkOption {

     

       174
       174
       -
         type = with types; nullOr (enum [ "gdm" ]);

     

       175
       175
       -
       };</screen>

     

       176
       176
       -
         </example>

     

       177
       177
       -
       

     

       178
       178
       -
         <example xml:id='ex-option-declaration-eot-backend-sddm'>

     

       179
       179
       -
          <title>Extending <literal>services.xserver.displayManager.enable</literal> in the <literal>sddm</literal> module</title>

     

       180
       180
       -
       <screen>

     

       181
       181
       -
       services.xserver.displayManager.enable = mkOption {

     

       182
       182
       -
         type = with types; nullOr (enum [ "sddm" ]);

     

       183
       183
       -
       };</screen>

     

       184
       184
       -
         </example>

     

       185
       185
       -
       

     

       186
       186
       -
         <para>

     

       187
       187
       -
          The placeholder declaration is a standard <literal>mkOption</literal>

     

       188
       188
       -
          declaration, but it is important that extensible option declarations only

     

       189
       189
       -
          use the <literal>type</literal> argument.

     

       190
       190
       -
         </para>

     

       191
       191
       -
       

     

       192
       192
       -
         <para>

     

       193
       193
       -
          Extensible option types work with any of the composed variants of

     

       194
       194
       -
          <literal>enum</literal> such as <literal>with types; nullOr (enum [ "foo"

     

       195
       195
       -
          "bar" ])</literal> or <literal>with types; listOf (enum [ "foo" "bar"

     

       196
       196
       -
          ])</literal>.

     

       197
       197
       -
         </para>

     

       198
       198
       -
        </section>

     

       199
       199
       -
       </section>

+91

nixos/doc/manual/development/option-def.section.md

···

       1
       1
       +
       # Option Definitions {#sec-option-definitions}

     

       2
       2
       +
       

     

       3
       3
       +
       Option definitions are generally straight-forward bindings of values to

     

       4
       4
       +
       option names, like

     

       5
       5
       +
       

     

       6
       6
       +
       ```nix

     

       7
       7
       +
       config = {

     

       8
       8
       +
         services.httpd.enable = true;

     

       9
       9
       +
       };

     

       10
       10
       +
       ```

     

       11
       11
       +
       

     

       12
       12
       +
       However, sometimes you need to wrap an option definition or set of

     

       13
       13
       +
       option definitions in a *property* to achieve certain effects:

     

       14
       14
       +
       

     

       15
       15
       +
       ## Delaying Conditionals {#sec-option-definitions-delaying-conditionals .unnumbered}

     

       16
       16
       +
       

     

       17
       17
       +
       If a set of option definitions is conditional on the value of another

     

       18
       18
       +
       option, you may need to use `mkIf`. Consider, for instance:

     

       19
       19
       +
       

     

       20
       20
       +
       ```nix

     

       21
       21
       +
       config = if config.services.httpd.enable then {

     

       22
       22
       +
         environment.systemPackages = [ ... ];

     

       23
       23
       +
         ...

     

       24
       24
       +
       } else {};

     

       25
       25
       +
       ```

     

       26
       26
       +
       

     

       27
       27
       +
       This definition will cause Nix to fail with an "infinite recursion"

     

       28
       28
       +
       error. Why? Because the value of `config.services.httpd.enable` depends

     

       29
       29
       +
       on the value being constructed here. After all, you could also write the

     

       30
       30
       +
       clearly circular and contradictory:

     

       31
       31
       +
       

     

       32
       32
       +
       ```nix

     

       33
       33
       +
       config = if config.services.httpd.enable then {

     

       34
       34
       +
         services.httpd.enable = false;

     

       35
       35
       +
       } else {

     

       36
       36
       +
         services.httpd.enable = true;

     

       37
       37
       +
       };

     

       38
       38
       +
       ```

     

       39
       39
       +
       

     

       40
       40
       +
       The solution is to write:

     

       41
       41
       +
       

     

       42
       42
       +
       ```nix

     

       43
       43
       +
       config = mkIf config.services.httpd.enable {

     

       44
       44
       +
         environment.systemPackages = [ ... ];

     

       45
       45
       +
         ...

     

       46
       46
       +
       };

     

       47
       47
       +
       ```

     

       48
       48
       +
       

     

       49
       49
       +
       The special function `mkIf` causes the evaluation of the conditional to

     

       50
       50
       +
       be "pushed down" into the individual definitions, as if you had written:

     

       51
       51
       +
       

     

       52
       52
       +
       ```nix

     

       53
       53
       +
       config = {

     

       54
       54
       +
         environment.systemPackages = if config.services.httpd.enable then [ ... ] else [];

     

       55
       55
       +
         ...

     

       56
       56
       +
       };

     

       57
       57
       +
       ```

     

       58
       58
       +
       

     

       59
       59
       +
       ## Setting Priorities {#sec-option-definitions-setting-priorities .unnumbered}

     

       60
       60
       +
       

     

       61
       61
       +
       A module can override the definitions of an option in other modules by

     

       62
       62
       +
       setting a *priority*. All option definitions that do not have the lowest

     

       63
       63
       +
       priority value are discarded. By default, option definitions have

     

       64
       64
       +
       priority 1000. You can specify an explicit priority by using

     

       65
       65
       +
       `mkOverride`, e.g.

     

       66
       66
       +
       

     

       67
       67
       +
       ```nix

     

       68
       68
       +
       services.openssh.enable = mkOverride 10 false;

     

       69
       69
       +
       ```

     

       70
       70
       +
       

     

       71
       71
       +
       This definition causes all other definitions with priorities above 10 to

     

       72
       72
       +
       be discarded. The function `mkForce` is equal to `mkOverride 50`.

     

       73
       73
       +
       

     

       74
       74
       +
       ## Merging Configurations {#sec-option-definitions-merging .unnumbered}

     

       75
       75
       +
       

     

       76
       76
       +
       In conjunction with `mkIf`, it is sometimes useful for a module to

     

       77
       77
       +
       return multiple sets of option definitions, to be merged together as if

     

       78
       78
       +
       they were declared in separate modules. This can be done using

     

       79
       79
       +
       `mkMerge`:

     

       80
       80
       +
       

     

       81
       81
       +
       ```nix

     

       82
       82
       +
       config = mkMerge

     

       83
       83
       +
         [ # Unconditional stuff.

     

       84
       84
       +
           { environment.systemPackages = [ ... ];

     

       85
       85
       +
           }

     

       86
       86
       +
           # Conditional stuff.

     

       87
       87
       +
           (mkIf config.services.bla.enable {

     

       88
       88
       +
             environment.systemPackages = [ ... ];

     

       89
       89
       +
           })

     

       90
       90
       +
         ];

     

       91
       91
       +
       ```

-99

nixos/doc/manual/development/option-def.xml

···

       1
       1
       -
       <section xmlns="http://docbook.org/ns/docbook"

     

       2
       2
       -
               xmlns:xlink="http://www.w3.org/1999/xlink"

     

       3
       3
       -
               xmlns:xi="http://www.w3.org/2001/XInclude"

     

       4
       4
       -
               version="5.0"

     

       5
       5
       -
               xml:id="sec-option-definitions">

     

       6
       6
       -
        <title>Option Definitions</title>

     

       7
       7
       -
       

     

       8
       8
       -
        <para>

     

       9
       9
       -
         Option definitions are generally straight-forward bindings of values to

     

       10
       10
       -
         option names, like

     

       11
       11
       -
       <programlisting>

     

       12
       12
       -
       config = {

     

       13
       13
       -
         services.httpd.enable = true;

     

       14
       14
       -
       };

     

       15
       15
       -
       </programlisting>

     

       16
       16
       -
         However, sometimes you need to wrap an option definition or set of option

     

       17
       17
       -
         definitions in a <emphasis>property</emphasis> to achieve certain effects:

     

       18
       18
       -
        </para>

     

       19
       19
       -
       

     

       20
       20
       -
        <simplesect xml:id="sec-option-definitions-delaying-conditionals">

     

       21
       21
       -
         <title>Delaying Conditionals</title>

     

       22
       22
       -
         <para>

     

       23
       23
       -
          If a set of option definitions is conditional on the value of another

     

       24
       24
       -
          option, you may need to use <varname>mkIf</varname>. Consider, for instance:

     

       25
       25
       -
       <programlisting>

     

       26
       26
       -
       config = if config.services.httpd.enable then {

     

       27
       27
       -
         environment.systemPackages = [ <replaceable>...</replaceable> ];

     

       28
       28
       -
         <replaceable>...</replaceable>

     

       29
       29
       -
       } else {};

     

       30
       30
       -
       </programlisting>

     

       31
       31
       -
          This definition will cause Nix to fail with an “infinite recursion”

     

       32
       32
       -
          error. Why? Because the value of

     

       33
       33
       -
          <option>config.services.httpd.enable</option> depends on the value being

     

       34
       34
       -
          constructed here. After all, you could also write the clearly circular and

     

       35
       35
       -
          contradictory:

     

       36
       36
       -
       <programlisting>

     

       37
       37
       -
       config = if config.services.httpd.enable then {

     

       38
       38
       -
         services.httpd.enable = false;

     

       39
       39
       -
       } else {

     

       40
       40
       -
         services.httpd.enable = true;

     

       41
       41
       -
       };

     

       42
       42
       -
       </programlisting>

     

       43
       43
       -
          The solution is to write:

     

       44
       44
       -
       <programlisting>

     

       45
       45
       -
       config = mkIf config.services.httpd.enable {

     

       46
       46
       -
         environment.systemPackages = [ <replaceable>...</replaceable> ];

     

       47
       47
       -
         <replaceable>...</replaceable>

     

       48
       48
       -
       };

     

       49
       49
       -
       </programlisting>

     

       50
       50
       -
          The special function <varname>mkIf</varname> causes the evaluation of the

     

       51
       51
       -
          conditional to be “pushed down” into the individual definitions, as if

     

       52
       52
       -
          you had written:

     

       53
       53
       -
       <programlisting>

     

       54
       54
       -
       config = {

     

       55
       55
       -
         environment.systemPackages = if config.services.httpd.enable then [ <replaceable>...</replaceable> ] else [];

     

       56
       56
       -
         <replaceable>...</replaceable>

     

       57
       57
       -
       };

     

       58
       58
       -
       </programlisting>

     

       59
       59
       -
         </para>

     

       60
       60
       -
        </simplesect>

     

       61
       61
       -
       

     

       62
       62
       -
        <simplesect xml:id="sec-option-definitions-setting-priorities">

     

       63
       63
       -
         <title>Setting Priorities</title>

     

       64
       64
       -
         <para>

     

       65
       65
       -
          A module can override the definitions of an option in other modules by

     

       66
       66
       -
          setting a <emphasis>priority</emphasis>. All option definitions that do not

     

       67
       67
       -
          have the lowest priority value are discarded. By default, option definitions

     

       68
       68
       -
          have priority 1000. You can specify an explicit priority by using

     

       69
       69
       -
          <varname>mkOverride</varname>, e.g.

     

       70
       70
       -
       <programlisting>

     

       71
       71
       -
       services.openssh.enable = mkOverride 10 false;

     

       72
       72
       -
       </programlisting>

     

       73
       73
       -
          This definition causes all other definitions with priorities above 10 to be

     

       74
       74
       -
          discarded. The function <varname>mkForce</varname> is equal to

     

       75
       75
       -
          <varname>mkOverride 50</varname>.

     

       76
       76
       -
         </para>

     

       77
       77
       -
        </simplesect>

     

       78
       78
       -
       

     

       79
       79
       -
        <simplesect xml:id="sec-option-definitions-merging">

     

       80
       80
       -
         <title>Merging Configurations</title>

     

       81
       81
       -
         <para>

     

       82
       82
       -
          In conjunction with <literal>mkIf</literal>, it is sometimes useful for a

     

       83
       83
       -
          module to return multiple sets of option definitions, to be merged together

     

       84
       84
       -
          as if they were declared in separate modules. This can be done using

     

       85
       85
       -
          <varname>mkMerge</varname>:

     

       86
       86
       -
       <programlisting>

     

       87
       87
       -
       config = mkMerge

     

       88
       88
       -
         [ # Unconditional stuff.

     

       89
       89
       -
           { environment.systemPackages = [ <replaceable>...</replaceable> ];

     

       90
       90
       -
           }

     

       91
       91
       -
           # Conditional stuff.

     

       92
       92
       -
           (mkIf config.services.bla.enable {

     

       93
       93
       -
             environment.systemPackages = [ <replaceable>...</replaceable> ];

     

       94
       94
       -
           })

     

       95
       95
       -
         ];

     

       96
       96
       -
       </programlisting>

     

       97
       97
       -
         </para>

     

       98
       98
       -
        </simplesect>

     

       99
       99
       -
       </section>

+558

nixos/doc/manual/development/option-types.section.md

···

       1
       1
       +
       # Options Types {#sec-option-types}

     

       2
       2
       +
       

     

       3
       3
       +
       Option types are a way to put constraints on the values a module option

     

       4
       4
       +
       can take. Types are also responsible of how values are merged in case of

     

       5
       5
       +
       multiple value definitions.

     

       6
       6
       +
       

     

       7
       7
       +
       ## Basic Types {#sec-option-types-basic}

     

       8
       8
       +
       

     

       9
       9
       +
       Basic types are the simplest available types in the module system. Basic

     

       10
       10
       +
       types include multiple string types that mainly differ in how definition

     

       11
       11
       +
       merging is handled.

     

       12
       12
       +
       

     

       13
       13
       +
       `types.bool`

     

       14
       14
       +
       

     

       15
       15
       +
       :   A boolean, its values can be `true` or `false`.

     

       16
       16
       +
       

     

       17
       17
       +
       `types.path`

     

       18
       18
       +
       

     

       19
       19
       +
       :   A filesystem path, defined as anything that when coerced to a string

     

       20
       20
       +
           starts with a slash. Even if derivations can be considered as path,

     

       21
       21
       +
           the more specific `types.package` should be preferred.

     

       22
       22
       +
       

     

       23
       23
       +
       `types.package`

     

       24
       24
       +
       

     

       25
       25
       +
       :   A derivation or a store path.

     

       26
       26
       +
       

     

       27
       27
       +
       `types.anything`

     

       28
       28
       +
       

     

       29
       29
       +
       :   A type that accepts any value and recursively merges attribute sets

     

       30
       30
       +
           together. This type is recommended when the option type is unknown.

     

       31
       31
       +
       

     

       32
       32
       +
           ::: {#ex-types-anything .example}

     

       33
       33
       +
           ::: {.title}

     

       34
       34
       +
           **Example: `types.anything` Example**

     

       35
       35
       +
           :::

     

       36
       36
       +
           Two definitions of this type like

     

       37
       37
       +
       

     

       38
       38
       +
           ```nix

     

       39
       39
       +
           {

     

       40
       40
       +
             str = lib.mkDefault "foo";

     

       41
       41
       +
             pkg.hello = pkgs.hello;

     

       42
       42
       +
             fun.fun = x: x + 1;

     

       43
       43
       +
           }

     

       44
       44
       +
           ```

     

       45
       45
       +
       

     

       46
       46
       +
           ```nix

     

       47
       47
       +
           {

     

       48
       48
       +
             str = lib.mkIf true "bar";

     

       49
       49
       +
             pkg.gcc = pkgs.gcc;

     

       50
       50
       +
             fun.fun = lib.mkForce (x: x + 2);

     

       51
       51
       +
           }

     

       52
       52
       +
           ```

     

       53
       53
       +
       

     

       54
       54
       +
           will get merged to

     

       55
       55
       +
       

     

       56
       56
       +
           ```nix

     

       57
       57
       +
           {

     

       58
       58
       +
             str = "bar";

     

       59
       59
       +
             pkg.gcc = pkgs.gcc;

     

       60
       60
       +
             pkg.hello = pkgs.hello;

     

       61
       61
       +
             fun.fun = x: x + 2;

     

       62
       62
       +
           }

     

       63
       63
       +
           ```

     

       64
       64
       +
           :::

     

       65
       65
       +
       

     

       66
       66
       +
       `types.attrs`

     

       67
       67
       +
       

     

       68
       68
       +
       :   A free-form attribute set.

     

       69
       69
       +
       

     

       70
       70
       +
           ::: {.warning}

     

       71
       71
       +
           This type will be deprecated in the future because it doesn\'t

     

       72
       72
       +
           recurse into attribute sets, silently drops earlier attribute

     

       73
       73
       +
           definitions, and doesn\'t discharge `lib.mkDefault`, `lib.mkIf`

     

       74
       74
       +
           and co. For allowing arbitrary attribute sets, prefer

     

       75
       75
       +
           `types.attrsOf types.anything` instead which doesn\'t have these

     

       76
       76
       +
           problems.

     

       77
       77
       +
           :::

     

       78
       78
       +
       

     

       79
       79
       +
       Integer-related types:

     

       80
       80
       +
       

     

       81
       81
       +
       `types.int`

     

       82
       82
       +
       

     

       83
       83
       +
       :   A signed integer.

     

       84
       84
       +
       

     

       85
       85
       +
       `types.ints.{s8, s16, s32}`

     

       86
       86
       +
       

     

       87
       87
       +
       :   Signed integers with a fixed length (8, 16 or 32 bits). They go from

     

       88
       88
       +
           −2^n/2 to

     

       89
       89
       +
           2^n/2−1 respectively (e.g. `−128` to

     

       90
       90
       +
           `127` for 8 bits).

     

       91
       91
       +
       

     

       92
       92
       +
       `types.ints.unsigned`

     

       93
       93
       +
       

     

       94
       94
       +
       :   An unsigned integer (that is >= 0).

     

       95
       95
       +
       

     

       96
       96
       +
       `types.ints.{u8, u16, u32}`

     

       97
       97
       +
       

     

       98
       98
       +
       :   Unsigned integers with a fixed length (8, 16 or 32 bits). They go

     

       99
       99
       +
           from 0 to 2^n−1 respectively (e.g. `0`

     

       100
       100
       +
           to `255` for 8 bits).

     

       101
       101
       +
       

     

       102
       102
       +
       `types.ints.positive`

     

       103
       103
       +
       

     

       104
       104
       +
       :   A positive integer (that is > 0).

     

       105
       105
       +
       

     

       106
       106
       +
       `types.port`

     

       107
       107
       +
       

     

       108
       108
       +
       :   A port number. This type is an alias to

     

       109
       109
       +
           `types.ints.u16`.

     

       110
       110
       +
       

     

       111
       111
       +
       String-related types:

     

       112
       112
       +
       

     

       113
       113
       +
       `types.str`

     

       114
       114
       +
       

     

       115
       115
       +
       :   A string. Multiple definitions cannot be merged.

     

       116
       116
       +
       

     

       117
       117
       +
       `types.lines`

     

       118
       118
       +
       

     

       119
       119
       +
       :   A string. Multiple definitions are concatenated with a new line

     

       120
       120
       +
           `"\n"`.

     

       121
       121
       +
       

     

       122
       122
       +
       `types.commas`

     

       123
       123
       +
       

     

       124
       124
       +
       :   A string. Multiple definitions are concatenated with a comma `","`.

     

       125
       125
       +
       

     

       126
       126
       +
       `types.envVar`

     

       127
       127
       +
       

     

       128
       128
       +
       :   A string. Multiple definitions are concatenated with a collon `":"`.

     

       129
       129
       +
       

     

       130
       130
       +
       `types.strMatching`

     

       131
       131
       +
       

     

       132
       132
       +
       :   A string matching a specific regular expression. Multiple

     

       133
       133
       +
           definitions cannot be merged. The regular expression is processed

     

       134
       134
       +
           using `builtins.match`.

     

       135
       135
       +
       

     

       136
       136
       +
       ## Value Types {#sec-option-types-value}

     

       137
       137
       +
       

     

       138
       138
       +
       Value types are types that take a value parameter.

     

       139
       139
       +
       

     

       140
       140
       +
       `types.enum` *`l`*

     

       141
       141
       +
       

     

       142
       142
       +
       :   One element of the list *`l`*, e.g. `types.enum [ "left" "right" ]`.

     

       143
       143
       +
           Multiple definitions cannot be merged.

     

       144
       144
       +
       

     

       145
       145
       +
       `types.separatedString` *`sep`*

     

       146
       146
       +
       

     

       147
       147
       +
       :   A string with a custom separator *`sep`*, e.g.

     

       148
       148
       +
           `types.separatedString "|"`.

     

       149
       149
       +
       

     

       150
       150
       +
       `types.ints.between` *`lowest highest`*

     

       151
       151
       +
       

     

       152
       152
       +
       :   An integer between *`lowest`* and *`highest`* (both inclusive). Useful

     

       153
       153
       +
           for creating types like `types.port`.

     

       154
       154
       +
       

     

       155
       155
       +
       `types.submodule` *`o`*

     

       156
       156
       +
       

     

       157
       157
       +
       :   A set of sub options *`o`*. *`o`* can be an attribute set, a function

     

       158
       158
       +
           returning an attribute set, or a path to a file containing such a

     

       159
       159
       +
           value. Submodules are used in composed types to create modular

     

       160
       160
       +
           options. This is equivalent to

     

       161
       161
       +
           `types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }`.

     

       162
       162
       +
           Submodules are detailed in [Submodule](#section-option-types-submodule).

     

       163
       163
       +
       

     

       164
       164
       +
       `types.submoduleWith` { *`modules`*, *`specialArgs`* ? {}, *`shorthandOnlyDefinesConfig`* ? false }

     

       165
       165
       +
       

     

       166
       166
       +
       :   Like `types.submodule`, but more flexible and with better defaults.

     

       167
       167
       +
           It has parameters

     

       168
       168
       +
       

     

       169
       169
       +
           -   *`modules`* A list of modules to use by default for this

     

       170
       170
       +
               submodule type. This gets combined with all option definitions

     

       171
       171
       +
               to build the final list of modules that will be included.

     

       172
       172
       +
       

     

       173
       173
       +
               ::: {.note}

     

       174
       174
       +
               Only options defined with this argument are included in rendered

     

       175
       175
       +
               documentation.

     

       176
       176
       +
               :::

     

       177
       177
       +
       

     

       178
       178
       +
           -   *`specialArgs`* An attribute set of extra arguments to be passed

     

       179
       179
       +
               to the module functions. The option `_module.args` should be

     

       180
       180
       +
               used instead for most arguments since it allows overriding.

     

       181
       181
       +
               *`specialArgs`* should only be used for arguments that can\'t go

     

       182
       182
       +
               through the module fixed-point, because of infinite recursion or

     

       183
       183
       +
               other problems. An example is overriding the `lib` argument,

     

       184
       184
       +
               because `lib` itself is used to define `_module.args`, which

     

       185
       185
       +
               makes using `_module.args` to define it impossible.

     

       186
       186
       +
       

     

       187
       187
       +
           -   *`shorthandOnlyDefinesConfig`* Whether definitions of this type

     

       188
       188
       +
               should default to the `config` section of a module (see

     

       189
       189
       +
               [Example: Structure of NixOS Modules](#ex-module-syntax))

     

       190
       190
       +
               if it is an attribute set. Enabling this only has a benefit

     

       191
       191
       +
               when the submodule defines an option named `config` or `options`.

     

       192
       192
       +
               In such a case it would allow the option to be set with

     

       193
       193
       +
               `the-submodule.config = "value"` instead of requiring

     

       194
       194
       +
               `the-submodule.config.config = "value"`. This is because

     

       195
       195
       +
               only when modules *don\'t* set the `config` or `options`

     

       196
       196
       +
               keys, all keys are interpreted as option definitions in the

     

       197
       197
       +
               `config` section. Enabling this option implicitly puts all

     

       198
       198
       +
               attributes in the `config` section.

     

       199
       199
       +
       

     

       200
       200
       +
               With this option enabled, defining a non-`config` section

     

       201
       201
       +
               requires using a function:

     

       202
       202
       +
               `the-submodule = { ... }: { options = { ... }; }`.

     

       203
       203
       +
       

     

       204
       204
       +
       ## Composed Types {#sec-option-types-composed}

     

       205
       205
       +
       

     

       206
       206
       +
       Composed types are types that take a type as parameter. `listOf

     

       207
       207
       +
          int` and `either int str` are examples of composed types.

     

       208
       208
       +
       

     

       209
       209
       +
       `types.listOf` *`t`*

     

       210
       210
       +
       

     

       211
       211
       +
       :   A list of *`t`* type, e.g. `types.listOf

     

       212
       212
       +
                 int`. Multiple definitions are merged with list concatenation.

     

       213
       213
       +
       

     

       214
       214
       +
       `types.attrsOf` *`t`*

     

       215
       215
       +
       

     

       216
       216
       +
       :   An attribute set of where all the values are of *`t`* type. Multiple

     

       217
       217
       +
           definitions result in the joined attribute set.

     

       218
       218
       +
       

     

       219
       219
       +
           ::: {.note}

     

       220
       220
       +
           This type is *strict* in its values, which in turn means attributes

     

       221
       221
       +
           cannot depend on other attributes. See `

     

       222
       222
       +
                  types.lazyAttrsOf` for a lazy version.

     

       223
       223
       +
           :::

     

       224
       224
       +
       

     

       225
       225
       +
       `types.lazyAttrsOf` *`t`*

     

       226
       226
       +
       

     

       227
       227
       +
       :   An attribute set of where all the values are of *`t`* type. Multiple

     

       228
       228
       +
           definitions result in the joined attribute set. This is the lazy

     

       229
       229
       +
           version of `types.attrsOf

     

       230
       230
       +
                 `, allowing attributes to depend on each other.

     

       231
       231
       +
       

     

       232
       232
       +
           ::: {.warning}

     

       233
       233
       +
           This version does not fully support conditional definitions! With an

     

       234
       234
       +
           option `foo` of this type and a definition

     

       235
       235
       +
           `foo.attr = lib.mkIf false 10`, evaluating `foo ? attr` will return

     

       236
       236
       +
           `true` even though it should be false. Accessing the value will then

     

       237
       237
       +
           throw an error. For types *`t`* that have an `emptyValue` defined,

     

       238
       238
       +
           that value will be returned instead of throwing an error. So if the

     

       239
       239
       +
           type of `foo.attr` was `lazyAttrsOf (nullOr int)`, `null` would be

     

       240
       240
       +
           returned instead for the same `mkIf false` definition.

     

       241
       241
       +
           :::

     

       242
       242
       +
       

     

       243
       243
       +
       `types.nullOr` *`t`*

     

       244
       244
       +
       

     

       245
       245
       +
       :   `null` or type *`t`*. Multiple definitions are merged according to

     

       246
       246
       +
           type *`t`*.

     

       247
       247
       +
       

     

       248
       248
       +
       `types.uniq` *`t`*

     

       249
       249
       +
       

     

       250
       250
       +
       :   Ensures that type *`t`* cannot be merged. It is used to ensure option

     

       251
       251
       +
           definitions are declared only once.

     

       252
       252
       +
       

     

       253
       253
       +
       `types.either` *`t1 t2`*

     

       254
       254
       +
       

     

       255
       255
       +
       :   Type *`t1`* or type *`t2`*, e.g. `with types; either int str`.

     

       256
       256
       +
           Multiple definitions cannot be merged.

     

       257
       257
       +
       

     

       258
       258
       +
       `types.oneOf` \[ *`t1 t2`* \... \]

     

       259
       259
       +
       

     

       260
       260
       +
       :   Type *`t1`* or type *`t2`* and so forth, e.g.

     

       261
       261
       +
           `with types; oneOf [ int str bool ]`. Multiple definitions cannot be

     

       262
       262
       +
           merged.

     

       263
       263
       +
       

     

       264
       264
       +
       `types.coercedTo` *`from f to`*

     

       265
       265
       +
       

     

       266
       266
       +
       :   Type *`to`* or type *`from`* which will be coerced to type *`to`* using

     

       267
       267
       +
           function *`f`* which takes an argument of type *`from`* and return a

     

       268
       268
       +
           value of type *`to`*. Can be used to preserve backwards compatibility

     

       269
       269
       +
           of an option if its type was changed.

     

       270
       270
       +
       

     

       271
       271
       +
       ## Submodule {#section-option-types-submodule}

     

       272
       272
       +
       

     

       273
       273
       +
       `submodule` is a very powerful type that defines a set of sub-options

     

       274
       274
       +
       that are handled like a separate module.

     

       275
       275
       +
       

     

       276
       276
       +
       It takes a parameter *`o`*, that should be a set, or a function returning

     

       277
       277
       +
       a set with an `options` key defining the sub-options. Submodule option

     

       278
       278
       +
       definitions are type-checked accordingly to the `options` declarations.

     

       279
       279
       +
       Of course, you can nest submodule option definitons for even higher

     

       280
       280
       +
       modularity.

     

       281
       281
       +
       

     

       282
       282
       +
       The option set can be defined directly

     

       283
       283
       +
       ([Example: Directly defined submodule](#ex-submodule-direct)) or as reference

     

       284
       284
       +
       ([Example: Submodule defined as a reference](#ex-submodule-reference)).

     

       285
       285
       +
       

     

       286
       286
       +
       ::: {#ex-submodule-direct .example}

     

       287
       287
       +
       ::: {.title}

     

       288
       288
       +
       **Example: Directly defined submodule**

     

       289
       289
       +
       :::

     

       290
       290
       +
       ```nix

     

       291
       291
       +
       options.mod = mkOption {

     

       292
       292
       +
         description = "submodule example";

     

       293
       293
       +
         type = with types; submodule {

     

       294
       294
       +
           options = {

     

       295
       295
       +
             foo = mkOption {

     

       296
       296
       +
               type = int;

     

       297
       297
       +
             };

     

       298
       298
       +
             bar = mkOption {

     

       299
       299
       +
               type = str;

     

       300
       300
       +
             };

     

       301
       301
       +
           };

     

       302
       302
       +
         };

     

       303
       303
       +
       };

     

       304
       304
       +
       ```

     

       305
       305
       +
       :::

     

       306
       306
       +
       

     

       307
       307
       +
       ::: {#ex-submodule-reference .example}

     

       308
       308
       +
       ::: {.title}

     

       309
       309
       +
       **Example: Submodule defined as a reference**

     

       310
       310
       +
       :::

     

       311
       311
       +
       ```nix

     

       312
       312
       +
       let

     

       313
       313
       +
         modOptions = {

     

       314
       314
       +
           options = {

     

       315
       315
       +
             foo = mkOption {

     

       316
       316
       +
               type = int;

     

       317
       317
       +
             };

     

       318
       318
       +
             bar = mkOption {

     

       319
       319
       +
               type = int;

     

       320
       320
       +
             };

     

       321
       321
       +
           };

     

       322
       322
       +
         };

     

       323
       323
       +
       in

     

       324
       324
       +
       options.mod = mkOption {

     

       325
       325
       +
         description = "submodule example";

     

       326
       326
       +
         type = with types; submodule modOptions;

     

       327
       327
       +
       };

     

       328
       328
       +
       ```

     

       329
       329
       +
       :::

     

       330
       330
       +
       

     

       331
       331
       +
       The `submodule` type is especially interesting when used with composed

     

       332
       332
       +
       types like `attrsOf` or `listOf`. When composed with `listOf`

     

       333
       333
       +
       ([Example: Declaration of a list of submodules](#ex-submodule-listof-declaration)), `submodule` allows

     

       334
       334
       +
       multiple definitions of the submodule option set

     

       335
       335
       +
       ([Example: Definition of a list of submodules](#ex-submodule-listof-definition)).

     

       336
       336
       +
       

     

       337
       337
       +
       ::: {#ex-submodule-listof-declaration .example}

     

       338
       338
       +
       ::: {.title}

     

       339
       339
       +
       **Example: Declaration of a list of submodules**

     

       340
       340
       +
       :::

     

       341
       341
       +
       ```nix

     

       342
       342
       +
       options.mod = mkOption {

     

       343
       343
       +
         description = "submodule example";

     

       344
       344
       +
         type = with types; listOf (submodule {

     

       345
       345
       +
           options = {

     

       346
       346
       +
             foo = mkOption {

     

       347
       347
       +
               type = int;

     

       348
       348
       +
             };

     

       349
       349
       +
             bar = mkOption {

     

       350
       350
       +
               type = str;

     

       351
       351
       +
             };

     

       352
       352
       +
           };

     

       353
       353
       +
         });

     

       354
       354
       +
       };

     

       355
       355
       +
       ```

     

       356
       356
       +
       :::

     

       357
       357
       +
       

     

       358
       358
       +
       ::: {#ex-submodule-listof-definition .example}

     

       359
       359
       +
       ::: {.title}

     

       360
       360
       +
       **Example: Definition of a list of submodules**

     

       361
       361
       +
       :::

     

       362
       362
       +
       ```nix

     

       363
       363
       +
       config.mod = [

     

       364
       364
       +
         { foo = 1; bar = "one"; }

     

       365
       365
       +
         { foo = 2; bar = "two"; }

     

       366
       366
       +
       ];

     

       367
       367
       +
       ```

     

       368
       368
       +
       :::

     

       369
       369
       +
       

     

       370
       370
       +
       When composed with `attrsOf`

     

       371
       371
       +
       ([Example: Declaration of attribute sets of submodules](#ex-submodule-attrsof-declaration)), `submodule` allows

     

       372
       372
       +
       multiple named definitions of the submodule option set

     

       373
       373
       +
       ([Example: Definition of attribute sets of submodules](#ex-submodule-attrsof-definition)).

     

       374
       374
       +
       

     

       375
       375
       +
       ::: {#ex-submodule-attrsof-declaration .example}

     

       376
       376
       +
       ::: {.title}

     

       377
       377
       +
       **Example: Declaration of attribute sets of submodules**

     

       378
       378
       +
       :::

     

       379
       379
       +
       ```nix

     

       380
       380
       +
       options.mod = mkOption {

     

       381
       381
       +
         description = "submodule example";

     

       382
       382
       +
         type = with types; attrsOf (submodule {

     

       383
       383
       +
           options = {

     

       384
       384
       +
             foo = mkOption {

     

       385
       385
       +
               type = int;

     

       386
       386
       +
             };

     

       387
       387
       +
             bar = mkOption {

     

       388
       388
       +
               type = str;

     

       389
       389
       +
             };

     

       390
       390
       +
           };

     

       391
       391
       +
         });

     

       392
       392
       +
       };

     

       393
       393
       +
       ```

     

       394
       394
       +
       :::

     

       395
       395
       +
       

     

       396
       396
       +
       ::: {#ex-submodule-attrsof-definition .example}

     

       397
       397
       +
       ::: {.title}

     

       398
       398
       +
       **Example: Definition of attribute sets of submodules**

     

       399
       399
       +
       :::

     

       400
       400
       +
       ```nix

     

       401
       401
       +
       config.mod.one = { foo = 1; bar = "one"; };

     

       402
       402
       +
       config.mod.two = { foo = 2; bar = "two"; };

     

       403
       403
       +
       ```

     

       404
       404
       +
       :::

     

       405
       405
       +
       

     

       406
       406
       +
       ## Extending types {#sec-option-types-extending}

     

       407
       407
       +
       

     

       408
       408
       +
       Types are mainly characterized by their `check` and `merge` functions.

     

       409
       409
       +
       

     

       410
       410
       +
       `check`

     

       411
       411
       +
       

     

       412
       412
       +
       :   The function to type check the value. Takes a value as parameter and

     

       413
       413
       +
           return a boolean. It is possible to extend a type check with the

     

       414
       414
       +
           `addCheck` function ([Example: Adding a type check](#ex-extending-type-check-1)),

     

       415
       415
       +
           or to fully override the check function

     

       416
       416
       +
           ([Example: Overriding a type check](#ex-extending-type-check-2)).

     

       417
       417
       +
       

     

       418
       418
       +
           ::: {#ex-extending-type-check-1 .example}

     

       419
       419
       +
           ::: {.title}

     

       420
       420
       +
           **Example: Adding a type check**

     

       421
       421
       +
           :::

     

       422
       422
       +
           ```nix

     

       423
       423
       +
           byte = mkOption {

     

       424
       424
       +
             description = "An integer between 0 and 255.";

     

       425
       425
       +
             type = types.addCheck types.int (x: x >= 0 && x <= 255);

     

       426
       426
       +
           };

     

       427
       427
       +
           ```

     

       428
       428
       +
           :::

     

       429
       429
       +
       

     

       430
       430
       +
           ::: {#ex-extending-type-check-2 .example}

     

       431
       431
       +
           ::: {.title}

     

       432
       432
       +
           **Example: Overriding a type check**

     

       433
       433
       +
           :::

     

       434
       434
       +
           ```nix

     

       435
       435
       +
           nixThings = mkOption {

     

       436
       436
       +
             description = "words that start with 'nix'";

     

       437
       437
       +
             type = types.str // {

     

       438
       438
       +
               check = (x: lib.hasPrefix "nix" x)

     

       439
       439
       +
             };

     

       440
       440
       +
           };

     

       441
       441
       +
           ```

     

       442
       442
       +
           :::

     

       443
       443
       +
       

     

       444
       444
       +
       `merge`

     

       445
       445
       +
       

     

       446
       446
       +
       :   Function to merge the options values when multiple values are set.

     

       447
       447
       +
           The function takes two parameters, `loc` the option path as a list

     

       448
       448
       +
           of strings, and `defs` the list of defined values as a list. It is

     

       449
       449
       +
           possible to override a type merge function for custom needs.

     

       450
       450
       +
       

     

       451
       451
       +
       ## Custom Types {#sec-option-types-custom}

     

       452
       452
       +
       

     

       453
       453
       +
       Custom types can be created with the `mkOptionType` function. As type

     

       454
       454
       +
       creation includes some more complex topics such as submodule handling,

     

       455
       455
       +
       it is recommended to get familiar with `types.nix` code before creating

     

       456
       456
       +
       a new type.

     

       457
       457
       +
       

     

       458
       458
       +
       The only required parameter is `name`.

     

       459
       459
       +
       

     

       460
       460
       +
       `name`

     

       461
       461
       +
       

     

       462
       462
       +
       :   A string representation of the type function name.

     

       463
       463
       +
       

     

       464
       464
       +
       `definition`

     

       465
       465
       +
       

     

       466
       466
       +
       :   Description of the type used in documentation. Give information of

     

       467
       467
       +
           the type and any of its arguments.

     

       468
       468
       +
       

     

       469
       469
       +
       `check`

     

       470
       470
       +
       

     

       471
       471
       +
       :   A function to type check the definition value. Takes the definition

     

       472
       472
       +
           value as a parameter and returns a boolean indicating the type check

     

       473
       473
       +
           result, `true` for success and `false` for failure.

     

       474
       474
       +
       

     

       475
       475
       +
       `merge`

     

       476
       476
       +
       

     

       477
       477
       +
       :   A function to merge multiple definitions values. Takes two

     

       478
       478
       +
           parameters:

     

       479
       479
       +
       

     

       480
       480
       +
           *`loc`*

     

       481
       481
       +
       

     

       482
       482
       +
           :   The option path as a list of strings, e.g. `["boot" "loader

     

       483
       483
       +
                        "grub" "enable"]`.

     

       484
       484
       +
       

     

       485
       485
       +
           *`defs`*

     

       486
       486
       +
       

     

       487
       487
       +
           :   The list of sets of defined `value` and `file` where the value

     

       488
       488
       +
               was defined, e.g. `[ {

     

       489
       489
       +
                        file = "/foo.nix"; value = 1; } { file = "/bar.nix"; value = 2 }

     

       490
       490
       +
                        ]`. The `merge` function should return the merged value

     

       491
       491
       +
               or throw an error in case the values are impossible or not meant

     

       492
       492
       +
               to be merged.

     

       493
       493
       +
       

     

       494
       494
       +
       `getSubOptions`

     

       495
       495
       +
       

     

       496
       496
       +
       :   For composed types that can take a submodule as type parameter, this

     

       497
       497
       +
           function generate sub-options documentation. It takes the current

     

       498
       498
       +
           option prefix as a list and return the set of sub-options. Usually

     

       499
       499
       +
           defined in a recursive manner by adding a term to the prefix, e.g.

     

       500
       500
       +
           `prefix:

     

       501
       501
       +
                 elemType.getSubOptions (prefix ++

     

       502
       502
       +
                 ["prefix"])` where *`"prefix"`* is the newly added prefix.

     

       503
       503
       +
       

     

       504
       504
       +
       `getSubModules`

     

       505
       505
       +
       

     

       506
       506
       +
       :   For composed types that can take a submodule as type parameter, this

     

       507
       507
       +
           function should return the type parameters submodules. If the type

     

       508
       508
       +
           parameter is called `elemType`, the function should just recursively

     

       509
       509
       +
           look into submodules by returning `elemType.getSubModules;`.

     

       510
       510
       +
       

     

       511
       511
       +
       `substSubModules`

     

       512
       512
       +
       

     

       513
       513
       +
       :   For composed types that can take a submodule as type parameter, this

     

       514
       514
       +
           function can be used to substitute the parameter of a submodule

     

       515
       515
       +
           type. It takes a module as parameter and return the type with the

     

       516
       516
       +
           submodule options substituted. It is usually defined as a type

     

       517
       517
       +
           function call with a recursive call to `substSubModules`, e.g for a

     

       518
       518
       +
           type `composedType` that take an `elemtype` type parameter, this

     

       519
       519
       +
           function should be defined as `m:

     

       520
       520
       +
                 composedType (elemType.substSubModules m)`.

     

       521
       521
       +
       

     

       522
       522
       +
       `typeMerge`

     

       523
       523
       +
       

     

       524
       524
       +
       :   A function to merge multiple type declarations. Takes the type to

     

       525
       525
       +
           merge `functor` as parameter. A `null` return value means that type

     

       526
       526
       +
           cannot be merged.

     

       527
       527
       +
       

     

       528
       528
       +
           *`f`*

     

       529
       529
       +
       

     

       530
       530
       +
           :   The type to merge `functor`.

     

       531
       531
       +
       

     

       532
       532
       +
           Note: There is a generic `defaultTypeMerge` that work with most of

     

       533
       533
       +
           value and composed types.

     

       534
       534
       +
       

     

       535
       535
       +
       `functor`

     

       536
       536
       +
       

     

       537
       537
       +
       :   An attribute set representing the type. It is used for type

     

       538
       538
       +
           operations and has the following keys:

     

       539
       539
       +
       

     

       540
       540
       +
           `type`

     

       541
       541
       +
       

     

       542
       542
       +
           :   The type function.

     

       543
       543
       +
       

     

       544
       544
       +
           `wrapped`

     

       545
       545
       +
       

     

       546
       546
       +
           :   Holds the type parameter for composed types.

     

       547
       547
       +
       

     

       548
       548
       +
           `payload`

     

       549
       549
       +
       

     

       550
       550
       +
           :   Holds the value parameter for value types. The types that have a

     

       551
       551
       +
               `payload` are the `enum`, `separatedString` and `submodule`

     

       552
       552
       +
               types.

     

       553
       553
       +
       

     

       554
       554
       +
           `binOp`

     

       555
       555
       +
       

     

       556
       556
       +
           :   A binary operation that can merge the payloads of two same

     

       557
       557
       +
               types. Defined as a function that take two payloads as

     

       558
       558
       +
               parameters and return the payloads merged.

-914

nixos/doc/manual/development/option-types.xml

···

       1
       1
       -
       <section xmlns="http://docbook.org/ns/docbook"

     

       2
       2
       -
               xmlns:xlink="http://www.w3.org/1999/xlink"

     

       3
       3
       -
               xmlns:xi="http://www.w3.org/2001/XInclude"

     

       4
       4
       -
               version="5.0"

     

       5
       5
       -
               xml:id="sec-option-types">

     

       6
       6
       -
        <title>Options Types</title>

     

       7
       7
       -
       

     

       8
       8
       -
        <para>

     

       9
       9
       -
         Option types are a way to put constraints on the values a module option can

     

       10
       10
       -
         take. Types are also responsible of how values are merged in case of multiple

     

       11
       11
       -
         value definitions.

     

       12
       12
       -
        </para>

     

       13
       13
       -
       

     

       14
       14
       -
        <section xml:id="sec-option-types-basic">

     

       15
       15
       -
         <title>Basic Types</title>

     

       16
       16
       -
       

     

       17
       17
       -
         <para>

     

       18
       18
       -
          Basic types are the simplest available types in the module system. Basic

     

       19
       19
       -
          types include multiple string types that mainly differ in how definition

     

       20
       20
       -
          merging is handled.

     

       21
       21
       -
         </para>

     

       22
       22
       -
       

     

       23
       23
       -
         <variablelist>

     

       24
       24
       -
          <varlistentry>

     

       25
       25
       -
           <term>

     

       26
       26
       -
            <varname>types.bool</varname>

     

       27
       27
       -
           </term>

     

       28
       28
       -
           <listitem>

     

       29
       29
       -
            <para>

     

       30
       30
       -
             A boolean, its values can be <literal>true</literal> or

     

       31
       31
       -
             <literal>false</literal>.

     

       32
       32
       -
            </para>

     

       33
       33
       -
           </listitem>

     

       34
       34
       -
          </varlistentry>

     

       35
       35
       -
          <varlistentry>

     

       36
       36
       -
           <term>

     

       37
       37
       -
            <varname>types.path</varname>

     

       38
       38
       -
           </term>

     

       39
       39
       -
           <listitem>

     

       40
       40
       -
            <para>

     

       41
       41
       -
             A filesystem path, defined as anything that when coerced to a string

     

       42
       42
       -
             starts with a slash. Even if derivations can be considered as path, the

     

       43
       43
       -
             more specific <literal>types.package</literal> should be preferred.

     

       44
       44
       -
            </para>

     

       45
       45
       -
           </listitem>

     

       46
       46
       -
          </varlistentry>

     

       47
       47
       -
          <varlistentry>

     

       48
       48
       -
           <term>

     

       49
       49
       -
            <varname>types.package</varname>

     

       50
       50
       -
           </term>

     

       51
       51
       -
           <listitem>

     

       52
       52
       -
            <para>

     

       53
       53
       -
             A derivation or a store path.

     

       54
       54
       -
            </para>

     

       55
       55
       -
           </listitem>

     

       56
       56
       -
          </varlistentry>

     

       57
       57
       -
          <varlistentry>

     

       58
       58
       -
           <term>

     

       59
       59
       -
            <varname>types.anything</varname>

     

       60
       60
       -
           </term>

     

       61
       61
       -
           <listitem>

     

       62
       62
       -
            <para>

     

       63
       63
       -
             A type that accepts any value and recursively merges attribute sets together.

     

       64
       64
       -
             This type is recommended when the option type is unknown.

     

       65
       65
       -
             <example xml:id="ex-types-anything">

     

       66
       66
       -
              <title><literal>types.anything</literal> Example</title>

     

       67
       67
       -
              <para>

     

       68
       68
       -
               Two definitions of this type like

     

       69
       69
       -
       <programlisting>

     

       70
       70
       -
       {

     

       71
       71
       -
         str = lib.mkDefault "foo";

     

       72
       72
       -
         pkg.hello = pkgs.hello;

     

       73
       73
       -
         fun.fun = x: x + 1;

     

       74
       74
       -
       }

     

       75
       75
       -
       </programlisting>

     

       76
       76
       -
       <programlisting>

     

       77
       77
       -
       {

     

       78
       78
       -
         str = lib.mkIf true "bar";

     

       79
       79
       -
         pkg.gcc = pkgs.gcc;

     

       80
       80
       -
         fun.fun = lib.mkForce (x: x + 2);

     

       81
       81
       -
       }

     

       82
       82
       -
       </programlisting>

     

       83
       83
       -
               will get merged to

     

       84
       84
       -
       <programlisting>

     

       85
       85
       -
       {

     

       86
       86
       -
         str = "bar";

     

       87
       87
       -
         pkg.gcc = pkgs.gcc;

     

       88
       88
       -
         pkg.hello = pkgs.hello;

     

       89
       89
       -
         fun.fun = x: x + 2;

     

       90
       90
       -
       }

     

       91
       91
       -
       </programlisting>

     

       92
       92
       -
              </para>

     

       93
       93
       -
             </example>

     

       94
       94
       -
            </para>

     

       95
       95
       -
           </listitem>

     

       96
       96
       -
          </varlistentry>

     

       97
       97
       -
          <varlistentry>

     

       98
       98
       -
           <term>

     

       99
       99
       -
            <varname>types.attrs</varname>

     

       100
       100
       -
           </term>

     

       101
       101
       -
           <listitem>

     

       102
       102
       -
            <para>

     

       103
       103
       -
             A free-form attribute set.

     

       104
       104
       -
             <warning><para>

     

       105
       105
       -
              This type will be deprecated in the future because it doesn't recurse

     

       106
       106
       -
              into attribute sets, silently drops earlier attribute definitions, and

     

       107
       107
       -
              doesn't discharge <literal>lib.mkDefault</literal>, <literal>lib.mkIf

     

       108
       108
       -
              </literal> and co. For allowing arbitrary attribute sets, prefer

     

       109
       109
       -
              <literal>types.attrsOf types.anything</literal> instead which doesn't

     

       110
       110
       -
              have these problems.

     

       111
       111
       -
             </para></warning>

     

       112
       112
       -
            </para>

     

       113
       113
       -
           </listitem>

     

       114
       114
       -
          </varlistentry>

     

       115
       115
       -
         </variablelist>

     

       116
       116
       -
       

     

       117
       117
       -
         <para>

     

       118
       118
       -
          Integer-related types:

     

       119
       119
       -
         </para>

     

       120
       120
       -
       

     

       121
       121
       -
         <variablelist>

     

       122
       122
       -
          <varlistentry>

     

       123
       123
       -
           <term>

     

       124
       124
       -
            <varname>types.int</varname>

     

       125
       125
       -
           </term>

     

       126
       126
       -
           <listitem>

     

       127
       127
       -
            <para>

     

       128
       128
       -
             A signed integer.

     

       129
       129
       -
            </para>

     

       130
       130
       -
           </listitem>

     

       131
       131
       -
          </varlistentry>

     

       132
       132
       -
          <varlistentry>

     

       133
       133
       -
           <term>

     

       134
       134
       -
            <varname>types.ints.{s8, s16, s32}</varname>

     

       135
       135
       -
           </term>

     

       136
       136
       -
           <listitem>

     

       137
       137
       -
            <para>

     

       138
       138
       -
             Signed integers with a fixed length (8, 16 or 32 bits). They go from

     

       139
       139
       -
             <inlineequation><mathphrase>−2<superscript>n</superscript>/2</mathphrase>

     

       140
       140
       -
             </inlineequation> to <inlineequation>

     

       141
       141
       -
             <mathphrase>2<superscript>n</superscript>/2−1</mathphrase>

     

       142
       142
       -
             </inlineequation> respectively (e.g. <literal>−128</literal> to

     

       143
       143
       -
             <literal>127</literal> for 8 bits).

     

       144
       144
       -
            </para>

     

       145
       145
       -
           </listitem>

     

       146
       146
       -
          </varlistentry>

     

       147
       147
       -
          <varlistentry>

     

       148
       148
       -
           <term>

     

       149
       149
       -
            <varname>types.ints.unsigned</varname>

     

       150
       150
       -
           </term>

     

       151
       151
       -
           <listitem>

     

       152
       152
       -
            <para>

     

       153
       153
       -
             An unsigned integer (that is >= 0).

     

       154
       154
       -
            </para>

     

       155
       155
       -
           </listitem>

     

       156
       156
       -
          </varlistentry>

     

       157
       157
       -
          <varlistentry xml:id='types.ints.ux'>

     

       158
       158
       -
           <term>

     

       159
       159
       -
            <varname>types.ints.{u8, u16, u32}</varname>

     

       160
       160
       -
           </term>

     

       161
       161
       -
           <listitem>

     

       162
       162
       -
            <para>

     

       163
       163
       -
             Unsigned integers with a fixed length (8, 16 or 32 bits). They go from

     

       164
       164
       -
             <inlineequation><mathphrase>0</mathphrase></inlineequation> to

     

       165
       165
       -
             <inlineequation>

     

       166
       166
       -
             <mathphrase>2<superscript>n</superscript>−1</mathphrase>

     

       167
       167
       -
             </inlineequation> respectively (e.g. <literal>0</literal> to

     

       168
       168
       -
             <literal>255</literal> for 8 bits).

     

       169
       169
       -
            </para>

     

       170
       170
       -
           </listitem>

     

       171
       171
       -
          </varlistentry>

     

       172
       172
       -
          <varlistentry>

     

       173
       173
       -
           <term>

     

       174
       174
       -
            <varname>types.ints.positive</varname>

     

       175
       175
       -
           </term>

     

       176
       176
       -
           <listitem>

     

       177
       177
       -
            <para>

     

       178
       178
       -
             A positive integer (that is > 0).

     

       179
       179
       -
            </para>

     

       180
       180
       -
           </listitem>

     

       181
       181
       -
          </varlistentry>

     

       182
       182
       -
          <varlistentry>

     

       183
       183
       -
           <term>

     

       184
       184
       -
            <varname>types.port</varname>

     

       185
       185
       -
           </term>

     

       186
       186
       -
           <listitem>

     

       187
       187
       -
            <para>

     

       188
       188
       -
             A port number. This type is an alias to

     

       189
       189
       -
             <link linkend='types.ints.ux'><varname>types.ints.u16</varname></link>.

     

       190
       190
       -
            </para>

     

       191
       191
       -
           </listitem>

     

       192
       192
       -
          </varlistentry>

     

       193
       193
       -
         </variablelist>

     

       194
       194
       -
       

     

       195
       195
       -
         <para>

     

       196
       196
       -
          String-related types:

     

       197
       197
       -
         </para>

     

       198
       198
       -
       

     

       199
       199
       -
         <variablelist>

     

       200
       200
       -
          <varlistentry>

     

       201
       201
       -
           <term>

     

       202
       202
       -
            <varname>types.str</varname>

     

       203
       203
       -
           </term>

     

       204
       204
       -
           <listitem>

     

       205
       205
       -
            <para>

     

       206
       206
       -
             A string. Multiple definitions cannot be merged.

     

       207
       207
       -
            </para>

     

       208
       208
       -
           </listitem>

     

       209
       209
       -
          </varlistentry>

     

       210
       210
       -
          <varlistentry>

     

       211
       211
       -
           <term>

     

       212
       212
       -
            <varname>types.lines</varname>

     

       213
       213
       -
           </term>

     

       214
       214
       -
           <listitem>

     

       215
       215
       -
            <para>

     

       216
       216
       -
             A string. Multiple definitions are concatenated with a new line

     

       217
       217
       -
             <literal>"\n"</literal>.

     

       218
       218
       -
            </para>

     

       219
       219
       -
           </listitem>

     

       220
       220
       -
          </varlistentry>

     

       221
       221
       -
          <varlistentry>

     

       222
       222
       -
           <term>

     

       223
       223
       -
            <varname>types.commas</varname>

     

       224
       224
       -
           </term>

     

       225
       225
       -
           <listitem>

     

       226
       226
       -
            <para>

     

       227
       227
       -
             A string. Multiple definitions are concatenated with a comma

     

       228
       228
       -
             <literal>","</literal>.

     

       229
       229
       -
            </para>

     

       230
       230
       -
           </listitem>

     

       231
       231
       -
          </varlistentry>

     

       232
       232
       -
          <varlistentry>

     

       233
       233
       -
           <term>

     

       234
       234
       -
            <varname>types.envVar</varname>

     

       235
       235
       -
           </term>

     

       236
       236
       -
           <listitem>

     

       237
       237
       -
            <para>

     

       238
       238
       -
             A string. Multiple definitions are concatenated with a collon

     

       239
       239
       -
             <literal>":"</literal>.

     

       240
       240
       -
            </para>

     

       241
       241
       -
           </listitem>

     

       242
       242
       -
          </varlistentry>

     

       243
       243
       -
          <varlistentry>

     

       244
       244
       -
           <term>

     

       245
       245
       -
            <varname>types.strMatching</varname>

     

       246
       246
       -
           </term>

     

       247
       247
       -
           <listitem>

     

       248
       248
       -
            <para>

     

       249
       249
       -
             A string matching a specific regular expression. Multiple definitions

     

       250
       250
       -
             cannot be merged. The regular expression is processed using

     

       251
       251
       -
             <literal>builtins.match</literal>.

     

       252
       252
       -
            </para>

     

       253
       253
       -
           </listitem>

     

       254
       254
       -
          </varlistentry>

     

       255
       255
       -
         </variablelist>

     

       256
       256
       -
        </section>

     

       257
       257
       -
       

     

       258
       258
       -
        <section xml:id="sec-option-types-value">

     

       259
       259
       -
         <title>Value Types</title>

     

       260
       260
       -
       

     

       261
       261
       -
         <para>

     

       262
       262
       -
          Value types are types that take a value parameter.

     

       263
       263
       -
         </para>

     

       264
       264
       -
       

     

       265
       265
       -
         <variablelist>

     

       266
       266
       -
          <varlistentry>

     

       267
       267
       -
           <term>

     

       268
       268
       -
            <varname>types.enum</varname> <replaceable>l</replaceable>

     

       269
       269
       -
           </term>

     

       270
       270
       -
           <listitem>

     

       271
       271
       -
            <para>

     

       272
       272
       -
             One element of the list <replaceable>l</replaceable>, e.g.

     

       273
       273
       -
             <literal>types.enum [ "left" "right" ]</literal>. Multiple definitions

     

       274
       274
       -
             cannot be merged.

     

       275
       275
       -
            </para>

     

       276
       276
       -
           </listitem>

     

       277
       277
       -
          </varlistentry>

     

       278
       278
       -
          <varlistentry>

     

       279
       279
       -
           <term>

     

       280
       280
       -
            <varname>types.separatedString</varname> <replaceable>sep</replaceable>

     

       281
       281
       -
           </term>

     

       282
       282
       -
           <listitem>

     

       283
       283
       -
            <para>

     

       284
       284
       -
             A string with a custom separator <replaceable>sep</replaceable>, e.g.

     

       285
       285
       -
             <literal>types.separatedString "|"</literal>.

     

       286
       286
       -
            </para>

     

       287
       287
       -
           </listitem>

     

       288
       288
       -
          </varlistentry>

     

       289
       289
       -
          <varlistentry>

     

       290
       290
       -
           <term>

     

       291
       291
       -
            <varname>types.ints.between</varname> <replaceable>lowest</replaceable> <replaceable>highest</replaceable>

     

       292
       292
       -
           </term>

     

       293
       293
       -
           <listitem>

     

       294
       294
       -
            <para>

     

       295
       295
       -
             An integer between <replaceable>lowest</replaceable> and

     

       296
       296
       -
             <replaceable>highest</replaceable> (both inclusive). Useful for creating

     

       297
       297
       -
             types like <literal>types.port</literal>.

     

       298
       298
       -
            </para>

     

       299
       299
       -
           </listitem>

     

       300
       300
       -
          </varlistentry>

     

       301
       301
       -
          <varlistentry>

     

       302
       302
       -
           <term>

     

       303
       303
       -
            <varname>types.submodule</varname> <replaceable>o</replaceable>

     

       304
       304
       -
           </term>

     

       305
       305
       -
           <listitem>

     

       306
       306
       -
            <para>

     

       307
       307
       -
             A set of sub options <replaceable>o</replaceable>.

     

       308
       308
       -
             <replaceable>o</replaceable> can be an attribute set, a function

     

       309
       309
       -
             returning an attribute set, or a path to a file containing such a value. Submodules are used in

     

       310
       310
       -
             composed types to create modular options. This is equivalent to

     

       311
       311
       -
             <literal>types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }</literal>.

     

       312
       312
       -
             Submodules are detailed in

     

       313
       313
       -
             <xref

     

       314
       314
       -
                 linkend='section-option-types-submodule' />.

     

       315
       315
       -
            </para>

     

       316
       316
       -
           </listitem>

     

       317
       317
       -
          </varlistentry>

     

       318
       318
       -
          <varlistentry>

     

       319
       319
       -
            <term>

     

       320
       320
       -
              <varname>types.submoduleWith</varname> {

     

       321
       321
       -
               <replaceable>modules</replaceable>,

     

       322
       322
       -
               <replaceable>specialArgs</replaceable> ? {},

     

       323
       323
       -
               <replaceable>shorthandOnlyDefinesConfig</replaceable> ? false }

     

       324
       324
       -
            </term>

     

       325
       325
       -
            <listitem>

     

       326
       326
       -
              <para>

     

       327
       327
       -
                Like <varname>types.submodule</varname>, but more flexible and with better defaults.

     

       328
       328
       -
                It has parameters

     

       329
       329
       -
                <itemizedlist>

     

       330
       330
       -
                  <listitem><para>

     

       331
       331
       -
                    <replaceable>modules</replaceable>

     

       332
       332
       -
                    A list of modules to use by default for this submodule type. This gets combined

     

       333
       333
       -
                    with all option definitions to build the final list of modules that will be included.

     

       334
       334
       -
                    <note><para>

     

       335
       335
       -
                      Only options defined with this argument are included in rendered documentation.

     

       336
       336
       -
                    </para></note>

     

       337
       337
       -
                  </para></listitem>

     

       338
       338
       -
                  <listitem><para>

     

       339
       339
       -
                    <replaceable>specialArgs</replaceable>

     

       340
       340
       -
                    An attribute set of extra arguments to be passed to the module functions.

     

       341
       341
       -
                    The option <literal>_module.args</literal> should be used instead

     

       342
       342
       -
                    for most arguments since it allows overriding. <replaceable>specialArgs</replaceable> should only be

     

       343
       343
       -
                    used for arguments that can&apos;t go through the module fixed-point, because of

     

       344
       344
       -
                    infinite recursion or other problems. An example is overriding the

     

       345
       345
       -
                    <varname>lib</varname> argument, because <varname>lib</varname> itself is used

     

       346
       346
       -
                    to define <literal>_module.args</literal>, which makes using

     

       347
       347
       -
                    <literal>_module.args</literal> to define it impossible.

     

       348
       348
       -
                  </para></listitem>

     

       349
       349
       -
                  <listitem><para>

     

       350
       350
       -
                    <replaceable>shorthandOnlyDefinesConfig</replaceable>

     

       351
       351
       -
                    Whether definitions of this type should default to the <literal>config</literal>

     

       352
       352
       -
                    section of a module (see <xref linkend='ex-module-syntax'/>) if it is an attribute

     

       353
       353
       -
                    set. Enabling this only has a benefit when the submodule defines an option named

     

       354
       354
       -
                    <literal>config</literal> or <literal>options</literal>. In such a case it would

     

       355
       355
       -
                    allow the option to be set with <literal>the-submodule.config = "value"</literal>

     

       356
       356
       -
                    instead of requiring <literal>the-submodule.config.config = "value"</literal>.

     

       357
       357
       -
                    This is because only when modules <emphasis>don&apos;t</emphasis> set the

     

       358
       358
       -
                    <literal>config</literal> or <literal>options</literal> keys, all keys are interpreted

     

       359
       359
       -
                    as option definitions in the <literal>config</literal> section. Enabling this option

     

       360
       360
       -
                    implicitly puts all attributes in the <literal>config</literal> section.

     

       361
       361
       -
                  </para>

     

       362
       362
       -
                  <para>

     

       363
       363
       -
                    With this option enabled, defining a non-<literal>config</literal> section requires

     

       364
       364
       -
                    using a function: <literal>the-submodule = { ... }: { options = { ... }; }</literal>.

     

       365
       365
       -
                  </para></listitem>

     

       366
       366
       -
                </itemizedlist>

     

       367
       367
       -
              </para>

     

       368
       368
       -
            </listitem>

     

       369
       369
       -
          </varlistentry>

     

       370
       370
       -
         </variablelist>

     

       371
       371
       -
        </section>

     

       372
       372
       -
       

     

       373
       373
       -
        <section xml:id="sec-option-types-composed">

     

       374
       374
       -
         <title>Composed Types</title>

     

       375
       375
       -
       

     

       376
       376
       -
         <para>

     

       377
       377
       -
          Composed types are types that take a type as parameter. <literal>listOf

     

       378
       378
       -
          int</literal> and <literal>either int str</literal> are examples of composed

     

       379
       379
       -
          types.

     

       380
       380
       -
         </para>

     

       381
       381
       -
       

     

       382
       382
       -
         <variablelist>

     

       383
       383
       -
          <varlistentry>

     

       384
       384
       -
           <term>

     

       385
       385
       -
            <varname>types.listOf</varname> <replaceable>t</replaceable>

     

       386
       386
       -
           </term>

     

       387
       387
       -
           <listitem>

     

       388
       388
       -
            <para>

     

       389
       389
       -
             A list of <replaceable>t</replaceable> type, e.g. <literal>types.listOf

     

       390
       390
       -
             int</literal>. Multiple definitions are merged with list concatenation.

     

       391
       391
       -
            </para>

     

       392
       392
       -
           </listitem>

     

       393
       393
       -
          </varlistentry>

     

       394
       394
       -
          <varlistentry>

     

       395
       395
       -
           <term>

     

       396
       396
       -
            <varname>types.attrsOf</varname> <replaceable>t</replaceable>

     

       397
       397
       -
           </term>

     

       398
       398
       -
           <listitem>

     

       399
       399
       -
            <para>

     

       400
       400
       -
             An attribute set of where all the values are of

     

       401
       401
       -
             <replaceable>t</replaceable> type. Multiple definitions result in the

     

       402
       402
       -
             joined attribute set.

     

       403
       403
       -
             <note><para>

     

       404
       404
       -
              This type is <emphasis>strict</emphasis> in its values, which in turn

     

       405
       405
       -
              means attributes cannot depend on other attributes. See <varname>

     

       406
       406
       -
              types.lazyAttrsOf</varname> for a lazy version.

     

       407
       407
       -
             </para></note>

     

       408
       408
       -
            </para>

     

       409
       409
       -
           </listitem>

     

       410
       410
       -
          </varlistentry>

     

       411
       411
       -
          <varlistentry>

     

       412
       412
       -
           <term>

     

       413
       413
       -
            <varname>types.lazyAttrsOf</varname> <replaceable>t</replaceable>

     

       414
       414
       -
           </term>

     

       415
       415
       -
           <listitem>

     

       416
       416
       -
            <para>

     

       417
       417
       -
             An attribute set of where all the values are of

     

       418
       418
       -
             <replaceable>t</replaceable> type. Multiple definitions result in the

     

       419
       419
       -
             joined attribute set. This is the lazy version of <varname>types.attrsOf

     

       420
       420
       -
             </varname>, allowing attributes to depend on each other.

     

       421
       421
       -
             <warning><para>

     

       422
       422
       -
              This version does not fully support conditional definitions! With an

     

       423
       423
       -
              option <varname>foo</varname> of this type and a definition

     

       424
       424
       -
              <literal>foo.attr = lib.mkIf false 10</literal>, evaluating

     

       425
       425
       -
              <literal>foo ? attr</literal> will return <literal>true</literal>

     

       426
       426
       -
              even though it should be false. Accessing the value will then throw

     

       427
       427
       -
              an error. For types <replaceable>t</replaceable> that have an

     

       428
       428
       -
              <literal>emptyValue</literal> defined, that value will be returned

     

       429
       429
       -
              instead of throwing an error. So if the type of <literal>foo.attr</literal>

     

       430
       430
       -
              was <literal>lazyAttrsOf (nullOr int)</literal>, <literal>null</literal>

     

       431
       431
       -
              would be returned instead for the same <literal>mkIf false</literal> definition.

     

       432
       432
       -
             </para></warning>

     

       433
       433
       -
            </para>

     

       434
       434
       -
           </listitem>

     

       435
       435
       -
          </varlistentry>

     

       436
       436
       -
          <varlistentry>

     

       437
       437
       -
           <term>

     

       438
       438
       -
            <varname>types.nullOr</varname> <replaceable>t</replaceable>

     

       439
       439
       -
           </term>

     

       440
       440
       -
           <listitem>

     

       441
       441
       -
            <para>

     

       442
       442
       -
             <literal>null</literal> or type <replaceable>t</replaceable>. Multiple

     

       443
       443
       -
             definitions are merged according to type <replaceable>t</replaceable>.

     

       444
       444
       -
            </para>

     

       445
       445
       -
           </listitem>

     

       446
       446
       -
          </varlistentry>

     

       447
       447
       -
          <varlistentry>

     

       448
       448
       -
           <term>

     

       449
       449
       -
            <varname>types.uniq</varname> <replaceable>t</replaceable>

     

       450
       450
       -
           </term>

     

       451
       451
       -
           <listitem>

     

       452
       452
       -
            <para>

     

       453
       453
       -
             Ensures that type <replaceable>t</replaceable> cannot be merged. It is

     

       454
       454
       -
             used to ensure option definitions are declared only once.

     

       455
       455
       -
            </para>

     

       456
       456
       -
           </listitem>

     

       457
       457
       -
          </varlistentry>

     

       458
       458
       -
          <varlistentry>

     

       459
       459
       -
           <term>

     

       460
       460
       -
            <varname>types.either</varname> <replaceable>t1</replaceable> <replaceable>t2</replaceable>

     

       461
       461
       -
           </term>

     

       462
       462
       -
           <listitem>

     

       463
       463
       -
            <para>

     

       464
       464
       -
             Type <replaceable>t1</replaceable> or type <replaceable>t2</replaceable>,

     

       465
       465
       -
             e.g. <literal>with types; either int str</literal>. Multiple definitions

     

       466
       466
       -
             cannot be merged.

     

       467
       467
       -
            </para>

     

       468
       468
       -
           </listitem>

     

       469
       469
       -
          </varlistentry>

     

       470
       470
       -
          <varlistentry>

     

       471
       471
       -
           <term>

     

       472
       472
       -
            <varname>types.oneOf</varname> [ <replaceable>t1</replaceable> <replaceable>t2</replaceable> ... ]

     

       473
       473
       -
           </term>

     

       474
       474
       -
           <listitem>

     

       475
       475
       -
            <para>

     

       476
       476
       -
             Type <replaceable>t1</replaceable> or type <replaceable>t2</replaceable> and so forth,

     

       477
       477
       -
             e.g. <literal>with types; oneOf [ int str bool ]</literal>. Multiple definitions

     

       478
       478
       -
             cannot be merged.

     

       479
       479
       -
            </para>

     

       480
       480
       -
           </listitem>

     

       481
       481
       -
          </varlistentry>

     

       482
       482
       -
          <varlistentry>

     

       483
       483
       -
           <term>

     

       484
       484
       -
            <varname>types.coercedTo</varname> <replaceable>from</replaceable> <replaceable>f</replaceable> <replaceable>to</replaceable>

     

       485
       485
       -
           </term>

     

       486
       486
       -
           <listitem>

     

       487
       487
       -
            <para>

     

       488
       488
       -
             Type <replaceable>to</replaceable> or type

     

       489
       489
       -
             <replaceable>from</replaceable> which will be coerced to type

     

       490
       490
       -
             <replaceable>to</replaceable> using function <replaceable>f</replaceable>

     

       491
       491
       -
             which takes an argument of type <replaceable>from</replaceable> and

     

       492
       492
       -
             return a value of type <replaceable>to</replaceable>. Can be used to

     

       493
       493
       -
             preserve backwards compatibility of an option if its type was changed.

     

       494
       494
       -
            </para>

     

       495
       495
       -
           </listitem>

     

       496
       496
       -
          </varlistentry>

     

       497
       497
       -
         </variablelist>

     

       498
       498
       -
        </section>

     

       499
       499
       -
       

     

       500
       500
       -
        <section xml:id='section-option-types-submodule'>

     

       501
       501
       -
         <title>Submodule</title>

     

       502
       502
       -
       

     

       503
       503
       -
         <para>

     

       504
       504
       -
          <literal>submodule</literal> is a very powerful type that defines a set of

     

       505
       505
       -
          sub-options that are handled like a separate module.

     

       506
       506
       -
         </para>

     

       507
       507
       -
       

     

       508
       508
       -
         <para>

     

       509
       509
       -
          It takes a parameter <replaceable>o</replaceable>, that should be a set, or

     

       510
       510
       -
          a function returning a set with an <literal>options</literal> key defining

     

       511
       511
       -
          the sub-options. Submodule option definitions are type-checked accordingly

     

       512
       512
       -
          to the <literal>options</literal> declarations. Of course, you can nest

     

       513
       513
       -
          submodule option definitons for even higher modularity.

     

       514
       514
       -
         </para>

     

       515
       515
       -
       

     

       516
       516
       -
         <para>

     

       517
       517
       -
          The option set can be defined directly

     

       518
       518
       -
          (<xref linkend='ex-submodule-direct' />) or as reference

     

       519
       519
       -
          (<xref linkend='ex-submodule-reference' />).

     

       520
       520
       -
         </para>

     

       521
       521
       -
       

     

       522
       522
       -
         <example xml:id='ex-submodule-direct'>

     

       523
       523
       -
          <title>Directly defined submodule</title>

     

       524
       524
       -
       <screen>

     

       525
       525
       -
       options.mod = mkOption {

     

       526
       526
       -
         description = "submodule example";

     

       527
       527
       -
         type = with types; submodule {

     

       528
       528
       -
           options = {

     

       529
       529
       -
             foo = mkOption {

     

       530
       530
       -
               type = int;

     

       531
       531
       -
             };

     

       532
       532
       -
             bar = mkOption {

     

       533
       533
       -
               type = str;

     

       534
       534
       -
             };

     

       535
       535
       -
           };

     

       536
       536
       -
         };

     

       537
       537
       -
       };</screen>

     

       538
       538
       -
         </example>

     

       539
       539
       -
       

     

       540
       540
       -
         <example xml:id='ex-submodule-reference'>

     

       541
       541
       -
          <title>Submodule defined as a reference</title>

     

       542
       542
       -
       <screen>

     

       543
       543
       -
       let

     

       544
       544
       -
         modOptions = {

     

       545
       545
       -
           options = {

     

       546
       546
       -
             foo = mkOption {

     

       547
       547
       -
               type = int;

     

       548
       548
       -
             };

     

       549
       549
       -
             bar = mkOption {

     

       550
       550
       -
               type = int;

     

       551
       551
       -
             };

     

       552
       552
       -
           };

     

       553
       553
       -
         };

     

       554
       554
       -
       in

     

       555
       555
       -
       options.mod = mkOption {

     

       556
       556
       -
         description = "submodule example";

     

       557
       557
       -
         type = with types; submodule modOptions;

     

       558
       558
       -
       };</screen>

     

       559
       559
       -
         </example>

     

       560
       560
       -
       

     

       561
       561
       -
         <para>

     

       562
       562
       -
          The <literal>submodule</literal> type is especially interesting when used

     

       563
       563
       -
          with composed types like <literal>attrsOf</literal> or

     

       564
       564
       -
          <literal>listOf</literal>. When composed with <literal>listOf</literal>

     

       565
       565
       -
          (<xref linkend='ex-submodule-listof-declaration' />),

     

       566
       566
       -
          <literal>submodule</literal> allows multiple definitions of the submodule

     

       567
       567
       -
          option set (<xref linkend='ex-submodule-listof-definition' />).

     

       568
       568
       -
         </para>

     

       569
       569
       -
       

     

       570
       570
       -
         <example xml:id='ex-submodule-listof-declaration'>

     

       571
       571
       -
          <title>Declaration of a list of submodules</title>

     

       572
       572
       -
       <screen>

     

       573
       573
       -
       options.mod = mkOption {

     

       574
       574
       -
         description = "submodule example";

     

       575
       575
       -
         type = with types; listOf (submodule {

     

       576
       576
       -
           options = {

     

       577
       577
       -
             foo = mkOption {

     

       578
       578
       -
               type = int;

     

       579
       579
       -
             };

     

       580
       580
       -
             bar = mkOption {

     

       581
       581
       -
               type = str;

     

       582
       582
       -
             };

     

       583
       583
       -
           };

     

       584
       584
       -
         });

     

       585
       585
       -
       };</screen>

     

       586
       586
       -
         </example>

     

       587
       587
       -
       

     

       588
       588
       -
         <example xml:id='ex-submodule-listof-definition'>

     

       589
       589
       -
          <title>Definition of a list of submodules</title>

     

       590
       590
       -
       <screen>

     

       591
       591
       -
       config.mod = [

     

       592
       592
       -
         { foo = 1; bar = "one"; }

     

       593
       593
       -
         { foo = 2; bar = "two"; }

     

       594
       594
       -
       ];</screen>

     

       595
       595
       -
         </example>

     

       596
       596
       -
       

     

       597
       597
       -
         <para>

     

       598
       598
       -
          When composed with <literal>attrsOf</literal>

     

       599
       599
       -
          (<xref linkend='ex-submodule-attrsof-declaration' />),

     

       600
       600
       -
          <literal>submodule</literal> allows multiple named definitions of the

     

       601
       601
       -
          submodule option set (<xref linkend='ex-submodule-attrsof-definition' />).

     

       602
       602
       -
         </para>

     

       603
       603
       -
       

     

       604
       604
       -
         <example xml:id='ex-submodule-attrsof-declaration'>

     

       605
       605
       -
          <title>Declaration of attribute sets of submodules</title>

     

       606
       606
       -
       <screen>

     

       607
       607
       -
       options.mod = mkOption {

     

       608
       608
       -
         description = "submodule example";

     

       609
       609
       -
         type = with types; attrsOf (submodule {

     

       610
       610
       -
           options = {

     

       611
       611
       -
             foo = mkOption {

     

       612
       612
       -
               type = int;

     

       613
       613
       -
             };

     

       614
       614
       -
             bar = mkOption {

     

       615
       615
       -
               type = str;

     

       616
       616
       -
             };

     

       617
       617
       -
           };

     

       618
       618
       -
         });

     

       619
       619
       -
       };</screen>

     

       620
       620
       -
         </example>

     

       621
       621
       -
       

     

       622
       622
       -
         <example xml:id='ex-submodule-attrsof-definition'>

     

       623
       623
       -
          <title>Declaration of attribute sets of submodules</title>

     

       624
       624
       -
       <screen>

     

       625
       625
       -
       config.mod.one = { foo = 1; bar = "one"; };

     

       626
       626
       -
       config.mod.two = { foo = 2; bar = "two"; };</screen>

     

       627
       627
       -
         </example>

     

       628
       628
       -
        </section>

     

       629
       629
       -
       

     

       630
       630
       -
        <section xml:id="sec-option-types-extending">

     

       631
       631
       -
         <title>Extending types</title>

     

       632
       632
       -
       

     

       633
       633
       -
         <para>

     

       634
       634
       -
          Types are mainly characterized by their <literal>check</literal> and

     

       635
       635
       -
          <literal>merge</literal> functions.

     

       636
       636
       -
         </para>

     

       637
       637
       -
       

     

       638
       638
       -
         <variablelist>

     

       639
       639
       -
          <varlistentry>

     

       640
       640
       -
           <term>

     

       641
       641
       -
            <varname>check</varname>

     

       642
       642
       -
           </term>

     

       643
       643
       -
           <listitem>

     

       644
       644
       -
            <para>

     

       645
       645
       -
             The function to type check the value. Takes a value as parameter and

     

       646
       646
       -
             return a boolean. It is possible to extend a type check with the

     

       647
       647
       -
             <literal>addCheck</literal> function

     

       648
       648
       -
             (<xref

     

       649
       649
       -
                 linkend='ex-extending-type-check-1' />), or to fully

     

       650
       650
       -
             override the check function

     

       651
       651
       -
             (<xref linkend='ex-extending-type-check-2' />).

     

       652
       652
       -
            </para>

     

       653
       653
       -
            <example xml:id='ex-extending-type-check-1'>

     

       654
       654
       -
             <title>Adding a type check</title>

     

       655
       655
       -
       <screen>

     

       656
       656
       -
       byte = mkOption {

     

       657
       657
       -
         description = "An integer between 0 and 255.";

     

       658
       658
       -
         type = types.addCheck types.int (x: x &gt;= 0 &amp;&amp; x &lt;= 255);

     

       659
       659
       -
       };</screen>

     

       660
       660
       -
            </example>

     

       661
       661
       -
            <example xml:id='ex-extending-type-check-2'>

     

       662
       662
       -
             <title>Overriding a type check</title>

     

       663
       663
       -
       <screen>

     

       664
       664
       -
       nixThings = mkOption {

     

       665
       665
       -
         description = "words that start with 'nix'";

     

       666
       666
       -
         type = types.str // {

     

       667
       667
       -
           check = (x: lib.hasPrefix "nix" x)

     

       668
       668
       -
         };

     

       669
       669
       -
       };</screen>

     

       670
       670
       -
            </example>

     

       671
       671
       -
           </listitem>

     

       672
       672
       -
          </varlistentry>

     

       673
       673
       -
          <varlistentry>

     

       674
       674
       -
           <term>

     

       675
       675
       -
            <varname>merge</varname>

     

       676
       676
       -
           </term>

     

       677
       677
       -
           <listitem>

     

       678
       678
       -
            <para>

     

       679
       679
       -
             Function to merge the options values when multiple values are set. The

     

       680
       680
       -
             function takes two parameters, <literal>loc</literal> the option path as

     

       681
       681
       -
             a list of strings, and <literal>defs</literal> the list of defined values

     

       682
       682
       -
             as a list. It is possible to override a type merge function for custom

     

       683
       683
       -
             needs.

     

       684
       684
       -
            </para>

     

       685
       685
       -
           </listitem>

     

       686
       686
       -
          </varlistentry>

     

       687
       687
       -
         </variablelist>

     

       688
       688
       -
        </section>

     

       689
       689
       -
       

     

       690
       690
       -
        <section xml:id="sec-option-types-custom">

     

       691
       691
       -
         <title>Custom Types</title>

     

       692
       692
       -
       

     

       693
       693
       -
         <para>

     

       694
       694
       -
          Custom types can be created with the <literal>mkOptionType</literal>

     

       695
       695
       -
          function. As type creation includes some more complex topics such as

     

       696
       696
       -
          submodule handling, it is recommended to get familiar with

     

       697
       697
       -
          <filename

     

       698
       698
       -
         xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/types.nix">types.nix</filename>

     

       699
       699
       -
          code before creating a new type.

     

       700
       700
       -
         </para>

     

       701
       701
       -
       

     

       702
       702
       -
         <para>

     

       703
       703
       -
          The only required parameter is <literal>name</literal>.

     

       704
       704
       -
         </para>

     

       705
       705
       -
       

     

       706
       706
       -
         <variablelist>

     

       707
       707
       -
          <varlistentry>

     

       708
       708
       -
           <term>

     

       709
       709
       -
            <varname>name</varname>

     

       710
       710
       -
           </term>

     

       711
       711
       -
           <listitem>

     

       712
       712
       -
            <para>

     

       713
       713
       -
             A string representation of the type function name.

     

       714
       714
       -
            </para>

     

       715
       715
       -
           </listitem>

     

       716
       716
       -
          </varlistentry>

     

       717
       717
       -
          <varlistentry>

     

       718
       718
       -
           <term>

     

       719
       719
       -
            <varname>definition</varname>

     

       720
       720
       -
           </term>

     

       721
       721
       -
           <listitem>

     

       722
       722
       -
            <para>

     

       723
       723
       -
             Description of the type used in documentation. Give information of the

     

       724
       724
       -
             type and any of its arguments.

     

       725
       725
       -
            </para>

     

       726
       726
       -
           </listitem>

     

       727
       727
       -
          </varlistentry>

     

       728
       728
       -
          <varlistentry>

     

       729
       729
       -
           <term>

     

       730
       730
       -
            <varname>check</varname>

     

       731
       731
       -
           </term>

     

       732
       732
       -
           <listitem>

     

       733
       733
       -
            <para>

     

       734
       734
       -
             A function to type check the definition value. Takes the definition value

     

       735
       735
       -
             as a parameter and returns a boolean indicating the type check result,

     

       736
       736
       -
             <literal>true</literal> for success and <literal>false</literal> for

     

       737
       737
       -
             failure.

     

       738
       738
       -
            </para>

     

       739
       739
       -
           </listitem>

     

       740
       740
       -
          </varlistentry>

     

       741
       741
       -
          <varlistentry>

     

       742
       742
       -
           <term>

     

       743
       743
       -
            <varname>merge</varname>

     

       744
       744
       -
           </term>

     

       745
       745
       -
           <listitem>

     

       746
       746
       -
            <para>

     

       747
       747
       -
             A function to merge multiple definitions values. Takes two parameters:

     

       748
       748
       -
            </para>

     

       749
       749
       -
            <variablelist>

     

       750
       750
       -
             <varlistentry>

     

       751
       751
       -
              <term>

     

       752
       752
       -
               <replaceable>loc</replaceable>

     

       753
       753
       -
              </term>

     

       754
       754
       -
              <listitem>

     

       755
       755
       -
               <para>

     

       756
       756
       -
                The option path as a list of strings, e.g. <literal>["boot" "loader

     

       757
       757
       -
                "grub" "enable"]</literal>.

     

       758
       758
       -
               </para>

     

       759
       759
       -
              </listitem>

     

       760
       760
       -
             </varlistentry>

     

       761
       761
       -
             <varlistentry>

     

       762
       762
       -
              <term>

     

       763
       763
       -
               <replaceable>defs</replaceable>

     

       764
       764
       -
              </term>

     

       765
       765
       -
              <listitem>

     

       766
       766
       -
               <para>

     

       767
       767
       -
                The list of sets of defined <literal>value</literal> and

     

       768
       768
       -
                <literal>file</literal> where the value was defined, e.g. <literal>[ {

     

       769
       769
       -
                file = "/foo.nix"; value = 1; } { file = "/bar.nix"; value = 2 }

     

       770
       770
       -
                ]</literal>. The <literal>merge</literal> function should return the

     

       771
       771
       -
                merged value or throw an error in case the values are impossible or

     

       772
       772
       -
                not meant to be merged.

     

       773
       773
       -
               </para>

     

       774
       774
       -
              </listitem>

     

       775
       775
       -
             </varlistentry>

     

       776
       776
       -
            </variablelist>

     

       777
       777
       -
           </listitem>

     

       778
       778
       -
          </varlistentry>

     

       779
       779
       -
          <varlistentry>

     

       780
       780
       -
           <term>

     

       781
       781
       -
            <varname>getSubOptions</varname>

     

       782
       782
       -
           </term>

     

       783
       783
       -
           <listitem>

     

       784
       784
       -
            <para>

     

       785
       785
       -
             For composed types that can take a submodule as type parameter, this

     

       786
       786
       -
             function generate sub-options documentation. It takes the current option

     

       787
       787
       -
             prefix as a list and return the set of sub-options. Usually defined in a

     

       788
       788
       -
             recursive manner by adding a term to the prefix, e.g. <literal>prefix:

     

       789
       789
       -
             elemType.getSubOptions (prefix ++

     

       790
       790
       -
             [<replaceable>"prefix"</replaceable>])</literal> where

     

       791
       791
       -
             <replaceable>"prefix"</replaceable> is the newly added prefix.

     

       792
       792
       -
            </para>

     

       793
       793
       -
           </listitem>

     

       794
       794
       -
          </varlistentry>

     

       795
       795
       -
          <varlistentry>

     

       796
       796
       -
           <term>

     

       797
       797
       -
            <varname>getSubModules</varname>

     

       798
       798
       -
           </term>

     

       799
       799
       -
           <listitem>

     

       800
       800
       -
            <para>

     

       801
       801
       -
             For composed types that can take a submodule as type parameter, this

     

       802
       802
       -
             function should return the type parameters submodules. If the type

     

       803
       803
       -
             parameter is called <literal>elemType</literal>, the function should just

     

       804
       804
       -
             recursively look into submodules by returning

     

       805
       805
       -
             <literal>elemType.getSubModules;</literal>.

     

       806
       806
       -
            </para>

     

       807
       807
       -
           </listitem>

     

       808
       808
       -
          </varlistentry>

     

       809
       809
       -
          <varlistentry>

     

       810
       810
       -
           <term>

     

       811
       811
       -
            <varname>substSubModules</varname>

     

       812
       812
       -
           </term>

     

       813
       813
       -
           <listitem>

     

       814
       814
       -
            <para>

     

       815
       815
       -
             For composed types that can take a submodule as type parameter, this

     

       816
       816
       -
             function can be used to substitute the parameter of a submodule type. It

     

       817
       817
       -
             takes a module as parameter and return the type with the submodule

     

       818
       818
       -
             options substituted. It is usually defined as a type function call with a

     

       819
       819
       -
             recursive call to <literal>substSubModules</literal>, e.g for a type

     

       820
       820
       -
             <literal>composedType</literal> that take an <literal>elemtype</literal>

     

       821
       821
       -
             type parameter, this function should be defined as <literal>m:

     

       822
       822
       -
             composedType (elemType.substSubModules m)</literal>.

     

       823
       823
       -
            </para>

     

       824
       824
       -
           </listitem>

     

       825
       825
       -
          </varlistentry>

     

       826
       826
       -
          <varlistentry>

     

       827
       827
       -
           <term>

     

       828
       828
       -
            <varname>typeMerge</varname>

     

       829
       829
       -
           </term>

     

       830
       830
       -
           <listitem>

     

       831
       831
       -
            <para>

     

       832
       832
       -
             A function to merge multiple type declarations. Takes the type to merge

     

       833
       833
       -
             <literal>functor</literal> as parameter. A <literal>null</literal> return

     

       834
       834
       -
             value means that type cannot be merged.

     

       835
       835
       -
            </para>

     

       836
       836
       -
            <variablelist>

     

       837
       837
       -
             <varlistentry>

     

       838
       838
       -
              <term>

     

       839
       839
       -
               <replaceable>f</replaceable>

     

       840
       840
       -
              </term>

     

       841
       841
       -
              <listitem>

     

       842
       842
       -
               <para>

     

       843
       843
       -
                The type to merge <literal>functor</literal>.

     

       844
       844
       -
               </para>

     

       845
       845
       -
              </listitem>

     

       846
       846
       -
             </varlistentry>

     

       847
       847
       -
            </variablelist>

     

       848
       848
       -
            <para>

     

       849
       849
       -
             Note: There is a generic <literal>defaultTypeMerge</literal> that work

     

       850
       850
       -
             with most of value and composed types.

     

       851
       851
       -
            </para>

     

       852
       852
       -
           </listitem>

     

       853
       853
       -
          </varlistentry>

     

       854
       854
       -
          <varlistentry>

     

       855
       855
       -
           <term>

     

       856
       856
       -
            <varname>functor</varname>

     

       857
       857
       -
           </term>

     

       858
       858
       -
           <listitem>

     

       859
       859
       -
            <para>

     

       860
       860
       -
             An attribute set representing the type. It is used for type operations

     

       861
       861
       -
             and has the following keys:

     

       862
       862
       -
            </para>

     

       863
       863
       -
            <variablelist>

     

       864
       864
       -
             <varlistentry>

     

       865
       865
       -
              <term>

     

       866
       866
       -
               <varname>type</varname>

     

       867
       867
       -
              </term>

     

       868
       868
       -
              <listitem>

     

       869
       869
       -
               <para>

     

       870
       870
       -
                The type function.

     

       871
       871
       -
               </para>

     

       872
       872
       -
              </listitem>

     

       873
       873
       -
             </varlistentry>

     

       874
       874
       -
             <varlistentry>

     

       875
       875
       -
              <term>

     

       876
       876
       -
               <varname>wrapped</varname>

     

       877
       877
       -
              </term>

     

       878
       878
       -
              <listitem>

     

       879
       879
       -
               <para>

     

       880
       880
       -
                Holds the type parameter for composed types.

     

       881
       881
       -
               </para>

     

       882
       882
       -
              </listitem>

     

       883
       883
       -
             </varlistentry>

     

       884
       884
       -
             <varlistentry>

     

       885
       885
       -
              <term>

     

       886
       886
       -
               <varname>payload</varname>

     

       887
       887
       -
              </term>

     

       888
       888
       -
              <listitem>

     

       889
       889
       -
               <para>

     

       890
       890
       -
                Holds the value parameter for value types. The types that have a

     

       891
       891
       -
                <literal>payload</literal> are the <literal>enum</literal>,

     

       892
       892
       -
                <literal>separatedString</literal> and <literal>submodule</literal>

     

       893
       893
       -
                types.

     

       894
       894
       -
               </para>

     

       895
       895
       -
              </listitem>

     

       896
       896
       -
             </varlistentry>

     

       897
       897
       -
             <varlistentry>

     

       898
       898
       -
              <term>

     

       899
       899
       -
               <varname>binOp</varname>

     

       900
       900
       -
              </term>

     

       901
       901
       -
              <listitem>

     

       902
       902
       -
               <para>

     

       903
       903
       -
                A binary operation that can merge the payloads of two same types.

     

       904
       904
       -
                Defined as a function that take two payloads as parameters and return

     

       905
       905
       -
                the payloads merged.

     

       906
       906
       -
               </para>

     

       907
       907
       -
              </listitem>

     

       908
       908
       -
             </varlistentry>

     

       909
       909
       -
            </variablelist>

     

       910
       910
       -
           </listitem>

     

       911
       911
       -
          </varlistentry>

     

       912
       912
       -
         </variablelist>

     

       913
       913
       -
        </section>

     

       914
       914
       -
       </section>

+64

nixos/doc/manual/development/replace-modules.section.md

···

       1
       1
       +
       # Replace Modules {#sec-replace-modules}

     

       2
       2
       +
       

     

       3
       3
       +
       Modules that are imported can also be disabled. The option declarations,

     

       4
       4
       +
       config implementation and the imports of a disabled module will be

     

       5
       5
       +
       ignored, allowing another to take it\'s place. This can be used to

     

       6
       6
       +
       import a set of modules from another channel while keeping the rest of

     

       7
       7
       +
       the system on a stable release.

     

       8
       8
       +
       

     

       9
       9
       +
       `disabledModules` is a top level attribute like `imports`, `options` and

     

       10
       10
       +
       `config`. It contains a list of modules that will be disabled. This can

     

       11
       11
       +
       either be the full path to the module or a string with the filename

     

       12
       12
       +
       relative to the modules path (eg. \<nixpkgs/nixos/modules> for nixos).

     

       13
       13
       +
       

     

       14
       14
       +
       This example will replace the existing postgresql module with the

     

       15
       15
       +
       version defined in the nixos-unstable channel while keeping the rest of

     

       16
       16
       +
       the modules and packages from the original nixos channel. This only

     

       17
       17
       +
       overrides the module definition, this won\'t use postgresql from

     

       18
       18
       +
       nixos-unstable unless explicitly configured to do so.

     

       19
       19
       +
       

     

       20
       20
       +
       ```nix

     

       21
       21
       +
       { config, lib, pkgs, ... }:

     

       22
       22
       +
       

     

       23
       23
       +
       {

     

       24
       24
       +
         disabledModules = [ "services/databases/postgresql.nix" ];

     

       25
       25
       +
       

     

       26
       26
       +
         imports =

     

       27
       27
       +
           [ # Use postgresql service from nixos-unstable channel.

     

       28
       28
       +
             # sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos-unstable

     

       29
       29
       +
             <nixos-unstable/nixos/modules/services/databases/postgresql.nix>

     

       30
       30
       +
           ];

     

       31
       31
       +
       

     

       32
       32
       +
         services.postgresql.enable = true;

     

       33
       33
       +
       }

     

       34
       34
       +
       ```

     

       35
       35
       +
       

     

       36
       36
       +
       This example shows how to define a custom module as a replacement for an

     

       37
       37
       +
       existing module. Importing this module will disable the original module

     

       38
       38
       +
       without having to know it\'s implementation details.

     

       39
       39
       +
       

     

       40
       40
       +
       ```nix

     

       41
       41
       +
       { config, lib, pkgs, ... }:

     

       42
       42
       +
       

     

       43
       43
       +
       with lib;

     

       44
       44
       +
       

     

       45
       45
       +
       let

     

       46
       46
       +
         cfg = config.programs.man;

     

       47
       47
       +
       in

     

       48
       48
       +
       

     

       49
       49
       +
       {

     

       50
       50
       +
         disabledModules = [ "services/programs/man.nix" ];

     

       51
       51
       +
       

     

       52
       52
       +
         options = {

     

       53
       53
       +
           programs.man.enable = mkOption {

     

       54
       54
       +
             type = types.bool;

     

       55
       55
       +
             default = true;

     

       56
       56
       +
             description = "Whether to enable manual pages.";

     

       57
       57
       +
           };

     

       58
       58
       +
         };

     

       59
       59
       +
       

     

       60
       60
       +
         config = mkIf cfg.enabled {

     

       61
       61
       +
           warnings = [ "disabled manpages for production deployments." ];

     

       62
       62
       +
         };

     

       63
       63
       +
       }

     

       64
       64
       +
       ```

-79

nixos/doc/manual/development/replace-modules.xml

···

       1
       1
       -
       <section xmlns="http://docbook.org/ns/docbook"

     

       2
       2
       -
               xmlns:xlink="http://www.w3.org/1999/xlink"

     

       3
       3
       -
               xmlns:xi="http://www.w3.org/2001/XInclude"

     

       4
       4
       -
               version="5.0"

     

       5
       5
       -
               xml:id="sec-replace-modules">

     

       6
       6
       -
        <title>Replace Modules</title>

     

       7
       7
       -
       

     

       8
       8
       -
        <para>

     

       9
       9
       -
         Modules that are imported can also be disabled. The option declarations,

     

       10
       10
       -
         config implementation and the imports of a disabled module will be ignored, allowing another

     

       11
       11
       -
         to take it's place. This can be used to import a set of modules from another

     

       12
       12
       -
         channel while keeping the rest of the system on a stable release.

     

       13
       13
       -
        </para>

     

       14
       14
       -
       

     

       15
       15
       -
        <para>

     

       16
       16
       -
         <literal>disabledModules</literal> is a top level attribute like

     

       17
       17
       -
         <literal>imports</literal>, <literal>options</literal> and

     

       18
       18
       -
         <literal>config</literal>. It contains a list of modules that will be

     

       19
       19
       -
         disabled. This can either be the full path to the module or a string with the

     

       20
       20
       -
         filename relative to the modules path (eg. &lt;nixpkgs/nixos/modules&gt; for

     

       21
       21
       -
         nixos).

     

       22
       22
       -
        </para>

     

       23
       23
       -
       

     

       24
       24
       -
        <para>

     

       25
       25
       -
         This example will replace the existing postgresql module with the version

     

       26
       26
       -
         defined in the nixos-unstable channel while keeping the rest of the modules

     

       27
       27
       -
         and packages from the original nixos channel. This only overrides the module

     

       28
       28
       -
         definition, this won't use postgresql from nixos-unstable unless explicitly

     

       29
       29
       -
         configured to do so.

     

       30
       30
       -
        </para>

     

       31
       31
       -
       

     

       32
       32
       -
       <programlisting>

     

       33
       33
       -
       { config, lib, pkgs, ... }:

     

       34
       34
       -
       

     

       35
       35
       -
       {

     

       36
       36
       -
         disabledModules = [ "services/databases/postgresql.nix" ];

     

       37
       37
       -
       

     

       38
       38
       -
         imports =

     

       39
       39
       -
           [ # Use postgresql service from nixos-unstable channel.

     

       40
       40
       -
             # sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos-unstable

     

       41
       41
       -
             &lt;nixos-unstable/nixos/modules/services/databases/postgresql.nix&gt;

     

       42
       42
       -
           ];

     

       43
       43
       -
       

     

       44
       44
       -
         services.postgresql.enable = true;

     

       45
       45
       -
       }

     

       46
       46
       -
       </programlisting>

     

       47
       47
       -
       

     

       48
       48
       -
        <para>

     

       49
       49
       -
         This example shows how to define a custom module as a replacement for an

     

       50
       50
       -
         existing module. Importing this module will disable the original module

     

       51
       51
       -
         without having to know it's implementation details.

     

       52
       52
       -
        </para>

     

       53
       53
       -
       

     

       54
       54
       -
       <programlisting>

     

       55
       55
       -
       { config, lib, pkgs, ... }:

     

       56
       56
       -
       

     

       57
       57
       -
       with lib;

     

       58
       58
       -
       

     

       59
       59
       -
       let

     

       60
       60
       -
         cfg = config.programs.man;

     

       61
       61
       -
       in

     

       62
       62
       -
       

     

       63
       63
       -
       {

     

       64
       64
       -
         disabledModules = [ "services/programs/man.nix" ];

     

       65
       65
       -
       

     

       66
       66
       -
         options = {

     

       67
       67
       -
           programs.man.enable = mkOption {

     

       68
       68
       -
             type = types.bool;

     

       69
       69
       -
             default = true;

     

       70
       70
       -
             description = "Whether to enable manual pages.";

     

       71
       71
       -
           };

     

       72
       72
       -
         };

     

       73
       73
       -
       

     

       74
       74
       -
         config = mkIf cfg.enabled {

     

       75
       75
       -
           warnings = [ "disabled manpages for production deployments." ];

     

       76
       76
       -
         };

     

       77
       77
       -
       }

     

       78
       78
       -
       </programlisting>

     

       79
       79
       -
       </section>

+192

nixos/doc/manual/development/settings-options.section.md

···

       1
       1
       +
       # Options for Program Settings {#sec-settings-options}

     

       2
       2
       +
       

     

       3
       3
       +
       Many programs have configuration files where program-specific settings

     

       4
       4
       +
       can be declared. File formats can be separated into two categories:

     

       5
       5
       +
       

     

       6
       6
       +
       -   Nix-representable ones: These can trivially be mapped to a subset of

     

       7
       7
       +
           Nix syntax. E.g. JSON is an example, since its values like

     

       8
       8
       +
           `{"foo":{"bar":10}}` can be mapped directly to Nix:

     

       9
       9
       +
           `{ foo = { bar = 10; }; }`. Other examples are INI, YAML and TOML.

     

       10
       10
       +
           The following section explains the convention for these settings.

     

       11
       11
       +
       

     

       12
       12
       +
       -   Non-nix-representable ones: These can\'t be trivially mapped to a

     

       13
       13
       +
           subset of Nix syntax. Most generic programming languages are in this

     

       14
       14
       +
           group, e.g. bash, since the statement `if true; then echo hi; fi`

     

       15
       15
       +
           doesn\'t have a trivial representation in Nix.

     

       16
       16
       +
       

     

       17
       17
       +
           Currently there are no fixed conventions for these, but it is common

     

       18
       18
       +
           to have a `configFile` option for setting the configuration file

     

       19
       19
       +
           path directly. The default value of `configFile` can be an

     

       20
       20
       +
           auto-generated file, with convenient options for controlling the

     

       21
       21
       +
           contents. For example an option of type `attrsOf str` can be used

     

       22
       22
       +
           for representing environment variables which generates a section

     

       23
       23
       +
           like `export FOO="foo"`. Often it can also be useful to also include

     

       24
       24
       +
           an `extraConfig` option of type `lines` to allow arbitrary text

     

       25
       25
       +
           after the autogenerated part of the file.

     

       26
       26
       +
       

     

       27
       27
       +
       ## Nix-representable Formats (JSON, YAML, TOML, INI, \...) {#sec-settings-nix-representable}

     

       28
       28
       +
       

     

       29
       29
       +
       By convention, formats like this are handled with a generic `settings`

     

       30
       30
       +
       option, representing the full program configuration as a Nix value. The

     

       31
       31
       +
       type of this option should represent the format. The most common formats

     

       32
       32
       +
       have a predefined type and string generator already declared under

     

       33
       33
       +
       `pkgs.formats`:

     

       34
       34
       +
       

     

       35
       35
       +
       `pkgs.formats.json` { }

     

       36
       36
       +
       

     

       37
       37
       +
       :   A function taking an empty attribute set (for future extensibility)

     

       38
       38
       +
           and returning a set with JSON-specific attributes `type` and

     

       39
       39
       +
           `generate` as specified [below](#pkgs-formats-result).

     

       40
       40
       +
       

     

       41
       41
       +
       `pkgs.formats.yaml` { }

     

       42
       42
       +
       

     

       43
       43
       +
       :   A function taking an empty attribute set (for future extensibility)

     

       44
       44
       +
           and returning a set with YAML-specific attributes `type` and

     

       45
       45
       +
           `generate` as specified [below](#pkgs-formats-result).

     

       46
       46
       +
       

     

       47
       47
       +
       `pkgs.formats.ini` { *`listsAsDuplicateKeys`* ? false, *`listToValue`* ? null, \... }

     

       48
       48
       +
       

     

       49
       49
       +
       :   A function taking an attribute set with values

     

       50
       50
       +
       

     

       51
       51
       +
           `listsAsDuplicateKeys`

     

       52
       52
       +
       

     

       53
       53
       +
           :   A boolean for controlling whether list values can be used to

     

       54
       54
       +
               represent duplicate INI keys

     

       55
       55
       +
       

     

       56
       56
       +
           `listToValue`

     

       57
       57
       +
       

     

       58
       58
       +
           :   A function for turning a list of values into a single value.

     

       59
       59
       +
       

     

       60
       60
       +
           It returns a set with INI-specific attributes `type` and `generate`

     

       61
       61
       +
           as specified [below](#pkgs-formats-result).

     

       62
       62
       +
       

     

       63
       63
       +
       `pkgs.formats.toml` { }

     

       64
       64
       +
       

     

       65
       65
       +
       :   A function taking an empty attribute set (for future extensibility)

     

       66
       66
       +
           and returning a set with TOML-specific attributes `type` and

     

       67
       67
       +
           `generate` as specified [below](#pkgs-formats-result).

     

       68
       68
       +
       

     

       69
       69
       +
       ::: {#pkgs-formats-result}

     

       70
       70
       +
       These functions all return an attribute set with these values:

     

       71
       71
       +
       :::

     

       72
       72
       +
       

     

       73
       73
       +
       `type`

     

       74
       74
       +
       

     

       75
       75
       +
       :   A module system type representing a value of the format

     

       76
       76
       +
       

     

       77
       77
       +
       `generate` *`filename jsonValue`*

     

       78
       78
       +
       

     

       79
       79
       +
       :   A function that can render a value of the format to a file. Returns

     

       80
       80
       +
           a file path.

     

       81
       81
       +
       

     

       82
       82
       +
           ::: {.note}

     

       83
       83
       +
           This function puts the value contents in the Nix store. So this

     

       84
       84
       +
           should be avoided for secrets.

     

       85
       85
       +
           :::

     

       86
       86
       +
       

     

       87
       87
       +
       ::: {#ex-settings-nix-representable .example}

     

       88
       88
       +
       ::: {.title}

     

       89
       89
       +
       **Example: Module with conventional `settings` option**

     

       90
       90
       +
       :::

     

       91
       91
       +
       The following shows a module for an example program that uses a JSON

     

       92
       92
       +
       configuration file. It demonstrates how above values can be used, along

     

       93
       93
       +
       with some other related best practices. See the comments for

     

       94
       94
       +
       explanations.

     

       95
       95
       +
       

     

       96
       96
       +
       ```nix

     

       97
       97
       +
       { options, config, lib, pkgs, ... }:

     

       98
       98
       +
       let

     

       99
       99
       +
         cfg = config.services.foo;

     

       100
       100
       +
         # Define the settings format used for this program

     

       101
       101
       +
         settingsFormat = pkgs.formats.json {};

     

       102
       102
       +
       in {

     

       103
       103
       +
       

     

       104
       104
       +
         options.services.foo = {

     

       105
       105
       +
           enable = lib.mkEnableOption "foo service";

     

       106
       106
       +
       

     

       107
       107
       +
           settings = lib.mkOption {

     

       108
       108
       +
             # Setting this type allows for correct merging behavior

     

       109
       109
       +
             type = settingsFormat.type;

     

       110
       110
       +
             default = {};

     

       111
       111
       +
             description = ''

     

       112
       112
       +
               Configuration for foo, see

     

       113
       113
       +
               <link xlink:href="https://example.com/docs/foo"/>

     

       114
       114
       +
               for supported settings.

     

       115
       115
       +
             '';

     

       116
       116
       +
           };

     

       117
       117
       +
         };

     

       118
       118
       +
       

     

       119
       119
       +
         config = lib.mkIf cfg.enable {

     

       120
       120
       +
           # We can assign some default settings here to make the service work by just

     

       121
       121
       +
           # enabling it. We use `mkDefault` for values that can be changed without

     

       122
       122
       +
           # problems

     

       123
       123
       +
           services.foo.settings = {

     

       124
       124
       +
             # Fails at runtime without any value set

     

       125
       125
       +
             log_level = lib.mkDefault "WARN";

     

       126
       126
       +
       

     

       127
       127
       +
             # We assume systemd's `StateDirectory` is used, so we require this value,

     

       128
       128
       +
             # therefore no mkDefault

     

       129
       129
       +
             data_path = "/var/lib/foo";

     

       130
       130
       +
       

     

       131
       131
       +
             # Since we use this to create a user we need to know the default value at

     

       132
       132
       +
             # eval time

     

       133
       133
       +
             user = lib.mkDefault "foo";

     

       134
       134
       +
           };

     

       135
       135
       +
       

     

       136
       136
       +
           environment.etc."foo.json".source =

     

       137
       137
       +
             # The formats generator function takes a filename and the Nix value

     

       138
       138
       +
             # representing the format value and produces a filepath with that value

     

       139
       139
       +
             # rendered in the format

     

       140
       140
       +
             settingsFormat.generate "foo-config.json" cfg.settings;

     

       141
       141
       +
       

     

       142
       142
       +
           # We know that the `user` attribute exists because we set a default value

     

       143
       143
       +
           # for it above, allowing us to use it without worries here

     

       144
       144
       +
           users.users.${cfg.settings.user} = { isSystemUser = true; };

     

       145
       145
       +
       

     

       146
       146
       +
           # ...

     

       147
       147
       +
         };

     

       148
       148
       +
       }

     

       149
       149
       +
       ```

     

       150
       150
       +
       :::

     

       151
       151
       +
       

     

       152
       152
       +
       ### Option declarations for attributes {#sec-settings-attrs-options}

     

       153
       153
       +
       

     

       154
       154
       +
       Some `settings` attributes may deserve some extra care. They may need a

     

       155
       155
       +
       different type, default or merging behavior, or they are essential

     

       156
       156
       +
       options that should show their documentation in the manual. This can be

     

       157
       157
       +
       done using [](#sec-freeform-modules).

     

       158
       158
       +
       

     

       159
       159
       +
       We extend above example using freeform modules to declare an option for

     

       160
       160
       +
       the port, which will enforce it to be a valid integer and make it show

     

       161
       161
       +
       up in the manual.

     

       162
       162
       +
       

     

       163
       163
       +
       ::: {#ex-settings-typed-attrs .example}

     

       164
       164
       +
       ::: {.title}

     

       165
       165
       +
       **Example: Declaring a type-checked `settings` attribute**

     

       166
       166
       +
       :::

     

       167
       167
       +
       ```nix

     

       168
       168
       +
       settings = lib.mkOption {

     

       169
       169
       +
         type = lib.types.submodule {

     

       170
       170
       +
       

     

       171
       171
       +
           freeformType = settingsFormat.type;

     

       172
       172
       +
       

     

       173
       173
       +
           # Declare an option for the port such that the type is checked and this option

     

       174
       174
       +
           # is shown in the manual.

     

       175
       175
       +
           options.port = lib.mkOption {

     

       176
       176
       +
             type = lib.types.port;

     

       177
       177
       +
             default = 8080;

     

       178
       178
       +
             description = ''

     

       179
       179
       +
               Which port this service should listen on.

     

       180
       180
       +
             '';

     

       181
       181
       +
           };

     

       182
       182
       +
       

     

       183
       183
       +
         };

     

       184
       184
       +
         default = {};

     

       185
       185
       +
         description = ''

     

       186
       186
       +
           Configuration for Foo, see

     

       187
       187
       +
           <link xlink:href="https://example.com/docs/foo"/>

     

       188
       188
       +
           for supported values.

     

       189
       189
       +
         '';

     

       190
       190
       +
       };

     

       191
       191
       +
       ```

     

       192
       192
       +
       :::

-226

nixos/doc/manual/development/settings-options.xml

···

       1
       1
       -
       <section xmlns="http://docbook.org/ns/docbook"

     

       2
       2
       -
               xmlns:xlink="http://www.w3.org/1999/xlink"

     

       3
       3
       -
               xmlns:xi="http://www.w3.org/2001/XInclude"

     

       4
       4
       -
               version="5.0"

     

       5
       5
       -
               xml:id="sec-settings-options">

     

       6
       6
       -
        <title>Options for Program Settings</title>

     

       7
       7
       -
       

     

       8
       8
       -
        <para>

     

       9
       9
       -
          Many programs have configuration files where program-specific settings can be declared. File formats can be separated into two categories:

     

       10
       10
       -
          <itemizedlist>

     

       11
       11
       -
            <listitem>

     

       12
       12
       -
              <para>

     

       13
       13
       -
                Nix-representable ones: These can trivially be mapped to a subset of Nix syntax. E.g. JSON is an example, since its values like <literal>{"foo":{"bar":10}}</literal> can be mapped directly to Nix: <literal>{ foo = { bar = 10; }; }</literal>. Other examples are INI, YAML and TOML. The following section explains the convention for these settings.

     

       14
       14
       -
              </para>

     

       15
       15
       -
            </listitem>

     

       16
       16
       -
            <listitem>

     

       17
       17
       -
              <para>

     

       18
       18
       -
                Non-nix-representable ones: These can't be trivially mapped to a subset of Nix syntax. Most generic programming languages are in this group, e.g. bash, since the statement <literal>if true; then echo hi; fi</literal> doesn't have a trivial representation in Nix.

     

       19
       19
       -
              </para>

     

       20
       20
       -
              <para>

     

       21
       21
       -
                Currently there are no fixed conventions for these, but it is common to have a <literal>configFile</literal> option for setting the configuration file path directly. The default value of <literal>configFile</literal> can be an auto-generated file, with convenient options for controlling the contents. For example an option of type <literal>attrsOf str</literal> can be used for representing environment variables which generates a section like <literal>export FOO="foo"</literal>. Often it can also be useful to also include an <literal>extraConfig</literal> option of type <literal>lines</literal> to allow arbitrary text after the autogenerated part of the file.

     

       22
       22
       -
              </para>

     

       23
       23
       -
            </listitem>

     

       24
       24
       -
          </itemizedlist>

     

       25
       25
       -
        </para>

     

       26
       26
       -
        <section xml:id="sec-settings-nix-representable">

     

       27
       27
       -
          <title>Nix-representable Formats (JSON, YAML, TOML, INI, ...)</title>

     

       28
       28
       -
          <para>

     

       29
       29
       -
            By convention, formats like this are handled with a generic <literal>settings</literal> option, representing the full program configuration as a Nix value. The type of this option should represent the format. The most common formats have a predefined type and string generator already declared under <literal>pkgs.formats</literal>:

     

       30
       30
       -
            <variablelist>

     

       31
       31
       -
              <varlistentry>

     

       32
       32
       -
                <term>

     

       33
       33
       -
                  <varname>pkgs.formats.json</varname> { }

     

       34
       34
       -
                </term>

     

       35
       35
       -
                <listitem>

     

       36
       36
       -
                  <para>

     

       37
       37
       -
                    A function taking an empty attribute set (for future extensibility) and returning a set with JSON-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.

     

       38
       38
       -
                  </para>

     

       39
       39
       -
                </listitem>

     

       40
       40
       -
              </varlistentry>

     

       41
       41
       -
              <varlistentry>

     

       42
       42
       -
                <term>

     

       43
       43
       -
                  <varname>pkgs.formats.yaml</varname> { }

     

       44
       44
       -
                </term>

     

       45
       45
       -
                <listitem>

     

       46
       46
       -
                  <para>

     

       47
       47
       -
                    A function taking an empty attribute set (for future extensibility) and returning a set with YAML-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.

     

       48
       48
       -
                  </para>

     

       49
       49
       -
                </listitem>

     

       50
       50
       -
              </varlistentry>

     

       51
       51
       -
              <varlistentry>

     

       52
       52
       -
                <term>

     

       53
       53
       -
                  <varname>pkgs.formats.ini</varname> { <replaceable>listsAsDuplicateKeys</replaceable> ? false, <replaceable>listToValue</replaceable> ? null, ... }

     

       54
       54
       -
                </term>

     

       55
       55
       -
                <listitem>

     

       56
       56
       -
                  <para>

     

       57
       57
       -
                    A function taking an attribute set with values

     

       58
       58
       -
                    <variablelist>

     

       59
       59
       -
                      <varlistentry>

     

       60
       60
       -
                        <term>

     

       61
       61
       -
                          <varname>listsAsDuplicateKeys</varname>

     

       62
       62
       -
                        </term>

     

       63
       63
       -
                        <listitem>

     

       64
       64
       -
                          <para>

     

       65
       65
       -
                            A boolean for controlling whether list values can be used to represent duplicate INI keys

     

       66
       66
       -
                          </para>

     

       67
       67
       -
                        </listitem>

     

       68
       68
       -
                      </varlistentry>

     

       69
       69
       -
                      <varlistentry>

     

       70
       70
       -
                        <term>

     

       71
       71
       -
                          <varname>listToValue</varname>

     

       72
       72
       -
                        </term>

     

       73
       73
       -
                        <listitem>

     

       74
       74
       -
                          <para>

     

       75
       75
       -
                            A function for turning a list of values into a single value.

     

       76
       76
       -
                          </para>

     

       77
       77
       -
                        </listitem>

     

       78
       78
       -
                      </varlistentry>

     

       79
       79
       -
                    </variablelist>

     

       80
       80
       -
                   It returns a set with INI-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.

     

       81
       81
       -
                  </para>

     

       82
       82
       -
                </listitem>

     

       83
       83
       -
              </varlistentry>

     

       84
       84
       -
              <varlistentry>

     

       85
       85
       -
                <term>

     

       86
       86
       -
                  <varname>pkgs.formats.toml</varname> { }

     

       87
       87
       -
                </term>

     

       88
       88
       -
                <listitem>

     

       89
       89
       -
                  <para>

     

       90
       90
       -
                    A function taking an empty attribute set (for future extensibility) and returning a set with TOML-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.

     

       91
       91
       -
                  </para>

     

       92
       92
       -
                </listitem>

     

       93
       93
       -
              </varlistentry>

     

       94
       94
       -
            </variablelist>

     

       95
       95
       -
       

     

       96
       96
       -
          </para>

     

       97
       97
       -
          <para xml:id="pkgs-formats-result">

     

       98
       98
       -
            These functions all return an attribute set with these values:

     

       99
       99
       -
           <variablelist>

     

       100
       100
       -
             <varlistentry>

     

       101
       101
       -
               <term>

     

       102
       102
       -
                 <varname>type</varname>

     

       103
       103
       -
               </term>

     

       104
       104
       -
               <listitem>

     

       105
       105
       -
                 <para>

     

       106
       106
       -
                   A module system type representing a value of the format

     

       107
       107
       -
                 </para>

     

       108
       108
       -
               </listitem>

     

       109
       109
       -
             </varlistentry>

     

       110
       110
       -
             <varlistentry>

     

       111
       111
       -
               <term>

     

       112
       112
       -
                 <varname>generate</varname> <replaceable>filename</replaceable> <replaceable>jsonValue</replaceable>

     

       113
       113
       -
               </term>

     

       114
       114
       -
               <listitem>

     

       115
       115
       -
                 <para>

     

       116
       116
       -
                  A function that can render a value of the format to a file. Returns a file path.

     

       117
       117
       -
                  <note>

     

       118
       118
       -
                   <para>

     

       119
       119
       -
                    This function puts the value contents in the Nix store. So this should be avoided for secrets.

     

       120
       120
       -
                   </para>

     

       121
       121
       -
                  </note>

     

       122
       122
       -
                 </para>

     

       123
       123
       -
               </listitem>

     

       124
       124
       -
             </varlistentry>

     

       125
       125
       -
           </variablelist>

     

       126
       126
       -
          </para>

     

       127
       127
       -
          <example xml:id="ex-settings-nix-representable">

     

       128
       128
       -
            <title>Module with conventional <literal>settings</literal> option</title>

     

       129
       129
       -
            <para>

     

       130
       130
       -
              The following shows a module for an example program that uses a JSON configuration file. It demonstrates how above values can be used, along with some other related best practices. See the comments for explanations.

     

       131
       131
       -
            </para>

     

       132
       132
       -
       <programlisting>

     

       133
       133
       -
       { options, config, lib, pkgs, ... }:

     

       134
       134
       -
       let

     

       135
       135
       -
         cfg = config.services.foo;

     

       136
       136
       -
         # Define the settings format used for this program

     

       137
       137
       -
         settingsFormat = pkgs.formats.json {};

     

       138
       138
       -
       in {

     

       139
       139
       -
       

     

       140
       140
       -
         options.services.foo = {

     

       141
       141
       -
           enable = lib.mkEnableOption "foo service";

     

       142
       142
       -
       

     

       143
       143
       -
           settings = lib.mkOption {

     

       144
       144
       -
             # Setting this type allows for correct merging behavior

     

       145
       145
       -
             type = settingsFormat.type;

     

       146
       146
       -
             default = {};

     

       147
       147
       -
             description = ''

     

       148
       148
       -
               Configuration for foo, see

     

       149
       149
       -
               &lt;link xlink:href="https://example.com/docs/foo"/&gt;

     

       150
       150
       -
               for supported settings.

     

       151
       151
       -
             '';

     

       152
       152
       -
           };

     

       153
       153
       -
         };

     

       154
       154
       -
       

     

       155
       155
       -
         config = lib.mkIf cfg.enable {

     

       156
       156
       -
           # We can assign some default settings here to make the service work by just

     

       157
       157
       -
           # enabling it. We use `mkDefault` for values that can be changed without

     

       158
       158
       -
           # problems

     

       159
       159
       -
           services.foo.settings = {

     

       160
       160
       -
             # Fails at runtime without any value set

     

       161
       161
       -
             log_level = lib.mkDefault "WARN";

     

       162
       162
       -
       

     

       163
       163
       -
             # We assume systemd's `StateDirectory` is used, so we require this value,

     

       164
       164
       -
             # therefore no mkDefault

     

       165
       165
       -
             data_path = "/var/lib/foo";

     

       166
       166
       -
       

     

       167
       167
       -
             # Since we use this to create a user we need to know the default value at

     

       168
       168
       -
             # eval time

     

       169
       169
       -
             user = lib.mkDefault "foo";

     

       170
       170
       -
           };

     

       171
       171
       -
       

     

       172
       172
       -
           environment.etc."foo.json".source =

     

       173
       173
       -
             # The formats generator function takes a filename and the Nix value

     

       174
       174
       -
             # representing the format value and produces a filepath with that value

     

       175
       175
       -
             # rendered in the format

     

       176
       176
       -
             settingsFormat.generate "foo-config.json" cfg.settings;

     

       177
       177
       -
       

     

       178
       178
       -
           # We know that the `user` attribute exists because we set a default value

     

       179
       179
       -
           # for it above, allowing us to use it without worries here

     

       180
       180
       -
           users.users.${cfg.settings.user} = { isSystemUser = true; };

     

       181
       181
       -
       

     

       182
       182
       -
           # ...

     

       183
       183
       -
         };

     

       184
       184
       -
       }

     

       185
       185
       -
       </programlisting>

     

       186
       186
       -
          </example>

     

       187
       187
       -
          <section xml:id="sec-settings-attrs-options">

     

       188
       188
       -
           <title>Option declarations for attributes</title>

     

       189
       189
       -
           <para>

     

       190
       190
       -
            Some <literal>settings</literal> attributes may deserve some extra care. They may need a different type, default or merging behavior, or they are essential options that should show their documentation in the manual. This can be done using <xref linkend='sec-freeform-modules'/>.

     

       191
       191
       -
            <example xml:id="ex-settings-typed-attrs">

     

       192
       192
       -
             <title>Declaring a type-checked <literal>settings</literal> attribute</title>

     

       193
       193
       -
             <para>

     

       194
       194
       -
              We extend above example using freeform modules to declare an option for the port, which will enforce it to be a valid integer and make it show up in the manual.

     

       195
       195
       -
             </para>

     

       196
       196
       -
       <programlisting>

     

       197
       197
       -
       settings = lib.mkOption {

     

       198
       198
       -
         type = lib.types.submodule {

     

       199
       199
       -
       

     

       200
       200
       -
           freeformType = settingsFormat.type;

     

       201
       201
       -
       

     

       202
       202
       -
           # Declare an option for the port such that the type is checked and this option

     

       203
       203
       -
           # is shown in the manual.

     

       204
       204
       -
           options.port = lib.mkOption {

     

       205
       205
       -
             type = lib.types.port;

     

       206
       206
       -
             default = 8080;

     

       207
       207
       -
             description = ''

     

       208
       208
       -
               Which port this service should listen on.

     

       209
       209
       -
             '';

     

       210
       210
       -
           };

     

       211
       211
       -
       

     

       212
       212
       -
         };

     

       213
       213
       -
         default = {};

     

       214
       214
       -
         description = ''

     

       215
       215
       -
           Configuration for Foo, see

     

       216
       216
       -
           &lt;link xlink:href="https://example.com/docs/foo"/&gt;

     

       217
       217
       -
           for supported values.

     

       218
       218
       -
         '';

     

       219
       219
       -
       };

     

       220
       220
       -
       </programlisting>

     

       221
       221
       -
            </example>

     

       222
       222
       -
           </para>

     

       223
       223
       -
          </section>

     

       224
       224
       -
        </section>

     

       225
       225
       -
       

     

       226
       226
       -
       </section>

+8 -8

nixos/doc/manual/development/writing-modules.xml

···

       179
       179
        
       }

     

       180
       180
        
       </programlisting>

     

       181
       181
        
        </example>

     

       182
       182
       -
        <xi:include href="option-declarations.xml" />

     

       183
       183
       -
        <xi:include href="option-types.xml" />

     

       184
       184
       -
        <xi:include href="option-def.xml" />

     

       182
       182
       +
        <xi:include href="../from_md/development/option-declarations.section.xml" />

     

       183
       183
       +
        <xi:include href="../from_md/development/option-types.section.xml" />

     

       184
       184
       +
        <xi:include href="../from_md/development/option-def.section.xml" />

     

       185
       185
        
        <xi:include href="../from_md/development/assertions.section.xml" />

     

       186
       186
       -
        <xi:include href="meta-attributes.xml" />

     

       187
       187
       -
        <xi:include href="importing-modules.xml" />

     

       188
       188
       -
        <xi:include href="replace-modules.xml" />

     

       189
       189
       -
        <xi:include href="freeform-modules.xml" />

     

       190
       190
       -
        <xi:include href="settings-options.xml" />

     

       186
       186
       +
        <xi:include href="../from_md/development/meta-attributes.section.xml" />

     

       187
       187
       +
        <xi:include href="../from_md/development/importing-modules.section.xml" />

     

       188
       188
       +
        <xi:include href="../from_md/development/replace-modules.section.xml" />

     

       189
       189
       +
        <xi:include href="../from_md/development/freeform-modules.section.xml" />

     

       190
       190
       +
        <xi:include href="../from_md/development/settings-options.section.xml" />

     

       191
       191
        
       </chapter>

+87

nixos/doc/manual/from_md/development/freeform-modules.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-freeform-modules">

     

       2
       2
       +
         <title>Freeform modules</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Freeform modules allow you to define values for option paths that

     

       5
       5
       +
           have not been declared explicitly. This can be used to add

     

       6
       6
       +
           attribute-specific types to what would otherwise have to be

     

       7
       7
       +
           <literal>attrsOf</literal> options in order to accept all attribute

     

       8
       8
       +
           names.

     

       9
       9
       +
         </para>

     

       10
       10
       +
         <para>

     

       11
       11
       +
           This feature can be enabled by using the attribute

     

       12
       12
       +
           <literal>freeformType</literal> to define a freeform type. By doing

     

       13
       13
       +
           this, all assignments without an associated option will be merged

     

       14
       14
       +
           using the freeform type and combined into the resulting

     

       15
       15
       +
           <literal>config</literal> set. Since this feature nullifies name

     

       16
       16
       +
           checking for entire option trees, it is only recommended for use in

     

       17
       17
       +
           submodules.

     

       18
       18
       +
         </para>

     

       19
       19
       +
         <anchor xml:id="ex-freeform-module" />

     

       20
       20
       +
         <para>

     

       21
       21
       +
           <emphasis role="strong">Example: Freeform submodule</emphasis>

     

       22
       22
       +
         </para>

     

       23
       23
       +
         <para>

     

       24
       24
       +
           The following shows a submodule assigning a freeform type that

     

       25
       25
       +
           allows arbitrary attributes with <literal>str</literal> values below

     

       26
       26
       +
           <literal>settings</literal>, but also declares an option for the

     

       27
       27
       +
           <literal>settings.port</literal> attribute to have it type-checked

     

       28
       28
       +
           and assign a default value. See

     

       29
       29
       +
           <link linkend="ex-settings-typed-attrs">Example: Declaring a

     

       30
       30
       +
           type-checked <literal>settings</literal> attribute</link> for a more

     

       31
       31
       +
           complete example.

     

       32
       32
       +
         </para>

     

       33
       33
       +
         <programlisting language="bash">

     

       34
       34
       +
       { lib, config, ... }: {

     

       35
       35
       +
       

     

       36
       36
       +
         options.settings = lib.mkOption {

     

       37
       37
       +
           type = lib.types.submodule {

     

       38
       38
       +
       

     

       39
       39
       +
             freeformType = with lib.types; attrsOf str;

     

       40
       40
       +
       

     

       41
       41
       +
             # We want this attribute to be checked for the correct type

     

       42
       42
       +
             options.port = lib.mkOption {

     

       43
       43
       +
               type = lib.types.port;

     

       44
       44
       +
               # Declaring the option also allows defining a default value

     

       45
       45
       +
               default = 8080;

     

       46
       46
       +
             };

     

       47
       47
       +
       

     

       48
       48
       +
           };

     

       49
       49
       +
         };

     

       50
       50
       +
       }

     

       51
       51
       +
       </programlisting>

     

       52
       52
       +
         <para>

     

       53
       53
       +
           And the following shows what such a module then allows

     

       54
       54
       +
         </para>

     

       55
       55
       +
         <programlisting language="bash">

     

       56
       56
       +
       {

     

       57
       57
       +
         # Not a declared option, but the freeform type allows this

     

       58
       58
       +
         settings.logLevel = &quot;debug&quot;;

     

       59
       59
       +
       

     

       60
       60
       +
         # Not allowed because the the freeform type only allows strings

     

       61
       61
       +
         # settings.enable = true;

     

       62
       62
       +
       

     

       63
       63
       +
         # Allowed because there is a port option declared

     

       64
       64
       +
         settings.port = 80;

     

       65
       65
       +
       

     

       66
       66
       +
         # Not allowed because the port option doesn't allow strings

     

       67
       67
       +
         # settings.port = &quot;443&quot;;

     

       68
       68
       +
       }

     

       69
       69
       +
       </programlisting>

     

       70
       70
       +
         <note>

     

       71
       71
       +
           <para>

     

       72
       72
       +
             Freeform attributes cannot depend on other attributes of the same

     

       73
       73
       +
             set without infinite recursion:

     

       74
       74
       +
           </para>

     

       75
       75
       +
           <programlisting language="bash">

     

       76
       76
       +
       {

     

       77
       77
       +
         # This throws infinite recursion encountered

     

       78
       78
       +
         settings.logLevel = lib.mkIf (config.settings.port == 80) &quot;debug&quot;;

     

       79
       79
       +
       }

     

       80
       80
       +
       </programlisting>

     

       81
       81
       +
           <para>

     

       82
       82
       +
             To prevent this, declare options for all attributes that need to

     

       83
       83
       +
             depend on others. For above example this means to declare

     

       84
       84
       +
             <literal>logLevel</literal> to be an option.

     

       85
       85
       +
           </para>

     

       86
       86
       +
         </note>

     

       87
       87
       +
       </section>

+47

nixos/doc/manual/from_md/development/importing-modules.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-importing-modules">

     

       2
       2
       +
         <title>Importing Modules</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Sometimes NixOS modules need to be used in configuration but exist

     

       5
       5
       +
           outside of Nixpkgs. These modules can be imported:

     

       6
       6
       +
         </para>

     

       7
       7
       +
         <programlisting language="bash">

     

       8
       8
       +
       { config, lib, pkgs, ... }:

     

       9
       9
       +
       

     

       10
       10
       +
       {

     

       11
       11
       +
         imports =

     

       12
       12
       +
           [ # Use a locally-available module definition in

     

       13
       13
       +
             # ./example-module/default.nix

     

       14
       14
       +
               ./example-module

     

       15
       15
       +
           ];

     

       16
       16
       +
       

     

       17
       17
       +
         services.exampleModule.enable = true;

     

       18
       18
       +
       }

     

       19
       19
       +
       </programlisting>

     

       20
       20
       +
         <para>

     

       21
       21
       +
           The environment variable <literal>NIXOS_EXTRA_MODULE_PATH</literal>

     

       22
       22
       +
           is an absolute path to a NixOS module that is included alongside the

     

       23
       23
       +
           Nixpkgs NixOS modules. Like any NixOS module, this module can import

     

       24
       24
       +
           additional modules:

     

       25
       25
       +
         </para>

     

       26
       26
       +
         <programlisting language="bash">

     

       27
       27
       +
       # ./module-list/default.nix

     

       28
       28
       +
       [

     

       29
       29
       +
         ./example-module1

     

       30
       30
       +
         ./example-module2

     

       31
       31
       +
       ]

     

       32
       32
       +
       </programlisting>

     

       33
       33
       +
         <programlisting language="bash">

     

       34
       34
       +
       # ./extra-module/default.nix

     

       35
       35
       +
       { imports = import ./module-list.nix; }

     

       36
       36
       +
       </programlisting>

     

       37
       37
       +
         <programlisting language="bash">

     

       38
       38
       +
       # NIXOS_EXTRA_MODULE_PATH=/absolute/path/to/extra-module

     

       39
       39
       +
       { config, lib, pkgs, ... }:

     

       40
       40
       +
       

     

       41
       41
       +
       {

     

       42
       42
       +
         # No `imports` needed

     

       43
       43
       +
       

     

       44
       44
       +
         services.exampleModule1.enable = true;

     

       45
       45
       +
       }

     

       46
       46
       +
       </programlisting>

     

       47
       47
       +
       </section>

+55

nixos/doc/manual/from_md/development/meta-attributes.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-meta-attributes">

     

       2
       2
       +
         <title>Meta Attributes</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Like Nix packages, NixOS modules can declare meta-attributes to

     

       5
       5
       +
           provide extra information. Module meta attributes are defined in the

     

       6
       6
       +
           <literal>meta.nix</literal> special module.

     

       7
       7
       +
         </para>

     

       8
       8
       +
         <para>

     

       9
       9
       +
           <literal>meta</literal> is a top level attribute like

     

       10
       10
       +
           <literal>options</literal> and <literal>config</literal>. Available

     

       11
       11
       +
           meta-attributes are <literal>maintainers</literal> and

     

       12
       12
       +
           <literal>doc</literal>.

     

       13
       13
       +
         </para>

     

       14
       14
       +
         <para>

     

       15
       15
       +
           Each of the meta-attributes must be defined at most once per module

     

       16
       16
       +
           file.

     

       17
       17
       +
         </para>

     

       18
       18
       +
         <programlisting language="bash">

     

       19
       19
       +
       { config, lib, pkgs, ... }:

     

       20
       20
       +
       {

     

       21
       21
       +
         options = {

     

       22
       22
       +
           ...

     

       23
       23
       +
         };

     

       24
       24
       +
       

     

       25
       25
       +
         config = {

     

       26
       26
       +
           ...

     

       27
       27
       +
         };

     

       28
       28
       +
       

     

       29
       29
       +
         meta = {

     

       30
       30
       +
           maintainers = with lib.maintainers; [ ericsagnes ];

     

       31
       31
       +
           doc = ./default.xml;

     

       32
       32
       +
         };

     

       33
       33
       +
       }

     

       34
       34
       +
       </programlisting>

     

       35
       35
       +
         <itemizedlist>

     

       36
       36
       +
           <listitem>

     

       37
       37
       +
             <para>

     

       38
       38
       +
               <literal>maintainers</literal> contains a list of the module

     

       39
       39
       +
               maintainers.

     

       40
       40
       +
             </para>

     

       41
       41
       +
           </listitem>

     

       42
       42
       +
           <listitem>

     

       43
       43
       +
             <para>

     

       44
       44
       +
               <literal>doc</literal> points to a valid DocBook file containing

     

       45
       45
       +
               the module documentation. Its contents is automatically added to

     

       46
       46
       +
               <xref linkend="ch-configuration" />. Changes to a module

     

       47
       47
       +
               documentation have to be checked to not break building the NixOS

     

       48
       48
       +
               manual:

     

       49
       49
       +
             </para>

     

       50
       50
       +
             <programlisting>

     

       51
       51
       +
       $ nix-build nixos/release.nix -A manual.x86_64-linux

     

       52
       52
       +
       </programlisting>

     

       53
       53
       +
           </listitem>

     

       54
       54
       +
         </itemizedlist>

     

       55
       55
       +
       </section>

+203

nixos/doc/manual/from_md/development/option-declarations.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-option-declarations">

     

       2
       2
       +
         <title>Option Declarations</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           An option declaration specifies the name, type and description of a

     

       5
       5
       +
           NixOS configuration option. It is invalid to define an option that

     

       6
       6
       +
           hasn’t been declared in any module. An option declaration generally

     

       7
       7
       +
           looks like this:

     

       8
       8
       +
         </para>

     

       9
       9
       +
         <programlisting language="bash">

     

       10
       10
       +
       options = {

     

       11
       11
       +
         name = mkOption {

     

       12
       12
       +
           type = type specification;

     

       13
       13
       +
           default = default value;

     

       14
       14
       +
           example = example value;

     

       15
       15
       +
           description = &quot;Description for use in the NixOS manual.&quot;;

     

       16
       16
       +
         };

     

       17
       17
       +
       };

     

       18
       18
       +
       </programlisting>

     

       19
       19
       +
         <para>

     

       20
       20
       +
           The attribute names within the <literal>name</literal> attribute

     

       21
       21
       +
           path must be camel cased in general but should, as an exception,

     

       22
       22
       +
           match the

     

       23
       23
       +
           <link xlink:href="https://nixos.org/nixpkgs/manual/#sec-package-naming">

     

       24
       24
       +
           package attribute name</link> when referencing a Nixpkgs package.

     

       25
       25
       +
           For example, the option

     

       26
       26
       +
           <literal>services.nix-serve.bindAddress</literal> references the

     

       27
       27
       +
           <literal>nix-serve</literal> Nixpkgs package.

     

       28
       28
       +
         </para>

     

       29
       29
       +
         <para>

     

       30
       30
       +
           The function <literal>mkOption</literal> accepts the following

     

       31
       31
       +
           arguments.

     

       32
       32
       +
         </para>

     

       33
       33
       +
         <variablelist>

     

       34
       34
       +
           <varlistentry>

     

       35
       35
       +
             <term>

     

       36
       36
       +
               <literal>type</literal>

     

       37
       37
       +
             </term>

     

       38
       38
       +
             <listitem>

     

       39
       39
       +
               <para>

     

       40
       40
       +
                 The type of the option (see

     

       41
       41
       +
                 <xref linkend="sec-option-types" />). It may be omitted, but

     

       42
       42
       +
                 that’s not advisable since it may lead to errors that are hard

     

       43
       43
       +
                 to diagnose.

     

       44
       44
       +
               </para>

     

       45
       45
       +
             </listitem>

     

       46
       46
       +
           </varlistentry>

     

       47
       47
       +
           <varlistentry>

     

       48
       48
       +
             <term>

     

       49
       49
       +
               <literal>default</literal>

     

       50
       50
       +
             </term>

     

       51
       51
       +
             <listitem>

     

       52
       52
       +
               <para>

     

       53
       53
       +
                 The default value used if no value is defined by any module. A

     

       54
       54
       +
                 default is not required; but if a default is not given, then

     

       55
       55
       +
                 users of the module will have to define the value of the

     

       56
       56
       +
                 option, otherwise an error will be thrown.

     

       57
       57
       +
               </para>

     

       58
       58
       +
             </listitem>

     

       59
       59
       +
           </varlistentry>

     

       60
       60
       +
           <varlistentry>

     

       61
       61
       +
             <term>

     

       62
       62
       +
               <literal>example</literal>

     

       63
       63
       +
             </term>

     

       64
       64
       +
             <listitem>

     

       65
       65
       +
               <para>

     

       66
       66
       +
                 An example value that will be shown in the NixOS manual.

     

       67
       67
       +
               </para>

     

       68
       68
       +
             </listitem>

     

       69
       69
       +
           </varlistentry>

     

       70
       70
       +
           <varlistentry>

     

       71
       71
       +
             <term>

     

       72
       72
       +
               <literal>description</literal>

     

       73
       73
       +
             </term>

     

       74
       74
       +
             <listitem>

     

       75
       75
       +
               <para>

     

       76
       76
       +
                 A textual description of the option, in DocBook format, that

     

       77
       77
       +
                 will be included in the NixOS manual.

     

       78
       78
       +
               </para>

     

       79
       79
       +
             </listitem>

     

       80
       80
       +
           </varlistentry>

     

       81
       81
       +
         </variablelist>

     

       82
       82
       +
         <section xml:id="sec-option-declarations-eot">

     

       83
       83
       +
           <title>Extensible Option Types</title>

     

       84
       84
       +
           <para>

     

       85
       85
       +
             Extensible option types is a feature that allow to extend certain

     

       86
       86
       +
             types declaration through multiple module files. This feature only

     

       87
       87
       +
             work with a restricted set of types, namely

     

       88
       88
       +
             <literal>enum</literal> and <literal>submodules</literal> and any

     

       89
       89
       +
             composed forms of them.

     

       90
       90
       +
           </para>

     

       91
       91
       +
           <para>

     

       92
       92
       +
             Extensible option types can be used for <literal>enum</literal>

     

       93
       93
       +
             options that affects multiple modules, or as an alternative to

     

       94
       94
       +
             related <literal>enable</literal> options.

     

       95
       95
       +
           </para>

     

       96
       96
       +
           <para>

     

       97
       97
       +
             As an example, we will take the case of display managers. There is

     

       98
       98
       +
             a central display manager module for generic display manager

     

       99
       99
       +
             options and a module file per display manager backend (sddm, gdm

     

       100
       100
       +
             ...).

     

       101
       101
       +
           </para>

     

       102
       102
       +
           <para>

     

       103
       103
       +
             There are two approach to this module structure:

     

       104
       104
       +
           </para>

     

       105
       105
       +
           <itemizedlist>

     

       106
       106
       +
             <listitem>

     

       107
       107
       +
               <para>

     

       108
       108
       +
                 Managing the display managers independently by adding an

     

       109
       109
       +
                 enable option to every display manager module backend. (NixOS)

     

       110
       110
       +
               </para>

     

       111
       111
       +
             </listitem>

     

       112
       112
       +
             <listitem>

     

       113
       113
       +
               <para>

     

       114
       114
       +
                 Managing the display managers in the central module by adding

     

       115
       115
       +
                 an option to select which display manager backend to use.

     

       116
       116
       +
               </para>

     

       117
       117
       +
             </listitem>

     

       118
       118
       +
           </itemizedlist>

     

       119
       119
       +
           <para>

     

       120
       120
       +
             Both approaches have problems.

     

       121
       121
       +
           </para>

     

       122
       122
       +
           <para>

     

       123
       123
       +
             Making backends independent can quickly become hard to manage. For

     

       124
       124
       +
             display managers, there can be only one enabled at a time, but the

     

       125
       125
       +
             type system can not enforce this restriction as there is no

     

       126
       126
       +
             relation between each backend <literal>enable</literal> option. As

     

       127
       127
       +
             a result, this restriction has to be done explicitely by adding

     

       128
       128
       +
             assertions in each display manager backend module.

     

       129
       129
       +
           </para>

     

       130
       130
       +
           <para>

     

       131
       131
       +
             On the other hand, managing the display managers backends in the

     

       132
       132
       +
             central module will require to change the central module option

     

       133
       133
       +
             every time a new backend is added or removed.

     

       134
       134
       +
           </para>

     

       135
       135
       +
           <para>

     

       136
       136
       +
             By using extensible option types, it is possible to create a

     

       137
       137
       +
             placeholder option in the central module

     

       138
       138
       +
             (<link linkend="ex-option-declaration-eot-service">Example:

     

       139
       139
       +
             Extensible type placeholder in the service module</link>), and to

     

       140
       140
       +
             extend it in each backend module

     

       141
       141
       +
             (<link linkend="ex-option-declaration-eot-backend-gdm">Example:

     

       142
       142
       +
             Extending

     

       143
       143
       +
             <literal>services.xserver.displayManager.enable</literal> in the

     

       144
       144
       +
             <literal>gdm</literal> module</link>,

     

       145
       145
       +
             <link linkend="ex-option-declaration-eot-backend-sddm">Example:

     

       146
       146
       +
             Extending

     

       147
       147
       +
             <literal>services.xserver.displayManager.enable</literal> in the

     

       148
       148
       +
             <literal>sddm</literal> module</link>).

     

       149
       149
       +
           </para>

     

       150
       150
       +
           <para>

     

       151
       151
       +
             As a result, <literal>displayManager.enable</literal> option

     

       152
       152
       +
             values can be added without changing the main service module file

     

       153
       153
       +
             and the type system automatically enforce that there can only be a

     

       154
       154
       +
             single display manager enabled.

     

       155
       155
       +
           </para>

     

       156
       156
       +
           <anchor xml:id="ex-option-declaration-eot-service" />

     

       157
       157
       +
           <para>

     

       158
       158
       +
             <emphasis role="strong">Example: Extensible type placeholder in

     

       159
       159
       +
             the service module</emphasis>

     

       160
       160
       +
           </para>

     

       161
       161
       +
           <programlisting language="bash">

     

       162
       162
       +
       services.xserver.displayManager.enable = mkOption {

     

       163
       163
       +
         description = &quot;Display manager to use&quot;;

     

       164
       164
       +
         type = with types; nullOr (enum [ ]);

     

       165
       165
       +
       };

     

       166
       166
       +
       </programlisting>

     

       167
       167
       +
           <anchor xml:id="ex-option-declaration-eot-backend-gdm" />

     

       168
       168
       +
           <para>

     

       169
       169
       +
             <emphasis role="strong">Example: Extending

     

       170
       170
       +
             <literal>services.xserver.displayManager.enable</literal> in the

     

       171
       171
       +
             <literal>gdm</literal> module</emphasis>

     

       172
       172
       +
           </para>

     

       173
       173
       +
           <programlisting language="bash">

     

       174
       174
       +
       services.xserver.displayManager.enable = mkOption {

     

       175
       175
       +
         type = with types; nullOr (enum [ &quot;gdm&quot; ]);

     

       176
       176
       +
       };

     

       177
       177
       +
       </programlisting>

     

       178
       178
       +
           <anchor xml:id="ex-option-declaration-eot-backend-sddm" />

     

       179
       179
       +
           <para>

     

       180
       180
       +
             <emphasis role="strong">Example: Extending

     

       181
       181
       +
             <literal>services.xserver.displayManager.enable</literal> in the

     

       182
       182
       +
             <literal>sddm</literal> module</emphasis>

     

       183
       183
       +
           </para>

     

       184
       184
       +
           <programlisting language="bash">

     

       185
       185
       +
       services.xserver.displayManager.enable = mkOption {

     

       186
       186
       +
         type = with types; nullOr (enum [ &quot;sddm&quot; ]);

     

       187
       187
       +
       };

     

       188
       188
       +
       </programlisting>

     

       189
       189
       +
           <para>

     

       190
       190
       +
             The placeholder declaration is a standard

     

       191
       191
       +
             <literal>mkOption</literal> declaration, but it is important that

     

       192
       192
       +
             extensible option declarations only use the

     

       193
       193
       +
             <literal>type</literal> argument.

     

       194
       194
       +
           </para>

     

       195
       195
       +
           <para>

     

       196
       196
       +
             Extensible option types work with any of the composed variants of

     

       197
       197
       +
             <literal>enum</literal> such as

     

       198
       198
       +
             <literal>with types; nullOr (enum [ &quot;foo&quot; &quot;bar&quot; ])</literal>

     

       199
       199
       +
             or

     

       200
       200
       +
             <literal>with types; listOf (enum [ &quot;foo&quot; &quot;bar&quot; ])</literal>.

     

       201
       201
       +
           </para>

     

       202
       202
       +
         </section>

     

       203
       203
       +
       </section>

+104

nixos/doc/manual/from_md/development/option-def.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-option-definitions">

     

       2
       2
       +
         <title>Option Definitions</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Option definitions are generally straight-forward bindings of values

     

       5
       5
       +
           to option names, like

     

       6
       6
       +
         </para>

     

       7
       7
       +
         <programlisting language="bash">

     

       8
       8
       +
       config = {

     

       9
       9
       +
         services.httpd.enable = true;

     

       10
       10
       +
       };

     

       11
       11
       +
       </programlisting>

     

       12
       12
       +
         <para>

     

       13
       13
       +
           However, sometimes you need to wrap an option definition or set of

     

       14
       14
       +
           option definitions in a <emphasis>property</emphasis> to achieve

     

       15
       15
       +
           certain effects:

     

       16
       16
       +
         </para>

     

       17
       17
       +
         <section xml:id="sec-option-definitions-delaying-conditionals">

     

       18
       18
       +
           <title>Delaying Conditionals</title>

     

       19
       19
       +
           <para>

     

       20
       20
       +
             If a set of option definitions is conditional on the value of

     

       21
       21
       +
             another option, you may need to use <literal>mkIf</literal>.

     

       22
       22
       +
             Consider, for instance:

     

       23
       23
       +
           </para>

     

       24
       24
       +
           <programlisting language="bash">

     

       25
       25
       +
       config = if config.services.httpd.enable then {

     

       26
       26
       +
         environment.systemPackages = [ ... ];

     

       27
       27
       +
         ...

     

       28
       28
       +
       } else {};

     

       29
       29
       +
       </programlisting>

     

       30
       30
       +
           <para>

     

       31
       31
       +
             This definition will cause Nix to fail with an <quote>infinite

     

       32
       32
       +
             recursion</quote> error. Why? Because the value of

     

       33
       33
       +
             <literal>config.services.httpd.enable</literal> depends on the

     

       34
       34
       +
             value being constructed here. After all, you could also write the

     

       35
       35
       +
             clearly circular and contradictory:

     

       36
       36
       +
           </para>

     

       37
       37
       +
           <programlisting language="bash">

     

       38
       38
       +
       config = if config.services.httpd.enable then {

     

       39
       39
       +
         services.httpd.enable = false;

     

       40
       40
       +
       } else {

     

       41
       41
       +
         services.httpd.enable = true;

     

       42
       42
       +
       };

     

       43
       43
       +
       </programlisting>

     

       44
       44
       +
           <para>

     

       45
       45
       +
             The solution is to write:

     

       46
       46
       +
           </para>

     

       47
       47
       +
           <programlisting language="bash">

     

       48
       48
       +
       config = mkIf config.services.httpd.enable {

     

       49
       49
       +
         environment.systemPackages = [ ... ];

     

       50
       50
       +
         ...

     

       51
       51
       +
       };

     

       52
       52
       +
       </programlisting>

     

       53
       53
       +
           <para>

     

       54
       54
       +
             The special function <literal>mkIf</literal> causes the evaluation

     

       55
       55
       +
             of the conditional to be <quote>pushed down</quote> into the

     

       56
       56
       +
             individual definitions, as if you had written:

     

       57
       57
       +
           </para>

     

       58
       58
       +
           <programlisting language="bash">

     

       59
       59
       +
       config = {

     

       60
       60
       +
         environment.systemPackages = if config.services.httpd.enable then [ ... ] else [];

     

       61
       61
       +
         ...

     

       62
       62
       +
       };

     

       63
       63
       +
       </programlisting>

     

       64
       64
       +
         </section>

     

       65
       65
       +
         <section xml:id="sec-option-definitions-setting-priorities">

     

       66
       66
       +
           <title>Setting Priorities</title>

     

       67
       67
       +
           <para>

     

       68
       68
       +
             A module can override the definitions of an option in other

     

       69
       69
       +
             modules by setting a <emphasis>priority</emphasis>. All option

     

       70
       70
       +
             definitions that do not have the lowest priority value are

     

       71
       71
       +
             discarded. By default, option definitions have priority 1000. You

     

       72
       72
       +
             can specify an explicit priority by using

     

       73
       73
       +
             <literal>mkOverride</literal>, e.g.

     

       74
       74
       +
           </para>

     

       75
       75
       +
           <programlisting language="bash">

     

       76
       76
       +
       services.openssh.enable = mkOverride 10 false;

     

       77
       77
       +
       </programlisting>

     

       78
       78
       +
           <para>

     

       79
       79
       +
             This definition causes all other definitions with priorities above

     

       80
       80
       +
             10 to be discarded. The function <literal>mkForce</literal> is

     

       81
       81
       +
             equal to <literal>mkOverride 50</literal>.

     

       82
       82
       +
           </para>

     

       83
       83
       +
         </section>

     

       84
       84
       +
         <section xml:id="sec-option-definitions-merging">

     

       85
       85
       +
           <title>Merging Configurations</title>

     

       86
       86
       +
           <para>

     

       87
       87
       +
             In conjunction with <literal>mkIf</literal>, it is sometimes

     

       88
       88
       +
             useful for a module to return multiple sets of option definitions,

     

       89
       89
       +
             to be merged together as if they were declared in separate

     

       90
       90
       +
             modules. This can be done using <literal>mkMerge</literal>:

     

       91
       91
       +
           </para>

     

       92
       92
       +
           <programlisting language="bash">

     

       93
       93
       +
       config = mkMerge

     

       94
       94
       +
         [ # Unconditional stuff.

     

       95
       95
       +
           { environment.systemPackages = [ ... ];

     

       96
       96
       +
           }

     

       97
       97
       +
           # Conditional stuff.

     

       98
       98
       +
           (mkIf config.services.bla.enable {

     

       99
       99
       +
             environment.systemPackages = [ ... ];

     

       100
       100
       +
           })

     

       101
       101
       +
         ];

     

       102
       102
       +
       </programlisting>

     

       103
       103
       +
         </section>

     

       104
       104
       +
       </section>

+987

nixos/doc/manual/from_md/development/option-types.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-option-types">

     

       2
       2
       +
         <title>Options Types</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Option types are a way to put constraints on the values a module

     

       5
       5
       +
           option can take. Types are also responsible of how values are merged

     

       6
       6
       +
           in case of multiple value definitions.

     

       7
       7
       +
         </para>

     

       8
       8
       +
         <section xml:id="sec-option-types-basic">

     

       9
       9
       +
           <title>Basic Types</title>

     

       10
       10
       +
           <para>

     

       11
       11
       +
             Basic types are the simplest available types in the module system.

     

       12
       12
       +
             Basic types include multiple string types that mainly differ in

     

       13
       13
       +
             how definition merging is handled.

     

       14
       14
       +
           </para>

     

       15
       15
       +
           <variablelist>

     

       16
       16
       +
             <varlistentry>

     

       17
       17
       +
               <term>

     

       18
       18
       +
                 <literal>types.bool</literal>

     

       19
       19
       +
               </term>

     

       20
       20
       +
               <listitem>

     

       21
       21
       +
                 <para>

     

       22
       22
       +
                   A boolean, its values can be <literal>true</literal> or

     

       23
       23
       +
                   <literal>false</literal>.

     

       24
       24
       +
                 </para>

     

       25
       25
       +
               </listitem>

     

       26
       26
       +
             </varlistentry>

     

       27
       27
       +
             <varlistentry>

     

       28
       28
       +
               <term>

     

       29
       29
       +
                 <literal>types.path</literal>

     

       30
       30
       +
               </term>

     

       31
       31
       +
               <listitem>

     

       32
       32
       +
                 <para>

     

       33
       33
       +
                   A filesystem path, defined as anything that when coerced to

     

       34
       34
       +
                   a string starts with a slash. Even if derivations can be

     

       35
       35
       +
                   considered as path, the more specific

     

       36
       36
       +
                   <literal>types.package</literal> should be preferred.

     

       37
       37
       +
                 </para>

     

       38
       38
       +
               </listitem>

     

       39
       39
       +
             </varlistentry>

     

       40
       40
       +
             <varlistentry>

     

       41
       41
       +
               <term>

     

       42
       42
       +
                 <literal>types.package</literal>

     

       43
       43
       +
               </term>

     

       44
       44
       +
               <listitem>

     

       45
       45
       +
                 <para>

     

       46
       46
       +
                   A derivation or a store path.

     

       47
       47
       +
                 </para>

     

       48
       48
       +
               </listitem>

     

       49
       49
       +
             </varlistentry>

     

       50
       50
       +
             <varlistentry>

     

       51
       51
       +
               <term>

     

       52
       52
       +
                 <literal>types.anything</literal>

     

       53
       53
       +
               </term>

     

       54
       54
       +
               <listitem>

     

       55
       55
       +
                 <para>

     

       56
       56
       +
                   A type that accepts any value and recursively merges

     

       57
       57
       +
                   attribute sets together. This type is recommended when the

     

       58
       58
       +
                   option type is unknown.

     

       59
       59
       +
                 </para>

     

       60
       60
       +
                 <anchor xml:id="ex-types-anything" />

     

       61
       61
       +
                 <para>

     

       62
       62
       +
                   <emphasis role="strong">Example:

     

       63
       63
       +
                   <literal>types.anything</literal> Example</emphasis>

     

       64
       64
       +
                 </para>

     

       65
       65
       +
                 <para>

     

       66
       66
       +
                   Two definitions of this type like

     

       67
       67
       +
                 </para>

     

       68
       68
       +
                 <programlisting language="bash">

     

       69
       69
       +
       {

     

       70
       70
       +
         str = lib.mkDefault &quot;foo&quot;;

     

       71
       71
       +
         pkg.hello = pkgs.hello;

     

       72
       72
       +
         fun.fun = x: x + 1;

     

       73
       73
       +
       }

     

       74
       74
       +
       </programlisting>

     

       75
       75
       +
                 <programlisting language="bash">

     

       76
       76
       +
       {

     

       77
       77
       +
         str = lib.mkIf true &quot;bar&quot;;

     

       78
       78
       +
         pkg.gcc = pkgs.gcc;

     

       79
       79
       +
         fun.fun = lib.mkForce (x: x + 2);

     

       80
       80
       +
       }

     

       81
       81
       +
       </programlisting>

     

       82
       82
       +
                 <para>

     

       83
       83
       +
                   will get merged to

     

       84
       84
       +
                 </para>

     

       85
       85
       +
                 <programlisting language="bash">

     

       86
       86
       +
       {

     

       87
       87
       +
         str = &quot;bar&quot;;

     

       88
       88
       +
         pkg.gcc = pkgs.gcc;

     

       89
       89
       +
         pkg.hello = pkgs.hello;

     

       90
       90
       +
         fun.fun = x: x + 2;

     

       91
       91
       +
       }

     

       92
       92
       +
       </programlisting>

     

       93
       93
       +
               </listitem>

     

       94
       94
       +
             </varlistentry>

     

       95
       95
       +
             <varlistentry>

     

       96
       96
       +
               <term>

     

       97
       97
       +
                 <literal>types.attrs</literal>

     

       98
       98
       +
               </term>

     

       99
       99
       +
               <listitem>

     

       100
       100
       +
                 <para>

     

       101
       101
       +
                   A free-form attribute set.

     

       102
       102
       +
                 </para>

     

       103
       103
       +
                 <warning>

     

       104
       104
       +
                   <para>

     

       105
       105
       +
                     This type will be deprecated in the future because it

     

       106
       106
       +
                     doesn't recurse into attribute sets, silently drops

     

       107
       107
       +
                     earlier attribute definitions, and doesn't discharge

     

       108
       108
       +
                     <literal>lib.mkDefault</literal>,

     

       109
       109
       +
                     <literal>lib.mkIf</literal> and co. For allowing arbitrary

     

       110
       110
       +
                     attribute sets, prefer

     

       111
       111
       +
                     <literal>types.attrsOf types.anything</literal> instead

     

       112
       112
       +
                     which doesn't have these problems.

     

       113
       113
       +
                   </para>

     

       114
       114
       +
                 </warning>

     

       115
       115
       +
               </listitem>

     

       116
       116
       +
             </varlistentry>

     

       117
       117
       +
           </variablelist>

     

       118
       118
       +
           <para>

     

       119
       119
       +
             Integer-related types:

     

       120
       120
       +
           </para>

     

       121
       121
       +
           <variablelist>

     

       122
       122
       +
             <varlistentry>

     

       123
       123
       +
               <term>

     

       124
       124
       +
                 <literal>types.int</literal>

     

       125
       125
       +
               </term>

     

       126
       126
       +
               <listitem>

     

       127
       127
       +
                 <para>

     

       128
       128
       +
                   A signed integer.

     

       129
       129
       +
                 </para>

     

       130
       130
       +
               </listitem>

     

       131
       131
       +
             </varlistentry>

     

       132
       132
       +
             <varlistentry>

     

       133
       133
       +
               <term>

     

       134
       134
       +
                 <literal>types.ints.{s8, s16, s32}</literal>

     

       135
       135
       +
               </term>

     

       136
       136
       +
               <listitem>

     

       137
       137
       +
                 <para>

     

       138
       138
       +
                   Signed integers with a fixed length (8, 16 or 32 bits). They

     

       139
       139
       +
                   go from −2^n/2 to 2^n/2−1 respectively (e.g.

     

       140
       140
       +
                   <literal>−128</literal> to <literal>127</literal> for 8

     

       141
       141
       +
                   bits).

     

       142
       142
       +
                 </para>

     

       143
       143
       +
               </listitem>

     

       144
       144
       +
             </varlistentry>

     

       145
       145
       +
             <varlistentry>

     

       146
       146
       +
               <term>

     

       147
       147
       +
                 <literal>types.ints.unsigned</literal>

     

       148
       148
       +
               </term>

     

       149
       149
       +
               <listitem>

     

       150
       150
       +
                 <para>

     

       151
       151
       +
                   An unsigned integer (that is &gt;= 0).

     

       152
       152
       +
                 </para>

     

       153
       153
       +
               </listitem>

     

       154
       154
       +
             </varlistentry>

     

       155
       155
       +
             <varlistentry>

     

       156
       156
       +
               <term>

     

       157
       157
       +
                 <literal>types.ints.{u8, u16, u32}</literal>

     

       158
       158
       +
               </term>

     

       159
       159
       +
               <listitem>

     

       160
       160
       +
                 <para>

     

       161
       161
       +
                   Unsigned integers with a fixed length (8, 16 or 32 bits).

     

       162
       162
       +
                   They go from 0 to 2^n−1 respectively (e.g.

     

       163
       163
       +
                   <literal>0</literal> to <literal>255</literal> for 8 bits).

     

       164
       164
       +
                 </para>

     

       165
       165
       +
               </listitem>

     

       166
       166
       +
             </varlistentry>

     

       167
       167
       +
             <varlistentry>

     

       168
       168
       +
               <term>

     

       169
       169
       +
                 <literal>types.ints.positive</literal>

     

       170
       170
       +
               </term>

     

       171
       171
       +
               <listitem>

     

       172
       172
       +
                 <para>

     

       173
       173
       +
                   A positive integer (that is &gt; 0).

     

       174
       174
       +
                 </para>

     

       175
       175
       +
               </listitem>

     

       176
       176
       +
             </varlistentry>

     

       177
       177
       +
             <varlistentry>

     

       178
       178
       +
               <term>

     

       179
       179
       +
                 <literal>types.port</literal>

     

       180
       180
       +
               </term>

     

       181
       181
       +
               <listitem>

     

       182
       182
       +
                 <para>

     

       183
       183
       +
                   A port number. This type is an alias to

     

       184
       184
       +
                   <literal>types.ints.u16</literal>.

     

       185
       185
       +
                 </para>

     

       186
       186
       +
               </listitem>

     

       187
       187
       +
             </varlistentry>

     

       188
       188
       +
           </variablelist>

     

       189
       189
       +
           <para>

     

       190
       190
       +
             String-related types:

     

       191
       191
       +
           </para>

     

       192
       192
       +
           <variablelist>

     

       193
       193
       +
             <varlistentry>

     

       194
       194
       +
               <term>

     

       195
       195
       +
                 <literal>types.str</literal>

     

       196
       196
       +
               </term>

     

       197
       197
       +
               <listitem>

     

       198
       198
       +
                 <para>

     

       199
       199
       +
                   A string. Multiple definitions cannot be merged.

     

       200
       200
       +
                 </para>

     

       201
       201
       +
               </listitem>

     

       202
       202
       +
             </varlistentry>

     

       203
       203
       +
             <varlistentry>

     

       204
       204
       +
               <term>

     

       205
       205
       +
                 <literal>types.lines</literal>

     

       206
       206
       +
               </term>

     

       207
       207
       +
               <listitem>

     

       208
       208
       +
                 <para>

     

       209
       209
       +
                   A string. Multiple definitions are concatenated with a new

     

       210
       210
       +
                   line <literal>&quot;\n&quot;</literal>.

     

       211
       211
       +
                 </para>

     

       212
       212
       +
               </listitem>

     

       213
       213
       +
             </varlistentry>

     

       214
       214
       +
             <varlistentry>

     

       215
       215
       +
               <term>

     

       216
       216
       +
                 <literal>types.commas</literal>

     

       217
       217
       +
               </term>

     

       218
       218
       +
               <listitem>

     

       219
       219
       +
                 <para>

     

       220
       220
       +
                   A string. Multiple definitions are concatenated with a comma

     

       221
       221
       +
                   <literal>&quot;,&quot;</literal>.

     

       222
       222
       +
                 </para>

     

       223
       223
       +
               </listitem>

     

       224
       224
       +
             </varlistentry>

     

       225
       225
       +
             <varlistentry>

     

       226
       226
       +
               <term>

     

       227
       227
       +
                 <literal>types.envVar</literal>

     

       228
       228
       +
               </term>

     

       229
       229
       +
               <listitem>

     

       230
       230
       +
                 <para>

     

       231
       231
       +
                   A string. Multiple definitions are concatenated with a

     

       232
       232
       +
                   collon <literal>&quot;:&quot;</literal>.

     

       233
       233
       +
                 </para>

     

       234
       234
       +
               </listitem>

     

       235
       235
       +
             </varlistentry>

     

       236
       236
       +
             <varlistentry>

     

       237
       237
       +
               <term>

     

       238
       238
       +
                 <literal>types.strMatching</literal>

     

       239
       239
       +
               </term>

     

       240
       240
       +
               <listitem>

     

       241
       241
       +
                 <para>

     

       242
       242
       +
                   A string matching a specific regular expression. Multiple

     

       243
       243
       +
                   definitions cannot be merged. The regular expression is

     

       244
       244
       +
                   processed using <literal>builtins.match</literal>.

     

       245
       245
       +
                 </para>

     

       246
       246
       +
               </listitem>

     

       247
       247
       +
             </varlistentry>

     

       248
       248
       +
           </variablelist>

     

       249
       249
       +
         </section>

     

       250
       250
       +
         <section xml:id="sec-option-types-value">

     

       251
       251
       +
           <title>Value Types</title>

     

       252
       252
       +
           <para>

     

       253
       253
       +
             Value types are types that take a value parameter.

     

       254
       254
       +
           </para>

     

       255
       255
       +
           <variablelist>

     

       256
       256
       +
             <varlistentry>

     

       257
       257
       +
               <term>

     

       258
       258
       +
                 <literal>types.enum</literal>

     

       259
       259
       +
                 <emphasis><literal>l</literal></emphasis>

     

       260
       260
       +
               </term>

     

       261
       261
       +
               <listitem>

     

       262
       262
       +
                 <para>

     

       263
       263
       +
                   One element of the list

     

       264
       264
       +
                   <emphasis><literal>l</literal></emphasis>, e.g.

     

       265
       265
       +
                   <literal>types.enum [ &quot;left&quot; &quot;right&quot; ]</literal>.

     

       266
       266
       +
                   Multiple definitions cannot be merged.

     

       267
       267
       +
                 </para>

     

       268
       268
       +
               </listitem>

     

       269
       269
       +
             </varlistentry>

     

       270
       270
       +
             <varlistentry>

     

       271
       271
       +
               <term>

     

       272
       272
       +
                 <literal>types.separatedString</literal>

     

       273
       273
       +
                 <emphasis><literal>sep</literal></emphasis>

     

       274
       274
       +
               </term>

     

       275
       275
       +
               <listitem>

     

       276
       276
       +
                 <para>

     

       277
       277
       +
                   A string with a custom separator

     

       278
       278
       +
                   <emphasis><literal>sep</literal></emphasis>, e.g.

     

       279
       279
       +
                   <literal>types.separatedString &quot;|&quot;</literal>.

     

       280
       280
       +
                 </para>

     

       281
       281
       +
               </listitem>

     

       282
       282
       +
             </varlistentry>

     

       283
       283
       +
             <varlistentry>

     

       284
       284
       +
               <term>

     

       285
       285
       +
                 <literal>types.ints.between</literal>

     

       286
       286
       +
                 <emphasis><literal>lowest highest</literal></emphasis>

     

       287
       287
       +
               </term>

     

       288
       288
       +
               <listitem>

     

       289
       289
       +
                 <para>

     

       290
       290
       +
                   An integer between

     

       291
       291
       +
                   <emphasis><literal>lowest</literal></emphasis> and

     

       292
       292
       +
                   <emphasis><literal>highest</literal></emphasis> (both

     

       293
       293
       +
                   inclusive). Useful for creating types like

     

       294
       294
       +
                   <literal>types.port</literal>.

     

       295
       295
       +
                 </para>

     

       296
       296
       +
               </listitem>

     

       297
       297
       +
             </varlistentry>

     

       298
       298
       +
             <varlistentry>

     

       299
       299
       +
               <term>

     

       300
       300
       +
                 <literal>types.submodule</literal>

     

       301
       301
       +
                 <emphasis><literal>o</literal></emphasis>

     

       302
       302
       +
               </term>

     

       303
       303
       +
               <listitem>

     

       304
       304
       +
                 <para>

     

       305
       305
       +
                   A set of sub options

     

       306
       306
       +
                   <emphasis><literal>o</literal></emphasis>.

     

       307
       307
       +
                   <emphasis><literal>o</literal></emphasis> can be an

     

       308
       308
       +
                   attribute set, a function returning an attribute set, or a

     

       309
       309
       +
                   path to a file containing such a value. Submodules are used

     

       310
       310
       +
                   in composed types to create modular options. This is

     

       311
       311
       +
                   equivalent to

     

       312
       312
       +
                   <literal>types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }</literal>.

     

       313
       313
       +
                   Submodules are detailed in

     

       314
       314
       +
                   <link linkend="section-option-types-submodule">Submodule</link>.

     

       315
       315
       +
                 </para>

     

       316
       316
       +
               </listitem>

     

       317
       317
       +
             </varlistentry>

     

       318
       318
       +
             <varlistentry>

     

       319
       319
       +
               <term>

     

       320
       320
       +
                 <literal>types.submoduleWith</literal> {

     

       321
       321
       +
                 <emphasis><literal>modules</literal></emphasis>,

     

       322
       322
       +
                 <emphasis><literal>specialArgs</literal></emphasis> ? {},

     

       323
       323
       +
                 <emphasis><literal>shorthandOnlyDefinesConfig</literal></emphasis>

     

       324
       324
       +
                 ? false }

     

       325
       325
       +
               </term>

     

       326
       326
       +
               <listitem>

     

       327
       327
       +
                 <para>

     

       328
       328
       +
                   Like <literal>types.submodule</literal>, but more flexible

     

       329
       329
       +
                   and with better defaults. It has parameters

     

       330
       330
       +
                 </para>

     

       331
       331
       +
                 <itemizedlist>

     

       332
       332
       +
                   <listitem>

     

       333
       333
       +
                     <para>

     

       334
       334
       +
                       <emphasis><literal>modules</literal></emphasis> A list

     

       335
       335
       +
                       of modules to use by default for this submodule type.

     

       336
       336
       +
                       This gets combined with all option definitions to build

     

       337
       337
       +
                       the final list of modules that will be included.

     

       338
       338
       +
                     </para>

     

       339
       339
       +
                     <note>

     

       340
       340
       +
                       <para>

     

       341
       341
       +
                         Only options defined with this argument are included

     

       342
       342
       +
                         in rendered documentation.

     

       343
       343
       +
                       </para>

     

       344
       344
       +
                     </note>

     

       345
       345
       +
                   </listitem>

     

       346
       346
       +
                   <listitem>

     

       347
       347
       +
                     <para>

     

       348
       348
       +
                       <emphasis><literal>specialArgs</literal></emphasis> An

     

       349
       349
       +
                       attribute set of extra arguments to be passed to the

     

       350
       350
       +
                       module functions. The option

     

       351
       351
       +
                       <literal>_module.args</literal> should be used instead

     

       352
       352
       +
                       for most arguments since it allows overriding.

     

       353
       353
       +
                       <emphasis><literal>specialArgs</literal></emphasis>

     

       354
       354
       +
                       should only be used for arguments that can't go through

     

       355
       355
       +
                       the module fixed-point, because of infinite recursion or

     

       356
       356
       +
                       other problems. An example is overriding the

     

       357
       357
       +
                       <literal>lib</literal> argument, because

     

       358
       358
       +
                       <literal>lib</literal> itself is used to define

     

       359
       359
       +
                       <literal>_module.args</literal>, which makes using

     

       360
       360
       +
                       <literal>_module.args</literal> to define it impossible.

     

       361
       361
       +
                     </para>

     

       362
       362
       +
                   </listitem>

     

       363
       363
       +
                   <listitem>

     

       364
       364
       +
                     <para>

     

       365
       365
       +
                       <emphasis><literal>shorthandOnlyDefinesConfig</literal></emphasis>

     

       366
       366
       +
                       Whether definitions of this type should default to the

     

       367
       367
       +
                       <literal>config</literal> section of a module (see

     

       368
       368
       +
                       <link linkend="ex-module-syntax">Example: Structure of

     

       369
       369
       +
                       NixOS Modules</link>) if it is an attribute set.

     

       370
       370
       +
                       Enabling this only has a benefit when the submodule

     

       371
       371
       +
                       defines an option named <literal>config</literal> or

     

       372
       372
       +
                       <literal>options</literal>. In such a case it would

     

       373
       373
       +
                       allow the option to be set with

     

       374
       374
       +
                       <literal>the-submodule.config = &quot;value&quot;</literal>

     

       375
       375
       +
                       instead of requiring

     

       376
       376
       +
                       <literal>the-submodule.config.config = &quot;value&quot;</literal>.

     

       377
       377
       +
                       This is because only when modules

     

       378
       378
       +
                       <emphasis>don't</emphasis> set the

     

       379
       379
       +
                       <literal>config</literal> or <literal>options</literal>

     

       380
       380
       +
                       keys, all keys are interpreted as option definitions in

     

       381
       381
       +
                       the <literal>config</literal> section. Enabling this

     

       382
       382
       +
                       option implicitly puts all attributes in the

     

       383
       383
       +
                       <literal>config</literal> section.

     

       384
       384
       +
                     </para>

     

       385
       385
       +
                     <para>

     

       386
       386
       +
                       With this option enabled, defining a

     

       387
       387
       +
                       non-<literal>config</literal> section requires using a

     

       388
       388
       +
                       function:

     

       389
       389
       +
                       <literal>the-submodule = { ... }: { options = { ... }; }</literal>.

     

       390
       390
       +
                     </para>

     

       391
       391
       +
                   </listitem>

     

       392
       392
       +
                 </itemizedlist>

     

       393
       393
       +
               </listitem>

     

       394
       394
       +
             </varlistentry>

     

       395
       395
       +
           </variablelist>

     

       396
       396
       +
         </section>

     

       397
       397
       +
         <section xml:id="sec-option-types-composed">

     

       398
       398
       +
           <title>Composed Types</title>

     

       399
       399
       +
           <para>

     

       400
       400
       +
             Composed types are types that take a type as parameter.

     

       401
       401
       +
             <literal>listOf int</literal> and

     

       402
       402
       +
             <literal>either int str</literal> are examples of composed types.

     

       403
       403
       +
           </para>

     

       404
       404
       +
           <variablelist>

     

       405
       405
       +
             <varlistentry>

     

       406
       406
       +
               <term>

     

       407
       407
       +
                 <literal>types.listOf</literal>

     

       408
       408
       +
                 <emphasis><literal>t</literal></emphasis>

     

       409
       409
       +
               </term>

     

       410
       410
       +
               <listitem>

     

       411
       411
       +
                 <para>

     

       412
       412
       +
                   A list of <emphasis><literal>t</literal></emphasis> type,

     

       413
       413
       +
                   e.g. <literal>types.listOf int</literal>. Multiple

     

       414
       414
       +
                   definitions are merged with list concatenation.

     

       415
       415
       +
                 </para>

     

       416
       416
       +
               </listitem>

     

       417
       417
       +
             </varlistentry>

     

       418
       418
       +
             <varlistentry>

     

       419
       419
       +
               <term>

     

       420
       420
       +
                 <literal>types.attrsOf</literal>

     

       421
       421
       +
                 <emphasis><literal>t</literal></emphasis>

     

       422
       422
       +
               </term>

     

       423
       423
       +
               <listitem>

     

       424
       424
       +
                 <para>

     

       425
       425
       +
                   An attribute set of where all the values are of

     

       426
       426
       +
                   <emphasis><literal>t</literal></emphasis> type. Multiple

     

       427
       427
       +
                   definitions result in the joined attribute set.

     

       428
       428
       +
                 </para>

     

       429
       429
       +
                 <note>

     

       430
       430
       +
                   <para>

     

       431
       431
       +
                     This type is <emphasis>strict</emphasis> in its values,

     

       432
       432
       +
                     which in turn means attributes cannot depend on other

     

       433
       433
       +
                     attributes. See <literal> types.lazyAttrsOf</literal> for

     

       434
       434
       +
                     a lazy version.

     

       435
       435
       +
                   </para>

     

       436
       436
       +
                 </note>

     

       437
       437
       +
               </listitem>

     

       438
       438
       +
             </varlistentry>

     

       439
       439
       +
             <varlistentry>

     

       440
       440
       +
               <term>

     

       441
       441
       +
                 <literal>types.lazyAttrsOf</literal>

     

       442
       442
       +
                 <emphasis><literal>t</literal></emphasis>

     

       443
       443
       +
               </term>

     

       444
       444
       +
               <listitem>

     

       445
       445
       +
                 <para>

     

       446
       446
       +
                   An attribute set of where all the values are of

     

       447
       447
       +
                   <emphasis><literal>t</literal></emphasis> type. Multiple

     

       448
       448
       +
                   definitions result in the joined attribute set. This is the

     

       449
       449
       +
                   lazy version of <literal>types.attrsOf </literal>, allowing

     

       450
       450
       +
                   attributes to depend on each other.

     

       451
       451
       +
                 </para>

     

       452
       452
       +
                 <warning>

     

       453
       453
       +
                   <para>

     

       454
       454
       +
                     This version does not fully support conditional

     

       455
       455
       +
                     definitions! With an option <literal>foo</literal> of this

     

       456
       456
       +
                     type and a definition

     

       457
       457
       +
                     <literal>foo.attr = lib.mkIf false 10</literal>,

     

       458
       458
       +
                     evaluating <literal>foo ? attr</literal> will return

     

       459
       459
       +
                     <literal>true</literal> even though it should be false.

     

       460
       460
       +
                     Accessing the value will then throw an error. For types

     

       461
       461
       +
                     <emphasis><literal>t</literal></emphasis> that have an

     

       462
       462
       +
                     <literal>emptyValue</literal> defined, that value will be

     

       463
       463
       +
                     returned instead of throwing an error. So if the type of

     

       464
       464
       +
                     <literal>foo.attr</literal> was

     

       465
       465
       +
                     <literal>lazyAttrsOf (nullOr int)</literal>,

     

       466
       466
       +
                     <literal>null</literal> would be returned instead for the

     

       467
       467
       +
                     same <literal>mkIf false</literal> definition.

     

       468
       468
       +
                   </para>

     

       469
       469
       +
                 </warning>

     

       470
       470
       +
               </listitem>

     

       471
       471
       +
             </varlistentry>

     

       472
       472
       +
             <varlistentry>

     

       473
       473
       +
               <term>

     

       474
       474
       +
                 <literal>types.nullOr</literal>

     

       475
       475
       +
                 <emphasis><literal>t</literal></emphasis>

     

       476
       476
       +
               </term>

     

       477
       477
       +
               <listitem>

     

       478
       478
       +
                 <para>

     

       479
       479
       +
                   <literal>null</literal> or type

     

       480
       480
       +
                   <emphasis><literal>t</literal></emphasis>. Multiple

     

       481
       481
       +
                   definitions are merged according to type

     

       482
       482
       +
                   <emphasis><literal>t</literal></emphasis>.

     

       483
       483
       +
                 </para>

     

       484
       484
       +
               </listitem>

     

       485
       485
       +
             </varlistentry>

     

       486
       486
       +
             <varlistentry>

     

       487
       487
       +
               <term>

     

       488
       488
       +
                 <literal>types.uniq</literal>

     

       489
       489
       +
                 <emphasis><literal>t</literal></emphasis>

     

       490
       490
       +
               </term>

     

       491
       491
       +
               <listitem>

     

       492
       492
       +
                 <para>

     

       493
       493
       +
                   Ensures that type <emphasis><literal>t</literal></emphasis>

     

       494
       494
       +
                   cannot be merged. It is used to ensure option definitions

     

       495
       495
       +
                   are declared only once.

     

       496
       496
       +
                 </para>

     

       497
       497
       +
               </listitem>

     

       498
       498
       +
             </varlistentry>

     

       499
       499
       +
             <varlistentry>

     

       500
       500
       +
               <term>

     

       501
       501
       +
                 <literal>types.either</literal>

     

       502
       502
       +
                 <emphasis><literal>t1 t2</literal></emphasis>

     

       503
       503
       +
               </term>

     

       504
       504
       +
               <listitem>

     

       505
       505
       +
                 <para>

     

       506
       506
       +
                   Type <emphasis><literal>t1</literal></emphasis> or type

     

       507
       507
       +
                   <emphasis><literal>t2</literal></emphasis>, e.g.

     

       508
       508
       +
                   <literal>with types; either int str</literal>. Multiple

     

       509
       509
       +
                   definitions cannot be merged.

     

       510
       510
       +
                 </para>

     

       511
       511
       +
               </listitem>

     

       512
       512
       +
             </varlistentry>

     

       513
       513
       +
             <varlistentry>

     

       514
       514
       +
               <term>

     

       515
       515
       +
                 <literal>types.oneOf</literal> [

     

       516
       516
       +
                 <emphasis><literal>t1 t2</literal></emphasis> ... ]

     

       517
       517
       +
               </term>

     

       518
       518
       +
               <listitem>

     

       519
       519
       +
                 <para>

     

       520
       520
       +
                   Type <emphasis><literal>t1</literal></emphasis> or type

     

       521
       521
       +
                   <emphasis><literal>t2</literal></emphasis> and so forth,

     

       522
       522
       +
                   e.g. <literal>with types; oneOf [ int str bool ]</literal>.

     

       523
       523
       +
                   Multiple definitions cannot be merged.

     

       524
       524
       +
                 </para>

     

       525
       525
       +
               </listitem>

     

       526
       526
       +
             </varlistentry>

     

       527
       527
       +
             <varlistentry>

     

       528
       528
       +
               <term>

     

       529
       529
       +
                 <literal>types.coercedTo</literal>

     

       530
       530
       +
                 <emphasis><literal>from f to</literal></emphasis>

     

       531
       531
       +
               </term>

     

       532
       532
       +
               <listitem>

     

       533
       533
       +
                 <para>

     

       534
       534
       +
                   Type <emphasis><literal>to</literal></emphasis> or type

     

       535
       535
       +
                   <emphasis><literal>from</literal></emphasis> which will be

     

       536
       536
       +
                   coerced to type <emphasis><literal>to</literal></emphasis>

     

       537
       537
       +
                   using function <emphasis><literal>f</literal></emphasis>

     

       538
       538
       +
                   which takes an argument of type

     

       539
       539
       +
                   <emphasis><literal>from</literal></emphasis> and return a

     

       540
       540
       +
                   value of type <emphasis><literal>to</literal></emphasis>.

     

       541
       541
       +
                   Can be used to preserve backwards compatibility of an option

     

       542
       542
       +
                   if its type was changed.

     

       543
       543
       +
                 </para>

     

       544
       544
       +
               </listitem>

     

       545
       545
       +
             </varlistentry>

     

       546
       546
       +
           </variablelist>

     

       547
       547
       +
         </section>

     

       548
       548
       +
         <section xml:id="section-option-types-submodule">

     

       549
       549
       +
           <title>Submodule</title>

     

       550
       550
       +
           <para>

     

       551
       551
       +
             <literal>submodule</literal> is a very powerful type that defines

     

       552
       552
       +
             a set of sub-options that are handled like a separate module.

     

       553
       553
       +
           </para>

     

       554
       554
       +
           <para>

     

       555
       555
       +
             It takes a parameter <emphasis><literal>o</literal></emphasis>,

     

       556
       556
       +
             that should be a set, or a function returning a set with an

     

       557
       557
       +
             <literal>options</literal> key defining the sub-options. Submodule

     

       558
       558
       +
             option definitions are type-checked accordingly to the

     

       559
       559
       +
             <literal>options</literal> declarations. Of course, you can nest

     

       560
       560
       +
             submodule option definitons for even higher modularity.

     

       561
       561
       +
           </para>

     

       562
       562
       +
           <para>

     

       563
       563
       +
             The option set can be defined directly

     

       564
       564
       +
             (<link linkend="ex-submodule-direct">Example: Directly defined

     

       565
       565
       +
             submodule</link>) or as reference

     

       566
       566
       +
             (<link linkend="ex-submodule-reference">Example: Submodule defined

     

       567
       567
       +
             as a reference</link>).

     

       568
       568
       +
           </para>

     

       569
       569
       +
           <anchor xml:id="ex-submodule-direct" />

     

       570
       570
       +
           <para>

     

       571
       571
       +
             <emphasis role="strong">Example: Directly defined

     

       572
       572
       +
             submodule</emphasis>

     

       573
       573
       +
           </para>

     

       574
       574
       +
           <programlisting language="bash">

     

       575
       575
       +
       options.mod = mkOption {

     

       576
       576
       +
         description = &quot;submodule example&quot;;

     

       577
       577
       +
         type = with types; submodule {

     

       578
       578
       +
           options = {

     

       579
       579
       +
             foo = mkOption {

     

       580
       580
       +
               type = int;

     

       581
       581
       +
             };

     

       582
       582
       +
             bar = mkOption {

     

       583
       583
       +
               type = str;

     

       584
       584
       +
             };

     

       585
       585
       +
           };

     

       586
       586
       +
         };

     

       587
       587
       +
       };

     

       588
       588
       +
       </programlisting>

     

       589
       589
       +
           <anchor xml:id="ex-submodule-reference" />

     

       590
       590
       +
           <para>

     

       591
       591
       +
             <emphasis role="strong">Example: Submodule defined as a

     

       592
       592
       +
             reference</emphasis>

     

       593
       593
       +
           </para>

     

       594
       594
       +
           <programlisting language="bash">

     

       595
       595
       +
       let

     

       596
       596
       +
         modOptions = {

     

       597
       597
       +
           options = {

     

       598
       598
       +
             foo = mkOption {

     

       599
       599
       +
               type = int;

     

       600
       600
       +
             };

     

       601
       601
       +
             bar = mkOption {

     

       602
       602
       +
               type = int;

     

       603
       603
       +
             };

     

       604
       604
       +
           };

     

       605
       605
       +
         };

     

       606
       606
       +
       in

     

       607
       607
       +
       options.mod = mkOption {

     

       608
       608
       +
         description = &quot;submodule example&quot;;

     

       609
       609
       +
         type = with types; submodule modOptions;

     

       610
       610
       +
       };

     

       611
       611
       +
       </programlisting>

     

       612
       612
       +
           <para>

     

       613
       613
       +
             The <literal>submodule</literal> type is especially interesting

     

       614
       614
       +
             when used with composed types like <literal>attrsOf</literal> or

     

       615
       615
       +
             <literal>listOf</literal>. When composed with

     

       616
       616
       +
             <literal>listOf</literal>

     

       617
       617
       +
             (<link linkend="ex-submodule-listof-declaration">Example:

     

       618
       618
       +
             Declaration of a list of submodules</link>),

     

       619
       619
       +
             <literal>submodule</literal> allows multiple definitions of the

     

       620
       620
       +
             submodule option set

     

       621
       621
       +
             (<link linkend="ex-submodule-listof-definition">Example:

     

       622
       622
       +
             Definition of a list of submodules</link>).

     

       623
       623
       +
           </para>

     

       624
       624
       +
           <anchor xml:id="ex-submodule-listof-declaration" />

     

       625
       625
       +
           <para>

     

       626
       626
       +
             <emphasis role="strong">Example: Declaration of a list of

     

       627
       627
       +
             submodules</emphasis>

     

       628
       628
       +
           </para>

     

       629
       629
       +
           <programlisting language="bash">

     

       630
       630
       +
       options.mod = mkOption {

     

       631
       631
       +
         description = &quot;submodule example&quot;;

     

       632
       632
       +
         type = with types; listOf (submodule {

     

       633
       633
       +
           options = {

     

       634
       634
       +
             foo = mkOption {

     

       635
       635
       +
               type = int;

     

       636
       636
       +
             };

     

       637
       637
       +
             bar = mkOption {

     

       638
       638
       +
               type = str;

     

       639
       639
       +
             };

     

       640
       640
       +
           };

     

       641
       641
       +
         });

     

       642
       642
       +
       };

     

       643
       643
       +
       </programlisting>

     

       644
       644
       +
           <anchor xml:id="ex-submodule-listof-definition" />

     

       645
       645
       +
           <para>

     

       646
       646
       +
             <emphasis role="strong">Example: Definition of a list of

     

       647
       647
       +
             submodules</emphasis>

     

       648
       648
       +
           </para>

     

       649
       649
       +
           <programlisting language="bash">

     

       650
       650
       +
       config.mod = [

     

       651
       651
       +
         { foo = 1; bar = &quot;one&quot;; }

     

       652
       652
       +
         { foo = 2; bar = &quot;two&quot;; }

     

       653
       653
       +
       ];

     

       654
       654
       +
       </programlisting>

     

       655
       655
       +
           <para>

     

       656
       656
       +
             When composed with <literal>attrsOf</literal>

     

       657
       657
       +
             (<link linkend="ex-submodule-attrsof-declaration">Example:

     

       658
       658
       +
             Declaration of attribute sets of submodules</link>),

     

       659
       659
       +
             <literal>submodule</literal> allows multiple named definitions of

     

       660
       660
       +
             the submodule option set

     

       661
       661
       +
             (<link linkend="ex-submodule-attrsof-definition">Example:

     

       662
       662
       +
             Definition of attribute sets of submodules</link>).

     

       663
       663
       +
           </para>

     

       664
       664
       +
           <anchor xml:id="ex-submodule-attrsof-declaration" />

     

       665
       665
       +
           <para>

     

       666
       666
       +
             <emphasis role="strong">Example: Declaration of attribute sets of

     

       667
       667
       +
             submodules</emphasis>

     

       668
       668
       +
           </para>

     

       669
       669
       +
           <programlisting language="bash">

     

       670
       670
       +
       options.mod = mkOption {

     

       671
       671
       +
         description = &quot;submodule example&quot;;

     

       672
       672
       +
         type = with types; attrsOf (submodule {

     

       673
       673
       +
           options = {

     

       674
       674
       +
             foo = mkOption {

     

       675
       675
       +
               type = int;

     

       676
       676
       +
             };

     

       677
       677
       +
             bar = mkOption {

     

       678
       678
       +
               type = str;

     

       679
       679
       +
             };

     

       680
       680
       +
           };

     

       681
       681
       +
         });

     

       682
       682
       +
       };

     

       683
       683
       +
       </programlisting>

     

       684
       684
       +
           <anchor xml:id="ex-submodule-attrsof-definition" />

     

       685
       685
       +
           <para>

     

       686
       686
       +
             <emphasis role="strong">Example: Definition of attribute sets of

     

       687
       687
       +
             submodules</emphasis>

     

       688
       688
       +
           </para>

     

       689
       689
       +
           <programlisting language="bash">

     

       690
       690
       +
       config.mod.one = { foo = 1; bar = &quot;one&quot;; };

     

       691
       691
       +
       config.mod.two = { foo = 2; bar = &quot;two&quot;; };

     

       692
       692
       +
       </programlisting>

     

       693
       693
       +
         </section>

     

       694
       694
       +
         <section xml:id="sec-option-types-extending">

     

       695
       695
       +
           <title>Extending types</title>

     

       696
       696
       +
           <para>

     

       697
       697
       +
             Types are mainly characterized by their <literal>check</literal>

     

       698
       698
       +
             and <literal>merge</literal> functions.

     

       699
       699
       +
           </para>

     

       700
       700
       +
           <variablelist>

     

       701
       701
       +
             <varlistentry>

     

       702
       702
       +
               <term>

     

       703
       703
       +
                 <literal>check</literal>

     

       704
       704
       +
               </term>

     

       705
       705
       +
               <listitem>

     

       706
       706
       +
                 <para>

     

       707
       707
       +
                   The function to type check the value. Takes a value as

     

       708
       708
       +
                   parameter and return a boolean. It is possible to extend a

     

       709
       709
       +
                   type check with the <literal>addCheck</literal> function

     

       710
       710
       +
                   (<link linkend="ex-extending-type-check-1">Example: Adding a

     

       711
       711
       +
                   type check</link>), or to fully override the check function

     

       712
       712
       +
                   (<link linkend="ex-extending-type-check-2">Example:

     

       713
       713
       +
                   Overriding a type check</link>).

     

       714
       714
       +
                 </para>

     

       715
       715
       +
                 <anchor xml:id="ex-extending-type-check-1" />

     

       716
       716
       +
                 <para>

     

       717
       717
       +
                   <emphasis role="strong">Example: Adding a type

     

       718
       718
       +
                   check</emphasis>

     

       719
       719
       +
                 </para>

     

       720
       720
       +
                 <programlisting language="bash">

     

       721
       721
       +
       byte = mkOption {

     

       722
       722
       +
         description = &quot;An integer between 0 and 255.&quot;;

     

       723
       723
       +
         type = types.addCheck types.int (x: x &gt;= 0 &amp;&amp; x &lt;= 255);

     

       724
       724
       +
       };

     

       725
       725
       +
       </programlisting>

     

       726
       726
       +
                 <anchor xml:id="ex-extending-type-check-2" />

     

       727
       727
       +
                 <para>

     

       728
       728
       +
                   <emphasis role="strong">Example: Overriding a type

     

       729
       729
       +
                   check</emphasis>

     

       730
       730
       +
                 </para>

     

       731
       731
       +
                 <programlisting language="bash">

     

       732
       732
       +
       nixThings = mkOption {

     

       733
       733
       +
         description = &quot;words that start with 'nix'&quot;;

     

       734
       734
       +
         type = types.str // {

     

       735
       735
       +
           check = (x: lib.hasPrefix &quot;nix&quot; x)

     

       736
       736
       +
         };

     

       737
       737
       +
       };

     

       738
       738
       +
       </programlisting>

     

       739
       739
       +
               </listitem>

     

       740
       740
       +
             </varlistentry>

     

       741
       741
       +
             <varlistentry>

     

       742
       742
       +
               <term>

     

       743
       743
       +
                 <literal>merge</literal>

     

       744
       744
       +
               </term>

     

       745
       745
       +
               <listitem>

     

       746
       746
       +
                 <para>

     

       747
       747
       +
                   Function to merge the options values when multiple values

     

       748
       748
       +
                   are set. The function takes two parameters,

     

       749
       749
       +
                   <literal>loc</literal> the option path as a list of strings,

     

       750
       750
       +
                   and <literal>defs</literal> the list of defined values as a

     

       751
       751
       +
                   list. It is possible to override a type merge function for

     

       752
       752
       +
                   custom needs.

     

       753
       753
       +
                 </para>

     

       754
       754
       +
               </listitem>

     

       755
       755
       +
             </varlistentry>

     

       756
       756
       +
           </variablelist>

     

       757
       757
       +
         </section>

     

       758
       758
       +
         <section xml:id="sec-option-types-custom">

     

       759
       759
       +
           <title>Custom Types</title>

     

       760
       760
       +
           <para>

     

       761
       761
       +
             Custom types can be created with the

     

       762
       762
       +
             <literal>mkOptionType</literal> function. As type creation

     

       763
       763
       +
             includes some more complex topics such as submodule handling, it

     

       764
       764
       +
             is recommended to get familiar with <literal>types.nix</literal>

     

       765
       765
       +
             code before creating a new type.

     

       766
       766
       +
           </para>

     

       767
       767
       +
           <para>

     

       768
       768
       +
             The only required parameter is <literal>name</literal>.

     

       769
       769
       +
           </para>

     

       770
       770
       +
           <variablelist>

     

       771
       771
       +
             <varlistentry>

     

       772
       772
       +
               <term>

     

       773
       773
       +
                 <literal>name</literal>

     

       774
       774
       +
               </term>

     

       775
       775
       +
               <listitem>

     

       776
       776
       +
                 <para>

     

       777
       777
       +
                   A string representation of the type function name.

     

       778
       778
       +
                 </para>

     

       779
       779
       +
               </listitem>

     

       780
       780
       +
             </varlistentry>

     

       781
       781
       +
             <varlistentry>

     

       782
       782
       +
               <term>

     

       783
       783
       +
                 <literal>definition</literal>

     

       784
       784
       +
               </term>

     

       785
       785
       +
               <listitem>

     

       786
       786
       +
                 <para>

     

       787
       787
       +
                   Description of the type used in documentation. Give

     

       788
       788
       +
                   information of the type and any of its arguments.

     

       789
       789
       +
                 </para>

     

       790
       790
       +
               </listitem>

     

       791
       791
       +
             </varlistentry>

     

       792
       792
       +
             <varlistentry>

     

       793
       793
       +
               <term>

     

       794
       794
       +
                 <literal>check</literal>

     

       795
       795
       +
               </term>

     

       796
       796
       +
               <listitem>

     

       797
       797
       +
                 <para>

     

       798
       798
       +
                   A function to type check the definition value. Takes the

     

       799
       799
       +
                   definition value as a parameter and returns a boolean

     

       800
       800
       +
                   indicating the type check result, <literal>true</literal>

     

       801
       801
       +
                   for success and <literal>false</literal> for failure.

     

       802
       802
       +
                 </para>

     

       803
       803
       +
               </listitem>

     

       804
       804
       +
             </varlistentry>

     

       805
       805
       +
             <varlistentry>

     

       806
       806
       +
               <term>

     

       807
       807
       +
                 <literal>merge</literal>

     

       808
       808
       +
               </term>

     

       809
       809
       +
               <listitem>

     

       810
       810
       +
                 <para>

     

       811
       811
       +
                   A function to merge multiple definitions values. Takes two

     

       812
       812
       +
                   parameters:

     

       813
       813
       +
                 </para>

     

       814
       814
       +
                 <variablelist>

     

       815
       815
       +
                   <varlistentry>

     

       816
       816
       +
                     <term>

     

       817
       817
       +
                       <emphasis><literal>loc</literal></emphasis>

     

       818
       818
       +
                     </term>

     

       819
       819
       +
                     <listitem>

     

       820
       820
       +
                       <para>

     

       821
       821
       +
                         The option path as a list of strings, e.g.

     

       822
       822
       +
                         <literal>[&quot;boot&quot; &quot;loader &quot;grub&quot; &quot;enable&quot;]</literal>.

     

       823
       823
       +
                       </para>

     

       824
       824
       +
                     </listitem>

     

       825
       825
       +
                   </varlistentry>

     

       826
       826
       +
                   <varlistentry>

     

       827
       827
       +
                     <term>

     

       828
       828
       +
                       <emphasis><literal>defs</literal></emphasis>

     

       829
       829
       +
                     </term>

     

       830
       830
       +
                     <listitem>

     

       831
       831
       +
                       <para>

     

       832
       832
       +
                         The list of sets of defined <literal>value</literal>

     

       833
       833
       +
                         and <literal>file</literal> where the value was

     

       834
       834
       +
                         defined, e.g.

     

       835
       835
       +
                         <literal>[ { file = &quot;/foo.nix&quot;; value = 1; } { file = &quot;/bar.nix&quot;; value = 2 } ]</literal>.

     

       836
       836
       +
                         The <literal>merge</literal> function should return

     

       837
       837
       +
                         the merged value or throw an error in case the values

     

       838
       838
       +
                         are impossible or not meant to be merged.

     

       839
       839
       +
                       </para>

     

       840
       840
       +
                     </listitem>

     

       841
       841
       +
                   </varlistentry>

     

       842
       842
       +
                 </variablelist>

     

       843
       843
       +
               </listitem>

     

       844
       844
       +
             </varlistentry>

     

       845
       845
       +
             <varlistentry>

     

       846
       846
       +
               <term>

     

       847
       847
       +
                 <literal>getSubOptions</literal>

     

       848
       848
       +
               </term>

     

       849
       849
       +
               <listitem>

     

       850
       850
       +
                 <para>

     

       851
       851
       +
                   For composed types that can take a submodule as type

     

       852
       852
       +
                   parameter, this function generate sub-options documentation.

     

       853
       853
       +
                   It takes the current option prefix as a list and return the

     

       854
       854
       +
                   set of sub-options. Usually defined in a recursive manner by

     

       855
       855
       +
                   adding a term to the prefix, e.g.

     

       856
       856
       +
                   <literal>prefix: elemType.getSubOptions (prefix ++ [&quot;prefix&quot;])</literal>

     

       857
       857
       +
                   where

     

       858
       858
       +
                   <emphasis><literal>&quot;prefix&quot;</literal></emphasis>

     

       859
       859
       +
                   is the newly added prefix.

     

       860
       860
       +
                 </para>

     

       861
       861
       +
               </listitem>

     

       862
       862
       +
             </varlistentry>

     

       863
       863
       +
             <varlistentry>

     

       864
       864
       +
               <term>

     

       865
       865
       +
                 <literal>getSubModules</literal>

     

       866
       866
       +
               </term>

     

       867
       867
       +
               <listitem>

     

       868
       868
       +
                 <para>

     

       869
       869
       +
                   For composed types that can take a submodule as type

     

       870
       870
       +
                   parameter, this function should return the type parameters

     

       871
       871
       +
                   submodules. If the type parameter is called

     

       872
       872
       +
                   <literal>elemType</literal>, the function should just

     

       873
       873
       +
                   recursively look into submodules by returning

     

       874
       874
       +
                   <literal>elemType.getSubModules;</literal>.

     

       875
       875
       +
                 </para>

     

       876
       876
       +
               </listitem>

     

       877
       877
       +
             </varlistentry>

     

       878
       878
       +
             <varlistentry>

     

       879
       879
       +
               <term>

     

       880
       880
       +
                 <literal>substSubModules</literal>

     

       881
       881
       +
               </term>

     

       882
       882
       +
               <listitem>

     

       883
       883
       +
                 <para>

     

       884
       884
       +
                   For composed types that can take a submodule as type

     

       885
       885
       +
                   parameter, this function can be used to substitute the

     

       886
       886
       +
                   parameter of a submodule type. It takes a module as

     

       887
       887
       +
                   parameter and return the type with the submodule options

     

       888
       888
       +
                   substituted. It is usually defined as a type function call

     

       889
       889
       +
                   with a recursive call to <literal>substSubModules</literal>,

     

       890
       890
       +
                   e.g for a type <literal>composedType</literal> that take an

     

       891
       891
       +
                   <literal>elemtype</literal> type parameter, this function

     

       892
       892
       +
                   should be defined as

     

       893
       893
       +
                   <literal>m: composedType (elemType.substSubModules m)</literal>.

     

       894
       894
       +
                 </para>

     

       895
       895
       +
               </listitem>

     

       896
       896
       +
             </varlistentry>

     

       897
       897
       +
             <varlistentry>

     

       898
       898
       +
               <term>

     

       899
       899
       +
                 <literal>typeMerge</literal>

     

       900
       900
       +
               </term>

     

       901
       901
       +
               <listitem>

     

       902
       902
       +
                 <para>

     

       903
       903
       +
                   A function to merge multiple type declarations. Takes the

     

       904
       904
       +
                   type to merge <literal>functor</literal> as parameter. A

     

       905
       905
       +
                   <literal>null</literal> return value means that type cannot

     

       906
       906
       +
                   be merged.

     

       907
       907
       +
                 </para>

     

       908
       908
       +
                 <variablelist>

     

       909
       909
       +
                   <varlistentry>

     

       910
       910
       +
                     <term>

     

       911
       911
       +
                       <emphasis><literal>f</literal></emphasis>

     

       912
       912
       +
                     </term>

     

       913
       913
       +
                     <listitem>

     

       914
       914
       +
                       <para>

     

       915
       915
       +
                         The type to merge <literal>functor</literal>.

     

       916
       916
       +
                       </para>

     

       917
       917
       +
                     </listitem>

     

       918
       918
       +
                   </varlistentry>

     

       919
       919
       +
                 </variablelist>

     

       920
       920
       +
                 <para>

     

       921
       921
       +
                   Note: There is a generic <literal>defaultTypeMerge</literal>

     

       922
       922
       +
                   that work with most of value and composed types.

     

       923
       923
       +
                 </para>

     

       924
       924
       +
               </listitem>

     

       925
       925
       +
             </varlistentry>

     

       926
       926
       +
             <varlistentry>

     

       927
       927
       +
               <term>

     

       928
       928
       +
                 <literal>functor</literal>

     

       929
       929
       +
               </term>

     

       930
       930
       +
               <listitem>

     

       931
       931
       +
                 <para>

     

       932
       932
       +
                   An attribute set representing the type. It is used for type

     

       933
       933
       +
                   operations and has the following keys:

     

       934
       934
       +
                 </para>

     

       935
       935
       +
                 <variablelist>

     

       936
       936
       +
                   <varlistentry>

     

       937
       937
       +
                     <term>

     

       938
       938
       +
                       <literal>type</literal>

     

       939
       939
       +
                     </term>

     

       940
       940
       +
                     <listitem>

     

       941
       941
       +
                       <para>

     

       942
       942
       +
                         The type function.

     

       943
       943
       +
                       </para>

     

       944
       944
       +
                     </listitem>

     

       945
       945
       +
                   </varlistentry>

     

       946
       946
       +
                   <varlistentry>

     

       947
       947
       +
                     <term>

     

       948
       948
       +
                       <literal>wrapped</literal>

     

       949
       949
       +
                     </term>

     

       950
       950
       +
                     <listitem>

     

       951
       951
       +
                       <para>

     

       952
       952
       +
                         Holds the type parameter for composed types.

     

       953
       953
       +
                       </para>

     

       954
       954
       +
                     </listitem>

     

       955
       955
       +
                   </varlistentry>

     

       956
       956
       +
                   <varlistentry>

     

       957
       957
       +
                     <term>

     

       958
       958
       +
                       <literal>payload</literal>

     

       959
       959
       +
                     </term>

     

       960
       960
       +
                     <listitem>

     

       961
       961
       +
                       <para>

     

       962
       962
       +
                         Holds the value parameter for value types. The types

     

       963
       963
       +
                         that have a <literal>payload</literal> are the

     

       964
       964
       +
                         <literal>enum</literal>,

     

       965
       965
       +
                         <literal>separatedString</literal> and

     

       966
       966
       +
                         <literal>submodule</literal> types.

     

       967
       967
       +
                       </para>

     

       968
       968
       +
                     </listitem>

     

       969
       969
       +
                   </varlistentry>

     

       970
       970
       +
                   <varlistentry>

     

       971
       971
       +
                     <term>

     

       972
       972
       +
                       <literal>binOp</literal>

     

       973
       973
       +
                     </term>

     

       974
       974
       +
                     <listitem>

     

       975
       975
       +
                       <para>

     

       976
       976
       +
                         A binary operation that can merge the payloads of two

     

       977
       977
       +
                         same types. Defined as a function that take two

     

       978
       978
       +
                         payloads as parameters and return the payloads merged.

     

       979
       979
       +
                       </para>

     

       980
       980
       +
                     </listitem>

     

       981
       981
       +
                   </varlistentry>

     

       982
       982
       +
                 </variablelist>

     

       983
       983
       +
               </listitem>

     

       984
       984
       +
             </varlistentry>

     

       985
       985
       +
           </variablelist>

     

       986
       986
       +
         </section>

     

       987
       987
       +
       </section>

+70

nixos/doc/manual/from_md/development/replace-modules.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-replace-modules">

     

       2
       2
       +
         <title>Replace Modules</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Modules that are imported can also be disabled. The option

     

       5
       5
       +
           declarations, config implementation and the imports of a disabled

     

       6
       6
       +
           module will be ignored, allowing another to take it's place. This

     

       7
       7
       +
           can be used to import a set of modules from another channel while

     

       8
       8
       +
           keeping the rest of the system on a stable release.

     

       9
       9
       +
         </para>

     

       10
       10
       +
         <para>

     

       11
       11
       +
           <literal>disabledModules</literal> is a top level attribute like

     

       12
       12
       +
           <literal>imports</literal>, <literal>options</literal> and

     

       13
       13
       +
           <literal>config</literal>. It contains a list of modules that will

     

       14
       14
       +
           be disabled. This can either be the full path to the module or a

     

       15
       15
       +
           string with the filename relative to the modules path (eg.

     

       16
       16
       +
           &lt;nixpkgs/nixos/modules&gt; for nixos).

     

       17
       17
       +
         </para>

     

       18
       18
       +
         <para>

     

       19
       19
       +
           This example will replace the existing postgresql module with the

     

       20
       20
       +
           version defined in the nixos-unstable channel while keeping the rest

     

       21
       21
       +
           of the modules and packages from the original nixos channel. This

     

       22
       22
       +
           only overrides the module definition, this won't use postgresql from

     

       23
       23
       +
           nixos-unstable unless explicitly configured to do so.

     

       24
       24
       +
         </para>

     

       25
       25
       +
         <programlisting language="bash">

     

       26
       26
       +
       { config, lib, pkgs, ... }:

     

       27
       27
       +
       

     

       28
       28
       +
       {

     

       29
       29
       +
         disabledModules = [ &quot;services/databases/postgresql.nix&quot; ];

     

       30
       30
       +
       

     

       31
       31
       +
         imports =

     

       32
       32
       +
           [ # Use postgresql service from nixos-unstable channel.

     

       33
       33
       +
             # sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos-unstable

     

       34
       34
       +
             &lt;nixos-unstable/nixos/modules/services/databases/postgresql.nix&gt;

     

       35
       35
       +
           ];

     

       36
       36
       +
       

     

       37
       37
       +
         services.postgresql.enable = true;

     

       38
       38
       +
       }

     

       39
       39
       +
       </programlisting>

     

       40
       40
       +
         <para>

     

       41
       41
       +
           This example shows how to define a custom module as a replacement

     

       42
       42
       +
           for an existing module. Importing this module will disable the

     

       43
       43
       +
           original module without having to know it's implementation details.

     

       44
       44
       +
         </para>

     

       45
       45
       +
         <programlisting language="bash">

     

       46
       46
       +
       { config, lib, pkgs, ... }:

     

       47
       47
       +
       

     

       48
       48
       +
       with lib;

     

       49
       49
       +
       

     

       50
       50
       +
       let

     

       51
       51
       +
         cfg = config.programs.man;

     

       52
       52
       +
       in

     

       53
       53
       +
       

     

       54
       54
       +
       {

     

       55
       55
       +
         disabledModules = [ &quot;services/programs/man.nix&quot; ];

     

       56
       56
       +
       

     

       57
       57
       +
         options = {

     

       58
       58
       +
           programs.man.enable = mkOption {

     

       59
       59
       +
             type = types.bool;

     

       60
       60
       +
             default = true;

     

       61
       61
       +
             description = &quot;Whether to enable manual pages.&quot;;

     

       62
       62
       +
           };

     

       63
       63
       +
         };

     

       64
       64
       +
       

     

       65
       65
       +
         config = mkIf cfg.enabled {

     

       66
       66
       +
           warnings = [ &quot;disabled manpages for production deployments.&quot; ];

     

       67
       67
       +
         };

     

       68
       68
       +
       }

     

       69
       69
       +
       </programlisting>

     

       70
       70
       +
       </section>

+285

nixos/doc/manual/from_md/development/settings-options.section.xml

···

       1
       1
       +
       <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-settings-options">

     

       2
       2
       +
         <title>Options for Program Settings</title>

     

       3
       3
       +
         <para>

     

       4
       4
       +
           Many programs have configuration files where program-specific

     

       5
       5
       +
           settings can be declared. File formats can be separated into two

     

       6
       6
       +
           categories:

     

       7
       7
       +
         </para>

     

       8
       8
       +
         <itemizedlist>

     

       9
       9
       +
           <listitem>

     

       10
       10
       +
             <para>

     

       11
       11
       +
               Nix-representable ones: These can trivially be mapped to a

     

       12
       12
       +
               subset of Nix syntax. E.g. JSON is an example, since its values

     

       13
       13
       +
               like <literal>{&quot;foo&quot;:{&quot;bar&quot;:10}}</literal>

     

       14
       14
       +
               can be mapped directly to Nix:

     

       15
       15
       +
               <literal>{ foo = { bar = 10; }; }</literal>. Other examples are

     

       16
       16
       +
               INI, YAML and TOML. The following section explains the

     

       17
       17
       +
               convention for these settings.

     

       18
       18
       +
             </para>

     

       19
       19
       +
           </listitem>

     

       20
       20
       +
           <listitem>

     

       21
       21
       +
             <para>

     

       22
       22
       +
               Non-nix-representable ones: These can't be trivially mapped to a

     

       23
       23
       +
               subset of Nix syntax. Most generic programming languages are in

     

       24
       24
       +
               this group, e.g. bash, since the statement

     

       25
       25
       +
               <literal>if true; then echo hi; fi</literal> doesn't have a

     

       26
       26
       +
               trivial representation in Nix.

     

       27
       27
       +
             </para>

     

       28
       28
       +
             <para>

     

       29
       29
       +
               Currently there are no fixed conventions for these, but it is

     

       30
       30
       +
               common to have a <literal>configFile</literal> option for

     

       31
       31
       +
               setting the configuration file path directly. The default value

     

       32
       32
       +
               of <literal>configFile</literal> can be an auto-generated file,

     

       33
       33
       +
               with convenient options for controlling the contents. For

     

       34
       34
       +
               example an option of type <literal>attrsOf str</literal> can be

     

       35
       35
       +
               used for representing environment variables which generates a

     

       36
       36
       +
               section like <literal>export FOO=&quot;foo&quot;</literal>.

     

       37
       37
       +
               Often it can also be useful to also include an

     

       38
       38
       +
               <literal>extraConfig</literal> option of type

     

       39
       39
       +
               <literal>lines</literal> to allow arbitrary text after the

     

       40
       40
       +
               autogenerated part of the file.

     

       41
       41
       +
             </para>

     

       42
       42
       +
           </listitem>

     

       43
       43
       +
         </itemizedlist>

     

       44
       44
       +
         <section xml:id="sec-settings-nix-representable">

     

       45
       45
       +
           <title>Nix-representable Formats (JSON, YAML, TOML, INI,

     

       46
       46
       +
           ...)</title>

     

       47
       47
       +
           <para>

     

       48
       48
       +
             By convention, formats like this are handled with a generic

     

       49
       49
       +
             <literal>settings</literal> option, representing the full program

     

       50
       50
       +
             configuration as a Nix value. The type of this option should

     

       51
       51
       +
             represent the format. The most common formats have a predefined

     

       52
       52
       +
             type and string generator already declared under

     

       53
       53
       +
             <literal>pkgs.formats</literal>:

     

       54
       54
       +
           </para>

     

       55
       55
       +
           <variablelist>

     

       56
       56
       +
             <varlistentry>

     

       57
       57
       +
               <term>

     

       58
       58
       +
                 <literal>pkgs.formats.json</literal> { }

     

       59
       59
       +
               </term>

     

       60
       60
       +
               <listitem>

     

       61
       61
       +
                 <para>

     

       62
       62
       +
                   A function taking an empty attribute set (for future

     

       63
       63
       +
                   extensibility) and returning a set with JSON-specific

     

       64
       64
       +
                   attributes <literal>type</literal> and

     

       65
       65
       +
                   <literal>generate</literal> as specified

     

       66
       66
       +
                   <link linkend="pkgs-formats-result">below</link>.

     

       67
       67
       +
                 </para>

     

       68
       68
       +
               </listitem>

     

       69
       69
       +
             </varlistentry>

     

       70
       70
       +
             <varlistentry>

     

       71
       71
       +
               <term>

     

       72
       72
       +
                 <literal>pkgs.formats.yaml</literal> { }

     

       73
       73
       +
               </term>

     

       74
       74
       +
               <listitem>

     

       75
       75
       +
                 <para>

     

       76
       76
       +
                   A function taking an empty attribute set (for future

     

       77
       77
       +
                   extensibility) and returning a set with YAML-specific

     

       78
       78
       +
                   attributes <literal>type</literal> and

     

       79
       79
       +
                   <literal>generate</literal> as specified

     

       80
       80
       +
                   <link linkend="pkgs-formats-result">below</link>.

     

       81
       81
       +
                 </para>

     

       82
       82
       +
               </listitem>

     

       83
       83
       +
             </varlistentry>

     

       84
       84
       +
             <varlistentry>

     

       85
       85
       +
               <term>

     

       86
       86
       +
                 <literal>pkgs.formats.ini</literal> {

     

       87
       87
       +
                 <emphasis><literal>listsAsDuplicateKeys</literal></emphasis> ?

     

       88
       88
       +
                 false, <emphasis><literal>listToValue</literal></emphasis> ?

     

       89
       89
       +
                 null, ... }

     

       90
       90
       +
               </term>

     

       91
       91
       +
               <listitem>

     

       92
       92
       +
                 <para>

     

       93
       93
       +
                   A function taking an attribute set with values

     

       94
       94
       +
                 </para>

     

       95
       95
       +
                 <variablelist>

     

       96
       96
       +
                   <varlistentry>

     

       97
       97
       +
                     <term>

     

       98
       98
       +
                       <literal>listsAsDuplicateKeys</literal>

     

       99
       99
       +
                     </term>

     

       100
       100
       +
                     <listitem>

     

       101
       101
       +
                       <para>

     

       102
       102
       +
                         A boolean for controlling whether list values can be

     

       103
       103
       +
                         used to represent duplicate INI keys

     

       104
       104
       +
                       </para>

     

       105
       105
       +
                     </listitem>

     

       106
       106
       +
                   </varlistentry>

     

       107
       107
       +
                   <varlistentry>

     

       108
       108
       +
                     <term>

     

       109
       109
       +
                       <literal>listToValue</literal>

     

       110
       110
       +
                     </term>

     

       111
       111
       +
                     <listitem>

     

       112
       112
       +
                       <para>

     

       113
       113
       +
                         A function for turning a list of values into a single

     

       114
       114
       +
                         value.

     

       115
       115
       +
                       </para>

     

       116
       116
       +
                     </listitem>

     

       117
       117
       +
                   </varlistentry>

     

       118
       118
       +
                 </variablelist>

     

       119
       119
       +
                 <para>

     

       120
       120
       +
                   It returns a set with INI-specific attributes

     

       121
       121
       +
                   <literal>type</literal> and <literal>generate</literal> as

     

       122
       122
       +
                   specified <link linkend="pkgs-formats-result">below</link>.

     

       123
       123
       +
                 </para>

     

       124
       124
       +
               </listitem>

     

       125
       125
       +
             </varlistentry>

     

       126
       126
       +
             <varlistentry>

     

       127
       127
       +
               <term>

     

       128
       128
       +
                 <literal>pkgs.formats.toml</literal> { }

     

       129
       129
       +
               </term>

     

       130
       130
       +
               <listitem>

     

       131
       131
       +
                 <para>

     

       132
       132
       +
                   A function taking an empty attribute set (for future

     

       133
       133
       +
                   extensibility) and returning a set with TOML-specific

     

       134
       134
       +
                   attributes <literal>type</literal> and

     

       135
       135
       +
                   <literal>generate</literal> as specified

     

       136
       136
       +
                   <link linkend="pkgs-formats-result">below</link>.

     

       137
       137
       +
                 </para>

     

       138
       138
       +
               </listitem>

     

       139
       139
       +
             </varlistentry>

     

       140
       140
       +
           </variablelist>

     

       141
       141
       +
           <para xml:id="pkgs-formats-result">

     

       142
       142
       +
             These functions all return an attribute set with these values:

     

       143
       143
       +
           </para>

     

       144
       144
       +
           <variablelist>

     

       145
       145
       +
             <varlistentry>

     

       146
       146
       +
               <term>

     

       147
       147
       +
                 <literal>type</literal>

     

       148
       148
       +
               </term>

     

       149
       149
       +
               <listitem>

     

       150
       150
       +
                 <para>

     

       151
       151
       +
                   A module system type representing a value of the format

     

       152
       152
       +
                 </para>

     

       153
       153
       +
               </listitem>

     

       154
       154
       +
             </varlistentry>

     

       155
       155
       +
             <varlistentry>

     

       156
       156
       +
               <term>

     

       157
       157
       +
                 <literal>generate</literal>

     

       158
       158
       +
                 <emphasis><literal>filename jsonValue</literal></emphasis>

     

       159
       159
       +
               </term>

     

       160
       160
       +
               <listitem>

     

       161
       161
       +
                 <para>

     

       162
       162
       +
                   A function that can render a value of the format to a file.

     

       163
       163
       +
                   Returns a file path.

     

       164
       164
       +
                 </para>

     

       165
       165
       +
                 <note>

     

       166
       166
       +
                   <para>

     

       167
       167
       +
                     This function puts the value contents in the Nix store. So

     

       168
       168
       +
                     this should be avoided for secrets.

     

       169
       169
       +
                   </para>

     

       170
       170
       +
                 </note>

     

       171
       171
       +
               </listitem>

     

       172
       172
       +
             </varlistentry>

     

       173
       173
       +
           </variablelist>

     

       174
       174
       +
           <anchor xml:id="ex-settings-nix-representable" />

     

       175
       175
       +
           <para>

     

       176
       176
       +
             <emphasis role="strong">Example: Module with conventional

     

       177
       177
       +
             <literal>settings</literal> option</emphasis>

     

       178
       178
       +
           </para>

     

       179
       179
       +
           <para>

     

       180
       180
       +
             The following shows a module for an example program that uses a

     

       181
       181
       +
             JSON configuration file. It demonstrates how above values can be

     

       182
       182
       +
             used, along with some other related best practices. See the

     

       183
       183
       +
             comments for explanations.

     

       184
       184
       +
           </para>

     

       185
       185
       +
           <programlisting language="bash">

     

       186
       186
       +
       { options, config, lib, pkgs, ... }:

     

       187
       187
       +
       let

     

       188
       188
       +
         cfg = config.services.foo;

     

       189
       189
       +
         # Define the settings format used for this program

     

       190
       190
       +
         settingsFormat = pkgs.formats.json {};

     

       191
       191
       +
       in {

     

       192
       192
       +
       

     

       193
       193
       +
         options.services.foo = {

     

       194
       194
       +
           enable = lib.mkEnableOption &quot;foo service&quot;;

     

       195
       195
       +
       

     

       196
       196
       +
           settings = lib.mkOption {

     

       197
       197
       +
             # Setting this type allows for correct merging behavior

     

       198
       198
       +
             type = settingsFormat.type;

     

       199
       199
       +
             default = {};

     

       200
       200
       +
             description = ''

     

       201
       201
       +
               Configuration for foo, see

     

       202
       202
       +
               &lt;link xlink:href=&quot;https://example.com/docs/foo&quot;/&gt;

     

       203
       203
       +
               for supported settings.

     

       204
       204
       +
             '';

     

       205
       205
       +
           };

     

       206
       206
       +
         };

     

       207
       207
       +
       

     

       208
       208
       +
         config = lib.mkIf cfg.enable {

     

       209
       209
       +
           # We can assign some default settings here to make the service work by just

     

       210
       210
       +
           # enabling it. We use `mkDefault` for values that can be changed without

     

       211
       211
       +
           # problems

     

       212
       212
       +
           services.foo.settings = {

     

       213
       213
       +
             # Fails at runtime without any value set

     

       214
       214
       +
             log_level = lib.mkDefault &quot;WARN&quot;;

     

       215
       215
       +
       

     

       216
       216
       +
             # We assume systemd's `StateDirectory` is used, so we require this value,

     

       217
       217
       +
             # therefore no mkDefault

     

       218
       218
       +
             data_path = &quot;/var/lib/foo&quot;;

     

       219
       219
       +
       

     

       220
       220
       +
             # Since we use this to create a user we need to know the default value at

     

       221
       221
       +
             # eval time

     

       222
       222
       +
             user = lib.mkDefault &quot;foo&quot;;

     

       223
       223
       +
           };

     

       224
       224
       +
       

     

       225
       225
       +
           environment.etc.&quot;foo.json&quot;.source =

     

       226
       226
       +
             # The formats generator function takes a filename and the Nix value

     

       227
       227
       +
             # representing the format value and produces a filepath with that value

     

       228
       228
       +
             # rendered in the format

     

       229
       229
       +
             settingsFormat.generate &quot;foo-config.json&quot; cfg.settings;

     

       230
       230
       +
       

     

       231
       231
       +
           # We know that the `user` attribute exists because we set a default value

     

       232
       232
       +
           # for it above, allowing us to use it without worries here

     

       233
       233
       +
           users.users.${cfg.settings.user} = { isSystemUser = true; };

     

       234
       234
       +
       

     

       235
       235
       +
           # ...

     

       236
       236
       +
         };

     

       237
       237
       +
       }

     

       238
       238
       +
       </programlisting>

     

       239
       239
       +
           <section xml:id="sec-settings-attrs-options">

     

       240
       240
       +
             <title>Option declarations for attributes</title>

     

       241
       241
       +
             <para>

     

       242
       242
       +
               Some <literal>settings</literal> attributes may deserve some

     

       243
       243
       +
               extra care. They may need a different type, default or merging

     

       244
       244
       +
               behavior, or they are essential options that should show their

     

       245
       245
       +
               documentation in the manual. This can be done using

     

       246
       246
       +
               <xref linkend="sec-freeform-modules" />.

     

       247
       247
       +
             </para>

     

       248
       248
       +
             <para>

     

       249
       249
       +
               We extend above example using freeform modules to declare an

     

       250
       250
       +
               option for the port, which will enforce it to be a valid integer

     

       251
       251
       +
               and make it show up in the manual.

     

       252
       252
       +
             </para>

     

       253
       253
       +
             <anchor xml:id="ex-settings-typed-attrs" />

     

       254
       254
       +
             <para>

     

       255
       255
       +
               <emphasis role="strong">Example: Declaring a type-checked

     

       256
       256
       +
               <literal>settings</literal> attribute</emphasis>

     

       257
       257
       +
             </para>

     

       258
       258
       +
             <programlisting language="bash">

     

       259
       259
       +
       settings = lib.mkOption {

     

       260
       260
       +
         type = lib.types.submodule {

     

       261
       261
       +
       

     

       262
       262
       +
           freeformType = settingsFormat.type;

     

       263
       263
       +
       

     

       264
       264
       +
           # Declare an option for the port such that the type is checked and this option

     

       265
       265
       +
           # is shown in the manual.

     

       266
       266
       +
           options.port = lib.mkOption {

     

       267
       267
       +
             type = lib.types.port;

     

       268
       268
       +
             default = 8080;

     

       269
       269
       +
             description = ''

     

       270
       270
       +
               Which port this service should listen on.

     

       271
       271
       +
             '';

     

       272
       272
       +
           };

     

       273
       273
       +
       

     

       274
       274
       +
         };

     

       275
       275
       +
         default = {};

     

       276
       276
       +
         description = ''

     

       277
       277
       +
           Configuration for Foo, see

     

       278
       278
       +
           &lt;link xlink:href=&quot;https://example.com/docs/foo&quot;/&gt;

     

       279
       279
       +
           for supported values.

     

       280
       280
       +
         '';

     

       281
       281
       +
       };

     

       282
       282
       +
       </programlisting>

     

       283
       283
       +
           </section>

     

       284
       284
       +
         </section>

     

       285
       285
       +
       </section>