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nixos/docs/option-declarations: Document mkEnableOption and mkPackageOption
This is a squashed commit. These are the original commit messages: lib/option: Improve comment better comment Update documentation Updated nixos/doc/manual/development/options-declarations.md with info on mkEnableOption and mkPackageOption. Updated the comment on mkEnableOption in lib/options.nix remove trailing whitespace nixos/doc/option-declarations: Update IDs & formatting nixos/docs/option-declarations: Escape angle brackets Build DB from MD (Amended) Fix typo Co-authored-by: pennae <82953136+pennae@users.noreply.github.com> (Amended) Build DB from MD (again)
This commit is contained in:
Anselm Schüler
parent
fdf7ede344
commit
c008b3d100
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@ -100,12 +100,37 @@ rec {
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type = lib.types.bool;
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};
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/* Creaties an Option attribute set for an option that specifies the
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package a module should use.
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/* Creates an Option attribute set for an option that specifies the
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package a module should use for some purpose.
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The argument default is an attribute set path in pkgs.
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Type: mkPackageOption :: pkgs -> string -> { default :: [string], example :: null | string | [string] } -> option
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The package is specified as a list of strings representing its attribute path in nixpkgs.
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Because of this, you need to pass nixpkgs itself as the first argument.
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The second argument is the name of the option, used in the description "The <name> package to use.".
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You can also pass an example value, either a literal string or a package's attribute path.
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You can omit the default path if the name of the option is also attribute path in nixpkgs.
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Example:
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mkPackageOption pkgs "hello" { }
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=> { _type = "option"; default = «derivation /nix/store/3r2vg51hlxj3cx5vscp0vkv60bqxkaq0-hello-2.10.drv»; defaultText = { ... }; description = "The hello package to use."; type = { ... }; }
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Example:
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mkPackageOption pkgs "GHC" {
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default = [ "ghc" ];
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example = "pkgs.haskell.package.ghc921.ghc.withPackages (hkgs: [ hkgs.primes ])";
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}
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=> { _type = "option"; default = «derivation /nix/store/jxx55cxsjrf8kyh3fp2ya17q99w7541r-ghc-8.10.7.drv»; defaultText = { ... }; description = "The GHC package to use."; example = { ... }; type = { ... }; }
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*/
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mkPackageOption = pkgs: name:
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mkPackageOption =
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# Package set (a specific version of nixpkgs)
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pkgs:
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# Name for the package, shown in option description
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name:
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{ default ? [ name ], example ? null }:
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let default' = if !isList default then [ default ] else default;
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in mkOption {
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@ -57,6 +57,80 @@ The function `mkOption` accepts the following arguments.
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: A textual description of the option, in DocBook format, that will be
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included in the NixOS manual.
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## Utility functions for common option patterns {#sec-option-declarations-util}
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### `mkEnableOption` {#sec-option-declarations-util-mkEnableOption}
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Creates an Option attribute set for a boolean value option i.e an
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option to be toggled on or off.
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This function takes a single string argument, the name of the thing to be toggled.
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The option's description is "Whether to enable \<name\>.".
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For example:
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::: {#ex-options-declarations-util-mkEnableOption-magic .example}
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```nix
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lib.mkEnableOption "magic"
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# is like
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lib.mkOption {
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type = lib.types.bool;
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default = false;
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example = true;
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description = "Whether to enable magic.";
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}
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```
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### `mkPackageOption` {#sec-option-declarations-util-mkPackageOption}
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Usage:
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```nix
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mkPackageOption pkgs "name" { default = [ "path" "in" "pkgs" ]; example = "literal example"; }
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```
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Creates an Option attribute set for an option that specifies the package a module should use for some purpose.
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**Note**: You shouldn’t necessarily make package options for all of your modules. You can always overwrite a specific package throughout nixpkgs by using [nixpkgs overlays](https://nixos.org/manual/nixpkgs/stable/#chap-overlays).
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The default package is specified as a list of strings representing its attribute path in nixpkgs. Because of this, you need to pass nixpkgs itself as the first argument.
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The second argument is the name of the option, used in the description "The \<name\> package to use.". You can also pass an example value, either a literal string or a package's attribute path.
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You can omit the default path if the name of the option is also attribute path in nixpkgs.
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::: {#ex-options-declarations-util-mkPackageOption .title}
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Examples:
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::: {#ex-options-declarations-util-mkPackageOption-hello .example}
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```nix
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lib.mkPackageOption pkgs "hello" { }
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# is like
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lib.mkOption {
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type = lib.types.package;
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default = pkgs.hello;
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defaultText = lib.literalExpression "pkgs.hello";
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description = "The hello package to use.";
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}
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```
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::: {#ex-options-declarations-util-mkPackageOption-ghc .example}
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```nix
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lib.mkPackageOption pkgs "GHC" {
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default = [ "ghc" ];
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example = "pkgs.haskell.package.ghc921.ghc.withPackages (hkgs: [ hkgs.primes ])";
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}
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# is like
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lib.mkOption {
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type = lib.types.package;
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default = pkgs.ghc;
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defaultText = lib.literalExpression "pkgs.ghc";
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example = lib.literalExpression "pkgs.haskell.package.ghc921.ghc.withPackages (hkgs: [ hkgs.primes ])";
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description = "The GHC package to use.";
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}
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```
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## Extensible Option Types {#sec-option-declarations-eot}
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Extensible option types is a feature that allow to extend certain types
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@ -97,25 +97,122 @@ options = {
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</listitem>
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</varlistentry>
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</variablelist>
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<section xml:id="sec-option-declarations-util">
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<title>Utility functions for common option patterns</title>
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<section xml:id="sec-option-declarations-util-mkEnableOption">
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<title><literal>mkEnableOption</literal></title>
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<para>
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Creates an Option attribute set for a boolean value option i.e
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an option to be toggled on or off.
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</para>
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<para>
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This function takes a single string argument, the name of the
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thing to be toggled.
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</para>
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<para>
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The option’s description is <quote>Whether to enable
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<name>.</quote>.
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</para>
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<para>
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For example:
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</para>
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<anchor xml:id="ex-options-declarations-util-mkEnableOption-magic" />
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<programlisting language="bash">
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lib.mkEnableOption "magic"
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# is like
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lib.mkOption {
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type = lib.types.bool;
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default = false;
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example = true;
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description = "Whether to enable magic.";
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}
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</programlisting>
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<section xml:id="sec-option-declarations-util-mkPackageOption">
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<title><literal>mkPackageOption</literal></title>
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<para>
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Usage:
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</para>
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<programlisting language="bash">
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mkPackageOption pkgs "name" { default = [ "path" "in" "pkgs" ]; example = "literal example"; }
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</programlisting>
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<para>
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Creates an Option attribute set for an option that specifies
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the package a module should use for some purpose.
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</para>
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<para>
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<emphasis role="strong">Note</emphasis>: You shouldn’t
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necessarily make package options for all of your modules. You
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can always overwrite a specific package throughout nixpkgs by
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using
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<link xlink:href="https://nixos.org/manual/nixpkgs/stable/#chap-overlays">nixpkgs
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overlays</link>.
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</para>
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<para>
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The default package is specified as a list of strings
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representing its attribute path in nixpkgs. Because of this,
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you need to pass nixpkgs itself as the first argument.
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</para>
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<para>
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The second argument is the name of the option, used in the
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description <quote>The <name> package to use.</quote>.
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You can also pass an example value, either a literal string or
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a package’s attribute path.
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</para>
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<para>
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You can omit the default path if the name of the option is
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also attribute path in nixpkgs.
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</para>
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<anchor xml:id="ex-options-declarations-util-mkPackageOption" />
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<para>
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Examples:
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</para>
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<anchor xml:id="ex-options-declarations-util-mkPackageOption-hello" />
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<programlisting language="bash">
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lib.mkPackageOption pkgs "hello" { }
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# is like
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lib.mkOption {
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type = lib.types.package;
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default = pkgs.hello;
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defaultText = lib.literalExpression "pkgs.hello";
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description = "The hello package to use.";
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}
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</programlisting>
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<anchor xml:id="ex-options-declarations-util-mkPackageOption-ghc" />
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<programlisting language="bash">
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lib.mkPackageOption pkgs "GHC" {
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default = [ "ghc" ];
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example = "pkgs.haskell.package.ghc921.ghc.withPackages (hkgs: [ hkgs.primes ])";
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}
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# is like
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lib.mkOption {
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type = lib.types.package;
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default = pkgs.ghc;
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defaultText = lib.literalExpression "pkgs.ghc";
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example = lib.literalExpression "pkgs.haskell.package.ghc921.ghc.withPackages (hkgs: [ hkgs.primes ])";
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description = "The GHC package to use.";
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}
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</programlisting>
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<section xml:id="sec-option-declarations-eot">
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<title>Extensible Option Types</title>
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<para>
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Extensible option types is a feature that allow to extend certain
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types declaration through multiple module files. This feature only
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work with a restricted set of types, namely
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<literal>enum</literal> and <literal>submodules</literal> and any
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composed forms of them.
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Extensible option types is a feature that allow to extend
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certain types declaration through multiple module files.
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This feature only work with a restricted set of types,
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namely <literal>enum</literal> and
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<literal>submodules</literal> and any composed forms of
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them.
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</para>
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<para>
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Extensible option types can be used for <literal>enum</literal>
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options that affects multiple modules, or as an alternative to
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related <literal>enable</literal> options.
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Extensible option types can be used for
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<literal>enum</literal> options that affects multiple
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modules, or as an alternative to related
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<literal>enable</literal> options.
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</para>
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<para>
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As an example, we will take the case of display managers. There is
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a central display manager module for generic display manager
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options and a module file per display manager backend (sddm, gdm
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...).
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As an example, we will take the case of display managers.
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There is a central display manager module for generic
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display manager options and a module file per display
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manager backend (sddm, gdm ...).
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</para>
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<para>
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There are two approach to this module structure:
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@ -124,13 +221,15 @@ options = {
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<listitem>
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<para>
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Managing the display managers independently by adding an
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enable option to every display manager module backend. (NixOS)
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enable option to every display manager module backend.
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(NixOS)
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</para>
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</listitem>
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<listitem>
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<para>
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Managing the display managers in the central module by adding
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an option to select which display manager backend to use.
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Managing the display managers in the central module by
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adding an option to select which display manager backend
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to use.
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</para>
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</listitem>
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</itemizedlist>
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@ -138,43 +237,44 @@ options = {
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Both approaches have problems.
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</para>
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<para>
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Making backends independent can quickly become hard to manage. For
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display managers, there can be only one enabled at a time, but the
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type system can not enforce this restriction as there is no
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relation between each backend <literal>enable</literal> option. As
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a result, this restriction has to be done explicitely by adding
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assertions in each display manager backend module.
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Making backends independent can quickly become hard to
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manage. For display managers, there can be only one enabled
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at a time, but the type system can not enforce this
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restriction as there is no relation between each backend
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<literal>enable</literal> option. As a result, this
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restriction has to be done explicitely by adding assertions
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in each display manager backend module.
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</para>
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<para>
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On the other hand, managing the display managers backends in the
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central module will require to change the central module option
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every time a new backend is added or removed.
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On the other hand, managing the display managers backends in
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the central module will require to change the central module
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option every time a new backend is added or removed.
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</para>
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<para>
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By using extensible option types, it is possible to create a
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placeholder option in the central module
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(<link linkend="ex-option-declaration-eot-service">Example:
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Extensible type placeholder in the service module</link>), and to
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extend it in each backend module
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Extensible type placeholder in the service module</link>),
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and to extend it in each backend module
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(<link linkend="ex-option-declaration-eot-backend-gdm">Example:
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Extending
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<literal>services.xserver.displayManager.enable</literal> in the
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<literal>gdm</literal> module</link>,
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<literal>services.xserver.displayManager.enable</literal> in
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the <literal>gdm</literal> module</link>,
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<link linkend="ex-option-declaration-eot-backend-sddm">Example:
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Extending
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<literal>services.xserver.displayManager.enable</literal> in the
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<literal>sddm</literal> module</link>).
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<literal>services.xserver.displayManager.enable</literal> in
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the <literal>sddm</literal> module</link>).
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</para>
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<para>
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As a result, <literal>displayManager.enable</literal> option
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values can be added without changing the main service module file
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and the type system automatically enforce that there can only be a
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single display manager enabled.
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values can be added without changing the main service module
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file and the type system automatically enforce that there
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can only be a single display manager enabled.
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</para>
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<anchor xml:id="ex-option-declaration-eot-service" />
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<para>
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<emphasis role="strong">Example: Extensible type placeholder in
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the service module</emphasis>
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<emphasis role="strong">Example: Extensible type placeholder
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in the service module</emphasis>
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</para>
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<programlisting language="bash">
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services.xserver.displayManager.enable = mkOption {
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@ -185,8 +285,8 @@ services.xserver.displayManager.enable = mkOption {
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<anchor xml:id="ex-option-declaration-eot-backend-gdm" />
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<para>
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<emphasis role="strong">Example: Extending
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<literal>services.xserver.displayManager.enable</literal> in the
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<literal>gdm</literal> module</emphasis>
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<literal>services.xserver.displayManager.enable</literal> in
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the <literal>gdm</literal> module</emphasis>
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</para>
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<programlisting language="bash">
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services.xserver.displayManager.enable = mkOption {
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@ -196,8 +296,8 @@ services.xserver.displayManager.enable = mkOption {
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<anchor xml:id="ex-option-declaration-eot-backend-sddm" />
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<para>
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<emphasis role="strong">Example: Extending
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<literal>services.xserver.displayManager.enable</literal> in the
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<literal>sddm</literal> module</emphasis>
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<literal>services.xserver.displayManager.enable</literal> in
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the <literal>sddm</literal> module</emphasis>
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</para>
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<programlisting language="bash">
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services.xserver.displayManager.enable = mkOption {
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@ -206,16 +306,19 @@ services.xserver.displayManager.enable = mkOption {
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</programlisting>
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<para>
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The placeholder declaration is a standard
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<literal>mkOption</literal> declaration, but it is important that
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extensible option declarations only use the
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<literal>mkOption</literal> declaration, but it is important
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that extensible option declarations only use the
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<literal>type</literal> argument.
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</para>
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<para>
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Extensible option types work with any of the composed variants of
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<literal>enum</literal> such as
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Extensible option types work with any of the composed
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variants of <literal>enum</literal> such as
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<literal>with types; nullOr (enum [ "foo" "bar" ])</literal>
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or
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<literal>with types; listOf (enum [ "foo" "bar" ])</literal>.
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</para>
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</section>
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</section>
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</section>
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</section>
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</section>
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