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diff --git a/nixos/doc/manual/development/option-types.xml b/nixos/doc/manual/development/option-types.xml new file mode 100644 index 000000000000..47dd09158e91 --- /dev/null +++ b/nixos/doc/manual/development/option-types.xml @@ -0,0 +1,770 @@ +<section xmlns="http://docbook.org/ns/docbook" + xmlns:xlink="http://www.w3.org/1999/xlink" + xmlns:xi="http://www.w3.org/2001/XInclude" + version="5.0" + xml:id="sec-option-types"> + <title>Options Types</title> + + <para> + Option types are a way to put constraints on the values a module option can + take. Types are also responsible of how values are merged in case of multiple + value definitions. + </para> + + <section> + <title>Basic Types</title> + + <para> + Basic types are the simplest available types in the module system. Basic + types include multiple string types that mainly differ in how definition + merging is handled. + </para> + + <variablelist> + <varlistentry> + <term> + <varname>types.attrs</varname> + </term> + <listitem> + <para> + A free-form attribute set. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.bool</varname> + </term> + <listitem> + <para> + A boolean, its values can be <literal>true</literal> or + <literal>false</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.path</varname> + </term> + <listitem> + <para> + A filesystem path, defined as anything that when coerced to a string + starts with a slash. Even if derivations can be considered as path, the + more specific <literal>types.package</literal> should be preferred. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.package</varname> + </term> + <listitem> + <para> + A derivation or a store path. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + Integer-related types: + </para> + + <variablelist> + <varlistentry> + <term> + <varname>types.int</varname> + </term> + <listitem> + <para> + A signed integer. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.ints.{s8, s16, s32}</varname> + </term> + <listitem> + <para> + Signed integers with a fixed length (8, 16 or 32 bits). They go from + <inlineequation><mathphrase>−2<superscript>n</superscript>/2</mathphrase> + </inlineequation> to <inlineequation> + <mathphrase>2<superscript>n</superscript>/2−1</mathphrase> + </inlineequation> respectively (e.g. <literal>−128</literal> to + <literal>127</literal> for 8 bits). + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.ints.unsigned</varname> + </term> + <listitem> + <para> + An unsigned integer (that is >= 0). + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.ints.{u8, u16, u32}</varname> + </term> + <listitem> + <para> + Unsigned integers with a fixed length (8, 16 or 32 bits). They go from + <inlineequation><mathphrase>0</mathphrase></inlineequation> to + <inlineequation> + <mathphrase>2<superscript>n</superscript>−1</mathphrase> + </inlineequation> respectively (e.g. <literal>0</literal> to + <literal>255</literal> for 8 bits). + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.ints.positive</varname> + </term> + <listitem> + <para> + A positive integer (that is > 0). + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + String-related types: + </para> + + <variablelist> + <varlistentry> + <term> + <varname>types.str</varname> + </term> + <listitem> + <para> + A string. Multiple definitions cannot be merged. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.lines</varname> + </term> + <listitem> + <para> + A string. Multiple definitions are concatenated with a new line + <literal>"\n"</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.commas</varname> + </term> + <listitem> + <para> + A string. Multiple definitions are concatenated with a comma + <literal>","</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.envVar</varname> + </term> + <listitem> + <para> + A string. Multiple definitions are concatenated with a collon + <literal>":"</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.strMatching</varname> + </term> + <listitem> + <para> + A string matching a specific regular expression. Multiple definitions + cannot be merged. The regular expression is processed using + <literal>builtins.match</literal>. + </para> + </listitem> + </varlistentry> + </variablelist> + </section> + + <section> + <title>Value Types</title> + + <para> + Value types are types that take a value parameter. + </para> + + <variablelist> + <varlistentry> + <term> + <varname>types.enum</varname> <replaceable>l</replaceable> + </term> + <listitem> + <para> + One element of the list <replaceable>l</replaceable>, e.g. + <literal>types.enum [ "left" "right" ]</literal>. Multiple definitions + cannot be merged. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.separatedString</varname> <replaceable>sep</replaceable> + </term> + <listitem> + <para> + A string with a custom separator <replaceable>sep</replaceable>, e.g. + <literal>types.separatedString "|"</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.ints.between</varname> <replaceable>lowest</replaceable> <replaceable>highest</replaceable> + </term> + <listitem> + <para> + An integer between <replaceable>lowest</replaceable> and + <replaceable>highest</replaceable> (both inclusive). Useful for creating + types like <literal>types.port</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.submodule</varname> <replaceable>o</replaceable> + </term> + <listitem> + <para> + A set of sub options <replaceable>o</replaceable>. + <replaceable>o</replaceable> can be an attribute set or a function + returning an attribute set. Submodules are used in composed types to + create modular options. Submodule are detailed in + <xref + linkend='section-option-types-submodule' />. + </para> + </listitem> + </varlistentry> + </variablelist> + </section> + + <section> + <title>Composed Types</title> + + <para> + Composed types are types that take a type as parameter. <literal>listOf + int</literal> and <literal>either int str</literal> are examples of composed + types. + </para> + + <variablelist> + <varlistentry> + <term> + <varname>types.listOf</varname> <replaceable>t</replaceable> + </term> + <listitem> + <para> + A list of <replaceable>t</replaceable> type, e.g. <literal>types.listOf + int</literal>. Multiple definitions are merged with list concatenation. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.attrsOf</varname> <replaceable>t</replaceable> + </term> + <listitem> + <para> + An attribute set of where all the values are of + <replaceable>t</replaceable> type. Multiple definitions result in the + joined attribute set. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.loaOf</varname> <replaceable>t</replaceable> + </term> + <listitem> + <para> + An attribute set or a list of <replaceable>t</replaceable> type. Multiple + definitions are merged according to the value. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.nullOr</varname> <replaceable>t</replaceable> + </term> + <listitem> + <para> + <literal>null</literal> or type <replaceable>t</replaceable>. Multiple + definitions are merged according to type <replaceable>t</replaceable>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.uniq</varname> <replaceable>t</replaceable> + </term> + <listitem> + <para> + Ensures that type <replaceable>t</replaceable> cannot be merged. It is + used to ensure option definitions are declared only once. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.either</varname> <replaceable>t1</replaceable> <replaceable>t2</replaceable> + </term> + <listitem> + <para> + Type <replaceable>t1</replaceable> or type <replaceable>t2</replaceable>, + e.g. <literal>with types; either int str</literal>. Multiple definitions + cannot be merged. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>types.coercedTo</varname> <replaceable>from</replaceable> <replaceable>f</replaceable> <replaceable>to</replaceable> + </term> + <listitem> + <para> + Type <replaceable>to</replaceable> or type + <replaceable>from</replaceable> which will be coerced to type + <replaceable>to</replaceable> using function <replaceable>f</replaceable> + which takes an argument of type <replaceable>from</replaceable> and + return a value of type <replaceable>to</replaceable>. Can be used to + preserve backwards compatibility of an option if its type was changed. + </para> + </listitem> + </varlistentry> + </variablelist> + </section> + + <section xml:id='section-option-types-submodule'> + <title>Submodule</title> + + <para> + <literal>submodule</literal> is a very powerful type that defines a set of + sub-options that are handled like a separate module. + </para> + + <para> + It takes a parameter <replaceable>o</replaceable>, that should be a set, or + a function returning a set with an <literal>options</literal> key defining + the sub-options. Submodule option definitions are type-checked accordingly + to the <literal>options</literal> declarations. Of course, you can nest + submodule option definitons for even higher modularity. + </para> + + <para> + The option set can be defined directly + (<xref linkend='ex-submodule-direct' />) or as reference + (<xref linkend='ex-submodule-reference' />). + </para> + + <example xml:id='ex-submodule-direct'> + <title>Directly defined submodule</title> +<screen> +options.mod = mkOption { + description = "submodule example"; + type = with types; submodule { + options = { + foo = mkOption { + type = int; + }; + bar = mkOption { + type = str; + }; + }; + }; +};</screen> + </example> + + <example xml:id='ex-submodule-reference'> + <title>Submodule defined as a reference</title> +<screen> +let + modOptions = { + options = { + foo = mkOption { + type = int; + }; + bar = mkOption { + type = int; + }; + }; + }; +in +options.mod = mkOption { + description = "submodule example"; + type = with types; submodule modOptions; +};</screen> + </example> + + <para> + The <literal>submodule</literal> type is especially interesting when used + with composed types like <literal>attrsOf</literal> or + <literal>listOf</literal>. When composed with <literal>listOf</literal> + (<xref linkend='ex-submodule-listof-declaration' />), + <literal>submodule</literal> allows multiple definitions of the submodule + option set (<xref linkend='ex-submodule-listof-definition' />). + </para> + + <example xml:id='ex-submodule-listof-declaration'> + <title>Declaration of a list of submodules</title> +<screen> +options.mod = mkOption { + description = "submodule example"; + type = with types; listOf (submodule { + options = { + foo = mkOption { + type = int; + }; + bar = mkOption { + type = str; + }; + }; + }); +};</screen> + </example> + + <example xml:id='ex-submodule-listof-definition'> + <title>Definition of a list of submodules</title> +<screen> +config.mod = [ + { foo = 1; bar = "one"; } + { foo = 2; bar = "two"; } +];</screen> + </example> + + <para> + When composed with <literal>attrsOf</literal> + (<xref linkend='ex-submodule-attrsof-declaration' />), + <literal>submodule</literal> allows multiple named definitions of the + submodule option set (<xref linkend='ex-submodule-attrsof-definition' />). + </para> + + <example xml:id='ex-submodule-attrsof-declaration'> + <title>Declaration of attribute sets of submodules</title> +<screen> +options.mod = mkOption { + description = "submodule example"; + type = with types; attrsOf (submodule { + options = { + foo = mkOption { + type = int; + }; + bar = mkOption { + type = str; + }; + }; + }); +};</screen> + </example> + + <example xml:id='ex-submodule-attrsof-definition'> + <title>Declaration of attribute sets of submodules</title> +<screen> +config.mod.one = { foo = 1; bar = "one"; }; +config.mod.two = { foo = 2; bar = "two"; };</screen> + </example> + </section> + + <section> + <title>Extending types</title> + + <para> + Types are mainly characterized by their <literal>check</literal> and + <literal>merge</literal> functions. + </para> + + <variablelist> + <varlistentry> + <term> + <varname>check</varname> + </term> + <listitem> + <para> + The function to type check the value. Takes a value as parameter and + return a boolean. It is possible to extend a type check with the + <literal>addCheck</literal> function + (<xref + linkend='ex-extending-type-check-1' />), or to fully + override the check function + (<xref linkend='ex-extending-type-check-2' />). + </para> + <example xml:id='ex-extending-type-check-1'> + <title>Adding a type check</title> +<screen> +byte = mkOption { + description = "An integer between 0 and 255."; + type = addCheck types.int (x: x >= 0 && x <= 255); +};</screen> + </example> + <example xml:id='ex-extending-type-check-2'> + <title>Overriding a type check</title> +<screen> +nixThings = mkOption { + description = "words that start with 'nix'"; + type = types.str // { + check = (x: lib.hasPrefix "nix" x) + }; +};</screen> + </example> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>merge</varname> + </term> + <listitem> + <para> + Function to merge the options values when multiple values are set. The + function takes two parameters, <literal>loc</literal> the option path as + a list of strings, and <literal>defs</literal> the list of defined values + as a list. It is possible to override a type merge function for custom + needs. + </para> + </listitem> + </varlistentry> + </variablelist> + </section> + + <section> + <title>Custom Types</title> + + <para> + Custom types can be created with the <literal>mkOptionType</literal> + function. As type creation includes some more complex topics such as + submodule handling, it is recommended to get familiar with + <filename + xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/types.nix">types.nix</filename> + code before creating a new type. + </para> + + <para> + The only required parameter is <literal>name</literal>. + </para> + + <variablelist> + <varlistentry> + <term> + <varname>name</varname> + </term> + <listitem> + <para> + A string representation of the type function name. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>definition</varname> + </term> + <listitem> + <para> + Description of the type used in documentation. Give information of the + type and any of its arguments. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>check</varname> + </term> + <listitem> + <para> + A function to type check the definition value. Takes the definition value + as a parameter and returns a boolean indicating the type check result, + <literal>true</literal> for success and <literal>false</literal> for + failure. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>merge</varname> + </term> + <listitem> + <para> + A function to merge multiple definitions values. Takes two parameters: + </para> + <variablelist> + <varlistentry> + <term> + <replaceable>loc</replaceable> + </term> + <listitem> + <para> + The option path as a list of strings, e.g. <literal>["boot" "loader + "grub" "enable"]</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <replaceable>defs</replaceable> + </term> + <listitem> + <para> + The list of sets of defined <literal>value</literal> and + <literal>file</literal> where the value was defined, e.g. <literal>[ { + file = "/foo.nix"; value = 1; } { file = "/bar.nix"; value = 2 } + ]</literal>. The <literal>merge</literal> function should return the + merged value or throw an error in case the values are impossible or + not meant to be merged. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>getSubOptions</varname> + </term> + <listitem> + <para> + For composed types that can take a submodule as type parameter, this + function generate sub-options documentation. It takes the current option + prefix as a list and return the set of sub-options. Usually defined in a + recursive manner by adding a term to the prefix, e.g. <literal>prefix: + elemType.getSubOptions (prefix ++ + [<replaceable>"prefix"</replaceable>])</literal> where + <replaceable>"prefix"</replaceable> is the newly added prefix. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>getSubModules</varname> + </term> + <listitem> + <para> + For composed types that can take a submodule as type parameter, this + function should return the type parameters submodules. If the type + parameter is called <literal>elemType</literal>, the function should just + recursively look into submodules by returning + <literal>elemType.getSubModules;</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>substSubModules</varname> + </term> + <listitem> + <para> + For composed types that can take a submodule as type parameter, this + function can be used to substitute the parameter of a submodule type. It + takes a module as parameter and return the type with the submodule + options substituted. It is usually defined as a type function call with a + recursive call to <literal>substSubModules</literal>, e.g for a type + <literal>composedType</literal> that take an <literal>elemtype</literal> + type parameter, this function should be defined as <literal>m: + composedType (elemType.substSubModules m)</literal>. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>typeMerge</varname> + </term> + <listitem> + <para> + A function to merge multiple type declarations. Takes the type to merge + <literal>functor</literal> as parameter. A <literal>null</literal> return + value means that type cannot be merged. + </para> + <variablelist> + <varlistentry> + <term> + <replaceable>f</replaceable> + </term> + <listitem> + <para> + The type to merge <literal>functor</literal>. + </para> + </listitem> + </varlistentry> + </variablelist> + <para> + Note: There is a generic <literal>defaultTypeMerge</literal> that work + with most of value and composed types. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>functor</varname> + </term> + <listitem> + <para> + An attribute set representing the type. It is used for type operations + and has the following keys: + </para> + <variablelist> + <varlistentry> + <term> + <varname>type</varname> + </term> + <listitem> + <para> + The type function. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>wrapped</varname> + </term> + <listitem> + <para> + Holds the type parameter for composed types. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>payload</varname> + </term> + <listitem> + <para> + Holds the value parameter for value types. The types that have a + <literal>payload</literal> are the <literal>enum</literal>, + <literal>separatedString</literal> and <literal>submodule</literal> + types. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + <varname>binOp</varname> + </term> + <listitem> + <para> + A binary operation that can merge the payloads of two same types. + Defined as a function that take two payloads as parameters and return + the payloads merged. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + </variablelist> + </section> +</section> |