nixpkgs/pkgs/lib/options.nix

# Nixpkgs/NixOS option handling.

let lib = import ./default.nix; in

with { inherit (builtins) head length; };
with import ./trivial.nix;
with import ./lists.nix;
with import ./misc.nix;
with import ./attrsets.nix;
with import ./properties.nix;

rec {

  inherit (lib) typeOf;
  

  isOption = attrs: (typeOf attrs) == "option";
  mkOption = attrs: attrs // {
    _type = "option";
    # name (this is the name of the attributem it is automatically generated by the traversal)
    # default (value used when no definition exists)
    # example (documentation)
    # description (documentation)
    # type (option type, provide a default merge function and ensure type correctness)
    # merge (function used to merge definitions into one definition: [ /type/ ] -> /type/)
    # apply (convert the option value to ease the manipulation of the option result)
    # options (set of sub-options declarations & definitions)
    # extraConfigs (list of possible configurations)
  };

  mapSubOptions = f: opt:
    if opt ? options then
      opt // {
        options = map f (toList opt.options);
      }
    else
      opt;

  # Make the option declaration more user-friendly by adding default
  # settings and some verifications based on the declaration content (like
  # type correctness).
  addOptionMakeUp = {name, recurseInto}: decl:
    let
      init = {
        inherit name;
        merge = mergeDefaultOption;
        apply = lib.id;
      };

      functionsFromType = opt:
        if decl ? type && decl.type ? merge then
          opt
          // optionalAttrs (decl.type ? merge) { inherit (decl.type) merge; }
          // optionalAttrs (decl.type ? check) { inherit (decl.type) check; }
        else
          opt;

      addDeclaration = opt: opt // decl;

      ensureMergeInputType = opt:
        if opt ? check then
          opt // {
            merge = list:
              if all opt.check list then
                opt.merge list
              else
                throw "One of the definitions has a bad type.";
          }
        else opt;

      ensureDefaultType = opt:
        if opt ? check && opt ? default then
          opt // {
            default =
              if opt.check opt.default then
                opt.default
              else
                throw "The default value has a bad type.";
          }
        else opt;

      handleOptionSets = opt:
        if opt ? type && opt.type.hasOptions then
          let
            
            optionConfig = vals: args:
              map (f: lib.applyIfFunction f args)
                (opt.options ++ toList vals);

            # Evaluate sub-modules.
            subModuleMerge = path: vals:
              lib.fix (args:
                let result = recurseInto path (optionConfig vals args); in {
                  inherit (result) config options;
                  name = lib.removePrefix (opt.name + ".") path;
                }
              );

            # Add _options in sub-modules to make it viewable from other
            # modules.
            subModuleMergeConfig = path: vals:
              let result = subModuleMerge path vals; in
                { _args = result; } // result.config;

          in
            opt // {
              merge = list:
                opt.type.iter
                  subModuleMergeConfig
                  opt.name
                  (opt.merge list);
              options =
                let path = opt.type.docPath opt.name; in
                  (subModuleMerge path []).options;
            }
        else
          opt;
    in
      foldl (opt: f: f opt) init [
        # default settings
        functionsFromType

        # user settings
        addDeclaration

        # override settings
        ensureMergeInputType
        ensureDefaultType
        handleOptionSets
      ];

  # Merge a list of options containning different field.  This is useful to
  # separate the merge & apply fields from the interface.
  mergeOptionDecls = opts:
    if opts == [] then {}
    else if length opts == 1 then
      let opt = head opts; in
      if opt ? options then
        opt // { options = toList opt.options; }
      else
        opt
    else
      fold (opt1: opt2:
        lib.addErrorContext "opt1 = ${lib.showVal opt1}\nopt2 = ${lib.showVal opt2}" (
        # You cannot merge if two options have the same field.
        assert opt1 ? default -> ! opt2 ? default;
        assert opt1 ? example -> ! opt2 ? example;
        assert opt1 ? description -> ! opt2 ? description;
        assert opt1 ? merge -> ! opt2 ? merge;
        assert opt1 ? apply -> ! opt2 ? apply;
        assert opt1 ? type -> ! opt2 ? type;
        opt1 // opt2
        // optionalAttrs (opt1 ? options || opt2 ? options) {
            options =
               (toList (opt1.options or []))
            ++ (toList (opt2.options or []));
          }
        // optionalAttrs (opt1 ? extraConfigs || opt2 ? extraConfigs) {
            extraConfigs = opt1.extraConfigs or [] ++ opt2.extraConfigs or [];
          }
      )) {} opts;

  
  # !!! This function will be removed because this can be done with the
  # multiple option declarations.
  addDefaultOptionValues = defs: opts: opts //
    builtins.listToAttrs (map (defName:
      { name = defName;
        value = 
          let
            defValue = builtins.getAttr defName defs;
            optValue = builtins.getAttr defName opts;
          in
          if typeOf defValue == "option"
          then
            # `defValue' is an option.
            if hasAttr defName opts
            then builtins.getAttr defName opts
            else defValue.default
          else
            # `defValue' is an attribute set containing options.
            # So recurse.
            if hasAttr defName opts && isAttrs optValue 
            then addDefaultOptionValues defValue optValue
            else addDefaultOptionValues defValue {};
      }
    ) (attrNames defs));

  mergeDefaultOption = list:
    if length list == 1 then head list
    else if all builtins.isFunction list then x: mergeDefaultOption (map (f: f x) list)
    else if all isList list then concatLists list
    else if all isAttrs list then fold lib.mergeAttrs {} list
    else if all builtins.isBool list then fold lib.or false list
    else if all builtins.isString list then lib.concatStrings list
    else if all builtins.isInt list && all (x: x == head list) list
         then head list
    else throw "Cannot merge values.";

  mergeTypedOption = typeName: predicate: merge: list:
    if all predicate list then merge list
    else throw "Expect a ${typeName}.";

  mergeEnableOption = mergeTypedOption "boolean"
    (x: true == x || false == x) (fold lib.or false);

  mergeListOption = mergeTypedOption "list" isList concatLists;

  mergeStringOption = mergeTypedOption "string"
    (x: if builtins ? isString then builtins.isString x else x + "")
    lib.concatStrings;

  mergeOneOption = list:
    if list == [] then abort "This case should never happen."
    else if length list != 1 then throw "Multiple definitions. Only one is allowed for this option."
    else head list;


  fixableMergeFun = merge: f: config:
    merge (
      # generate the list of option sets.
      f config
    );

  fixableMergeModules = merge: initModules: {...}@args: config:
    fixableMergeFun merge (config:
      lib.moduleClosure initModules (args // { inherit config; })
    ) config;


  fixableDefinitionsOf = initModules: {...}@args:
    fixableMergeModules (modules: (lib.moduleMerge "" modules).config) initModules args;

  fixableDeclarationsOf = initModules: {...}@args:
    fixableMergeModules (modules: (lib.moduleMerge "" modules).options) initModules args;

  definitionsOf = initModules: {...}@args:
    (lib.fix (module:
      fixableMergeModules (lib.moduleMerge "") initModules args module.config
    )).config;

  declarationsOf = initModules: {...}@args:
    (lib.fix (module:
      fixableMergeModules (lib.moduleMerge "") initModules args module.config
    )).options;


  # Generate documentation template from the list of option declaration like
  # the set generated with filterOptionSets.
  optionAttrSetToDocList = ignore: newOptionAttrSetToDocList;
  newOptionAttrSetToDocList = attrs:
    let options = collect isOption attrs; in
      fold (opt: rest:
        let
          docOption = {
            inherit (opt) name;
            description = if opt ? description then opt.description else
              throw "Option ${opt.name}: No description.";

            declarations = map (x: toString x.source) opt.declarations;
            #definitions = map (x: toString x.source) opt.definitions;
          }
          // optionalAttrs (opt ? example) { example = scrubOptionValue opt.example; }
          // optionalAttrs (opt ? default) { default = scrubOptionValue opt.default; }
          // optionalAttrs (opt ? defaultText) { default = opt.defaultText; };

          subOptions =
            if opt ? options then
              newOptionAttrSetToDocList opt.options
            else
              [];
        in
          [ docOption ] ++ subOptions ++ rest
      ) [] options;


  /* This function recursively removes all derivation attributes from
     `x' except for the `name' attribute.  This is to make the
     generation of `options.xml' much more efficient: the XML
     representation of derivations is very large (on the order of
     megabytes) and is not actually used by the manual generator. */
  scrubOptionValue = x: 
    if isDerivation x then { type = "derivation"; drvPath = x.name; outPath = x.name; name = x.name; }
    else if isList x then map scrubOptionValue x
    else if isAttrs x then mapAttrs (n: v: scrubOptionValue v) (removeAttrs x ["_args"])
    else x;


  /* For use in the ‘example’ option attribute.  It causes the given
     text to be included verbatim in documentation.  This is necessary
     for example values that are not simple values, e.g.,
     functions. */
  literalExample = text: { _type = "literalExample"; inherit text; };


}