nixpkgs/lib/options.nix

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# Nixpkgs/NixOS option handling.
let lib = import ./default.nix; in
with import ./trivial.nix;
with import ./lists.nix;
with import ./misc.nix;
with import ./attrsets.nix;
with import ./strings.nix;
rec {
isOption = lib.isType "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)
};
mkEnableOption = name: mkOption {
default = false;
example = true;
description = "Whether to enable ${name}.";
type = lib.types.bool;
};
# !!! 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 isOption defValue
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:
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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."
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else if length list != 1 then throw "Multiple definitions. Only one is allowed for this option."
else head list;
# Generate documentation template from the list of option declaration like
# the set generated with filterOptionSets.
optionAttrSetToDocList = attrs:
let options = collect isOption attrs; in
fold (opt: rest:
let
docOption = {
inherit (opt) name;
description = opt.description or (throw "Option ${opt.name}: No description.");
declarations = map (x: toString x.source) opt.declarations;
#definitions = map (x: toString x.source) opt.definitions;
internal = opt.internal or false;
visible = opt.visible or true;
}
// 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
optionAttrSetToDocList opt.options
else
[];
in
# FIXME: expensive (O(n^2)
[ 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; };
/* Helper functions. */
showOption = concatStringsSep ".";
}