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with import ./lists.nix;
with import ./strings.nix;
with import ./trivial.nix;
with import ./attrsets.nix;
with import ./options.nix;
with import ./debug.nix;
with import ./types.nix;
rec {
/* Evaluate a set of modules. The result is a set of two
attributes: options: the nested set of all option declarations,
and config: the nested set of all option values.
!!! Please think twice before adding to this argument list! The more
that is specified here instead of in the modules themselves the harder
it is to transparently move a set of modules to be a submodule of another
config (as the proper arguments need to be replicated at each call to
evalModules) and the less declarative the module set is. */
evalModules = { modules
, prefix ? []
, # This should only be used for special arguments that need to be evaluated
# when resolving module structure (like in imports). For everything else,
# there's _module.args. If specialArgs.modulesPath is defined it will be
# used as the base path for disabledModules.
specialArgs ? {}
, # This would be remove in the future, Prefer _module.args option instead.
args ? {}
, # This would be remove in the future, Prefer _module.check option instead.
check ? true
# This internal module declare internal options under the `_module'
# attribute. These options are fragile, as they are used by the
# module system to change the interpretation of modules.
internalModule = rec {
_file = ./modules.nix;
key = _file;
options = {
_module.args = mkOption {
type = types.attrsOf types.unspecified;
internal = true;
description = "Arguments passed to each module.";
_module.check = mkOption {
type = types.bool;
internal = true;
default = check;
description = "Whether to check whether all option definitions have matching declarations.";
config = {
_module.args = args;
closed = closeModules (modules ++ [ internalModule ]) ({ inherit config options; lib = import ./.; } // specialArgs);
options = mergeModules prefix (reverseList (filterModules (specialArgs.modulesPath or "") closed));
# Traverse options and extract the option values into the final
# config set. At the same time, check whether all option
# definitions have matching declarations.
# !!! _module.check's value can't depend on any other config values
# without an infinite recursion. One way around this is to make the
# 'config' passed around to the modules be unconditionally unchecked,
# and only do the check in 'result'.
config = yieldConfig prefix options;
yieldConfig = prefix: set:
let res = removeAttrs (mapAttrs (n: v:
if isOption v then v.value
else yieldConfig (prefix ++ [n]) v) set) ["_definedNames"];
if options._module.check.value && set ? _definedNames then
foldl' (res: m:
foldl' (res: name:
if set ? ${name} then res else throw "The option `${showOption (prefix ++ [name])}' defined in `${m.file}' does not exist.")
res m.names)
res set._definedNames
result = { inherit options config; };
in result;
# Filter disabled modules. Modules can be disabled allowing
# their implementation to be replaced.
filterModules = modulesPath: modules:
moduleKey = m: if isString m then toString modulesPath + "/" + m else toString m;
disabledKeys = map moduleKey (concatMap (m: m.disabledModules) modules);
filter (m: !(elem m.key disabledKeys)) modules;
/* Close a set of modules under the imports relation. */
closeModules = modules: args:
toClosureList = file: parentKey: imap (n: x:
if isAttrs x || isFunction x then
let key = "${parentKey}:anon-${toString n}"; in
unifyModuleSyntax file key (unpackSubmodule (applyIfFunction key) x args)
let file = toString x; key = toString x; in
unifyModuleSyntax file key (applyIfFunction key (import x) args));
builtins.genericClosure {
startSet = toClosureList unknownModule "" modules;
operator = m: toClosureList m.file m.key m.imports;
/* Massage a module into canonical form, that is, a set consisting
of options, config and imports attributes. */
unifyModuleSyntax = file: key: m:
let metaSet = if m ? meta
then { meta = m.meta; }
else {};
if m ? config || m ? options then
let badAttrs = removeAttrs m ["_file" "key" "disabledModules" "imports" "options" "config" "meta"]; in
if badAttrs != {} then
throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'. This is caused by assignments to the top-level attributes `config' or `options'."
{ file = m._file or file;
key = toString m.key or key;
disabledModules = m.disabledModules or [];
imports = m.imports or [];
options = m.options or {};
config = mkMerge [ (m.config or {}) metaSet ];
{ file = m._file or file;
key = toString m.key or key;
disabledModules = m.disabledModules or [];
imports = m.require or [] ++ m.imports or [];
options = {};
config = mkMerge [ (removeAttrs m ["_file" "key" "disabledModules" "require" "imports"]) metaSet ];
applyIfFunction = key: f: args@{ config, options, lib, ... }: if isFunction f then
# Module arguments are resolved in a strict manner when attribute set
# deconstruction is used. As the arguments are now defined with the
# config._module.args option, the strictness used on the attribute
# set argument would cause an infinite loop, if the result of the
# option is given as argument.
# To work-around the strictness issue on the deconstruction of the
# attributes set argument, we create a new attribute set which is
# constructed to satisfy the expected set of attributes. Thus calling
# a module will resolve strictly the attributes used as argument but
# not their values. The values are forwarding the result of the
# evaluation of the option.
requiredArgs = builtins.attrNames (builtins.functionArgs f);
context = name: ''while evaluating the module argument `${name}' in "${key}":'';
extraArgs = builtins.listToAttrs (map (name: {
inherit name;
value = addErrorContext (context name)
(args.${name} or config._module.args.${name});
}) requiredArgs);
# Note: we append in the opposite order such that we can add an error
# context on the explicited arguments of "args" too. This update
# operator is used to make the "args@{ ... }: with args.lib;" notation
# works.
in f (args // extraArgs)
/* We have to pack and unpack submodules. We cannot wrap the expected
result of the function as we would no longer be able to list the arguments
of the submodule. (see applyIfFunction) */
unpackSubmodule = unpack: m: args:
if isType "submodule" m then
{ _file = m.file; } // (unpack m.submodule args)
else unpack m args;
packSubmodule = file: m:
{ _type = "submodule"; file = file; submodule = m; };
/* Merge a list of modules. This will recurse over the option
declarations in all modules, combining them into a single set.
At the same time, for each option declaration, it will merge the
corresponding option definitions in all machines, returning them
in the value attribute of each option. */
mergeModules = prefix: modules:
mergeModules' prefix modules
(concatMap (m: map (config: { inherit (m) file; inherit config; }) (pushDownProperties m.config)) modules);
mergeModules' = prefix: options: configs:
listToAttrs (map (name: {
# We're descending into attribute ‘name’.
inherit name;
value =
loc = prefix ++ [name];
# Get all submodules that declare ‘name’.
decls = concatMap (m:
if m.options ? ${name}
then [ { inherit (m) file; options = m.options.${name}; } ]
else []
) options;
# Get all submodules that define ‘name’.
defns = concatMap (m:
if m.config ? ${name}
then map (config: { inherit (m) file; inherit config; })
(pushDownProperties m.config.${name})
else []
) configs;
nrOptions = count (m: isOption m.options) decls;
# Extract the definitions for this loc
defns' = map (m: { inherit (m) file; value = m.config.${name}; })
(filter (m: m.config ? ${name}) configs);
if nrOptions == length decls then
let opt = fixupOptionType loc (mergeOptionDecls loc decls);
in evalOptionValue loc opt defns'
else if nrOptions != 0 then
firstOption = findFirst (m: isOption m.options) "" decls;
firstNonOption = findFirst (m: !isOption m.options) "" decls;
throw "The option `${showOption loc}' in `${firstOption.file}' is a prefix of options in `${firstNonOption.file}'."
mergeModules' loc decls defns;
}) (concatMap (m: attrNames m.options) options))
// { _definedNames = map (m: { inherit (m) file; names = attrNames m.config; }) configs; };
/* Merge multiple option declarations into a single declaration. In
general, there should be only one declaration of each option.
The exception is the options attribute, which specifies
sub-options. These can be specified multiple times to allow one
module to add sub-options to an option declared somewhere else
(e.g. multiple modules define sub-options for fileSystems).
'loc' is the list of attribute names where the option is located.
'opts' is a list of modules. Each module has an options attribute which
correspond to the definition of 'loc' in 'opt.file'. */
mergeOptionDecls = loc: opts:
foldl' (res: opt:
let t = res.type;
t' = opt.options.type;
mergedType = t.typeMerge t'.functor;
typesMergeable = mergedType != null;
typeSet = if (bothHave "type") && typesMergeable
then { type = mergedType; }
else {};
bothHave = k: opt.options ? ${k} && res ? ${k};
if bothHave "default" ||
bothHave "example" ||
bothHave "description" ||
bothHave "apply" ||
(bothHave "type" && (! typesMergeable))
throw "The option `${showOption loc}' in `${opt.file}' is already declared in ${showFiles res.declarations}."
/* Add the modules of the current option to the list of modules
already collected. The options attribute except either a list of
submodules or a submodule. For each submodule, we add the file of the
current option declaration as the file use for the submodule. If the
submodule defines any filename, then we ignore the enclosing option file. */
options' = toList opt.options.options;
coerceOption = file: opt:
if isFunction opt then packSubmodule file opt
else packSubmodule file { options = opt; };
getSubModules = opt.options.type.getSubModules or null;
submodules =
if getSubModules != null then map (packSubmodule opt.file) getSubModules ++ res.options
else if opt.options ? options then map (coerceOption opt.file) options' ++ res.options
else res.options;
in opt.options // res //
{ declarations = res.declarations ++ [opt.file];
options = submodules;
} // typeSet
) { inherit loc; declarations = []; options = []; } opts;
/* Merge all the definitions of an option to produce the final
config value. */
evalOptionValue = loc: opt: defs:
# Add in the default value for this option, if any.
defs' =
(optional (opt ? default)
{ file = head opt.declarations; value = mkOptionDefault opt.default; }) ++ defs;
# Handle properties, check types, and merge everything together.
res =
if opt.readOnly or false && length defs' > 1 then
throw "The option `${showOption loc}' is read-only, but it's set multiple times."
mergeDefinitions loc opt.type defs';
# Check whether the option is defined, and apply the ‘apply’
# function to the merged value. This allows options to yield a
# value computed from the definitions.
value =
if !res.isDefined then
throw "The option `${showOption loc}' is used but not defined."
else if opt ? apply then
opt.apply res.mergedValue
in opt //
{ value = addErrorContext "while evaluating the option `${showOption loc}':" value;
definitions = map (def: def.value) res.defsFinal;
files = map (def: def.file) res.defsFinal;
inherit (res) isDefined;
# Merge definitions of a value of a given type.
mergeDefinitions = loc: type: defs: rec {
defsFinal =
# Process mkMerge and mkIf properties.
defs' = concatMap (m:
map (value: { inherit (m) file; inherit value; }) (dischargeProperties m.value)
) defs;
# Process mkOverride properties.
defs'' = filterOverrides defs';
# Sort mkOrder properties.
defs''' =
# Avoid sorting if we don't have to.
if any (def: def.value._type or "" == "order") defs''
then sortProperties defs''
else defs'';
in defs''';
# Type-check the remaining definitions, and merge them.
mergedValue = foldl' (res: def:
if type.check def.value then res
else throw "The option value `${showOption loc}' in `${def.file}' is not a ${type.description}.")
(type.merge loc defsFinal) defsFinal;
isDefined = defsFinal != [];
optionalValue =
if isDefined then { value = mergedValue; }
else {};
/* Given a config set, expand mkMerge properties, and push down the
other properties into the children. The result is a list of
config sets that do not have properties at top-level. For
mkMerge [ { boot = set1; } (mkIf cond { boot = set2; services = set3; }) ]
is transformed into
[ { boot = set1; } { boot = mkIf cond set2; services = mkIf cond set3; } ].
This transform is the critical step that allows mkIf conditions
to refer to the full configuration without creating an infinite
pushDownProperties = cfg:
if cfg._type or "" == "merge" then
concatMap pushDownProperties cfg.contents
else if cfg._type or "" == "if" then
map (mapAttrs (n: v: mkIf cfg.condition v)) (pushDownProperties cfg.content)
else if cfg._type or "" == "override" then
map (mapAttrs (n: v: mkOverride cfg.priority v)) (pushDownProperties cfg.content)
else # FIXME: handle mkOrder?
[ cfg ];
/* Given a config value, expand mkMerge properties, and discharge
any mkIf conditions. That is, this is the place where mkIf
conditions are actually evaluated. The result is a list of
config values. For example, mkIf false x yields [],
mkIf true x yields [x], and
mkMerge [ 1 (mkIf true 2) (mkIf true (mkIf false 3)) ]
yields [ 1 2 ].
dischargeProperties = def:
if def._type or "" == "merge" then
concatMap dischargeProperties def.contents
else if def._type or "" == "if" then
if isBool def.condition then
if def.condition then
dischargeProperties def.content
[ ]
throw "mkIf called with a non-Boolean condition"
[ def ];
/* Given a list of config values, process the mkOverride properties,
that is, return the values that have the highest (that is,
numerically lowest) priority, and strip the mkOverride
properties. For example,
[ { file = "/1"; value = mkOverride 10 "a"; }
{ file = "/2"; value = mkOverride 20 "b"; }
{ file = "/3"; value = "z"; }
{ file = "/4"; value = mkOverride 10 "d"; }
[ { file = "/1"; value = "a"; }
{ file = "/4"; value = "d"; }
Note that "z" has the default priority 100.
filterOverrides = defs:
defaultPrio = 100;
getPrio = def: if def.value._type or "" == "override" then def.value.priority else defaultPrio;
highestPrio = foldl' (prio: def: min (getPrio def) prio) 9999 defs;
strip = def: if def.value._type or "" == "override" then def // { value = def.value.content; } else def;
in concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
/* Sort a list of properties. The sort priority of a property is
1000 by default, but can be overriden by wrapping the property
using mkOrder. */
sortProperties = defs:
strip = def:
if def.value._type or "" == "order"
then def // { value = def.value.content; inherit (def.value) priority; }
else def;
defs' = map strip defs;
compare = a: b: (a.priority or 1000) < (b.priority or 1000);
in sort compare defs';
/* Hack for backward compatibility: convert options of type
optionSet to options of type submodule. FIXME: remove
eventually. */
fixupOptionType = loc: opt:
options = opt.options or
(throw "Option `${showOption loc'}' has type optionSet but has no option attribute, in ${showFiles opt.declarations}.");
f = tp:
let optionSetIn = type: ( == type) && ( == "optionSet");
if == "option set" || == "submodule" then
throw "The option ${showOption loc} uses submodules without a wrapping type, in ${showFiles opt.declarations}."
else if optionSetIn "attrsOf" then types.attrsOf (types.submodule options)
else if optionSetIn "loaOf" then types.loaOf (types.submodule options)
else if optionSetIn "listOf" then types.listOf (types.submodule options)
else if optionSetIn "nullOr" then types.nullOr (types.submodule options)
else tp;
if opt.type.getSubModules or null == null
then opt // { type = f (opt.type or types.unspecified); }
else opt // { type = opt.type.substSubModules opt.options; options = []; };
/* Properties. */
mkIf = condition: content:
{ _type = "if";
inherit condition content;
mkAssert = assertion: message: content:
(if assertion then true else throw "\nFailed assertion: ${message}")
mkMerge = contents:
{ _type = "merge";
inherit contents;
mkOverride = priority: content:
{ _type = "override";
inherit priority content;
mkOptionDefault = mkOverride 1001; # priority of option defaults
mkDefault = mkOverride 1000; # used in config sections of non-user modules to set a default
mkForce = mkOverride 50;
mkVMOverride = mkOverride 10; # used by ‘nixos-rebuild build-vm’
mkStrict = builtins.trace "`mkStrict' is obsolete; use `mkOverride 0' instead." (mkOverride 0);
mkFixStrictness = id; # obsolete, no-op
mkOrder = priority: content:
{ _type = "order";
inherit priority content;
mkBefore = mkOrder 500;
mkAfter = mkOrder 1500;
# Convenient property used to transfer all definitions and their
# properties from one option to another. This property is useful for
# renaming options, and also for including properties from another module
# system, including sub-modules.
# { config, options, ... }:
# {
# # 'bar' might not always be defined in the current module-set.
# = mkAliasDefinitions ( or {});
# # 'barbaz' has to be defined in the current module-set.
# config.foobar.paths = mkAliasDefinitions options.barbaz.paths;
# }
# Note, this is different than taking the value of the option and using it
# as a definition, as the new definition will not keep the mkOverride /
# mkDefault properties of the previous option.
mkAliasDefinitions = mkAliasAndWrapDefinitions id;
mkAliasAndWrapDefinitions = wrap: option:
(optional (isOption option && option.isDefined)
(wrap (mkMerge option.definitions)));
/* Compatibility. */
fixMergeModules = modules: args: evalModules { inherit modules args; check = false; };
/* Return a module that causes a warning to be shown if the
specified option is defined. For example,
mkRemovedOptionModule [ "boot" "loader" "grub" "bootDevice" ] "<replacement instructions>"
causes a warning if the user defines boot.loader.grub.bootDevice.
replacementInstructions is a string that provides instructions on
how to achieve the same functionality without the removed option,
or alternatively a reasoning why the functionality is not needed.
replacementInstructions SHOULD be provided!
mkRemovedOptionModule = optionName: replacementInstructions:
{ options, ... }:
{ options = setAttrByPath optionName (mkOption {
visible = false;
config.warnings =
let opt = getAttrFromPath optionName options; in
optional opt.isDefined ''
The option definition `${showOption optionName}' in ${showFiles opt.files} no longer has any effect; please remove it.
/* Return a module that causes a warning to be shown if the
specified "from" option is defined; the defined value is however
forwarded to the "to" option. This can be used to rename options
while providing backward compatibility. For example,
mkRenamedOptionModule [ "boot" "copyKernels" ] [ "boot" "loader" "grub" "copyKernels" ]
forwards any definitions of boot.copyKernels to
boot.loader.grub.copyKernels while printing a warning.
mkRenamedOptionModule = from: to: doRename {
inherit from to;
visible = false;
warn = true;
use = builtins.trace "Obsolete option `${showOption from}' is used. It was renamed to `${showOption to}'.";
/* Return a module that causes a warning to be shown if any of the "from"
option is defined; the defined values can be used in the "mergeFn" to set
the "to" value.
This function can be used to merge multiple options into one that has a
different type.
"mergeFn" takes the module "config" as a parameter and must return a value
of "to" option type.
[ [ "a" "b" "c" ]
[ "d" "e" "f" ] ]
[ "x" "y" "z" ]
let value = p: getAttrFromPath p config;
if (value [ "a" "b" "c" ]) == true then "foo"
else if (value [ "d" "e" "f" ]) == true then "bar"
else "baz")
- options.a.b.c is a removed boolean option
- options.d.e.f is a removed boolean option
- options.x.y.z is a new str option that combines a.b.c and d.e.f
This show a warning if any a.b.c or d.e.f is set, and set the value of
x.y.z to the result of the merge function
mkMergedOptionModule = from: to: mergeFn:
{ config, options, ... }:
options = foldl recursiveUpdate {} (map (path: setAttrByPath path (mkOption {
visible = false;
# To use the value in mergeFn without triggering errors
default = "_mkMergedOptionModule";
})) from);
config = {
warnings = filter (x: x != "") (map (f:
let val = getAttrFromPath f config;
opt = getAttrFromPath f options;
(val != "_mkMergedOptionModule")
"The option `${showOption f}' defined in ${showFiles opt.files} has been changed to `${showOption to}' that has a different type. Please read `${showOption to}' documentation and update your configuration accordingly."
) from);
} // setAttrByPath to (mkMerge
(any (f: (getAttrFromPath f config) != "_mkMergedOptionModule") from)
(mergeFn config)));
/* Single "from" version of mkMergedOptionModule.
Return a module that causes a warning to be shown if the "from" option is
defined; the defined value can be used in the "mergeFn" to set the "to"
This function can be used to change an option into another that has a
different type.
"mergeFn" takes the module "config" as a parameter and must return a value of
"to" option type.
mkChangedOptionModule [ "a" "b" "c" ] [ "x" "y" "z" ]
let value = getAttrFromPath [ "a" "b" "c" ] config;
if value > 100 then "high"
else "normal")
- options.a.b.c is a removed int option
- options.x.y.z is a new str option that supersedes a.b.c
This show a warning if a.b.c is set, and set the value of x.y.z to the
result of the change function
mkChangedOptionModule = from: to: changeFn:
mkMergedOptionModule [ from ] to changeFn;
/* Like mkRenamedOptionModule, but doesn't show a warning. */
mkAliasOptionModule = from: to: doRename {
inherit from to;
visible = true;
warn = false;
use = id;
doRename = { from, to, visible, warn, use }:
toOf = attrByPath to
(abort "Renaming error: option `${showOption to}' does not exists.");
{ config, options, ... }:
{ options = setAttrByPath from (mkOption {
description = "Alias of <option>${showOption to}</option>.";
apply = x: use (toOf config);
config = {
warnings =
let opt = getAttrFromPath from options; in
optional (warn && opt.isDefined)
"The option `${showOption from}' defined in ${showFiles opt.files} has been renamed to `${showOption to}'.";
} // setAttrByPath to (mkAliasDefinitions (getAttrFromPath from options));