nixpkgs/lib/modules.nix at release-26.05 · NixOS/nixpkgs

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{ lib }:

let

inherit (lib)

addErrorContext

all

any

attrByPath

attrNames

catAttrs

concatLists

concatMap

concatStringsSep

elem

filter

foldl'

functionArgs

getAttrFromPath

genericClosure

head

imap1

init

isAttrs

isBool

isFunction

oldestSupportedReleaseIsAtLeast

isList

isString

last

length

mapAttrs

mapAttrsToList

mapAttrsRecursiveCond

min

optional

optionalAttrs

optionalString

pipe

recursiveUpdate

remove

reverseList

sort

sortOn

seq

setAttrByPath

substring

take

throwIfNot

trace

typeOf

types

unsafeGetAttrPos

warn

warnIf

zipAttrs

zipAttrsWith

;

inherit (lib.options)

isOption

mkOption

showDefs

showFiles

showOption

unknownModule

;

inherit (lib.strings)

isConvertibleWithToString

levenshtein

levenshteinAtMost

;

showDeclPrefix =

loc: decl: prefix:

" - option(s) with prefix `${showOption (loc ++ [ prefix ])}' in module `${decl._file}'";

showRawDecls =

loc: decls:

concatStringsSep "\n" (

sort (a: b: a < b) (concatMap (decl: map (showDeclPrefix loc decl) (attrNames decl.options)) decls)

);

/**

See https://nixos.org/manual/nixpkgs/unstable/#module-system-lib-evalModules

or file://./../doc/module-system/module-system.chapter.md

!!! 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 =

evalModulesArgs@{

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 ? { },

# `class`:

# A nominal type for modules. When set and non-null, this adds a check to

# make sure that only compatible modules are imported.

class ? null,

# 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,

let

withWarnings =

warnIf (evalModulesArgs ? args)

"The args argument to evalModules is deprecated. Please set config._module.args instead."

warnIf

(evalModulesArgs ? check)

"The check argument to evalModules is deprecated. Please set config._module.check instead."

legacyModules =

optional (evalModulesArgs ? args) {

config = {

_module.args = args;

};

}

++ optional (evalModulesArgs ? check) {

config = {

_module.check = mkDefault check;

};

regularModules = modules ++ legacyModules;

# 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.

# When extended with extendModules or moduleType, a fresh instance of

# this module is used, to avoid conflicts and allow chaining of

# extendModules.

internalModule = rec {

_file = "lib/modules.nix";

key = _file;

options = {

_module.args = mkOption {

# Because things like `mkIf` are entirely useless for

# `_module.args` (because there's no way modules can check which

# arguments were passed), we'll use `lazyAttrsOf` which drops

# support for that, in turn it's lazy in its values. This means e.g.

# a `_module.args.pkgs = import (fetchTarball { ... }) {}` won't

# start a download when `pkgs` wasn't evaluated.

type = types.lazyAttrsOf types.raw;

# Only render documentation once at the root of the option tree,

# not for all individual submodules.

# Allow merging option decls to make this internal regardless.

if prefix == [ ] then

null # unset => visible

else

"internal"

} =

true;

# TODO: Change the type of this option to a submodule with a

# freeformType, so that individual arguments can be documented

# separately

description = ''

Additional arguments passed to each module in addition to ones

like `lib`, `config`,

and `pkgs`, `modulesPath`.

This option is also available to all submodules. Submodules do not

inherit args from their parent module, nor do they provide args to

their parent module or sibling submodules. The sole exception to

this is the argument `name` which is provided by

parent modules to a submodule and contains the attribute name

the submodule is bound to, or a unique generated name if it is

not bound to an attribute.

Some arguments are already passed by default, of which the

following *cannot* be changed with this option:

- {var}`lib`: The nixpkgs library.

- {var}`config`: The results of all options after merging the values from all modules together.

- {var}`options`: The options declared in all modules.

- {var}`specialArgs`: The `specialArgs` argument passed to `evalModules`.

- All attributes of {var}`specialArgs`

Whereas option values can generally depend on other option values

thanks to laziness, this does not apply to `imports`, which

must be computed statically before anything else.

For this reason, callers of the module system can provide `specialArgs`

which are available during import resolution.

For NixOS, `specialArgs` includes

{var}`modulesPath`, which allows you to import

extra modules from the nixpkgs package tree without having to

somehow make the module aware of the location of the

`nixpkgs` or NixOS directories.

```

{ modulesPath, ... }: {

imports = [

(modulesPath + "/profiles/minimal.nix")

];

}

```

For NixOS, the default value for this option includes at least this argument:

- {var}`pkgs`: The nixpkgs package set according to

the {option}`nixpkgs.pkgs` option.

'';

};

_module.check = mkOption {

type = types.bool;

internal = true;

default = true;

description = "Whether to check whether all option definitions have matching declarations.";

};

_module.freeformType = mkOption {

type = types.nullOr types.optionType;

internal = true;

default = null;

description = ''

If set, merge all definitions that don't have an associated option

together using this type. The result then gets combined with the

values of all declared options to produce the final `

config` value.

If this is `null`, definitions without an option

will throw an error unless {option}`_module.check` is

turned off.

'';

};

_module.specialArgs = mkOption {

readOnly = true;

internal = true;

description = ''

Externally provided module arguments that can't be modified from

within a configuration, but can be used in module imports.

'';

};

config = {

_module.args = {

inherit extendModules;

moduleType = type;

};

_module.specialArgs = specialArgs;

};

# This function takes an empty attrset as an argument.

# It could theoretically be replaced with its body,

# but such a binding is avoided to allow for earlier grabage collection.

doCollect =

{ }:

collectModules class (specialArgs.modulesPath or "") (regularModules ++ [ internalModule ]) (

{

inherit

lib

options

specialArgs

;

_class = class;

_prefix = prefix;

config = addErrorContext "if you get an infinite recursion here, you probably reference `config` in `imports`. If you are trying to achieve a conditional import behavior dependent on `config`, consider importing unconditionally, and using `mkEnableOption` and `mkIf` to control its effect." config;

}

// specialArgs

);

merged = mergeModules prefix (reverseList (doCollect { }).modules);

options = merged.matchedOptions;

config =

let

# For definitions that have an associated option

declaredConfig = mapAttrsRecursiveCond (v: !isOption v) (_: v: v.value) options;

# If freeformType is set, this is for definitions that don't have an associated option

freeformConfig =

let

defs = map (def: {

file = def.file;

value = setAttrByPath def.prefix def.value;

}) merged.unmatchedDefns;

if defs == [ ] then { } else declaredConfig._module.freeformType.merge prefix defs;

if declaredConfig._module.freeformType == null then

declaredConfig

# Because all definitions that had an associated option ended in

# declaredConfig, freeformConfig can only contain the non-option

# paths, meaning recursiveUpdate will never override any value

else

recursiveUpdate freeformConfig declaredConfig;

checkUnmatched =

if config._module.check && config._module.freeformType == null && merged.unmatchedDefns != [ ] then

let

firstDef = head merged.unmatchedDefns;

baseMsg =

let

optText = showOption (prefix ++ firstDef.prefix);

defText =

addErrorContext

"while evaluating the error message for definitions for `${optText}', which is an option that does not exist"

(addErrorContext "while evaluating a definition from `${firstDef.file}'" (showDefs [ firstDef ]));

# absInvalidOptionParent is absolute; other variables are relative to the submodule prefix

absInvalidOptionParent = init (prefix ++ firstDef.prefix);

invalidOptionParent = init firstDef.prefix;

siblingOptionNames = attrNames (attrByPath invalidOptionParent { } options);

candidateNames =

if invalidOptionParent == [ ] then remove "_module" siblingOptionNames else siblingOptionNames;

invalidOptionName = last firstDef.prefix;

# For small option sets, check all; for large sets, only check distance ≤ 2

suggestions =

if length candidateNames < 100 then

pipe candidateNames [

(sortOn (levenshtein invalidOptionName))

(take 3)

]

else

pipe candidateNames [

# levenshteinAtMost is only fast for distance ≤ 2

(filter (levenshteinAtMost 2 invalidOptionName))

(sortOn (levenshtein invalidOptionName))

(take 3)

];

suggestion =

if suggestions == [ ] then

else if length suggestions == 1 then

"\n\nDid you mean `${showOption (absInvalidOptionParent ++ [ (head suggestions) ])}'?"

else

"\n\nDid you mean ${

concatStringsSep ", " (

map (s: "`${showOption (absInvalidOptionParent ++ [ s ])}'") (init suggestions)

)

} or `${showOption (absInvalidOptionParent ++ [ (last suggestions) ])}'?";

"The option `${optText}' does not exist. Definition values:${defText}${suggestion}";

attrNames options == [ "_module" ]

# No options were declared at all (`_module` is built in)

# but we do have unmatched definitions, and no freeformType (earlier conditions)

then

let

optionName = showOption prefix;

if optionName == "" then

throw ''

${baseMsg}

It seems as if you're trying to declare an option by placing it into `config' rather than `options'!

else

throw ''

${baseMsg}

However there are no options defined in `${showOption prefix}'. Are you sure you've

declared your options properly? This can happen if you e.g. declared your options in `types.submodule'

under `config' rather than `options'.

else

throw baseMsg

else

null;

checked = seq checkUnmatched;

extendModules =

extendArgs@{

modules ? [ ],

specialArgs ? { },

prefix ? [ ],

evalModules (

evalModulesArgs

// {

modules = regularModules ++ modules;

specialArgs = evalModulesArgs.specialArgs or { } // specialArgs;

prefix = extendArgs.prefix or evalModulesArgs.prefix or [ ];

}

);

type = types.submoduleWith {

inherit modules specialArgs class;

};

result = withWarnings {

_type = "configuration";

options = checked options;

config = checked (removeAttrs config [ "_module" ]);

_module = checked (config._module);

inherit (doCollect { }) graph;

inherit extendModules type class;

};

result;

# collectModules :: (class: String) -> (modulesPath: String) -> (modules: [ Module ]) -> (args: Attrs) -> ModulesTree

# Collects all modules recursively through `import` statements, filtering out

# all modules in disabledModules.

collectModules =

class:

let

# Like unifyModuleSyntax, but also imports paths and calls functions if necessary

loadModule =

args: fallbackFile: fallbackKey: m:

if isFunction m then

unifyModuleSyntax fallbackFile fallbackKey (applyModuleArgs fallbackKey m args)

else if isAttrs m then

if m._type or "module" == "module" then

unifyModuleSyntax fallbackFile fallbackKey m

else if m._type == "if" || m._type == "override" then

loadModule args fallbackFile fallbackKey { config = m; }

else

throw (

messages.not_a_module {

inherit fallbackFile;

value = m;

_type = m._type;

expectedClass = class;

prefix = args._prefix;

}

)

else if isList m then

let

defs = [

{

file = fallbackFile;

value = m;

}

];

throw "Module imports can't be nested lists. Perhaps you meant to remove one level of lists? Definitions: ${showDefs defs}"

else

unifyModuleSyntax (toString m) (toString m) (

applyModuleArgsIfFunction (toString m) (import m) args

);

checkModule =

if class != null then

if m._class == null || m._class == class then

else

throw ''

The module `${m._file or m.key}` (class: ${lib.strings.escapeNixString m._class}) cannot be imported into a module evaluation that expects class ${lib.strings.escapeNixString class}.

Help:

- Ensure that you are importing the correct module.

- Verify that the module's `_class`, ${lib.strings.escapeNixString m._class} matches the expected `class` ${lib.strings.escapeNixString class}.

- If you are using a custom class, make sure it is correctly defined and used consistently across your modules.

else

m: m;

# isDisabled :: String -> [ { disabled, file } ] -> StructuredModule -> bool

# Figures out whether a `StructuredModule` is disabled.

isDisabled =

modulesPath: disabledList:

let

moduleKey =

file: m:

if isString m then

if substring 0 1 m == "/" then m else toString modulesPath + "/" + m

else if isConvertibleWithToString m then

if m ? key && m.key != toString m then

throw "Module `${file}` contains a disabledModules item that is an attribute set that can be converted to a string (${toString m}) but also has a `.key` attribute (${m.key}) with a different value. This makes it ambiguous which module should be disabled."

else

toString m

else if m ? key then

m.key

else if isAttrs m then

throw "Module `${file}` contains a disabledModules item that is an attribute set, presumably a module, that does not have a `key` attribute. This means that the module system doesn't have any means to identify the module that should be disabled. Make sure that you've put the correct value in disabledModules: a string path relative to modulesPath, a path value, or an attribute set with a `key` attribute."

else

throw "Each disabledModules item must be a path, string, or a attribute set with a key attribute, or a value supported by toString. However, one of the disabledModules items in `${toString file}` is none of that, but is of type ${typeOf m}.";

disabledKeys = concatMap ({ file, disabled }: map (moduleKey file) disabled) disabledList;

structuredModule: elem structuredModule.key disabledKeys;

/**

Collects all modules recursively into a `[ StructuredModule ]` and a list of disabled modules:

{

disabled = [ <list of disabled modules> ];

# All modules of the main module list

modules = [

{

key = <key1>;

module = <module for key1>;

# All modules imported by the module for key1

modules = [

{

key = <key1-1>;

module = <module for key1-1>;

# All modules imported by the module for key1-1

modules = [ ... ];

}

...

];

}

...

];

}

collectStructuredModules =

let

collectResults = modules: {

disabled = concatLists (catAttrs "disabled" modules);

inherit modules;

};

parentFile: parentKey: initialModules: args:

collectResults (

imap1 (

n: x:

let

module = checkModule (loadModule args parentFile "${parentKey}:anon-${toString n}" x);

collectedImports = collectStructuredModules module._file module.key module.imports args;

{

key = module.key;

module = module;

modules = collectedImports.modules;

disabled =

(

if module.disabledModules != [ ] then

[

{

file = module._file;

disabled = module.disabledModules;

}

]

else

[ ]

)

++ collectedImports.disabled;

}

) initialModules

);

# filterModules :: String -> { disabled, modules } -> [ Module ]

# Filters a structure as emitted by collectStructuredModules by removing all disabled

# modules recursively. It returns the final list of unique-by-key modules

filterModules =

modulesPath:

{ disabled, modules }:

let

keyFilter = filter (attrs: !isDisabled modulesPath disabled attrs);

map (attrs: attrs.module) (genericClosure {

startSet = keyFilter modules;

operator = attrs: keyFilter attrs.modules;

});

toGraph =

modulesPath:

{ disabled, modules }:

let

isDisabledModule = isDisabled modulesPath disabled;

toModuleGraph = structuredModule: {

disabled = isDisabledModule structuredModule;

inherit (structuredModule) key;

file = structuredModule.module._file;

imports = map toModuleGraph structuredModule.modules;

};

map toModuleGraph (filter (x: x.key != "lib/modules.nix") modules);

modulesPath: initialModules: args: {

modules = filterModules modulesPath (collectStructuredModules unknownModule "" initialModules args);

# Intentionally not shared with `modules` above: this allows

# the return value of `collectStructuredModules`

# to be garbage collected after `filterModules` returns.

graph = toGraph modulesPath (collectStructuredModules unknownModule "" initialModules args);

};

/**

Wrap a module with a default location for reporting errors.

# Inputs

`file`

: 1\. Function argument

`m`

: 2\. Function argument

setDefaultModuleLocation = file: m: {

_file = file;

imports = [ m ];

};

/**

Massage a module into canonical form, that is, a set consisting

of ‘options’, ‘config’ and ‘imports’ attributes.

# Inputs

`file`

: 1\. Function argument

`key`

: 2\. Function argument

`m`

: 3\. Function argument

unifyModuleSyntax =

file: key: m:

let

addMeta =

config:

if m ? meta then

mkMerge [

config

{ meta = m.meta; }

]

else

config;

addFreeformType =

config:

if m ? freeformType then

mkMerge [

config

{ _module.freeformType = m.freeformType; }

]

else

config;

if m ? config || m ? options then

let

badAttrs = removeAttrs m [

"_class"

"_file"

"key"

"disabledModules"

"imports"

"options"

"config"

"meta"

"freeformType"

];

if badAttrs != { } then

throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'. This is caused by introducing a top-level `config' or `options' attribute. Add configuration attributes immediately on the top level instead, or move all of them (namely: ${toString (attrNames badAttrs)}) into the explicit `config' attribute."

else

{

_file = toString m._file or file;

_class = m._class or null;

key = toString m.key or key;

disabledModules = m.disabledModules or [ ];

imports = m.imports or [ ];

options = m.options or { };

config = addFreeformType (addMeta (m.config or { }));

}

else

# shorthand syntax

throwIfNot (isAttrs m) "module ${file} (${key}) does not look like a module." {

_file = toString m._file or file;

_class = m._class or null;

key = toString m.key or key;

disabledModules = m.disabledModules or [ ];

imports = m.require or [ ] ++ m.imports or [ ];

options = { };

config = addFreeformType (

removeAttrs m [

"_class"

"_file"

"key"

"disabledModules"

"require"

"imports"

"freeformType"

]

);

};

applyModuleArgsIfFunction =

key: f: args@{ config, ... }: if isFunction f then applyModuleArgs key f args else f;

applyModuleArgs =

key: f:

args@{ config, ... }:

let

# 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.

context = name: ''while evaluating the module argument `${name}' in "${key}":'';

extraArgs = mapAttrs (

addErrorContext (context name) (

args.${name} or (addErrorContext

"noting that argument `${name}` is not externally provided, so querying `_module.args` instead, requiring `config`"

config._module.args.${name}

)

) (functionArgs f);

# Note: we append in the opposite order such that we can add an error

# context on the explicit arguments of "args" too. This update

# operator is used to make the "args@{ ... }: with args.lib;" notation

# works.

f (args // extraArgs);

/**

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.

This returns a set like

{

# A recursive set of options along with their final values

matchedOptions = {

foo = { _type = "option"; value = "option value of foo"; ... };

bar.baz = { _type = "option"; value = "option value of bar.baz"; ... };

...

};

# A list of definitions that weren't matched by any option

unmatchedDefns = [

{ file = "file.nix"; prefix = [ "qux" ]; value = "qux"; }

...

];

}

# Inputs

`prefix`

: 1\. Function argument

`modules`

: 2\. Function argument

mergeModules =

prefix: modules:

mergeModules' prefix modules (

concatMap (

map (config: {

file = m._file;

inherit config;

}) (pushDownProperties m.config)

) modules

);

mergeModules' =

prefix: modules: configs:

let

# an attrset 'name' => list of submodules that declare ‘name’.

declsByName = zipAttrs (

map (

module:

let

subtree = module.options;

if !(isAttrs subtree) then

throw ''

An option declaration for `${concatStringsSep "." prefix}' has type

`${typeOf subtree}' rather than an attribute set.

Did you mean to define this outside of `options'?

else

mapAttrs (n: option: {

inherit (module) _file;

pos = unsafeGetAttrPos n subtree;

options = option;

}) subtree

) modules

);

# The root of any module definition must be an attrset.

checkedConfigs =

assert all (

# TODO: I have my doubts that this error would occur when option definitions are not matched.

# The implementation of this check used to be tied to a superficially similar check for

# options, so maybe that's why this is here.

isAttrs c.config

|| throw ''

In module `${c.file}', you're trying to define a value of type `${typeOf c.config}'

rather than an attribute set for the option

`${concatStringsSep "." prefix}'!

This usually happens if `${concatStringsSep "." prefix}' has option

definitions inside that are not matched. Please check how to properly define

this option by e.g. referring to `man 5 configuration.nix'!

) configs;

configs;

# an attrset 'name' => list of submodules that define ‘name’.

pushedDownDefinitionsByName = zipAttrsWith (n: concatLists) (

map (

module:

mapAttrs (

n: value:

map (config: {

inherit (module) file;

inherit config;

}) (pushDownProperties value)

) module.config

) checkedConfigs

);

# extract the definitions for each loc

rawDefinitionsByName = zipAttrs (

map (

module:

mapAttrs (n: value: {

inherit (module) file;

inherit value;

}) module.config

) checkedConfigs

);

# Convert an option tree decl to a submodule option decl

optionTreeToOption =

decl:

if isOption decl.options then

decl

else

decl

// {

options = mkOption {

type = types.submoduleWith {

modules = [ { options = decl.options; } ];

# `null` is not intended for use by modules. It is an internal

# value that means "whatever the user has declared elsewhere".

# This might become obsolete with https://github.com/NixOS/nixpkgs/issues/162398

shorthandOnlyDefinesConfig = null;

};

resultsByName = mapAttrs (

# We're descending into attribute ‘name’.

let

loc = prefix ++ [ name ];

defns = pushedDownDefinitionsByName.${name} or [ ];

defns' = rawDefinitionsByName.${name} or [ ];

optionDecls = filter (

m.options ? _type

&& (m.options._type == "option" || throwDeclarationTypeError loc m.options._type m._file)

) decls;

if length optionDecls == length decls then

let

opt = fixupOptionType loc (mergeOptionDecls loc decls);

{

matchedOptions = evalOptionValue loc opt defns';

unmatchedDefns = [ ];

}

else if optionDecls != [ ] then

all (x: x.options.type.name or null == "submodule") optionDecls

# Raw options can only be merged into submodules. Merging into

# attrsets might be nice, but ambiguous. Suppose we have

# attrset as a `attrsOf submodule`. User declares option

# attrset.foo.bar, this could mean:

# a. option `bar` is only available in `attrset.foo`

# b. option `foo.bar` is available in all `attrset.*`

# c. reject and require "<name>" as a reminder that it behaves like (b).

# d. magically combine (a) and (c).

# All of the above are merely syntax sugar though.

then

let

opt = fixupOptionType loc (mergeOptionDecls loc (map optionTreeToOption decls));

{

matchedOptions = evalOptionValue loc opt defns';

unmatchedDefns = [ ];

}

else

let

nonOptions = filter (m: !isOption m.options) decls;

throw "The option `${showOption loc}' in module `${(head optionDecls)._file}' would be a parent of the following options, but its type `${

(head optionDecls).options.type.description or "<no description>"

}' does not support nested options.\n${showRawDecls loc nonOptions}"

else

mergeModules' loc decls defns

) declsByName;

matchedOptions = mapAttrs (n: v: v.matchedOptions) resultsByName;

# an attrset 'name' => list of unmatched definitions for 'name'

unmatchedDefnsByName =

# Propagate all unmatched definitions from nested option sets

mapAttrs (n: v: v.unmatchedDefns) resultsByName

# Plus the definitions for the current prefix that don't have a matching option

// removeAttrs rawDefinitionsByName (attrNames matchedOptions);

{

inherit matchedOptions;

# Transforms unmatchedDefnsByName into a list of definitions

unmatchedDefns =

if configs == [ ] then

# When no config values exist, there can be no unmatched config, so

# we short circuit and avoid evaluating more _options_ than necessary.

[ ]

else

concatLists (

mapAttrsToList (

map (

def:

def

// {

# Set this so we know when the definition first left unmatched territory

prefix = [ name ] ++ (def.prefix or [ ]);

}

) defs

) unmatchedDefnsByName

);

};

throwDeclarationTypeError =

loc: actualTag: file:

let

name = lib.strings.escapeNixIdentifier (lib.lists.last loc);

path = showOption loc;

depth = length loc;

paragraphs = [

"In module ${file}: expected an option declaration at option path `${path}` but got an attribute set with type ${actualTag}"

]

++ optional (actualTag == "option-type") ''

When declaring an option, you must wrap the type in a `mkOption` call. It should look somewhat like:

${comment}

${name} = lib.mkOption {

description = ...;

type = <the type you wrote for ${name}>;

...

};

'';

# Ideally we'd know the exact syntax they used, but short of that,

# we can only reliably repeat the last. However, we repeat the

# full path in a non-misleading way here, in case they overlook

# the start of the message. Examples attract attention.

comment = optionalString (depth > 1) "\n # ${showOption loc}";

throw (concatStringsSep "\n\n" paragraphs);

/**

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'.

# Inputs

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