nixpkgs/lib/modules.nix

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with import ./lists.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. */
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evalModules = { modules, prefix ? [], args ? {}, check ? true }:
let
args' = args // { lib = import ./.; } // result;
closed = closeModules modules args';
# Note: the list of modules is reversed to maintain backward
# compatibility with the old module system. Not sure if this is
# the most sensible policy.
options = mergeModules prefix (reverseList 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.
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"];
in
if check && set ? _definedNames then
fold (m: res:
fold (name: res:
if set ? ${name} then res else throw "The option `${showOption (prefix ++ [name])}' defined in `${m.file}' does not exist.")
res m.names)
res set._definedNames
else
res;
result = { inherit options config; };
in result;
/* Close a set of modules under the imports relation. */
closeModules = modules: args:
let
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toClosureList = file: parentKey: imap (n: x:
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if isAttrs x || isFunction x then
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unifyModuleSyntax file "${parentKey}:anon-${toString n}" (applyIfFunction x args)
else
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unifyModuleSyntax (toString x) (toString x) (applyIfFunction (import x) args));
in
builtins.genericClosure {
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startSet = toClosureList unknownModule "" modules;
operator = m: toClosureList m.file m.key m.imports;
};
/* Massage a module into canonical form, that is, a set consisting
of options, config and imports attributes. */
unifyModuleSyntax = file: key: m:
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if m ? config || m ? options then
let badAttrs = removeAttrs m ["imports" "options" "config" "key" "_file"]; in
if badAttrs != {} then
throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'. This is caused by assignments to the top-level attributes `config' or `options'."
else
{ file = m._file or file;
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key = toString m.key or key;
imports = m.imports or [];
options = m.options or {};
config = m.config or {};
}
else
{ file = m._file or file;
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key = toString m.key or key;
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imports = m.require or [] ++ m.imports or [];
options = {};
config = removeAttrs m ["key" "_file" "require" "imports"];
};
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applyIfFunction = f: arg: if isFunction f then f arg else f;
/* 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 =
let
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loc = prefix ++ [name];
# Get all submodules that declare name.
decls = concatLists (map (m:
if m.options ? ${name}
then [ { inherit (m) file; options = m.options.${name}; } ]
else []
) options);
# Get all submodules that define name.
defns = concatLists (map (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;
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# Process mkMerge and mkIf properties.
defns' = concatMap (m:
if m.config ? ${name}
then map (m': { inherit (m) file; value = m'; }) (dischargeProperties m.config.${name})
else []
) configs;
in
if nrOptions == length decls then
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let opt = fixupOptionType loc (mergeOptionDecls loc decls);
in evalOptionValue loc opt defns'
else if nrOptions != 0 then
let
firstOption = findFirst (m: isOption m.options) "" decls;
firstNonOption = findFirst (m: !isOption m.options) "" decls;
in
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throw "The option `${showOption loc}' in `${firstOption.file}' is a prefix of options in `${firstNonOption.file}'."
else
mergeModules' loc decls defns;
}) (concatMap (m: attrNames m.options) options))
// { _definedNames = map (m: { inherit (m) file; names = attrNames m.config; }) configs; };
/* Merge multiple option declarations into a single declaration. In
general, there should be only one declaration of each option.
The exception is the options attribute, which specifies
sub-options. These can be specified multiple times to allow one
module to add sub-options to an option declared somewhere else
(e.g. multiple modules define sub-options for fileSystems).
'loc' is the list of attribute names where the option is located.
'opts' is a list of modules. Each module has an options attribute which
correspond to the definition of 'loc' in 'opt.file'. */
mergeOptionDecls = loc: opts:
fold (opt: res:
if opt.options ? default && res ? default ||
opt.options ? example && res ? example ||
opt.options ? description && res ? description ||
opt.options ? apply && res ? apply ||
# Accept to merge options which have identical types.
opt.options ? type && res ? type && opt.options.type.name != res.type.name
then
throw "The option `${showOption loc}' in `${opt.file}' is already declared in ${showFiles res.declarations}."
else
let
/* Add the modules of the current option to the list of modules
already collected. The options attribute except either a list of
submodules or a submodule. For each submodule, we add the file of the
current option declaration as the file use for the submodule. If the
submodule defines any filename, then we ignore the enclosing option file. */
options' = toList opt.options.options;
addModuleFile = m:
if isFunction m then args: { _file = opt.file; } // (m args)
else { _file = opt.file; } // m;
coerceOption = file: opt:
if isFunction opt then args: { _file = file; } // (opt args)
else { _file = file; options = opt; };
getSubModules = opt.options.type.getSubModules or null;
submodules =
if getSubModules != null then map addModuleFile getSubModules ++ res.options
else if opt.options ? options then map (coerceOption opt.file) options' ++ res.options
else res.options;
in opt.options // res //
{ declarations = [opt.file] ++ res.declarations;
options = submodules;
}
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) { inherit loc; declarations = []; options = []; } opts;
/* Merge all the definitions of an option to produce the final
config value. */
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evalOptionValue = loc: opt: defs:
let
# Process mkOverride properties, adding in the default
# value specified in the option declaration (if any).
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defsFinal' = filterOverrides
((if opt ? default then [{ file = head opt.declarations; value = mkOptionDefault opt.default; }] else []) ++ defs);
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# Sort mkOrder properties.
defsFinal =
# Avoid sorting if we don't have to.
if any (def: def.value._type or "" == "order") defsFinal'
then sortProperties defsFinal'
else defsFinal';
files = map (def: def.file) defsFinal;
# Type-check the remaining definitions, and merge them if
# possible.
merged =
if defsFinal == [] then
throw "The option `${showOption loc}' is used but not defined."
else
fold (def: res:
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if opt.type.check def.value then res
else throw "The option value `${showOption loc}' in `${def.file}' is not a ${opt.type.name}.")
(opt.type.merge loc defsFinal) defsFinal;
# Finally, apply the apply function to the merged
# value. This allows options to yield a value computed
# from the definitions.
value = (opt.apply or id) merged;
in opt //
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{ value = addErrorContext "while evaluating the option `${showOption loc}':" value;
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definitions = map (def: def.value) defsFinal;
isDefined = defsFinal != [];
inherit files;
};
/* Given a config set, expand mkMerge properties, and push down the
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other properties into the children. The result is a list of
config sets that do not have properties at top-level. For
example,
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
recursion.
*/
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)
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else if cfg._type or "" == "override" then
map (mapAttrs (n: v: mkOverride cfg.priority v)) (pushDownProperties cfg.content)
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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 def.condition then
dischargeProperties def.content
else
[ ]
else
[ def ];
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/* 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,
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[ { file = "/1"; value = mkOverride 10 "a"; }
{ file = "/2"; value = mkOverride 20 "b"; }
{ file = "/3"; value = "z"; }
{ file = "/4"; value = mkOverride 10 "d"; }
]
yields
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[ { file = "/1"; value = "a"; }
{ file = "/4"; value = "d"; }
]
Note that "z" has the default priority 100.
*/
filterOverrides = defs:
let
defaultPrio = 100;
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getPrio = def: if def.value._type or "" == "override" then def.value.priority else defaultPrio;
min = x: y: if x < y then x else y;
highestPrio = fold (def: prio: min (getPrio def) prio) 9999 defs;
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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;
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/* 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:
let
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:
let
options = opt.options or
(throw "Option `${showOption loc'}' has type optionSet but has no option attribute, in ${showFiles opt.declarations}.");
f = tp:
if tp.name == "option set" || tp.name == "submodule" then
throw "The option ${showOption loc} uses submodules without a wrapping type, in ${showFiles opt.declarations}."
else if tp.name == "attribute set of option sets" then types.attrsOf (types.submodule options)
else if tp.name == "list or attribute set of option sets" then types.loaOf (types.submodule options)
else if tp.name == "list of option sets" then types.listOf (types.submodule options)
else if tp.name == "null or option set" then types.nullOr (types.submodule options)
else tp;
in
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:
mkIf
(if assertion then true else throw "\nFailed assertion: ${message}")
content;
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
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mkOrder = priority: content:
{ _type = "order";
inherit priority content;
};
mkBefore = mkOrder 500;
mkAfter = mkOrder 1500;
/* Compatibility. */
fixMergeModules = modules: args: evalModules { inherit modules args; check = false; };
}