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 // 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 hasAttr name set 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:
if isAttrs x || builtins.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
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throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'."
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"];
};
applyIfFunction = f: arg: if builtins.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 hasAttr name m.options
then [ { inherit (m) file; options = getAttr name m.options; } ]
else []
) options);
# Get all submodules that define name.
defns = concatLists (map (m:
if hasAttr name m.config
then map (config: { inherit (m) file; inherit config; })
(pushDownProperties (getAttr name m.config))
else []
) configs);
nrOptions = count (m: isOption m.options) decls;
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# Process mkMerge and mkIf properties.
defns' = concatMap (m:
if hasAttr name m.config
then map (m': { inherit (m) file; value = m'; }) (dischargeProperties (getAttr name m.config))
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 `${firstNonOption.file}'."
else
mergeModules' loc decls defns;
}) (concatMap (m: attrNames m.options) options))
// { _definedNames = map (m: { inherit (m) file; names = attrNames m.config; }) configs; };
/* Merge multiple option declarations into a single declaration. In
general, there should be only one declaration of each option.
The exception is the options attribute, which specifies
sub-options. These can be specified multiple times to allow one
module to add sub-options to an option declared somewhere else
(e.g. multiple modules define sub-options for fileSystems). */
mergeOptionDecls = loc: opts:
fold (opt: res:
if opt.options ? default && res ? default ||
opt.options ? example && res ? example ||
opt.options ? description && res ? description ||
opt.options ? apply && res ? apply ||
opt.options ? type && res ? type
then
throw "The option `${showOption loc}' in `${opt.file}' is already declared in ${showFiles res.declarations}."
else
opt.options // res //
{ declarations = [opt.file] ++ res.declarations;
options = if opt.options ? options then [(toList opt.options.options ++ res.options)] else [];
}
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) { inherit loc; declarations = []; options = []; } opts;
/* Merge all the definitions of an option to produce the final
config value. */
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evalOptionValue = loc: opt: defs:
let
# Process mkOverride properties, adding in the default
# value specified in the option declaration (if any).
defsFinal = filterOverrides
((if opt ? default then [{ file = head opt.declarations; value = mkOptionDefault opt.default; }] else []) ++ defs);
files = map (def: def.file) defsFinal;
# Type-check the remaining definitions, and merge them if
# possible.
merged =
if defsFinal == [] then
throw "The option `${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
mkIf 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)
else
[ 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 builtins.lessThan 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;
/* Hack for backward compatibility: convert options of type
optionSet to configOf. FIXME: remove eventually. */
fixupOptionType = loc: opt:
let
options' = opt.options or
(throw "Option `${showOption loc'}' has type optionSet but has no option attribute.");
coerce = x:
if builtins.isFunction x then x
else { config, ... }: { options = x; };
options = map coerce (flatten options');
f = tp:
if tp.name == "option set" then types.submodule options
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 opt // { type = f (opt.type or types.unspecified); };
/* 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
mkFixStrictness = id; # obsolete, no-op
# FIXME: Add mkOrder back in. It's not currently used anywhere in
# NixOS, but it should be useful.
/* Compatibility. */
fixMergeModules = modules: args: evalModules { inherit modules args; check = false; };
}