{ lib }: # Operations on attribute sets. let inherit (builtins) head tail length; inherit (lib.trivial) and; inherit (lib.strings) concatStringsSep sanitizeDerivationName; inherit (lib.lists) fold concatMap concatLists; in rec { inherit (builtins) attrNames listToAttrs hasAttr isAttrs getAttr; /* Return an attribute from nested attribute sets. Example: x = { a = { b = 3; }; } attrByPath ["a" "b"] 6 x => 3 attrByPath ["z" "z"] 6 x => 6 */ attrByPath = attrPath: default: e: let attr = head attrPath; in if attrPath == [] then e else if e ? ${attr} then attrByPath (tail attrPath) default e.${attr} else default; /* Return if an attribute from nested attribute set exists. Example: x = { a = { b = 3; }; } hasAttrByPath ["a" "b"] x => true hasAttrByPath ["z" "z"] x => false */ hasAttrByPath = attrPath: e: let attr = head attrPath; in if attrPath == [] then true else if e ? ${attr} then hasAttrByPath (tail attrPath) e.${attr} else false; /* Return nested attribute set in which an attribute is set. Example: setAttrByPath ["a" "b"] 3 => { a = { b = 3; }; } */ setAttrByPath = attrPath: value: if attrPath == [] then value else listToAttrs [ { name = head attrPath; value = setAttrByPath (tail attrPath) value; } ]; /* Like `attrByPath' without a default value. If it doesn't find the path it will throw. Example: x = { a = { b = 3; }; } getAttrFromPath ["a" "b"] x => 3 getAttrFromPath ["z" "z"] x => error: cannot find attribute `z.z' */ getAttrFromPath = attrPath: set: let errorMsg = "cannot find attribute `" + concatStringsSep "." attrPath + "'"; in attrByPath attrPath (abort errorMsg) set; /* Return the specified attributes from a set. Example: attrVals ["a" "b" "c"] as => [as.a as.b as.c] */ attrVals = nameList: set: map (x: set.${x}) nameList; /* Return the values of all attributes in the given set, sorted by attribute name. Example: attrValues {c = 3; a = 1; b = 2;} => [1 2 3] */ attrValues = builtins.attrValues or (attrs: attrVals (attrNames attrs) attrs); /* Given a set of attribute names, return the set of the corresponding attributes from the given set. Example: getAttrs [ "a" "b" ] { a = 1; b = 2; c = 3; } => { a = 1; b = 2; } */ getAttrs = names: attrs: genAttrs names (name: attrs.${name}); /* Collect each attribute named `attr' from a list of attribute sets. Sets that don't contain the named attribute are ignored. Example: catAttrs "a" [{a = 1;} {b = 0;} {a = 2;}] => [1 2] */ catAttrs = builtins.catAttrs or (attr: l: concatLists (map (s: if s ? ${attr} then [s.${attr}] else []) l)); /* Filter an attribute set by removing all attributes for which the given predicate return false. Example: filterAttrs (n: v: n == "foo") { foo = 1; bar = 2; } => { foo = 1; } */ filterAttrs = pred: set: listToAttrs (concatMap (name: let v = set.${name}; in if pred name v then [(nameValuePair name v)] else []) (attrNames set)); /* Filter an attribute set recursively by removing all attributes for which the given predicate return false. Example: filterAttrsRecursive (n: v: v != null) { foo = { bar = null; }; } => { foo = {}; } */ filterAttrsRecursive = pred: set: listToAttrs ( concatMap (name: let v = set.${name}; in if pred name v then [ (nameValuePair name ( if isAttrs v then filterAttrsRecursive pred v else v )) ] else [] ) (attrNames set) ); /* Apply fold functions to values grouped by key. Example: foldAttrs (n: a: [n] ++ a) [] [{ a = 2; } { a = 3; }] => { a = [ 2 3 ]; } */ foldAttrs = op: nul: list_of_attrs: fold (n: a: fold (name: o: o // { ${name} = op n.${name} (a.${name} or nul); } ) a (attrNames n) ) {} list_of_attrs; /* Recursively collect sets that verify a given predicate named `pred' from the set `attrs'. The recursion is stopped when the predicate is verified. Type: collect :: (AttrSet -> Bool) -> AttrSet -> [x] Example: collect isList { a = { b = ["b"]; }; c = [1]; } => [["b"] [1]] collect (x: x ? outPath) { a = { outPath = "a/"; }; b = { outPath = "b/"; }; } => [{ outPath = "a/"; } { outPath = "b/"; }] */ collect = pred: attrs: if pred attrs then [ attrs ] else if isAttrs attrs then concatMap (collect pred) (attrValues attrs) else []; /* Return the cartesian product of attribute set value combinations. Example: cartesianProductOfSets { a = [ 1 2 ]; b = [ 10 20 ]; } => [ { a = 1; b = 10; } { a = 1; b = 20; } { a = 2; b = 10; } { a = 2; b = 20; } ] */ cartesianProductOfSets = attrsOfLists: lib.foldl' (listOfAttrs: attrName: concatMap (attrs: map (listValue: attrs // { ${attrName} = listValue; }) attrsOfLists.${attrName} ) listOfAttrs ) [{}] (attrNames attrsOfLists); /* Utility function that creates a {name, value} pair as expected by builtins.listToAttrs. Example: nameValuePair "some" 6 => { name = "some"; value = 6; } */ nameValuePair = name: value: { inherit name value; }; /* Apply a function to each element in an attribute set. The function takes two arguments --- the attribute name and its value --- and returns the new value for the attribute. The result is a new attribute set. Example: mapAttrs (name: value: name + "-" + value) { x = "foo"; y = "bar"; } => { x = "x-foo"; y = "y-bar"; } */ mapAttrs = builtins.mapAttrs or (f: set: listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))); /* Like `mapAttrs', but allows the name of each attribute to be changed in addition to the value. The applied function should return both the new name and value as a `nameValuePair'. Example: mapAttrs' (name: value: nameValuePair ("foo_" + name) ("bar-" + value)) { x = "a"; y = "b"; } => { foo_x = "bar-a"; foo_y = "bar-b"; } */ mapAttrs' = f: set: listToAttrs (map (attr: f attr set.${attr}) (attrNames set)); /* Call a function for each attribute in the given set and return the result in a list. Type: mapAttrsToList :: (String -> a -> b) -> AttrSet -> [b] Example: mapAttrsToList (name: value: name + value) { x = "a"; y = "b"; } => [ "xa" "yb" ] */ mapAttrsToList = f: attrs: map (name: f name attrs.${name}) (attrNames attrs); /* Like `mapAttrs', except that it recursively applies itself to attribute sets. Also, the first argument of the argument function is a *list* of the names of the containing attributes. Type: mapAttrsRecursive :: ([String] -> a -> b) -> AttrSet -> AttrSet Example: mapAttrsRecursive (path: value: concatStringsSep "-" (path ++ [value])) { n = { a = "A"; m = { b = "B"; c = "C"; }; }; d = "D"; } => { n = { a = "n-a-A"; m = { b = "n-m-b-B"; c = "n-m-c-C"; }; }; d = "d-D"; } */ mapAttrsRecursive = mapAttrsRecursiveCond (as: true); /* Like `mapAttrsRecursive', but it takes an additional predicate function that tells it whether to recursive into an attribute set. If it returns false, `mapAttrsRecursiveCond' does not recurse, but does apply the map function. If it returns true, it does recurse, and does not apply the map function. Type: mapAttrsRecursiveCond :: (AttrSet -> Bool) -> ([String] -> a -> b) -> AttrSet -> AttrSet Example: # To prevent recursing into derivations (which are attribute # sets with the attribute "type" equal to "derivation"): mapAttrsRecursiveCond (as: !(as ? "type" && as.type == "derivation")) (x: ... do something ...) attrs */ mapAttrsRecursiveCond = cond: f: set: let recurse = path: set: let g = name: value: if isAttrs value && cond value then recurse (path ++ [name]) value else f (path ++ [name]) value; in mapAttrs g set; in recurse [] set; /* Generate an attribute set by mapping a function over a list of attribute names. Example: genAttrs [ "foo" "bar" ] (name: "x_" + name) => { foo = "x_foo"; bar = "x_bar"; } */ genAttrs = names: f: listToAttrs (map (n: nameValuePair n (f n)) names); /* Check whether the argument is a derivation. Any set with { type = "derivation"; } counts as a derivation. Example: nixpkgs = import <nixpkgs> {} isDerivation nixpkgs.ruby => true isDerivation "foobar" => false */ isDerivation = x: isAttrs x && x ? type && x.type == "derivation"; /* Converts a store path to a fake derivation. */ toDerivation = path: let path' = builtins.storePath path; res = { type = "derivation"; name = sanitizeDerivationName (builtins.substring 33 (-1) (baseNameOf path')); outPath = path'; outputs = [ "out" ]; out = res; outputName = "out"; }; in res; /* If `cond' is true, return the attribute set `as', otherwise an empty attribute set. Example: optionalAttrs (true) { my = "set"; } => { my = "set"; } optionalAttrs (false) { my = "set"; } => { } */ optionalAttrs = cond: as: if cond then as else {}; /* Merge sets of attributes and use the function f to merge attributes values. Example: zipAttrsWithNames ["a"] (name: vs: vs) [{a = "x";} {a = "y"; b = "z";}] => { a = ["x" "y"]; } */ zipAttrsWithNames = names: f: sets: listToAttrs (map (name: { inherit name; value = f name (catAttrs name sets); }) names); /* Implementation note: Common names appear multiple times in the list of names, hopefully this does not affect the system because the maximal laziness avoid computing twice the same expression and listToAttrs does not care about duplicated attribute names. Example: zipAttrsWith (name: values: values) [{a = "x";} {a = "y"; b = "z";}] => { a = ["x" "y"]; b = ["z"] } */ zipAttrsWith = f: sets: zipAttrsWithNames (concatMap attrNames sets) f sets; /* Like `zipAttrsWith' with `(name: values: values)' as the function. Example: zipAttrs [{a = "x";} {a = "y"; b = "z";}] => { a = ["x" "y"]; b = ["z"] } */ zipAttrs = zipAttrsWith (name: values: values); /* Does the same as the update operator '//' except that attributes are merged until the given predicate is verified. The predicate should accept 3 arguments which are the path to reach the attribute, a part of the first attribute set and a part of the second attribute set. When the predicate is verified, the value of the first attribute set is replaced by the value of the second attribute set. Example: recursiveUpdateUntil (path: l: r: path == ["foo"]) { # first attribute set foo.bar = 1; foo.baz = 2; bar = 3; } { #second attribute set foo.bar = 1; foo.quz = 2; baz = 4; } returns: { foo.bar = 1; # 'foo.*' from the second set foo.quz = 2; # bar = 3; # 'bar' from the first set baz = 4; # 'baz' from the second set } */ recursiveUpdateUntil = pred: lhs: rhs: let f = attrPath: zipAttrsWith (n: values: let here = attrPath ++ [n]; in if tail values == [] || pred here (head (tail values)) (head values) then head values else f here values ); in f [] [rhs lhs]; /* A recursive variant of the update operator ‘//’. The recursion stops when one of the attribute values is not an attribute set, in which case the right hand side value takes precedence over the left hand side value. Example: recursiveUpdate { boot.loader.grub.enable = true; boot.loader.grub.device = "/dev/hda"; } { boot.loader.grub.device = ""; } returns: { boot.loader.grub.enable = true; boot.loader.grub.device = ""; } */ recursiveUpdate = lhs: rhs: recursiveUpdateUntil (path: lhs: rhs: !(isAttrs lhs && isAttrs rhs) ) lhs rhs; /* Returns true if the pattern is contained in the set. False otherwise. Example: matchAttrs { cpu = {}; } { cpu = { bits = 64; }; } => true */ matchAttrs = pattern: attrs: assert isAttrs pattern; fold and true (attrValues (zipAttrsWithNames (attrNames pattern) (n: values: let pat = head values; val = head (tail values); in if length values == 1 then false else if isAttrs pat then isAttrs val && matchAttrs pat val else pat == val ) [pattern attrs])); /* Override only the attributes that are already present in the old set useful for deep-overriding. Example: overrideExisting {} { a = 1; } => {} overrideExisting { b = 2; } { a = 1; } => { b = 2; } overrideExisting { a = 3; b = 2; } { a = 1; } => { a = 1; b = 2; } */ overrideExisting = old: new: mapAttrs (name: value: new.${name} or value) old; /* Get a package output. If no output is found, fallback to `.out` and then to the default. Example: getOutput "dev" pkgs.openssl => "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-dev" */ getOutput = output: pkg: if pkg.outputUnspecified or false then pkg.${output} or pkg.out or pkg else pkg; getBin = getOutput "bin"; getLib = getOutput "lib"; getDev = getOutput "dev"; getMan = getOutput "man"; /* Pick the outputs of packages to place in buildInputs */ chooseDevOutputs = drvs: builtins.map getDev drvs; /* Make various Nix tools consider the contents of the resulting attribute set when looking for what to build, find, etc. This function only affects a single attribute set; it does not apply itself recursively for nested attribute sets. */ recurseIntoAttrs = attrs: attrs // { recurseForDerivations = true; }; /* Undo the effect of recurseIntoAttrs. */ dontRecurseIntoAttrs = attrs: attrs // { recurseForDerivations = false; }; /*** deprecated stuff ***/ zipWithNames = zipAttrsWithNames; zip = builtins.trace "lib.zip is deprecated, use lib.zipAttrsWith instead" zipAttrsWith; }