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{ lib }:
# Operations on attribute sets.
let
inherit (builtins) head tail length;
inherit (lib.trivial) and;
inherit (lib.strings) concatStringsSep;
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 `getAttrPath' 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);
/* 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.${name} or nul); }
) a (attrNames n)
) {} list_of_attrs;
/* Recursively collect sets that verify a given predicate named `pred'
from the set `attrs'. The recursion is stopped when the predicate is
verified.
Type:
collect ::
(AttrSet -> Bool) -> AttrSet -> [x]
Example:
collect isList { a = { b = ["b"]; }; c = [1]; }
=> [["b"] [1]]
collect (x: x ? outPath)
{ a = { outPath = "a/"; }; b = { outPath = "b/"; }; }
=> [{ outPath = "a/"; } { outPath = "b/"; }]
*/
collect = pred: attrs:
if pred attrs then
[ attrs ]
else if isAttrs attrs then
concatMap (collect pred) (attrValues attrs)
else
[];
/* Utility function that creates a {name, value} pair as expected by
builtins.listToAttrs.
Example:
nameValuePair "some" 6
=> { name = "some"; value = 6; }
*/
nameValuePair = name: value: { inherit name value; };
/* Apply a function to each element in an attribute set. The
function takes two arguments --- the attribute name and its value
--- and returns the new value for the attribute. The result is a
new attribute set.
Example:
mapAttrs (name: value: name + "-" + value)
{ x = "foo"; y = "bar"; }
=> { x = "x-foo"; y = "y-bar"; }
*/
mapAttrs = builtins.mapAttrs or
(f: set:
listToAttrs (map (attr: { name = attr; value = f attr set.${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.${attr}) (attrNames set));
/* Call a function for each attribute in the given set and return
the result in a list.
Example:
mapAttrsToList (name: value: name + value)
{ x = "a"; y = "b"; }
=> [ "xa" "yb" ]
*/
mapAttrsToList = f: attrs:
map (name: f name attrs.${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. It is 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 = builtins.unsafeDiscardStringContext (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: value)' 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";
/* Pick the outputs of packages to place in buildInputs */
chooseDevOutputs = drvs: builtins.map getDev drvs;
/*** deprecated stuff ***/
zipWithNames = zipAttrsWithNames;
zip = builtins.trace
"lib.zip is deprecated, use lib.zipAttrsWith instead" zipAttrsWith;
}