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Diffstat (limited to 'lib/attrsets.nix')
| -rw-r--r-- | lib/attrsets.nix | 630 |
1 files changed, 630 insertions, 0 deletions
diff --git a/lib/attrsets.nix b/lib/attrsets.nix new file mode 100644 index 00000000000..516fdd8d33f --- /dev/null +++ b/lib/attrsets.nix @@ -0,0 +1,630 @@ +{ lib }: +# Operations on attribute sets. + +let + inherit (builtins) head tail length; + inherit (lib.trivial) id; + inherit (lib.strings) concatStringsSep concatMapStringsSep escapeNixIdentifier sanitizeDerivationName; + inherit (lib.lists) foldr foldl' concatMap concatLists elemAt all partition groupBy take foldl; +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: + let + len = length attrPath; + atDepth = n: + if n == len + then value + else { ${elemAt attrPath n} = atDepth (n + 1); }; + in atDepth 0; + + /* 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: + let errorMsg = "cannot find attribute `" + concatStringsSep "." attrPath + "'"; + in attrByPath attrPath (abort errorMsg); + + + /* Update or set specific paths of an attribute set. + + Takes a list of updates to apply and an attribute set to apply them to, + and returns the attribute set with the updates applied. Updates are + represented as { path = ...; update = ...; } values, where `path` is a + list of strings representing the attribute path that should be updated, + and `update` is a function that takes the old value at that attribute path + as an argument and returns the new + value it should be. + + Properties: + - Updates to deeper attribute paths are applied before updates to more + shallow attribute paths + - Multiple updates to the same attribute path are applied in the order + they appear in the update list + - If any but the last `path` element leads into a value that is not an + attribute set, an error is thrown + - If there is an update for an attribute path that doesn't exist, + accessing the argument in the update function causes an error, but + intermediate attribute sets are implicitly created as needed + + Example: + updateManyAttrsByPath [ + { + path = [ "a" "b" ]; + update = old: { d = old.c; }; + } + { + path = [ "a" "b" "c" ]; + update = old: old + 1; + } + { + path = [ "x" "y" ]; + update = old: "xy"; + } + ] { a.b.c = 0; } + => { a = { b = { d = 1; }; }; x = { y = "xy"; }; } + */ + updateManyAttrsByPath = let + # When recursing into attributes, instead of updating the `path` of each + # update using `tail`, which needs to allocate an entirely new list, + # we just pass a prefix length to use and make sure to only look at the + # path without the prefix length, so that we can reuse the original list + # entries. + go = prefixLength: hasValue: value: updates: + let + # Splits updates into ones on this level (split.right) + # And ones on levels further down (split.wrong) + split = partition (el: length el.path == prefixLength) updates; + + # Groups updates on further down levels into the attributes they modify + nested = groupBy (el: elemAt el.path prefixLength) split.wrong; + + # Applies only nested modification to the input value + withNestedMods = + # Return the value directly if we don't have any nested modifications + if split.wrong == [] then + if hasValue then value + else + # Throw an error if there is no value. This `head` call here is + # safe, but only in this branch since `go` could only be called + # with `hasValue == false` for nested updates, in which case + # it's also always called with at least one update + let updatePath = (head split.right).path; in + throw + ( "updateManyAttrsByPath: Path '${showAttrPath updatePath}' does " + + "not exist in the given value, but the first update to this " + + "path tries to access the existing value.") + else + # If there are nested modifications, try to apply them to the value + if ! hasValue then + # But if we don't have a value, just use an empty attribute set + # as the value, but simplify the code a bit + mapAttrs (name: go (prefixLength + 1) false null) nested + else if isAttrs value then + # If we do have a value and it's an attribute set, override it + # with the nested modifications + value // + mapAttrs (name: go (prefixLength + 1) (value ? ${name}) value.${name}) nested + else + # However if it's not an attribute set, we can't apply the nested + # modifications, throw an error + let updatePath = (head split.wrong).path; in + throw + ( "updateManyAttrsByPath: Path '${showAttrPath updatePath}' needs to " + + "be updated, but path '${showAttrPath (take prefixLength updatePath)}' " + + "of the given value is not an attribute set, so we can't " + + "update an attribute inside of it."); + + # We get the final result by applying all the updates on this level + # after having applied all the nested updates + # We use foldl instead of foldl' so that in case of multiple updates, + # intermediate values aren't evaluated if not needed + in foldl (acc: el: el.update acc) withNestedMods split.right; + + in updates: value: go 0 true value updates; + + /* 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: + foldr (n: a: + foldr (name: o: + o // { ${name} = op n.${name} (a.${name} or nul); } + ) a (attrNames n) + ) {}; + + + /* 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: + 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 recurse 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: + let + g = + name: value: + if isAttrs value && cond value + then recurse (path ++ [name]) value + else f (path ++ [name]) value; + in mapAttrs g; + 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: x.type or null == "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 = + builtins.zipAttrsWith or (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 length values == 1 + || pred here (elemAt values 1) (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 = recursiveUpdateUntil (path: lhs: rhs: !(isAttrs lhs && isAttrs 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; + all id (attrValues (zipAttrsWithNames (attrNames pattern) (n: values: + let pat = head values; val = elemAt values 1; 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; + + /* Turns a list of strings into a human-readable description of those + strings represented as an attribute path. The result of this function is + not intended to be machine-readable. + + Example: + showAttrPath [ "foo" "10" "bar" ] + => "foo.\"10\".bar" + showAttrPath [] + => "<root attribute path>" + */ + showAttrPath = path: + if path == [] then "<root attribute path>" + else concatMapStringsSep "." escapeNixIdentifier path; + + /* 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 ? outputSpecified || ! pkg.outputSpecified + 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; +} |