138 lines
4.3 KiB
Nix
138 lines
4.3 KiB
Nix
# Operations on attribute sets.
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with {
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inherit (builtins) head tail isString;
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inherit (import ./default.nix) fold;
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inherit (import ./strings.nix) concatStringsSep;
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};
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rec {
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inherit (builtins) attrNames listToAttrs hasAttr isAttrs;
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/* Return an attribute from nested attribute sets. For instance
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["x" "y"] applied to some set e returns e.x.y, if it exists. The
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default value is returned otherwise. */
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attrByPath = attrPath: default: e:
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let attr = head attrPath;
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in
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if attrPath == [] then e
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else if builtins ? hasAttr && hasAttr attr e
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then attrByPath (tail attrPath) default (getAttr attr e)
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else default;
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/* Backwards compatibility hack: lib.attrByPath used to be called
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lib.getAttr, which was confusing given that there was also a
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builtins.getAttr. Eventually we'll drop this hack and
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lib.getAttr will just be an alias for builtins.getAttr. */
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getAttr = a: b: if isString a
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then builtins.getAttr a b
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else c: builtins.trace "Deprecated use of lib.getAttr!" (attrByPath a b c);
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getAttrFromPath = attrPath: set:
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let errorMsg = "cannot find attribute `" + concatStringsSep "." attrPath + "'";
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in attrByPath attrPath (abort errorMsg) set;
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/* Return the specified attributes from a set.
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Example:
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attrVals ["a" "b" "c"] as
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=> [as.a as.b as.c]
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*/
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attrVals = nameList: set:
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map (x: getAttr x set) nameList;
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/* Return the values of all attributes in the given set, sorted by
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attribute name.
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Example:
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attrValues {c = 3; a = 1; b = 2;}
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=> [1 2 3]
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*/
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attrValues = attrs: attrVals (attrNames attrs) attrs;
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/* Collect each attribute named `attr' from a list of attribute
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sets. Sets that don't contain the named attribute are ignored.
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Example:
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catAttrs "a" [{a = 1;} {b = 0;} {a = 2;}]
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=> [1 2]
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*/
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catAttrs = attr: l: fold (s: l: if hasAttr attr s then [(getAttr attr s)] ++ l else l) [] l;
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/* Utility function that creates a {name, value} pair as expected by
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builtins.listToAttrs. */
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nameValuePair = name: value: { inherit name value; };
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/* Apply a function to each element in an attribute set. The
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function takes two arguments --- the attribute name and its value
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--- and returns the new value for the attribute. The result is a
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new attribute set.
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Example:
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mapAttrs (name: value: name + "-" + value)
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{x = "foo"; y = "bar";}
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=> {x = "x-foo"; y = "y-bar";}
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*/
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mapAttrs = f: set:
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listToAttrs (map (attr: nameValuePair attr (f attr (getAttr attr set))) (attrNames set));
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/* Like `mapAttrs', except that it recursively applies itself to
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attribute sets. Also, the first argument of the argument
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function is a *list* of the names of the containing attributes.
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Type:
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mapAttrsRecursive ::
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([String] -> a -> b) -> AttrSet -> AttrSet
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Example:
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mapAttrsRecursive (path: value: concatStringsSep "-" (path ++ [value]))
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{ n = { a = "A"; m = { b = "B"; c = "C"; }; }; d = "D"; }
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=> { n = { a = "n-a-A"; m = { b = "n-m-b-B"; c = "n-m-c-C"; }; }; d = "d-D"; }
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*/
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mapAttrsRecursive = mapAttrsRecursiveCond (as: true);
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/* Like `mapAttrsRecursive', but it takes an additional predicate
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function that tells it whether to recursive into an attribute
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set. If it returns false, `mapAttrsRecursiveCond' does not
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recurse, but does apply the map function. It is returns true, it
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does recurse, and does not apply the map function.
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Type:
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mapAttrsRecursiveCond ::
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(AttrSet -> Bool) -> ([String] -> a -> b) -> AttrSet -> AttrSet
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Example:
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# To prevent recursing into derivations (which are attribute
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# sets with the attribute "type" equal to "derivation"):
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mapAttrsRecursiveCond
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(as: !(as ? "type" && as.type == "derivation"))
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(x: ... do something ...)
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attrs
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*/
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mapAttrsRecursiveCond = cond: f: set:
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let
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recurse = path: set:
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let
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g =
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name: value:
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if isAttrs value && cond value
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then recurse (path ++ [name]) value
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else f (path ++ [name]) value;
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in mapAttrs g set;
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in recurse [] set;
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/* Check whether the argument is a derivation. */
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isDerivation = x: isAttrs x && x ? type && x.type == "derivation";
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}
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