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/**
Operations on attribute sets.
*/
{ lib }:
let
inherit (builtins) head length;
inherit (lib.strings)
concatStringsSep
concatMapStringsSep
escapeNixIdentifier
sanitizeDerivationName
;
inherit (lib.lists)
all
concatLists
concatMap
elemAt
filter
foldl
foldl'
foldr
groupBy
partition
reverseList
take
;
in
rec {
inherit (builtins)
attrNames
listToAttrs
hasAttr
isAttrs
getAttr
removeAttrs
intersectAttrs
;
/**
Returns an attribute from nested attribute sets.
Nix has an [attribute selection operator `.`](https://nixos.org/manual/nix/stable/language/operators#attribute-selection) which is sufficient for such queries, as long as the number of attributes is static. For example:
```nix
(x.a.b or 6) == attrByPath ["a" "b"] 6 x
# and
(x.${f p}."example.com" or 6) == attrByPath [ (f p) "example.com" ] 6 x
```
# Inputs
`attrPath`
: A list of strings representing the attribute path to return from `set`
`default`
: Default value if `attrPath` does not resolve to an existing value
`set`
: The nested attribute set to select values from
# Type
```
attrByPath :: [String] -> Any -> AttrSet -> Any
```
# Examples
:::{.example}
## `lib.attrsets.attrByPath` usage example
```nix
x = { a = { b = 3; }; }
# ["a" "b"] is equivalent to x.a.b
# 6 is a default value to return if the path does not exist in attrset
attrByPath ["a" "b"] 6 x
=> 3
attrByPath ["z" "z"] 6 x
=> 6
```
:::
*/
attrByPath =
attrPath: default: set:
let
lenAttrPath = length attrPath;
attrByPath' =
n: s:
(
if n == lenAttrPath then
s
else
(
let
attr = elemAt attrPath n;
in
if s ? ${attr} then attrByPath' (n + 1) s.${attr} else default
)
);
in
attrByPath' 0 set;
/**
Returns if an attribute from nested attribute set exists.
Nix has a [has attribute operator `?`](https://nixos.org/manual/nix/stable/language/operators#has-attribute), which is sufficient for such queries, as long as the number of attributes is static. For example:
```nix
(x?a.b) == hasAttrByPath ["a" "b"] x
# and
(x?${f p}."example.com") == hasAttrByPath [ (f p) "example.com" ] x
```
**Laws**:
1. ```nix
hasAttrByPath [] x == true
```
# Inputs
`attrPath`
: A list of strings representing the attribute path to check from `set`
`set`
: The nested attribute set to check
# Type
```
hasAttrByPath :: [String] -> AttrSet -> Bool
```
# Examples
:::{.example}
## `lib.attrsets.hasAttrByPath` usage example
```nix
x = { a = { b = 3; }; }
hasAttrByPath ["a" "b"] x
=> true
hasAttrByPath ["z" "z"] x
=> false
hasAttrByPath [] (throw "no need")
=> true
```
:::
*/
hasAttrByPath =
attrPath: e:
let
lenAttrPath = length attrPath;
hasAttrByPath' =
n: s:
(
n == lenAttrPath
|| (
let
attr = elemAt attrPath n;
in
if s ? ${attr} then hasAttrByPath' (n + 1) s.${attr} else false
)
);
in
hasAttrByPath' 0 e;
/**
Returns the longest prefix of an attribute path that refers to an existing attribute in a nesting of attribute sets.
Can be used after [`mapAttrsRecursiveCond`](#function-library-lib.attrsets.mapAttrsRecursiveCond) to apply a condition,
although this will evaluate the predicate function on sibling attributes as well.
Note that the empty attribute path is valid for all values, so this function only throws an exception if any of its inputs does.
**Laws**:
1. ```nix
attrsets.longestValidPathPrefix [] x == []
```
2. ```nix
hasAttrByPath (attrsets.longestValidPathPrefix p x) x == true
```
# Inputs
`attrPath`
: A list of strings representing the longest possible path that may be returned.
`v`
: The nested attribute set to check.
# Type
```
longestValidPathPrefix :: [String] -> AttrSet -> [String]
```
# Examples
:::{.example}
## `lib.attrsets.longestValidPathPrefix` usage example
```nix
x = { a = { b = 3; }; }
attrsets.longestValidPathPrefix ["a" "b" "c"] x
=> ["a" "b"]
attrsets.longestValidPathPrefix ["a"] x
=> ["a"]
attrsets.longestValidPathPrefix ["z" "z"] x
=> []
attrsets.longestValidPathPrefix ["z" "z"] (throw "no need")
=> []
```
:::
*/
longestValidPathPrefix =
attrPath: v:
let
lenAttrPath = length attrPath;
getPrefixForSetAtIndex =
# The nested attribute set to check, if it is an attribute set, which
# is not a given.
remainingSet:
# The index of the attribute we're about to check, as well as
# the length of the prefix we've already checked.
remainingPathIndex:
if remainingPathIndex == lenAttrPath then
# All previously checked attributes exist, and no attr names left,
# so we return the whole path.
attrPath
else
let
attr = elemAt attrPath remainingPathIndex;
in
if remainingSet ? ${attr} then
getPrefixForSetAtIndex remainingSet.${attr} # advance from the set to the attribute value
(remainingPathIndex + 1) # advance the path
else
# The attribute doesn't exist, so we return the prefix up to the
# previously checked length.
take remainingPathIndex attrPath;
in
getPrefixForSetAtIndex v 0;
/**
Create a new attribute set with `value` set at the nested attribute location specified in `attrPath`.
# Inputs
`attrPath`
: A list of strings representing the attribute path to set
`value`
: The value to set at the location described by `attrPath`
# Type
```
setAttrByPath :: [String] -> Any -> AttrSet
```
# Examples
:::{.example}
## `lib.attrsets.setAttrByPath` usage example
```nix
setAttrByPath ["a" "b"] 3
=> { a = { b = 3; }; }
```
:::
*/
setAttrByPath =
attrPath: value:
let
len = length attrPath;
atDepth = n: if n == len then value else { ${elemAt attrPath n} = atDepth (n + 1); };
in
atDepth 0;
/**
Like `attrByPath`, but without a default value. If it doesn't find the
path it will throw an error.
Nix has an [attribute selection operator](https://nixos.org/manual/nix/stable/language/operators#attribute-selection) which is sufficient for such queries, as long as the number of attributes is static. For example:
```nix
x.a.b == getAttrFromPath ["a" "b"] x
# and
x.${f p}."example.com" == getAttrFromPath [ (f p) "example.com" ] x
```
# Inputs
`attrPath`
: A list of strings representing the attribute path to get from `set`
`set`
: The nested attribute set to find the value in.
# Type
```
getAttrFromPath :: [String] -> AttrSet -> Any
```
# Examples
:::{.example}
## `lib.attrsets.getAttrFromPath` usage example
```nix
x = { a = { b = 3; }; }
getAttrFromPath ["a" "b"] x
=> 3
getAttrFromPath ["z" "z"] x
=> error: cannot find attribute `z.z'
```
:::
*/
getAttrFromPath =
attrPath: set:
attrByPath attrPath (abort ("cannot find attribute '" + concatStringsSep "." attrPath + "'")) set;
/**
Map each attribute in the given set and merge them into a new attribute set.
# Inputs
`f`
: 1\. Function argument
`v`
: 2\. Function argument
# Type
```
concatMapAttrs :: (String -> Any -> AttrSet) -> AttrSet -> AttrSet
```
# Examples
:::{.example}
## `lib.attrsets.concatMapAttrs` usage example
```nix
concatMapAttrs
(name: value: {
${name} = value;
${name + value} = value;
})
{ x = "a"; y = "b"; }
=> { x = "a"; xa = "a"; y = "b"; yb = "b"; }
```
:::
*/
concatMapAttrs =
f: v:
listToAttrs (
concatLists (reverseList (mapAttrsToList (name: value: attrsToList (f name value)) v))
);
/**
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
# Type
```
updateManyAttrsByPath :: [{ path :: [String]; update :: (Any -> Any); }] -> AttrSet -> AttrSet
```
# Examples
:::{.example}
## `lib.attrsets.updateManyAttrsByPath` usage example
```nix
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;
/**
Returns the specified attributes from a set.
# Inputs
`nameList`
: The list of attributes to fetch from `set`. Each attribute name must exist on the attribute set
`set`
: The set to get attribute values from
# Type
```
attrVals :: [String] -> { [String] :: a } -> [a]
```
# Examples
:::{.example}
## `lib.attrsets.attrVals` usage example
```nix
attrVals ["a" "b" "c"] as
=> [as.a as.b as.c]
```
:::
*/
attrVals = nameList: set: map (x: set.${x}) nameList;
/**
Returns the values of all attributes in the given set, sorted by
attribute name.
# Type
```
attrValues :: { [String] :: a } -> [a]
```
# Examples
:::{.example}
## `lib.attrsets.attrValues` usage example
```nix
attrValues {c = 3; a = 1; b = 2;}
=> [1 2 3]
```
:::
*/
attrValues = builtins.attrValues;
/**
Given a set of attribute names, return the set of the corresponding
attributes from the given set.
# Inputs
`names`
: A list of attribute names to get out of `set`
`set`
: The set to get the named attributes from
# Type
```
getAttrs :: [String] -> { [String] :: a } -> { [String] :: a }
```
# Examples
:::{.example}
## `lib.attrsets.getAttrs` usage example
```nix
getAttrs [ "a" "b" ] { a = 1; b = 2; c = 3; }
=> { a = 1; b = 2; }
```
:::
*/
getAttrs = names: attrs: genAttrs names (name: attrs.${name});
/**
Collect each attribute named `attr` from a list of attribute
sets. Sets that don't contain the named attribute are ignored.
# Inputs
`attr`
: The attribute name to get out of the sets.
`list`
: The list of attribute sets to go through
# Type
```
catAttrs :: String -> [{ [String] :: a }] -> [a]
```
# Examples
:::{.example}
## `lib.attrsets.catAttrs` usage example
```nix
catAttrs "a" [{a = 1;} {b = 0;} {a = 2;}]
=> [1 2]
```
:::
*/
catAttrs = builtins.catAttrs;
/**
Filter an attribute set by removing all attributes for which the
given predicate return false.
# Inputs
`pred`
: Predicate taking an attribute name and an attribute value, which returns `true` to include the attribute, or `false` to exclude the attribute.
<!-- TIP -->
If possible, decide on `name` first and on `value` only if necessary.
This avoids evaluating the value if the name is already enough, making it possible, potentially, to have the argument reference the return value.
(Depending on context, that could still be considered a self reference by users; a common pattern in Nix.)
<!-- TIP -->
`filterAttrs` is occasionally the cause of infinite recursion in configuration systems that allow self-references.
To support the widest range of user-provided logic, perform the `filterAttrs` call as late as possible.
Typically that's right before using it in a derivation, as opposed to an implicit conversion whose result is accessible to the user's expressions.
`set`
: The attribute set to filter
# Type
```
filterAttrs :: (String -> a -> Bool) -> { [String] :: a } -> { [String] :: a }
```
# Examples
:::{.example}
## `lib.attrsets.filterAttrs` usage example
```nix
filterAttrs (n: v: n == "foo") { foo = 1; bar = 2; }
=> { foo = 1; }
```
:::
*/
filterAttrs = pred: set: removeAttrs set (filter (name: !pred name set.${name}) (attrNames set));
/**
Filter an attribute set recursively by removing all attributes for
which the given predicate return false.
# Inputs
`pred`
: Predicate taking an attribute name and an attribute value, which returns `true` to include the attribute, or `false` to exclude the attribute.
`set`
: The attribute set to filter
# Type
```
filterAttrsRecursive :: (String -> Any -> Bool) -> AttrSet -> AttrSet
```
# Examples
:::{.example}
## `lib.attrsets.filterAttrsRecursive` usage example
```nix
filterAttrsRecursive (n: v: v != null) { foo = { bar = null; }; }
=> { foo = {}; }
```
:::
*/
filterAttrsRecursive =
pred: set:
listToAttrs (
concatMap (
name:
let
v = set.${name};
in
if pred name v then
[
(nameValuePair name (if isAttrs v then filterAttrsRecursive pred v else v))
]
else
[ ]
) (attrNames set)
);
/**
Like [`lib.lists.foldl'`](#function-library-lib.lists.foldl-prime) but for attribute sets.
Iterates over every name-value pair in the given attribute set.
The result of the callback function is often called `acc` for accumulator. It is passed between callbacks from left to right and the final `acc` is the return value of `foldlAttrs`.
::: {.note}
There is a completely different function `lib.foldAttrs`
which has nothing to do with this function, despite the similar name.
:::
# Inputs
`f`
: 1\. Function argument
`init`
: 2\. Function argument
`set`
: 3\. Function argument
# Type
```
foldlAttrs :: ( a -> String -> b -> a ) -> a -> { [String] :: b } -> a
```
# Examples
:::{.example}
## `lib.attrsets.foldlAttrs` usage example
```nix
foldlAttrs
(acc: name: value: {
sum = acc.sum + value;
names = acc.names ++ [name];
})
{ sum = 0; names = []; }
{
foo = 1;
bar = 10;
}
->
{
sum = 11;
names = ["bar" "foo"];
}
foldlAttrs
(throw "function not needed")
123
{};
->
123
foldlAttrs
(acc: _: _: acc)
3
{ z = throw "value not needed"; a = throw "value not needed"; };
->
3
The accumulator doesn't have to be an attrset.
It can be as simple as a number or string.
foldlAttrs
(acc: _: v: acc * 10 + v)
1
{ z = 1; a = 2; };
->
121
```
:::
*/
foldlAttrs =
f: init: set:
foldl' (acc: name: f acc name set.${name}) init (attrNames set);
/**
Apply fold functions to values grouped by key.
# Inputs
`op`
: A function, given a value and a collector combines the two.
`nul`
: The starting value.
`list_of_attrs`
: A list of attribute sets to fold together by key.
# Type
```
foldAttrs :: (a -> b -> b) -> b -> [{ [String] :: a }] -> { [String] :: b }
```
# Examples
:::{.example}
## `lib.attrsets.foldAttrs` usage example
```nix
foldAttrs (item: acc: [item] ++ acc) [] [{ a = 2; } { a = 3; }]
=> { a = [ 2 3 ]; }
```
:::
*/
foldAttrs =
op: nul: list_of_attrs:
foldr (
n: a: foldr (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.
# Inputs
`pred`
: Given an attribute's value, determine if recursion should stop.
`attrs`
: The attribute set to recursively collect.
# Type
```
collect :: (AttrSet -> Bool) -> AttrSet -> [Any]
```
# Examples
:::{.example}
## `lib.attrsets.collect` usage example
```nix
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.
# Inputs
`attrsOfLists`
: Attribute set with attributes that are lists of values
# Type
```
cartesianProduct :: { [String] :: [a] } -> [{ [String] :: a }]
```
# Examples
:::{.example}
## `lib.attrsets.cartesianProduct` usage example
```nix
cartesianProduct { a = [ 1 2 ]; b = [ 10 20 ]; }
=> [
{ a = 1; b = 10; }
{ a = 1; b = 20; }
{ a = 2; b = 10; }
{ a = 2; b = 20; }
]
```
:::
*/
cartesianProduct =
attrsOfLists:
foldl' (
listOfAttrs: attrName:
concatMap (
attrs: map (listValue: attrs // { ${attrName} = listValue; }) attrsOfLists.${attrName}
) listOfAttrs
) [ { } ] (attrNames attrsOfLists);
/**
Return the result of function `f` applied to the cartesian product of attribute set value combinations.
Equivalent to using `cartesianProduct` followed by `map`.
# Inputs
`f`
: A function, given an attribute set, it returns a new value.
`attrsOfLists`
: Attribute set with attributes that are lists of values
# Type
```
mapCartesianProduct :: ({ [String] :: a } -> b) -> { [String] :: a } -> [b]
```
# Examples
:::{.example}
## `lib.attrsets.mapCartesianProduct` usage example
```nix
mapCartesianProduct ({a, b}: "${a}-${b}") { a = [ "1" "2" ]; b = [ "3" "4" ]; }
=> [ "1-3" "1-4" "2-3" "2-4" ]
```
:::
*/
mapCartesianProduct = f: attrsOfLists: map f (cartesianProduct attrsOfLists);
/**
Utility function that creates a `{name, value}` pair as expected by `builtins.listToAttrs`.
# Inputs
`name`
: Attribute name
`value`
: Attribute value
# Type
```
nameValuePair :: String -> a -> { name :: String; value :: a; }
```
# Examples
:::{.example}
## `lib.attrsets.nameValuePair` usage example
```nix
nameValuePair "some" 6
=> { name = "some"; value = 6; }
```
:::
*/
nameValuePair = name: value: { inherit name value; };
/**
Apply a function to each element in an attribute set, creating a new attribute set.
# Inputs
`f`
: A function that takes an attribute name and its value, and returns the new value for the attribute.
`attrset`
: The attribute set to iterate through.