lib: add concatMapAttrsToList

This is the concatMap counterpart to mapAttrsToList.

Co-authored-by: Dusk Banks <[email protected]>

lib/attrsets.nix

@@ -1094,6 +1094,44 @@ rec {
     attrs:
     map (name: f name attrs.${name}) (attrNames attrs);
 
+  /**
+    Call a function for each attribute in the given set and return
+    the concatenated results.
+
+    # Inputs
+
+    `f`
+
+    : A function, given an attribute's name and value, returns a list of new values.
+
+    `attrs`
+
+    : Attribute set to map over.
+
+    # Type
+
+    ```
+    # FIXME
+    concatMapAttrsToList :: (String -> a -> b) -> AttrSet -> [b]
+    ```
+
+    # Examples
+    :::{.example}
+    ## `lib.attrsets.concatMapAttrsToList` usage example
+
+    ```nix
+    concatMapAttrsToList (name: value: [ name (name + value) ])
+       { x = "a"; y = "b"; }
+    => [ "x" "xa" "y" "yb" ]
+    ```
+
+    :::
+  */
+  concatMapAttrsToList =
+    f:
+    attrs:
+    concatMap (name: f name attrs.${name}) (attrNames attrs);
+
   /**
     Deconstruct an attrset to a list of name-value pairs as expected by [`builtins.listToAttrs`](https://nixos.org/manual/nix/stable/language/builtins.html#builtins-listToAttrs).
     Each element of the resulting list is an attribute set with these attributes:

lib/default.nix

@@ -84,7 +84,7 @@ let
     inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath
       getAttrFromPath attrVals attrNames attrValues getAttrs catAttrs filterAttrs
       filterAttrsRecursive foldlAttrs foldAttrs collect nameValuePair mapAttrs
-      mapAttrs' mapAttrsToList attrsToList concatMapAttrs mapAttrsRecursive
+      mapAttrs' mapAttrsToList concatMapAttrsToList attrsToList concatMapAttrs mapAttrsRecursive
       mapAttrsRecursiveCond genAttrs isDerivation toDerivation optionalAttrs
       zipAttrsWithNames zipAttrsWith zipAttrs recursiveUpdateUntil
       recursiveUpdate matchAttrs mergeAttrsList overrideExisting showAttrPath getOutput getFirstOutput