lib.getOptionalAttrs: init

lib/attrsets.nix

@@ -7,7 +7,7 @@ let
   inherit (builtins) head length;
   inherit (lib.trivial) mergeAttrs warn;
   inherit (lib.strings) concatStringsSep concatMapStringsSep escapeNixIdentifier sanitizeDerivationName;
-  inherit (lib.lists) foldr foldl' concatMap elemAt all partition groupBy take foldl;
+  inherit (lib.lists) foldr foldl' concatMap elemAt all partition groupBy take foldl intersectLists;
 in
 
 rec {
@@ -548,7 +548,7 @@ rec {
 
     `names`
 
-    : A list of attribute names to get out of `set`
+    : A list of attribute names to get out of `attrs`
 
     `attrs`
 
@@ -575,6 +575,44 @@ rec {
     names:
     attrs: genAttrs names (name: attrs.${name});
 
+  /**
+    Given a list of possible attribute names, return the set of
+    attribuets whose name is in the list from the given set.
+
+    It works like `getAttrs` when the first attribute is a list,
+    but skip attributes not in the input set
+    instead of throwing the "attribute is missing" error.
+
+    # Inputs
+
+    `names`
+
+    : A list of possible attribute names to get out of `attrs`.
+
+    `attrs`
+
+    : The set to get the existing named attribute from.
+
+    # Type
+
+    ```
+    getOptionalAttrs :: [String] -> AttrSet -> AttrSet
+    ```
+
+    # Example
+    :::{.example}
+
+    ## `lib.attrsets.getOptionalAttrs` usage example
+    ```nix
+    getOptionalAttrs [ "a" "b" "d" ] { a = 1; b = 2; c = 3; }
+    => { a = 1; b = 2; }
+    ```
+    :::
+  */
+  getOptionalAttrs =
+    names:
+    attrs: getAttrs (intersectLists (attrNames attrs) names) attrs;
+
   /**
     Collect each attribute named `attr` from a list of attribute
     sets.  Sets that don't contain the named attribute are ignored.

lib/default.nix

@@ -79,7 +79,7 @@ let
     inherit (self.fixedPoints) fix fix' converge extends composeExtensions
       composeManyExtensions makeExtensible makeExtensibleWithCustomName;
     inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath
-      getAttrFromPath attrVals attrValues getAttrs catAttrs filterAttrs
+      getAttrFromPath attrVals attrValues getAttrs getOptionalAttrs catAttrs filterAttrs
       filterAttrsRecursive foldlAttrs foldAttrs collect nameValuePair mapAttrs
       mapAttrs' mapAttrsToList attrsToList concatMapAttrs mapAttrsRecursive
       mapAttrsRecursiveCond genAttrs isDerivation toDerivation optionalAttrs

lib/tests/misc.nix

@@ -52,6 +52,8 @@ let
     functionArgs
     generators
     genList
+    getAttrs
+    getOptionalAttrs
     getExe
     getExe'
     groupBy
@@ -1854,6 +1856,45 @@ runTests {
     };
   };
 
+  testGetAttrsExample = {
+    expr = [
+      (getAttrs [ "a" "b" ] { a = 1; b = 2; c = 3; })
+    ];
+    expected = [
+      { a = 1; b = 2; }
+    ];
+  };
+
+  testGetAttrsEmptyList = {
+    expr = getAttrs [ ] { a = 1; b = 2; c = 3; };
+    expected = { };
+  };
+
+  testGetAttrsEmpty = {
+    expr = getAttrs [ ] { };
+    expected = { };
+  };
+
+  testGetOptionalAttrsExample = {
+    expr = getOptionalAttrs [ "a" "b" "d" ] { a = 1; b = 2; c = 3; };
+    expected = { a = 1; b = 2; };
+  };
+
+  testGetOptionalAttrsEmptyNames = {
+    expr = getOptionalAttrs [ ] { a = 1; b = 2; c = 3; };
+    expected = { };
+  };
+
+  testGetOptionalAttrsEmptyValues = {
+    expr = getOptionalAttrs [ "a" "b" "d" ] { };
+    expected = { };
+  };
+
+  testGetOptionalAttrsEmpty = {
+    expr = getOptionalAttrs [ ] { };
+    expected = { };
+  };
+
   ## Levenshtein distance functions and co.
   testCommonPrefixLengthEmpty = {
     expr = strings.commonPrefixLength "" "hello";