lib: improve filterAttrs (#345547)

lib/attrsets.nix

@@ -7,7 +7,7 @@ let
   inherit (builtins) head length;
   inherit (lib.trivial) oldestSupportedReleaseIsAtLeast mergeAttrs warn warnIf;
   inherit (lib.strings) concatStringsSep concatMapStringsSep escapeNixIdentifier sanitizeDerivationName;
-  inherit (lib.lists) foldr foldl' concatMap elemAt all partition groupBy take foldl;
+  inherit (lib.lists) filter foldr foldl' concatMap elemAt all partition groupBy take foldl;
 in
 
 rec {
@@ -644,8 +644,7 @@ rec {
   filterAttrs =
     pred:
     set:
-    listToAttrs (concatMap (name: let v = set.${name}; in if pred name v then [(nameValuePair name v)] else []) (attrNames set));
+    removeAttrs set (filter (name: ! pred name set.${name}) (attrNames set));
-
 
   /**
     Filter an attribute set recursively by removing all attributes for

lib/tests/misc.nix

@@ -47,6 +47,7 @@ let
     evalModules
     extends
     filter
+    filterAttrs
     fix
     fold
     foldAttrs
@@ -1102,6 +1103,25 @@ runTests {
     };
   };
 
+  testFilterAttrs = {
+    expr = filterAttrs (n: v: n != "a" && (v.hello or false) == true) {
+      a.hello = true;
+      b.hello = true;
+      c = {
+        hello = true;
+        world = false;
+      };
+      d.hello = false;
+    };
+    expected = {
+      b.hello = true;
+      c = {
+        hello = true;
+        world = false;
+      };
+    };
+  };
+
   # code from example
   testFoldlAttrs = {
     expr = {