lib: deprecate fold (#456532)

lib/lists.nix

@@ -9,7 +9,6 @@ let
     min
     id
     warn
-    pipe
     ;
   inherit (lib.attrsets) mapAttrs attrNames;
   inherit (lib) max;
@@ -144,10 +143,13 @@ rec {
     fold' 0;
 
   /**
-    `fold` is an alias of `foldr` for historic reasons
+    `fold` is an alias of `foldr` for historic reasons.
+
+    ::: {.warning}
+    This function will be removed in 26.05.
+    :::
   */
-  # FIXME(Profpatsch): deprecate?
-  fold = foldr;
+  fold = warn "fold has been deprecated, use foldr instead" foldr;
 
   /**
     “left fold”, like `foldr`, but from the left:

lib/tests/misc.nix

@@ -1288,25 +1288,23 @@ runTests {
     expected = [ 15 ];
   };
 
-  testFold =
+  testFoldr =
     let
-      f = op: fold: fold op 0 (range 0 100);
-      # fold with associative operator
+      f = op: foldr: foldr op 0 (range 0 100);
+      # foldr with associative operator
       assoc = f builtins.add;
-      # fold with non-associative operator
+      # foldr with non-associative operator
       nonAssoc = f builtins.sub;
     in
     {
       expr = {
         assocRight = assoc foldr;
-        # right fold with assoc operator is same as left fold
+        # foldr with assoc operator is same as foldl
         assocRightIsLeft = assoc foldr == assoc foldl;
         nonAssocRight = nonAssoc foldr;
         nonAssocLeft = nonAssoc foldl;
-        # with non-assoc operator the fold results are not the same
+        # with non-assoc operator the foldr results are not the same
         nonAssocRightIsNotLeft = nonAssoc foldl != nonAssoc foldr;
-        # fold is an alias for foldr
-        foldIsRight = nonAssoc fold == nonAssoc foldr;
       };
       expected = {
         assocRight = 5050;
@@ -1314,7 +1312,6 @@ runTests {
         nonAssocRight = 50;
         nonAssocLeft = (-5050);
         nonAssocRightIsNotLeft = true;
-        foldIsRight = true;
       };
     };
 

nixos/modules/services/matrix/mjolnir.nix

@@ -30,7 +30,7 @@ let
   moduleConfigFile = pkgs.writeText "module-config.yaml" (
     lib.generators.toYAML { } (
       lib.filterAttrs (_: v: v != null) (
-        lib.fold lib.recursiveUpdate { } [
+        lib.foldr lib.recursiveUpdate { } [
           yamlConfig
           cfg.settings
         ]

pkgs/applications/video/mpv/scripts.nix

@@ -6,7 +6,7 @@
 }:
 
 let
-  unionOfDisjoints = lib.fold lib.attrsets.unionOfDisjoint { };
+  unionOfDisjoints = lib.foldr lib.attrsets.unionOfDisjoint { };
 
   addTests =
     attrPath: drv: