lib/types: init defaultComposedFunctor for types.{attrsWith,listOf}

doc/redirects.json

@@ -71,6 +71,9 @@
   "sec-nixpkgs-release-25.05-lib-breaking": [
     "release-notes.html#sec-nixpkgs-release-25.05-lib-breaking"
   ],
+  "sec-nixpkgs-release-25.05-lib-deprecations": [
+    "release-notes.html#sec-nixpkgs-release-25.05-lib-deprecations"
+  ],
   "sec-overlays-install": [
     "index.html#sec-overlays-install"
   ],

doc/release-notes/rl-2505.section.md

@@ -17,3 +17,10 @@
 - Structure of the `functor` of some types has changed. `functor` is an implementation detail and should not be relied upon. If you did rely on it let us know in this [PR](https://github.com/NixOS/nixpkgs/pull/363565).
   - [`lib.types.enum`](https://nixos.org/manual/nixos/unstable/#sec-option-types-basic): Previously the `functor.payload` was the list of enum values directly. Now it is an attribute set containing the values in the `values` attribute.
   - [`lib.types.separatedString`](https://nixos.org/manual/nixos/unstable/#sec-option-types-string): Previously the `functor.payload` was the seperator directly. Now it is an attribute set containing the seperator in the `sep` attribute.
+
+### Deprecations {#sec-nixpkgs-release-25.05-lib-deprecations}
+
+`functor` is an implementation detail and should not be relied upon, but since its status wasn't clear and it has had some use cases without alternatives, changes are being handled as gracefully as possible. Deprecations within functor:
+- `functor.wrapped` is now deprecated for some types and using it will give a warning with migration instructions. It is deprecated for these types:
+    - `lib.types.attrsWith`
+    - `lib.types.listOf`

lib/types.nix

@@ -71,6 +71,26 @@ let
     let pos = builtins.unsafeGetAttrPos name v; in
     if pos == null then "" else " at ${pos.file}:${toString pos.line}:${toString pos.column}";
 
+  # Internal functor to help for migrating functor.wrapped to functor.payload.elemType
+  # Note that individual attributes can be overriden if needed.
+  elemTypeFunctor = name: { elemType, ... }@payload: {
+    inherit name payload;
+    type    = outer_types.types.${name};
+    binOp   = a: b:
+      let
+        merged = a.elemType.typeMerge b.elemType.functor;
+      in
+        if merged == null
+        then
+          null
+        else
+          { elemType = merged; };
+    wrappedDeprecationMessage = { loc }: lib.warn ''
+      The deprecated `type.functor.wrapped` attribute of the option `${showOption loc}` is accessed, use `type.nestedTypes.elemType` instead.
+    '' payload.elemType;
+  };
+
+
   outer_types =
 rec {
   isType = type: x: (x._type or "") == type;
@@ -580,7 +600,9 @@ rec {
       getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["*"]);
       getSubModules = elemType.getSubModules;
       substSubModules = m: listOf (elemType.substSubModules m);
-      functor = (defaultFunctor name) // { wrapped = elemType; };
+      functor = (elemTypeFunctor name { inherit elemType; }) // {
+        type = payload: types.listOf payload.elemType;
+      };
       nestedTypes.elemType = elemType;
     };
 
@@ -664,14 +686,10 @@ rec {
       getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<${placeholder}>"]);
       getSubModules = elemType.getSubModules;
       substSubModules = m: attrsWith { elemType = elemType.substSubModules m; inherit lazy placeholder; };
-      functor = defaultFunctor "attrsWith" // {
-        wrappedDeprecationMessage = { loc }: lib.warn ''
-          The deprecated `type.functor.wrapped` attribute of the option `${showOption loc}` is accessed, use `type.nestedTypes.elemType` instead.
-        '' elemType;
-        payload = {
-          # Important!: Add new function attributes here in case of future changes
+      functor = (elemTypeFunctor "attrsWith" {
           inherit elemType lazy placeholder;
-        };
+      }) // {
+        # Custom type merging required because of the "placeholder" attribute
         inherit binOp;
       };
       nestedTypes.elemType = elemType;

nixos/doc/manual/redirects.json

@@ -1904,6 +1904,9 @@
   "sec-nixpkgs-release-25.05-lib-breaking": [
     "release-notes.html#sec-nixpkgs-release-25.05-lib-breaking"
   ],
+  "sec-nixpkgs-release-25.05-lib-deprecations": [
+    "release-notes.html#sec-nixpkgs-release-25.05-lib-deprecations"
+  ],
   "sec-release-24.11": [
     "release-notes.html#sec-release-24.11"
   ],