feat(legacy): refactor legacy kubenix support

lib/extra.nix

@@ -40,4 +40,49 @@ rec {
     i = acc.i + 1;
     value = acc.value + (toInt char) * (exp 8 acc.i);
   }) {i = 0; value = 0;} (stringToCharacters value)).value;
+
+  submoduleWithSpecialArgs = opts: specialArgs:
+    let
+      opts' = toList opts;
+      inherit (lib.modules) evalModules;
+    in
+    mkOptionType rec {
+      name = "submodule";
+      check = x: isAttrs x || isFunction x;
+      merge = loc: defs:
+        let
+          coerce = def: if isFunction def then def else { config = def; };
+          modules = opts' ++ map (def: { _file = def.file; imports = [(coerce def.value)]; }) defs;
+        in (evalModules {
+          inherit modules specialArgs;
+          prefix = loc;
+        }).config;
+      getSubOptions = prefix: (evalModules
+        { modules = opts'; inherit prefix specialArgs;
+          # This is a work-around due to the fact that some sub-modules,
+          # such as the one included in an attribute set, expects a "args"
+          # attribute to be given to the sub-module. As the option
+          # evaluation does not have any specific attribute name, we
+          # provide a default one for the documentation.
+          #
+          # This is mandatory as some option declaration might use the
+          # "name" attribute given as argument of the submodule and use it
+          # as the default of option declarations.
+          #
+          # Using lookalike unicode single angle quotation marks because
+          # of the docbook transformation the options receive. In all uses
+          # > and < wouldn't be encoded correctly so the encoded values
+          # would be used, and use of `<` and `>` would break the XML document.
+          # It shouldn't cause an issue since this is cosmetic for the manual.
+          args.name = "‹name›";
+        }).options;
+      getSubModules = opts';
+      substSubModules = m: submoduleWithSpecialArgs m specialArgs;
+      functor = (defaultFunctor name) // {
+        # Merging of submodules is done as part of mergeOptionDecls, as we have to annotate
+        # each submodule with its location.
+        payload = [];
+        binOp = lhs: rhs: [];
+      };
+    };
 }