feat(overlays)!: redefine in terms of createThings

modules/flake/overlays/default.nix

@@ -0,0 +1,65 @@
+{ lib, config, self, inputs, ... }:
+
+let
+  inherit (config.lib)
+    createThings;
+in
+let
+  createOverlays = baseDir:
+    createThings {
+      inherit baseDir;
+      thingType = "overlay";
+    };
+in
+{
+  options = let
+    inherit (lib) types;
+  in {
+    flake.autoOverlays = lib.mkOption {
+      description = ''
+        Automagically generate overlays from walking directories with Nix files
+      '';
+      type = types.submodule (submodule: {
+        options = {
+          enable = lib.mkEnableOption "Automatic overlays extraction";
+          dir = lib.mkOption {
+            description = ''
+              Base directory of the contained overlays
+            '';
+            type = types.path;
+            default = "${self}/overlays";
+            defaultText = ''''${self}/overlays'';
+          };
+          result = lib.mkOption {
+            description = ''
+              The resulting automatic overlays
+            '';
+            type = types.attrsOf types.unspecified;
+            readOnly = true;
+            internal = true;
+            default =
+              lib.optionalAttrs
+                config.flake.autoOverlays.enable
+                (createOverlays config.flake.autoOverlays.dir);
+          };
+        };
+      });
+      default = {};
+    };
+  };
+
+  config = {
+    flake = let
+      overlays =
+        lib.pipe
+          config.flake.autoOverlays.result
+          [
+            (lib.mapAttrs
+              (name: overlay:
+                overlay))
+          ];
+    in {
+      inherit overlays;
+    };
+  };
+}