whole entire revamp

lib/modules.nix

@@ -0,0 +1,27 @@
+{ lib, ... }:
+
+let
+  inherit (builtins) attrValues readDir pathExists;
+  inherit (lib) id filterAttrs hasPrefix hasSuffix nameValuePair removeSuffix mapAttrs' trace fix fold isAttrs;
+in rec {
+  mapModules' = dir: fn: dirfn:
+    filterAttrs
+      (name: type: type != null && !(hasPrefix "_" name))
+      (mapAttrs'
+        (name: type:
+          let path = "${toString dir}/${name}"; in
+          if type == "directory"
+          then nameValuePair name (dirfn path)
+          else if
+            type == "regular" &&
+            name != "default.nix" &&
+            hasSuffix ".nix" name
+          then nameValuePair (removeSuffix ".nix" name) (fn path)
+          else nameValuePair "" null
+        )
+        (readDir dir));
+
+  mapModules = dir: fn: mapModules' dir fn (path: if pathExists "${path}/default.nix" then fn path else null);
+  mapModulesRec = dir: fn: mapModules' dir fn (path: mapModulesRec path fn);
+  mapModulesRec' = dir: fn: fix (f: attrs: fold (x: xs: (if isAttrs x then f x else [x]) ++ xs) [] (attrValues attrs)) (mapModulesRec dir fn);
+}