add (lib): add function to scan all files from dir

lib/utils.nix

@@ -0,0 +1,51 @@
+# This function is copied from:
+# https://github.com/yunfachi/nypkgs/blob/master/lib/umport.nix
+#
+# !!! REMOVING THIS NOTICE VIOLATES THE MIT LICENSE OF THE UMPORT PROJECT !!!
+# This notice must be retained in all copies of this function, including modified versions!
+# The MIT License can be found here:
+# https://github.com/yunfachi/nypkgs/blob/master/LICENSE
+
+{ lib, ... }:
+let
+  umport =
+    inputs@{
+      path ? null,
+      paths ? [ ],
+      include ? [ ],
+      exclude ? [ ],
+      recursive ? true,
+    }:
+    with lib;
+    with fileset;
+    let
+      excludedFiles = filter (path: pathIsRegularFile path) exclude;
+      excludedDirs = filter (path: pathIsDirectory path) exclude;
+      isExcluded =
+        path:
+        if elem path excludedFiles then
+          true
+        else
+          (filter (excludedDir: lib.path.hasPrefix excludedDir path) excludedDirs) != [ ];
+    in
+    unique (
+      (filter
+        (file: pathIsRegularFile file && hasSuffix ".nix" (builtins.toString file) && !isExcluded file)
+        (
+          concatMap (
+            _path:
+            if recursive then
+              toList _path
+            else
+              mapAttrsToList (
+                name: type: _path + (if type == "directory" then "/${name}/default.nix" else "/${name}")
+              ) (builtins.readDir _path)
+          ) (unique (if path == null then paths else [ path ] ++ paths))
+        )
+      )
+      ++ (if recursive then concatMap (path: toList path) (unique include) else unique include)
+    );
+in
+{
+  scan = umport;
+}