refactor(dotfiles): share Nix file discovery

src/dotfiles/default.nix

@@ -17,7 +17,7 @@ let
   util = import ./util.nix { inherit lib; };
 
   registry = import ./registry.nix {
-    inherit lib;
+    inherit lib util;
     hosts = self.nixosConfigurations;
     root = root + "/registry";
   };

src/dotfiles/guests.nix

@@ -276,10 +276,7 @@ let
       };
     };
 
-  names = map (file: lib.removeSuffix ".nix" file) (lib.attrNames guestFiles);
-  guestFiles = lib.filterAttrs (file: type: type == "regular" && lib.hasSuffix ".nix" file) (
-    builtins.readDir root
-  );
+  names = map (path: lib.removeSuffix ".nix" (builtins.baseNameOf path)) files;
 in
 {
   imports = files ++ map mkGuest names;

src/dotfiles/registry.nix

@@ -2,20 +2,14 @@
   hosts,
   lib,
   root,
+  util,
 }:
 let
-  definitions =
-    lib.mapAttrs'
-      (
-        name: _type:
-        let
-          path = root + "/${name}";
-        in
-        lib.nameValuePair (registryName name) (mkRegistry path)
-      )
-      (
-        lib.filterAttrs (name: type: type == "regular" && lib.hasSuffix ".nix" name) (builtins.readDir root)
-      );
+  definitions = lib.listToAttrs (
+    map (path: lib.nameValuePair (registryName (builtins.baseNameOf path)) (mkRegistry path)) (
+      util.collectNixFiles root
+    )
+  );
 
   registryName = fileName: lib.removeSuffix ".nix" fileName;