flake: filter out non-neovim files

flake.nix

@@ -22,6 +22,9 @@
       inherit (inputs.nixpkgs) lib;
       pkgs = inputs.nixpkgs.legacyPackages.${system};
       treefmtEval = inputs.treefmt-nix.lib.evalModule pkgs ./treefmt.nix;
+    in {
+      ### nix {run,shell,build}
+      packages.default = let
         runtimeDeps = with pkgs; [
           # mason / tree-sitter
           gcc
@@ -32,14 +35,17 @@
           ripgrep
           fd
         ];
-    in {
-      ### nix {run,shell,build}
-      packages.default =
+
+        src = lib.fileset.toSource {
+          fileset = lib.fileset.fileFilter (file: file.hasExt "lua") ./.;
+          root = ./.;
+        };
+      in
         pkgs.wrapNeovimUnstable pkgs.neovim-unwrapped
         (pkgs.neovimUtils.makeNeovimConfig {
             customRC = ''
-              set runtimepath^=${./.}
-              source ${./.}/init.lua
+              set runtimepath^=${src}
+              source ${src}/init.lua
             '';
           }
           // {wrapperArgs = ["--prefix" "PATH" ":" "${lib.makeBinPath runtimeDeps}"];});