feat(niri,xbacklight): Brightness control

modules/nixos/xbacklight-permissions.nix

@@ -0,0 +1,35 @@
+{ config, lib, pkgs, ... }:
+
+let cfg = config.sydnix.xbacklight-permissions;
+in {
+  options.sydnix.xbacklight-permissions = {
+    enable =
+      lib.mkEnableOption "the user group that is allowed to use xbacklight";
+    group = lib.mkOption {
+      type = lib.types.str;
+      default = "xbacklight";
+    };
+    paths = lib.mkOption {
+      type = with lib.types; listOf str;
+      default = [
+        "/sys/class/backlight/intel_backlight/brightness"
+      ];
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    users.groups.${cfg.group} = {};
+
+    systemd.tmpfiles.settings."50-xbacklight" =
+      lib.mergeAttrsList
+        (builtins.map
+          (path: {
+            ${path}.z = {
+              inherit (cfg) group;
+              mode = "0664";
+              user = "root";
+            };
+          })
+          cfg.paths);
+  };
+}