exwm: add module

adapted from nixpkgs's exwm service

modules/misc/news/2026/05/2026-05-15_09-37-08.nix

@@ -0,0 +1,8 @@
+{
+  time = "2026-05-15T13:37:08+00:00";
+  condition = true;
+  message = ''
+    A new module is available: `xsession.windowManager.exwm`. This
+    provides configuration for the Emacs X Window Manager.
+  '';
+}

modules/services/window-managers/default.nix

@@ -2,6 +2,7 @@
   imports = [
     ./awesome.nix
     ./bspwm
+    ./exwm.nix
     ./fluxbox.nix
     ./herbstluftwm.nix
     ./hyprland.nix

modules/services/window-managers/exwm.nix

@@ -0,0 +1,62 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  meta.maintainers = [ lib.hm.maintainers.garklein ];
+
+  options = {
+    xsession.windowManager.exwm = {
+      enable = lib.mkEnableOption "exwm";
+
+      loadScript = lib.mkOption {
+        default = "(require 'exwm)";
+        type = lib.types.lines;
+        example = ''
+          (require 'exwm)
+          (exwm-enable)
+        '';
+        description = ''
+          Emacs lisp code to be run after loading the user's init
+          file.
+        '';
+      };
+
+      package = lib.mkPackageOption pkgs "emacs" {
+        example = [ "emacs-gtk" ];
+      };
+
+      extraPackages = lib.mkOption {
+        type = lib.types.functionTo (lib.types.listOf lib.types.package);
+        default = _epkgs: [ ];
+        defaultText = lib.literalExpression "epkgs: []";
+        example = lib.literalExpression ''
+          epkgs: [
+            epkgs.emms
+            epkgs.magit
+            epkgs.proof-general
+          ]
+        '';
+        description = ''
+          Extra packages available to Emacs. The value must be a
+          function which receives the attrset defined in
+          {var}`emacs.pkgs` as the sole argument.
+        '';
+      };
+    };
+  };
+
+  config =
+    let
+      cfg = config.xsession.windowManager.exwm;
+      exwm-emacs = cfg.package.pkgs.withPackages (epkgs: cfg.extraPackages epkgs ++ [ epkgs.exwm ]);
+    in
+    lib.mkIf cfg.enable {
+      home.packages = [ exwm-emacs ];
+      xsession.windowManager.command = ''
+        ${exwm-emacs}/bin/emacs -l ${pkgs.writeText "emacs-exwm-load" "${cfg.loadScript}"}
+      '';
+    };
+}