NixOS, tuigreet, EXWM, and alpha-background
===========================================

When I was transitioning to NixOS, I had some trouble with my EXWM config. I figured I would put my solutions here in case they can help anyone else.

With tuigreet, I found that no X server was starting. tuigreet uses xstart, which isn't exposed by default on Nix. To use xstart, you need to set services.xserver.displayManager.startx.enable to true.

As for EXWM, I couldn't get the alpha-background frame parameter to work. I thought it might be a compositor issue, but the alpha frame parameter was working fine. It turns out that the default Nix Emacs doesn't use GTK, and alpha-background needs GTK to work. To fix this, we can tell EXWM to use emacs-gtk.

Here is my working configuration:

# set up exwm
services.xserver = {
  enable = true;
  displayManager.startx.enable = true;
  windowManager.exwm = {
    enable = true;
    package = pkgs.emacs-gtk;
  };
};

# make greetd load up exwm
services.greetd = let
  tuigreet = "${pkgs.greetd.tuigreet}/bin/tuigreet";
  xsessions = "${config.services.displayManager.sessionData.desktops}/share/xsessions";
in {
  enable = true;
  settings = {
    default_session = {
      command = "${tuigreet} -x ${xsessions}";
      user = "greeter";
    };
  };
};

Before the exwm.package option existed, I started Emacs manually like this:

services.xserver.windowManager.session = lib.singleton {
  name = "exwm";
  start = "${pkgs.emacs-gtk}/bin/emacs";
};

Alternatively, you could override EXWM's Emacs package like this:

nixpkgs.overlays = [ (final: prev: { emacs = prev.emacs-gtk; }) ];

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