Adding nixos-module for custom window manager for xsession

Help
1

Hello guys! May I ask if you have any helpful links which I should check out in order to write a home-manager module for my toy-wm (for x11) so I can see an entry in the login-manager to select it?

EDIT:
Ok, so here is my current flake.nix of my toy-wm simp-wm:

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    rust-overlay.url = "github:oxalica/rust-overlay";
  };

  outputs = { nixpkgs, rust-overlay, ... }:
    let
      system = "x86_64-linux";

      pkgs = import nixpkgs
        {
          inherit system;

          overlays = [ rust-overlay.overlays.default ];
        };

      toolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;

      simp-pkg = pkgs.callPackage
        ({ rustPlatform, lib, ... }: rustPlatform.buildRustPackage rec {
          pname = "simp-wm";
          version = "0.0.1";

          src = ./.;
          cargoLock.lockFile = ./Cargo.lock;

          buildInputs = with pkgs; [
            xorg.xmodmap
          ];

          nativeBuildInputs = buildInputs;
        })
        { };
    in
    {
      nixosModules.default = { config, lib, ... }: with lib;
        let
          cfg = config.services.xserver.windowManager.simp-wm;
        in
        {
          options.services.xserver.windowManager.simp-wm = {
            enable = mkEnableOption (lib.mdDoc "Simp WM");
          };

          config = mkIf cfg.enable {
            services.xserver.windowManager.session = [{
              name = "simp-wm";
              manage = "window";
              start = ''

                systemctl --user import-environment PATH DISPLAY XAUTHORITY DESKTOP_SESSION XDG_CONFIG_DIRS XDG_DATA_DIRS XDG_RUNTIME_DIR XDG_SESSION_ID DBUS_SESSION_BUS_ADDRESS || true
                dbus-update-activation-environment --systemd --all || true

                simp-wm

                waitPID=$!
              '';
            }];

            environment.systemPackages = [ simp-pkg pkgs.xorg.xmodmap ];
          };
        };

      devShells.${system}.default = pkgs.mkShell.override
        {
          stdenv = pkgs.stdenvAdapters.useMoldLinker pkgs.clangStdenv;
        }
        {
          packages = [ toolchain pkgs.xorg.xmodmap ];
        };
    };
}

but the problem is, that I’m getting the following error message in the logs, when I selected simp-wm in lightdm and login:

[+199.02s] DEBUG: Greeter requests session none+simp-wm
[+199.03s] DEBUG: Seat seat0: Failed to find session configuration none+simp-wm
[+199.03s] DEBUG: Seat seat0: Can't find session 'none+simp-wm'

If I’m not wrong, my nixosModules.default almost equals the i3.nix file from nixpkgs but my nixosModules can’t get started.

Does anyone know how to fix this?

2

Is this a wayland compositor or x11 window manager? For wayland you can checkout the existing sway/hyprland modules and for x11 there is maybe i3.

4

I edited my post. Any help is appreciated!