nixos/retroarch: add RetroArch as a desktop session

nixos/modules/services/x11/desktop-managers/default.nix

@@ -19,7 +19,7 @@ in
   # E.g., if Plasma 5 is enabled, it supersedes xterm.
   imports = [
     ./none.nix ./xterm.nix ./xfce.nix ./plasma5.nix ./lumina.nix
-    ./lxqt.nix ./enlightenment.nix ./gnome.nix ./kodi.nix
+    ./lxqt.nix ./enlightenment.nix ./gnome.nix ./retroarch.nix ./kodi.nix
     ./mate.nix ./pantheon.nix ./surf-display.nix ./cde.nix
     ./cinnamon.nix
   ];

nixos/modules/services/x11/desktop-managers/retroarch.nix

@@ -0,0 +1,40 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let cfg = config.services.xserver.desktopManager.retroarch;
+
+in {
+  options.services.xserver.desktopManager.retroarch = {
+    enable = mkEnableOption "RetroArch";
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.retroarch;
+      defaultText = literalExpression "pkgs.retroarch";
+      example = literalExpression "pkgs.retroarch-full";
+      description = "RetroArch package to use.";
+    };
+
+    extraArgs = mkOption {
+      type = types.listOf types.str;
+      default = [ ];
+      example = [ "--verbose" "--host" ];
+      description = "Extra arguments to pass to RetroArch.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services.xserver.desktopManager.session = [{
+      name = "RetroArch";
+      start = ''
+        ${cfg.package}/bin/retroarch -f ${escapeShellArgs cfg.extraArgs} &
+        waitPID=$!
+      '';
+    }];
+
+    environment.systemPackages = [ cfg.package ];
+  };
+
+  meta.maintainers = with maintainers; [ j0hax ];
+}

nixos/tests/all-tests.nix

@@ -439,6 +439,7 @@ in
   resolv = handleTest ./resolv.nix {};
   restartByActivationScript = handleTest ./restart-by-activation-script.nix {};
   restic = handleTest ./restic.nix {};
+  retroarch = handleTest ./retroarch.nix {};
   riak = handleTest ./riak.nix {};
   robustirc-bridge = handleTest ./robustirc-bridge.nix {};
   roundcube = handleTest ./roundcube.nix {};

nixos/tests/retroarch.nix

@@ -0,0 +1,49 @@
+import ./make-test-python.nix ({ pkgs, ... }:
+
+  {
+    name = "retroarch";
+    meta = with pkgs.lib.maintainers; { maintainers = [ j0hax ]; };
+
+    machine = { ... }:
+
+      {
+        imports = [ ./common/user-account.nix ];
+        services.xserver.enable = true;
+        services.xserver.desktopManager.retroarch = {
+          enable = true;
+          package = pkgs.retroarchFull;
+        };
+        services.xserver.displayManager = {
+          sddm.enable = true;
+          defaultSession = "RetroArch";
+          autoLogin = {
+            enable = true;
+            user = "alice";
+          };
+        };
+      };
+
+    testScript = { nodes, ... }:
+      let
+        user = nodes.machine.config.users.users.alice;
+        xdo = "${pkgs.xdotool}/bin/xdotool";
+      in ''
+        with subtest("Wait for login"):
+            start_all()
+            machine.wait_for_file("${user.home}/.Xauthority")
+            machine.succeed("xauth merge ${user.home}/.Xauthority")
+
+        with subtest("Check RetroArch started"):
+            machine.wait_until_succeeds("pgrep retroarch")
+            machine.wait_for_window("^RetroArch ")
+
+        with subtest("Check configuration created"):
+            machine.wait_for_file("${user.home}/.config/retroarch/retroarch.cfg")
+
+        with subtest("Wait to get a screenshot"):
+            machine.execute(
+                "${xdo} key Alt+F1 sleep 10"
+            )
+            machine.screenshot("screen")
+      '';
+  })