Merge pull request #73378 from worldofpeace/gdm-default-session

nixos/gdm: make desktopManager.default work

nixos/modules/services/x11/display-managers/gdm.nix

@@ -31,6 +31,44 @@ let
     load-module module-position-event-sounds
   '';
 
+  dmDefault = config.services.xserver.desktopManager.default;
+  wmDefault = config.services.xserver.windowManager.default;
+  hasDefaultUserSession = dmDefault != "none" || wmDefault != "none";
+  defaultSessionName = dmDefault + optionalString (wmDefault != "none") ("+" + wmDefault);
+
+  setSessionScript = pkgs.python3.pkgs.buildPythonApplication {
+    name = "set-session";
+
+    format = "other";
+
+    src = ./set-session.py;
+
+    dontUnpack = true;
+
+    strictDeps = false;
+
+    nativeBuildInputs = with pkgs; [
+      wrapGAppsHook
+      gobject-introspection
+    ];
+
+    buildInputs = with pkgs; [
+      accountsservice
+      glib
+    ];
+
+    propagatedBuildInputs = with pkgs.python3.pkgs; [
+      pygobject3
+      ordered-set
+    ];
+
+    installPhase = ''
+      mkdir -p $out/bin
+      cp $src $out/bin/set-session
+      chmod +x $out/bin/set-session
+    '';
+  };
+
 in
 
 {
@@ -156,6 +194,8 @@ in
           cat - > /run/gdm/.config/gnome-initial-setup-done <<- EOF
           yes
           EOF
+        '' + optionalString hasDefaultUserSession ''
+          ${setSessionScript}/bin/set-session ${defaultSessionName}
         '';
       };
 

nixos/modules/services/x11/display-managers/set-session.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python
+
+import gi, argparse, os, logging, sys
+
+gi.require_version("AccountsService", "1.0")
+from gi.repository import AccountsService, GLib
+from ordered_set import OrderedSet
+
+
+def get_session_file(session):
+    system_data_dirs = GLib.get_system_data_dirs()
+
+    session_dirs = OrderedSet(
+        os.path.join(data_dir, session)
+        for data_dir in system_data_dirs
+        for session in {"wayland-sessions", "xsessions"}
+    )
+
+    session_files = OrderedSet(
+        os.path.join(dir, session + ".desktop")
+        for dir in session_dirs
+        if os.path.exists(os.path.join(dir, session + ".desktop"))
+    )
+
+    # Deal with duplicate wayland-sessions and xsessions.
+    # Needed for the situation in gnome-session, where there's
+    # a xsession named the same as a wayland session.
+    if any(map(is_session_wayland, session_files)):
+        session_files = OrderedSet(
+            session for session in session_files if is_session_wayland(session)
+        )
+    else:
+        session_files = OrderedSet(
+            session for session in session_files if is_session_xsession(session)
+        )
+
+    if len(session_files) == 0:
+        logging.warning("No session files are found.")
+        sys.exit(0)
+    else:
+        return session_files[0]
+
+
+def is_session_xsession(session_file):
+    return "/xsessions/" in session_file
+
+
+def is_session_wayland(session_file):
+    return "/wayland-sessions/" in session_file
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Set session type for all normal users."
+    )
+    parser.add_argument("session", help="Name of session to set.")
+
+    args = parser.parse_args()
+
+    session = getattr(args, "session")
+    session_file = get_session_file(session)
+
+    user_manager = AccountsService.UserManager.get_default()
+    users = user_manager.list_users()
+
+    for user in users:
+        if user.is_system_account():
+            continue
+        else:
+            if is_session_wayland(session_file):
+                logging.debug(
+                    f"Setting session name: {session}, as we found the existing wayland-session: {session_file}"
+                )
+                user.set_session(session)
+            elif is_session_xsession(session_file):
+                logging.debug(
+                    f"Setting session name: {session}, as we found the existing xsession: {session_file}"
+                )
+                user.set_x_session(session)
+            else:
+                raise Exception(f"Couldn't figure out session type for {session_file}")
+
+
+if __name__ == "__main__":
+    main()