From e26bb57b735d4ce3e931d5632ea1a3f0c7fbfcf4 Mon Sep 17 00:00:00 2001
From: Johannes Kirschbauer <hsjobeki@gmail.com>
Date: Sat, 30 May 2026 00:04:51 +0200
Subject: [PATCH] nixos/displayManager: replace ad-hoc type // { check }
 overrides

Replace ad-hoc `type // { check }` overrides, which are incompatible
with the v2 merge mechanism (see #454964).
---
 .../services/display-managers/default.nix     | 41 ++++++-------------
 1 file changed, 13 insertions(+), 28 deletions(-)

diff --git a/nixos/modules/services/display-managers/default.nix b/nixos/modules/services/display-managers/default.nix
index 9b9937900b3b..418db90e7cc6 100644
--- a/nixos/modules/services/display-managers/default.nix
+++ b/nixos/modules/services/display-managers/default.nix
@@ -101,16 +101,7 @@ in
       };
 
       defaultSession = lib.mkOption {
-        type = lib.types.nullOr lib.types.str // {
-          description = "session name";
-          check =
-            d:
-            lib.assertMsg (d != null -> (lib.types.str.check d && lib.elem d cfg.sessionData.sessionNames)) ''
-              Default graphical session, '${d}', not found.
-              Valid names for 'services.displayManager.defaultSession' are:
-                ${lib.concatStringsSep "\n  " cfg.sessionData.sessionNames}
-            '';
-        };
+        type = lib.types.nullOr (lib.types.str // { description = "session name"; });
         default = null;
         example = "gnome";
         description = ''
@@ -130,26 +121,12 @@ in
 
       sessionPackages = lib.mkOption {
         type = lib.types.listOf (
-          lib.types.package
+          lib.types.addCheck lib.types.package (
+            p: p ? providedSessions && p.providedSessions != [ ] && lib.all lib.isString p.providedSessions
+          )
           // {
             description = "package with provided sessions";
-            check =
-              p:
-              lib.assertMsg
-                (
-                  lib.types.package.check p
-                  && p ? providedSessions
-                  && p.providedSessions != [ ]
-                  && lib.all lib.isString p.providedSessions
-                )
-                ''
-                  Package, '${p.name}', did not specify any session names, as strings, in
-                  'passthru.providedSessions'. This is required when used as a session package.
-
-                  The session names can be looked up in:
-                    ${p}/share/xsessions
-                    ${p}/share/wayland-sessions
-                '';
+            descriptionClass = "composite";
           }
         );
         default = [ ];
@@ -211,6 +188,14 @@ in
           services.displayManager.autoLogin.enable requires services.displayManager.autoLogin.user to be set
         '';
       }
+      {
+        assertion = cfg.defaultSession == null || lib.elem cfg.defaultSession cfg.sessionData.sessionNames;
+        message = ''
+          Default graphical session, '${toString cfg.defaultSession}', not found.
+          Valid names for 'services.displayManager.defaultSession' are:
+            ${lib.concatStringsSep "\n    " cfg.sessionData.sessionNames}
+        '';
+      }
     ];
 
     # Make xsessions and wayland sessions available in XDG_DATA_DIRS