From f32c37b88cb1cfbed408eca10d78b5db77516806 Mon Sep 17 00:00:00 2001
From: Timothy Gallion <timbama@gmail.com>
Date: Thu, 1 Jan 2026 15:17:53 -0500
Subject: [PATCH] lib.types.defaultTypeMerge: Fix for functors with no
 `wrapped` attr

Downstream types that want to use `lib.types.defaultTypeMerge` must include
`wrapped` even though it is deprecated or the internal
`wrappedDeprecationMessage`. This is caused by accessing the
`wrapped` attr in `lib.types.defaultTypeMerge`. The logic should first check
if the attr exists and then if it does check if it is null.
---
 lib/tests/modules.sh                          |  2 ++
 .../modules/default-type-merge-payload.nix    | 32 +++++++++++++++++++
 lib/types.nix                                 |  7 ++--
 3 files changed, 39 insertions(+), 2 deletions(-)
 create mode 100644 lib/tests/modules/default-type-merge-payload.nix

diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index bc89d4c20851..0ef680213946 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -728,6 +728,8 @@ checkConfigOutput 'ok' config.freeformItems.foo.bar ./adhoc-freeformType-survive
 # Test that specifying both functor.wrapped and functor.payload isn't allowed
 checkConfigError 'Type foo defines both `functor.payload` and `functor.wrapped` at the same time, which is not supported.' config.result ./default-type-merge-both.nix
 
+# Test that not including functor.wrapped is allowed
+checkConfigOutput 'ok' config.result ./default-type-merge-payload.nix
 
 # Anonymous submodules don't get nixed by import resolution/deduplication
 # because of an `extendModules` bug, issue 168767.
diff --git a/lib/tests/modules/default-type-merge-payload.nix b/lib/tests/modules/default-type-merge-payload.nix
new file mode 100644
index 000000000000..d6cdc5906074
--- /dev/null
+++ b/lib/tests/modules/default-type-merge-payload.nix
@@ -0,0 +1,32 @@
+{ lib, options, ... }:
+let
+  fooOf =
+    elemType:
+    lib.mkOptionType {
+      name = "foo";
+      functor = {
+        name = "foo";
+        type = payload: fooOf payload.elemType;
+        binOp = a: _b: a;
+        payload.elemType = elemType;
+      };
+    };
+in
+{
+  imports = [
+    {
+      options.foo = lib.mkOption {
+        type = fooOf lib.types.int;
+      };
+    }
+    {
+      options.foo = lib.mkOption {
+        type = fooOf lib.types.int;
+      };
+    }
+  ];
+
+  options.result = lib.mkOption {
+    default = builtins.seq options.foo "ok";
+  };
+}
diff --git a/lib/types.nix b/lib/types.nix
index 25286303f11e..cd0a73dab9e2 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -158,8 +158,11 @@ rec {
         assert (f'.payload != null) == (f.payload != null);
         f.payload != null;
       hasWrapped =
-        assert (f'.wrapped != null) == (f.wrapped != null);
-        f.wrapped != null;
+        let
+          hasWrappedNonNull = set: set ? "wrapped" && set.wrapped != null;
+        in
+        assert (hasWrappedNonNull f') == (hasWrappedNonNull f);
+        hasWrappedNonNull f;
 
       typeFromPayload = if mergedPayload == null then null else f.type mergedPayload;
       typeFromWrapped = if mergedWrapped == null then null else f.type mergedWrapped;