lib.types.defaultTypeMerge: Fix for functors with no wrapped attr (#476219)

lib/tests/modules.sh

@@ -734,6 +734,8 @@ 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.

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";
+  };
+}