lib.modules: Let module declare options directly in bare submodule

... where a bare submodule is an option that has a type like
`submoduleWith x`, as opposed to `attrsOf (submoduleWith x)`.

This makes migration unnecessary when introducing a freeform type
in an existing option tree.

Closes #146882

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/tests/modules/define-bare-submodule-values.nix b/lib/tests/modules/define-bare-submodule-values.nix
new file mode 100644
index 00000000000..00ede929ee6
--- /dev/null
+++ b/lib/tests/modules/define-bare-submodule-values.nix
@@ -0,0 +1,4 @@
+{
+  bare-submodule.nested = 42;
+  bare-submodule.deep = 420;
+}