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, 5 insertions, 0 deletions

diff --git a/lib/types.nix b/lib/types.nix
index 3fcac9c31b31..51046c2c31b6 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -642,6 +642,11 @@ rec {
               else throw "A submoduleWith option is declared multiple times with conflicting shorthandOnlyDefinesConfig values";
           };
         };
+      } // {
+        # Submodule-typed options get special treatment in order to facilitate
+        # certain migrations, such as the addition of freeformTypes onto
+        # existing option trees.
+        isSubmodule = true;
       };
 
     # A value from a set of allowed ones.