Show sub options of freeform types

lib/tests/misc.nix

@@ -542,4 +542,30 @@ runTests {
     name = "";
     expected = "unknown";
   };
+
+  testFreeformOptions = {
+    expr =
+      let
+        submodule = { lib, ... }: {
+          freeformType = lib.types.attrsOf (lib.types.submodule {
+            options.bar = lib.mkOption {};
+          });
+          options.bar = lib.mkOption {};
+        };
+
+        module = { lib, ... }: {
+          options.foo = lib.mkOption {
+            type = lib.types.submodule submodule;
+          };
+        };
+
+        options = (evalModules {
+          modules = [ module ];
+        }).options;
+
+        locs = filter (o: ! o.internal) (optionAttrSetToDocList options);
+      in map (o: o.loc) locs;
+    expected = [ [ "foo" ] [ "foo" "<name>" "bar" ] [ "foo" "bar" ] ];
+  };
+
 }

lib/types.nix

@@ -522,7 +522,12 @@ rec {
             # would be used, and use of `<` and `>` would break the XML document.
             # It shouldn't cause an issue since this is cosmetic for the manual.
             args.name = "‹name›";
-          }).options;
+          }).options // optionalAttrs (freeformType != null) {
+            # Expose the sub options of the freeform type. Note that the option
+            # discovery doesn't care about the attribute name used here, so this
+            # is just to avoid conflicts with potential options from the submodule
+            _freeformOptions = freeformType.getSubOptions prefix;
+          };
         getSubModules = modules;
         substSubModules = m: submoduleWith (attrs // {
           modules = m;