tests/types: add suboptions doc test

Verify we are able to extract suboptions properly with our custom lib
extension.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

docs/default.nix

@@ -298,4 +298,7 @@ in
     in
     builtins.toJSON result.config.meta.maintainers
   );
+
+  # Unstable, for tests.
+  _internal = { inherit docsLib; };
 }

tests/lib/types/default.nix

@@ -2,5 +2,7 @@
   lib-types-dag-submodule = ./dag-submodule.nix;
   lib-types-dag-merge = ./dag-merge.nix;
 
+  lib-types-either-suboptions-docs-lib = ./either-suboptions-docs-lib.nix;
+
   lib-types-gvariant-merge = ./gvariant-merge.nix;
 }

tests/lib/types/either-suboptions-docs-lib.nix

@@ -0,0 +1,49 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  inherit (lib) mkOption;
+
+  docs = import ../../../docs {
+    inherit pkgs lib;
+    inherit (config.home.version) release isReleaseBranch;
+  };
+
+  inherit (docs._internal.docsLib) types;
+
+  scalarOrSubmodule = types.either types.str (
+    types.submodule {
+      options = {
+        foo = mkOption { type = types.str; };
+        bar = mkOption { type = types.int; };
+      };
+    }
+  );
+
+  scalarOrSubmoduleSubOptions = scalarOrSubmodule.getSubOptions [ ];
+  nullOrScalarOrSubmoduleSubOptions = (types.nullOr scalarOrSubmodule).getSubOptions [ ];
+in
+{
+  assertions = [
+    {
+      assertion = scalarOrSubmoduleSubOptions ? foo;
+      message = "docsLib.types.either should expose submodule options when one side is scalar.";
+    }
+    {
+      assertion = scalarOrSubmoduleSubOptions ? bar;
+      message = "docsLib.types.either should expose all submodule options when one side is scalar.";
+    }
+    {
+      assertion = nullOrScalarOrSubmoduleSubOptions ? foo;
+      message = "docsLib.types.nullOr (types.either ...) should keep submodule options visible.";
+    }
+    {
+      assertion = nullOrScalarOrSubmoduleSubOptions ? bar;
+      message = "docsLib.types.nullOr (types.either ...) should keep all submodule options visible.";
+    }
+  ];
+}