In file included from /Users/andy2/workspace/OpenTTD.OpenTTD/src/ai/ai_instance.cpp:82: /Users/andy2/workspace/OpenTTD.OpenTTD/src/ai/../company_base.h:119:12: error: field has incomplete type 'RailTypes' RailTypes avail_railtypes; ///< Rail types available to ... ^ /Users/andy2/workspace/OpenTTD.OpenTTD/src/ai/../rail_type.h:53:6: note: forward declaration of 'RailTypes' enum RailTypes : uint64 {