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 {