If the generated library were to include the utility library, then at the build time of the generated library the visibility macros in the headers of the utility library would incorrectly say dllexport, meaning the generated library would be built as if the utility library's symbols also lived inside the generated library and need to be exported.
To fix this, the generated library should have its own visibility header and macro.
The package
rosidl_typesupport_cppships with a utility library calledrosidl_typesupport_cppwhich uses the preprocessor definitionROSIDL_TYPESUPPORT_CPP_BUILDING_DLLto control dllimport/dllexport on Windows.However, when a package generates a library for ROS messages, the
rosidl_typesupport_cppgenerator also generates a package specific library which also usesROSIDL_TYPESUPPORT_CPP_BUILDING_DLLas the preprocessor definition for it's visibility macros.If the generated library were to include the utility library, then at the build time of the generated library the visibility macros in the headers of the utility library would incorrectly say
dllexport, meaning the generated library would be built as if the utility library's symbols also lived inside the generated library and need to be exported.To fix this, the generated library should have its own visibility header and macro.