What is the correct way to add dependencies on EXPORTED_TARGETS in the same package

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When I have a package, which generates msgs and depends on these in the package itself. I have the following lines in my CMakeLists.txt:

add_library(my_lib src/a.cpp)
target_link_libraries(my_lib${catkin_LIBRARIES})
add_dependencies(my_lib ${${PROJECT_NAME}_EXPORTED_TARGETS})

add_executable(my_prog src/exec.cpp)
target_link_libraries(my_prog my_lib)

Would it than be necessary to add to following line? So does the dependency need to be added to executable too?

add_dependencies(my_prog ${${PROJECT_NAME}_EXPORTED_TARGETS})

First question: I don't think it is needed, because these dependencies are inherited from linking to my_lib. Am I correct?

Second question: Does this apply the same way to messages from other packages, so when using ${catkin_EXPORTED_TARGETS} instead of ${${PROJECT_NAME}_EXPORTED_TARGETS}?