Don't redefine add_dependencies

[rotu]

rosidl defines add_dependencies, and cmake will gladly redefine functions without a warning. If you have a multi-project CMake tree, this can lead to weirdness

CMake Error at src/ros2/demos/demo_nodes_cpp/CMakeLists.txt:42 (target_compile_definitions):
target_compile_definitions called with non-compilable target type
Call Stack (most recent call first):
install/share/rosidl_typesupport_cpp/cmake/rosidl_typesupport_cpp_generate_interfaces.cmake:129 (add_dependencies)
install/share/ament_cmake_core/cmake/core/ament_execute_extensions.cmake:48 (include)
install/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:286 (ament_execute_extensions)
src/ros2/demos/logging_demo/CMakeLists.txt:21 (rosidl_generate_interfaces)

Signed-off-by: Dan Rose dan@digilabs.io

[rotu]

Btw, @dirk-thomas, this might be interesting to you. I didn't realize until this point that functions and macros are defined globally. So while you can collect multiple projects with add_subdirectory (e.g. https://gist.github.com/rotu/1eac858b808b82bbf1b475f515e91636), I think it's too much to ask to expect the entire ROS2 tree to build in this way.

[dirk-thomas]

I think it's too much to ask to expect the entire ROS2 tree to build in this way.

That is the reason we have dropped this compared to ROS 1 / catkin (see http://design.ros2.org/articles/ament.html#building-within-a-single-cmake-context).

[dirk-thomas]

Thanks for the patch.

[rotu]

Thanks for the background! This has turned out to be a very educational misadventure