Fail at ROS2 IDL generation

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I tried to add support for ROS2 IDL generation with Rust.

It happens to work only when find_package are declared in packages containing message definitions with find_package(rosidl_default_generators REQUIRED) first.

It means that in std_msgs for example, the following will make the whole generation work.

find_package(rosidl_default_generators REQUIRED)
find_package(builtin_interfaces REQUIRED)

While this will fail :

find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)

With the following error.

CMake Error at /opt/ros/crystal/share/rosidl_cmake/cmake/rosidl_target_interfaces.cmake:44 (message):
  rosidl_target_interfaces() the second argument 'std_msgs' concatenated with
  the third argument 'rosidl_typesupport_c' using double underscores must be
  a valid target name
Call Stack (most recent call first):
  /home/sisyphe/Projects/tests/ros2_rust_ws/install/share/rosidl_generator_rs/cmake/rosidl_generator_rs_generate_interfaces.cmake:200 (rosidl_target_interfaces)
  /opt/ros/crystal/share/ament_cmake_core/cmake/core/ament_execute_extensions.cmake:38 (include)
  /opt/ros/crystal/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:280 (ament_execute_extensions)
  CMakeLists.txt:49 (rosidl_generate_interfaces)

The file rosidl_generator_rs_generate_interfaces.cmake generating this error can be found in this repository.

I seems that the required target does not exist at the right time but I don't know what dependency to add to fix this.

I don't understand the whole ROS2 IDL generation process yet and any help on how to be more knowledgeable on this matter might be useful.