Generating a .msg file dynamically at build time

edit

I have a non-ROS type definition file and a tool that translates these definitions to .msg files. I would catkin to first run the translation to produce the .msgs, and then add them to the package.

My attempt looked something like this:

set(GENERATED_MSGS_DIR "${CMAKE_CURRENT_BINARY_DIR}/msg")
add_custom_command(
    OUTPUT ${GENERATED_MSGS_DIR}
    COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/translate.py
            -o ${GENERATED_MSGS_DIR}
            ${CMAKE_CURRENT_SOURCE_DIR}/types.txt
    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
)

file(GLOB_RECURSE GENERATED_MSG_FILES RELATIVE ${GENERATED_MSGS_DIR} *.msg)
add_message_files(FILES ${GENERATED_MSG_FILES})
generate_messages()

However this doesn't quite work. CMake will only run the custom command if an output file is needed by a target that gets built. In this case, I don't know the name of the .msg files that will come out of the translator, just the directory they'll be added to. And add_message_files also doesn't seem to like getting files outside of the package's msg directory.

As an alternative I could have the translate script produce a complete ROS package, if there's a way to dynamically add that package directory as a dependency.