Fix build order

[peci1]

Messages need to be built before subt_ros_relay. This is a blocker for reliable workspace builds. Please merge ASAP!

I got this error today during docker image build. The error only shows sometimes as it is caused by build ordering. Building with a single build thread (in linear order) should reliably trigger the issue.

#50 126.2 Starting >>> subt_ros                                                          
Finished <<< subt_comms_test                                             [ 6.1 seconds ] 
Finished <<< subt_comms_relay                                            [ 25.4 seconds ]
_______________________________________________________________________________ke (21... 
#50 153.3 Errors << subt_ros:make /opt/ros/cras_subt/logs/subt_ros/build.make.000.log    
#50 153.3 /opt/ros/cras_subt/src/subt/subt_ros/src/SubtRosRelay.cc:33:10: fatal error: subt_ros/CompetitionClock.h: No such file or directory
#50 153.3  #include <subt_ros/CompetitionClock.h>
#50 153.3           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#50 153.3 compilation terminated.
#50 153.3 make[2]: *** [CMakeFiles/subt_ros_relay.dir/src/SubtRosRelay.cc.o] Error 1
#50 153.3 make[1]: *** [CMakeFiles/subt_ros_relay.dir/all] Error 2
#50 153.3 make[1]: *** Waiting for unfinished jobs....
#50 153.3 make: *** [all] Error 2

As per http://wiki.ros.org/catkin/CMakeLists.txt#Important_Prerequisites.2FConstraints :

If you have a package which builds messages and/or services as well as executables that use these, you need to create an explicit dependency on the automatically-generated message target so that they are built in the correct order. (some_target is the name of the target set by add_executable()): 

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

[adlarkin]

Can you please share the build steps you went through so that I can try to re-produce this error? I just tried building the subt_shell Docker image with catkin_make and catkin_make_isolated, and had no issues with either build tool.

[peci1]

This happened to me with catkin tools. Our docker file is way too much complicated and hooked into private repos, so it wouldn't help you much. But the bug is apparent according to the linked documentation - subt_ros_relay uses messages generated in subt_ros, so it should depend on these messages to be built.

[peci1]

The error is caused by concurrency, so it is not really easy to trigger it anyways. We have built the docker file several tens of times and this was the first time it failed.

[nkoenig]

This doesn't break the build, so I'm okay with merging it in.

[peci1]

Thanks ;)