Use case 3 notes

art depends on fhicl-cpp
art also depends on messagefacility which depends on fhicl-cpp
If one wishes to add a feature to fhicl-cpp, the system should say
that you must also "check-out" messagefacility.

So even though you are only concerned with art and fhicl-cpp, it seems that
you should also be "developing" messagefacility at_the_same_time.

I did, during the process get the error:
ERROR: Version conflict -- dependency tree requires versions conflicting with current setup of product fhiclcpp: version v2_16_04 vs v2_16_03

I had to unsetup fhiclcpp and re-run setup_for_development.

Maybe there should be a "clean env" command.