default repository checkout in install workspace fails to include nlohmann dependency

[v4hn]

Hi @pantor,

thank you for addressing issues related to this before, but I'm afaid the full issue is not resolved yet. Concretely, trying to set up another extensive ROS-O builder, I currently experience the problem that default ruckig sets BUILD_CLOUD_CLIENT=ON, but does not ensure that nlohmann/json.hpp is available after installation. The easiest way to fix this would be to add a <build_export_depend>nlohmann-json-dev</build_export_depend> in general and not use it when the cloud client is disabled, or provide a separate cmake target that sets the compile flag.

As we explicitly not use the webclient in MoveIt I just proposed to manually drop the compile flag from the exposed target to avoid the unnecessary (/undeclared) dependency. This essentially mirrors a second cmake target on the user side.

Cross-reference https://github.com/moveit/moveit/pull/3636

[pantor]

PR #203 installs the missing headers into include/ruckig/third_party. I'm not a big fan of bundling the dependencies into the package, but (1) I also want to support older platforms and (2) it's only two header files. WDYT?

[pantor]

Feel free to reopen if you still see any problems with the current solution.