Add missing build_export_depends to controller_interface

[cottsay]

These missing dependencies are not currently causing buildfarm problems because downstream packages have test dependencies on these, so they're getting installed anyway.

In an effort to streamline the buildfarm, we're considering disabling the tests in packaging jobs and dropping the unused dependencies. Test builds with this configuration have uncovered a few packaging bugs, and this is one of them.

To avoid regressing this package when we make this change, please release this change soon.

Thanks!

[cottsay]

Here's where the dependencies are exported:

ros2_control/controller_interface/CMakeLists.txt

Line 87 in e7366d0

ament_export_dependencies(${THIS_PACKAGE_INCLUDE_DEPENDS})

[destogl]

@cottsay thank you very much for this!!! We just had an issue because of it a few days ago, and I couldn't figure out why is this happening! Now it's clear.

Nevertheless, can you please clarify, why do we need this export in the package.xml because usually, we don't need it. Is it because we are using solely <build_depend> tag? And when we are using <depends> tag, then we get automatically <build_export_depend>?

[destogl]

Again, really, really, thank you very, very much!!!!

[bmagyar]

@Mergifyio backport humble

[mergify]

backport humble

✅ Backports have been created

• #990 Add missing build_export_depends to controller_interface (backport #989) has been created for branch humble

[cottsay]

can you please clarify, why do we need this export in the package.xml because usually, we don't need it. Is it because we are using solely <build_depend> tag? And when we are using <depends> tag, then we get automatically <build_export_depend>?

In this particular case, I noticed the problem when joint_state_broadcaster failed to build. It calls find_package(controller_interface REQUIRED) which required hardware_interface because of the ament_export_dependencies invocation in this package. Under the current buildfarm, hardware_interface was getting installed due to a test dependency, but with tests disabled there was nothing indicating that the package was needed, so it wasn't installed.

This package was declaring a build_depend on hardware_interface, which ensures that the package is present to build THIS package, but it doesn't affect downstream builds of packages which depend on this package. That's the role of build_export_depends, which specifically affects builds of packages which declare a build dependency on THIS package. In general, every package referenced by a ament_export_dependencies in CMake should have a corresponding build_export_depends dependency in the manifest.

A depends entry in the manifest does indeed cover build_export_depends (here's where that's discussed in the spec: https://ros.org/reps/rep-0149.html#depend-multiple)