meson: Make ply-boot-client a required dependency for offline-updates

[Conan-Kudo]

We already assume ply-boot-client 0.9.5 or higher in the code, so not making this a hard dependency is somewhat silly.

Fixes: 8d8417c ("offline-updates: Assume plymouth>=0.9.5 by default")

[ximion]

Why though? We don't actually link to it, and for distributions which don't enable systemd or offline-updates it's a pretty nonsensical extra dependency...

If anything, it should be behind the offline_update feature switch.

[Conan-Kudo]

That's fair. Is there a good reason for it to not be? Otherwise I'm going to move it there and make it required there.

[ximion]

That's fair. Is there a good reason for it to not be? Otherwise I'm going to move it there and make it required there.

The better question is: Should we have this dependency at all? I kept it as a purely informational piece for distributors to tell them which minimum Plymouth version we want for offline-updates to work. But we do not actually need Plymouth for a PackageKit build or test at all (that's why it's optional), so we might as well drop it. Making it a hard dependency for no reason is something I dislike, as it potentially complicates any bootstrapping processes in distributions for pretty much no reason at all.

[Conan-Kudo]

I think a dependency that's a proxy for ensuring the required capabilities for functionality to work is reasonable. We've needed to be able to tell in the past at build-time, and I don't see a reason why it wouldn't in the future.

It's pretty bloody difficult to debug breakages in this part of the code since a lot of distributions don't actually retain logs or data from this stage in the event of failures.

[arrowd]

FreeBSD does not have Plymouth, so please keep it optional.