ncm-systemd 24.10.0: validation fails if no unit is defined

[jouvin]

In ncm-systemd since 21.12.0, a validation has been added to the schema for the main type systemd_component that accesses unit property in the structure. If the component has been loaded but no unit has been defined, this result in a validation error has the unit property is undefined.

[jouvin]

Unfortunately a trivial fix like initializing unit with an empty dict doesn't work (not supported in Pan, when the type is a subtype if I'm right). And probably just disabling the validation when unit is not defined will not help as it will probably cause other problems when the component is executed...

[jrha]

Is supporting this actually a required use case?

[jouvin]

It is probably not a critical use case but I experienced the problem with a test (Debian) profile where we had no systemd unit configured. It was done in 2019 and was compiling. Upgrading it since then was causing compile error and we never took the time to understand where it was coming from... I'd say that I don't see a production use case requiring it but it makes profile development harder having something that breaks with a validation error difficult to interpret.

We could may be just make the validation error clearer, testing that unit is defined first rather than having the current error when accessing SELF dict with the unit key... This way we would ensure that there is nothing wrong happening during component execution if it is unhappy with the empty unit dict (but for me it works).

[jouvin]

In fact, error in quattor/template-library-examples#42 demonstrates a valid use case: a server where no explicit service is configured with ncm-systemd (all configured with ncm-chkconfig but running EL7+ that includes components/systemd/legacy/chkconfig (and thus ncm-systemd).

I'm opening a PR fixing it by defining unit property in config.pan.