nixos: warn on missing stateVersion

[oxij]

Motivation for this change

The first patch is OCD. The last patch is the part of #35366 everyone agreed upon. The middle one is plumbing.

Things done

• It works.
• Fits CONTRIBUTING.md.

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[matthewbauer]

Can you verify that this would be set in the vms? I belivenit was missing on those configs.

[oxij]

Can you verify that this would be set in the vms? I belivenit was missing on those configs.

You mean VMs? Is there a use case where this warning should not be given? Can you elaborate? The original thread doesn't mention any such things.

[matthewbauer]

So some VMs don’t generate their config with the perl script. I just want to make sure these have it set correctly (it may be in the profile but i can’t remember).

[oxij]

Well, building `.vm` attribute should work exactly as before as it uses normal `configuration.nix`. VM tests might generate some warnings, but that could be cleaned up later. Let's just check, I guess @GrahamcOfBorg test boot

[GrahamcOfBorg]

Failure on aarch64-linux (full log)

Partial log (click to expand)

Merge failed

[GrahamcOfBorg]

Failure on x86_64-linux (full log)

Partial log (click to expand)

Merge failed

[oxij]

Rebased. @GrahamcOfBorg test boot

[GrahamcOfBorg]

Success on x86_64-linux

Attempted: tests.boot

No partial log is available.

[GrahamcOfBorg]

Success on aarch64-linux

Attempted: tests.boot

No partial log is available.

[matthewbauer]

Ok sounds good as a warning. Look out for issues regarding this though. I think the fixes should be easy it’s just generated somewhere I can’t find now

[oxij]

Thanks!

[danbst]

The intent is that without stateVersion, you get the behaviour of the latest release, which presumably is not broken.

When doing release upgrades with nixos-rebuild, it is untrue that you get unbroken behavior without stateVersion.

To make warning more justified, we can do like this:

1. Each module exports whether it depends on system.nixos.stateVersion

system.nixos.dependsOnStateVersion = mkIf_isNotOverriden cfg.package [ "services.postgresql.enable" ];

(I don't think we can check whether cfg.package evaluation depends on system.nixos.stateVersion, but if it is overriden in user configuration, then user probably pins it to some concrete version, so he doesn't require setting system.nixos.stateVersion)
2. Here we check if system.nixos.dependsOnStateVersion is empty. If it is, then no warning - user is aware of all his stateful options or doesn't have stateful options enabled. Otherwise we display list of options that would case disruption on release upgrades and abort evaluation.

[oxij]

Sure, we can do that, but I think that's an overkill as it introduces yet another general warning mechanism for a single use case. But if we had more of those, I would be ok with something like that. As it stands now I'd prefer we go the way I specified above: split `stateVersion` into a bunch of per service options. That way you could migrate your services one by one between releases and we then could do warnings only when the service is enabled with the default warning system.