I didn't see much with a quick grep. I only really found nix.checkConfig, which is a nicer name for the same thing. The other alternative that comes to mind is to always ignore errors in the config, or skip checking completely. This would make the module slightly worse and less safe for current users, but one day can be improved again when (if?) upstream produces the appropriate tools

I only really found nix.checkConfig, which is a nicer name for the same thing.

I agree it's nicer. If we do choose to add a new option (which I'm still unsure of), perhaps it'd be better phrased as:

checkConfig = mkOption {
    type = types.bool;
    default = true;
    description = ...
}

I think this is easier to read, since it's shorter and phrased positively.

If we did that, I don't think we should call promtool if checkConfig = false, since:

• it isn't reasonable to expect users to check the promtool output and manually filter the errors they know are okay.
• this makes our Nix config unnecessarily complex, for little gain.

Users who want promtool checking, but have to disable it because it doesn't quite work for them should continue to work with upstream on resolving prometheus/prometheus#5222 .

LGTM, but we should evaluate whether to remove the option is prometheus/prometheus#6488 is accepted.