New Linter: discriminatedunions

[JoelSpeed]

Identify structs marked with +union

• Should have 1 required field with +uniondiscriminator
• Other fields should be optional and marked with +unionMember or +unionMember,optional
• For CRDs, should have a CEL validation rule has(self.<discriminator> && self.<discriminator> == "<member>" ? has(self.member) : !has(self.member) or equivalent if the member is optional
• Should not have non-member fields present (strong opinion, so, configurable)

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/lifecycle stale

[JoelSpeed]

/remove-lifecycle stale
/lifecycle frozen

[pmalek]

Is this for kubernetes/enhancements#1027 (ref: https://github.com/kubernetes/enhancements/blob/master/keps/sig-api-machinery/1027-api-unions/README.md)?

That KEP looks like never progressed beyond the initial kubernetes/enhancements#3377. Do you have any context on this @JoelSpeed?

[JoelSpeed]

It is yes!

The markers are implemented in the openapi generation tooling, but not much more has been implemented.

I have been leveraging some CEL expressions example to represent the behaviours described in the EP, as mentioned in the description.

Since OpenShift relies on DUs in lots of places, making sure they are marked up correctly would be helpful for us.

I have an open action item to discuss with the K8s declarative validation folks about whether they'll be using these markers for their validation generation, in which case this will also make sense for them as well