Lack of support for nested XR

[piotrkorlaga]

Thank you very much for the effort you put into developing this project. We really miss this in the crossplane ecosystem. It looks amazing, but I encounter one issue.

What problem are you facing?

Lack of support for nested XR.

How could Crossplane help solve your problem?

I encounter an issue when my composition creates a nested XR. In this case, I'm getting an error from https://github.com/crossplane-contrib/function-kcl

2025-09-22T11:14:48+02:00       DEBUG   Processing complete     {"resourceCount": 1, "totalDiffs": 0, "errorCount": 1}
crossplane-diff: error: unable to process one or more resources: unable to process resource xBackoffice/[redacted]: cannot render resources with requirements: pipeline step "create-transit-gateway-main" returned a fatal result: failed to run kcl function pipelines: EvaluationError
                          --> [redacted]
                           |
                        27 |     kind: "xTransitGateway" = "xTransitGateway"
                           |  expect "xTransitGateway", got str

Is the tool supposed to support nested XRs at this stage?

[jcogilvie]

I haven't strictly tested it with nested XRs, so I don't know. Internally, it uses the logic from crossplane trace to evaluate the dependency trees of things we need to diff, so if trace shows all your downstream resources, we should diff them.

If you can get me a reproduction case I can try to work through it.

[jcogilvie]

I'm in the process of implementing recursion if your first composition generates an XR that would be picked up by another composition, which is the way I think nested XRs might work. Does this line up with your use case, @piotrkorlaga?

The reason I ask is that right now I'd expect you to just get an incomplete diff rather than an error, so I'm a bit thrown off by that.

[piotrkorlaga]

@jcogilvie yeap, this is exactly the use case.
Not sure why we get the error but our composition is backed up by kcl function if that makes any difference.

I wonder how the example form this article https://blog.upbound.io/platform-engineering-simplified behave.

https://github.com/upbound/platform-ref-multi-k8s

Gonna check later.