Generate core types oapi schemas

[jonasz-lasut]

Description of your changes

Adds support for kubernetes core resources for Crossplane <2.2.0 that does not support required_schemas capability.
Generates openapi schemas with go generate ./... and later merges them with k8s.io/apiextensions-apiserver/pkg/generated/openapi schemas in the resolver.

Fixes #9

Tested using the following steps:

kind create cluster

helm install crossplane --version=2.1.3 --namespace crossplane-system --create-namespace crossplane-stable/crossplane --set args='{"--debug","--circuit-breaker-burst=500.0", "--circuit-breaker-refill-rate=5.0", "--circuit-breaker-cooldown=1m"}'

kubectl apply -f example/drc.yaml -f example/extensions.yaml -f example/core/xrd.yaml -f example/core/composition.yaml

kubectl apply -f example/core/xr.yaml

docker build . --platform=linux/amd64 --tag runtime-amd64

crossplane xpkg build --package-root=package --embed-runtime-image=runtime-amd64 --package-file=function-amd64.xpkg

crossplane xpkg push --package-files=function-amd64.xpkg ttl.sh/function-kro:0.0.0

kubectl patch function function-kro --type='json' -p='[{"op": "replace", "path": "/spec/package", "value":"ttl.sh/function-kro:0.0.0"}]'

Result:

judasz@fedora:~/code/function-kro$ k get -f example/core/xr.yaml -oyaml
apiVersion: core.example.crossplane.io/v1
kind: CoolSecret
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"core.example.crossplane.io/v1","kind":"CoolSecret","metadata":{"annotations":{},"name":"cool-secret","namespace":"default"},"spec":{"secretField":"cool-value"}}
  creationTimestamp: "2026-03-20T13:39:19Z"
  finalizers:
  - composite.apiextensions.crossplane.io
  generation: 4
  labels:
    crossplane.io/composite: cool-secret
  name: cool-secret
  namespace: default
  resourceVersion: "8738"
  uid: 265a095f-fc25-4101-8401-5cb7f5dfd0de
spec:
  crossplane:
    compositionRef:
      name: coolsecret-core
    compositionRevisionRef:
      name: coolsecret-core-7bed349
    compositionUpdatePolicy: Automatic
    resourceRefs:
    - apiVersion: v1
      kind: Secret
      name: cool-secret-8b3c0d296275
  secretField: cool-value
status:
  conditions:
  - lastTransitionTime: "2026-03-20T13:39:19Z"
    observedGeneration: 4
    reason: ReconcileSuccess
    status: "True"
    type: Synced
  - lastTransitionTime: "2026-03-20T13:39:19Z"
    observedGeneration: 4
    reason: Available
    status: "True"
    type: Ready
  - lastTransitionTime: "2026-03-20T13:39:19Z"
    observedGeneration: 4
    reason: WatchCircuitClosed
    status: "True"
    type: Responsive

Tool versions:

judasz@fedora:~/code/function-kro/example$ crossplane version
Client Version: v2.1.3
Server Version: v2.1.3
judasz@fedora:~/code/function-kro/example$ kubectl version
Client Version: v1.35.0
Kustomize Version: v5.7.1
Server Version: v1.35.0

I have:

• Read and followed Crossplane's contribution process.
  - [ ] Added or updated unit tests for my change. - did not add tests as the PR adds a go:generate script but I've added an example and tested the feature

[avarei]

at the moment assuming that a missing CRD is probably a k8s core resource is causing a strange behaviour when using crossplane render without extra-resources. (for a composition with non k8s core resources)

https://github.com/jonasz-lasut/function-kro/blob/0aa0fb2927f791f55492c1b398ea50f1b12e8e3f/fn.go#L423-L428

maybe this PR would also be an opportunity to throw an error if a crd was requested and not found instead of assuming it to be a k8s core resource?

[jonasz-lasut]

Hi @avarei , the issue with throwing error in that place instead of passing through to the next iteration is that we'd effectively halt the execution if we threw the error. We'd have to distinguish three cases -> crd found (add to crds, core resource found (just continue, handled by default resolved) and some resource not found (can be both core and crd, depends on if we have generated the core type).

I'll be happy to think about how we can solve that issue in a clean way but I'd rather do that in a separate PR to not block Crossplane <2.2 users to use function-kro with core resources.

If you open an issue please just mention me there and I'll be happy to take care of it :)

[jbw976]

This is amazing @jonasz-lasut, thank you for trying out this functionality! it will fill an important functionality gap when running on Crossplane pre-v2.2 🙇

when i did the v0.2.0 release, i made some changes to the resolver code to refactor it, which affects this PR. would you be able to rebase and reapply these changes to the latest in main? sorry for the hassle! 🙏

After that's done, please let me know so I can take this for a local test spin too! really excited for this!

[jbw976]

Thank you for integrating the feedback @jonasz-lasut! I was able to take this for a test spin on a v2.1 and v2.2 control plane - both worked perfectly! 💪

I only have a few small suggestions now, and then I think we can merge this and have awesome support for core types pre v2.2! 🙇

[jbw976]

yessss, nice work @jonasz-lasut! let's ship this!!! 🚀

[github-actions]

Successfully created backport PR for release-0.2:

• [Backport release-0.2] Generate core types oapi schemas #47