First read Stefan's https://kubernetes.io/blog/2019/06/20/crd-structural-schema/ about structural and non-structural schema.

This bug's PR is dev-approved and not yet merged, so I'm following issue DPTP-660 to do the pre-merge verifying for QE pre-merge verification goal of issue OCPQE-815 by using the bot to launch one 4.6 cluster with the open PR. after the cluster is ready, did the following verification steps:

To create a CRD in apiextensions.k8s.io/v1beta1:

- with a structural schema
- but without preserveUnknownFields being set at all
$ cat crd.yaml
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: testcrs.example.com
spec:
  group: example.com
  names:
    kind: TestCR
    plural: testcrs
  scope: Namespaced
  validation:
    openAPIV3Schema:
      type: object
      description: this is description for the crd
      properties:
        spec:
          type: object
          description: this is description for spec
          properties:
            a:
              type: string
              description: this is description for field a
  version: v1
  versions:
  - name: v1
    served: true
    storage: true

$ oc create -f crd.yaml

Then check oc explain, indeed cannot show description of fields.
Then check oc get crd testcrs.example.com -o yaml, 4.6.0-0.ci.test-2020-10-29-093230-ci-ln-hw6j6fb env shows condition NonStructuralSchema as below, this is expected by the PR (4.6.0-0.nightly-2020-10-14-095718 env does not show it).
...
spec:
...
  preserveUnknownFields: true
...
  conditions:
  ...
  - lastTransitionTime: "2020-10-29T10:52:41Z"
  message: 'spec.preserveUnknownFields: Invalid value: true: must be false'
  reason: Violations
  status: "True"
  type: NonStructuralSchema

So the bug is pre-merge verified. After the PR gets merged, the bug will be moved to VERIFIED by the bot automatically or, if not working, by me manually.

This will be solved in 4.7. We won't backport it due to complexity and capacity. Severity is low.