create webhook: return error when used with a core type

[estroz]

When I run kubebuilder create webhook on a core type, ex. v1.Pod, the command attempts to define methods on a non-existent locally-defined type. Instead, the command should return an error explaining that core types are not supported by this command.

$ go version
go version go1.15.2 linux/amd64
$ kubebuilder version
Version: main.version{KubeBuilderVersion:"v3.0.0-alpha.0-195-g37485126", KubernetesVendor:"unknown", GitCommit:"37485126f95ceb2e92a86497c31f400c8b89f957", BuildDate:"2021-04-12T18:30:56Z", GoOs:"linux", GoArch:"amd64"}
$ cat go.mod | grep controller-runtime
sigs.k8s.io/controller-runtime v0.7.2

/kind bug

[Adirio]

More than an issue, they are a unsupported feature. We only support webhooks for types we have scaffolded ourselves.

[estroz]

/reopen
/lifecycle frozen

[cloudziu]

Hello, do you plan to add scaffolding webhooks for core resources?

[camilamacedo86]

Hello, do you plan to add scaffolding webhooks for core resources?

Yes, we should do that as we do for controllers.
we are able to scaffold controllers for Core Types nowadays so we should do the same for webhooks.
After we get merged #4150 it might be eiser because the of the changes in the code of SetupManager

Then to achieve this goal we will need to

• If is a core type add the import based on : https://github.com/kubernetes-sigs/kubebuilder/blame/ec15b002ee99d2c84f99cf129403d05f4cfc6407/pkg/plugins/golang/options.go#L27-L53
• Create alias with the groupversion
• Ensure that the Resource.ImportAlias return this case accurate.
• Ensure that PROJECT file will be updated with the path for the external/core api

- controller: true
  domain: testproject.org
  kind: Pod
  path: <we should add the endpoint for the core api >
  version: v1
  webhooks:
    conversion: true
    defaulting: true
    validation: true
    webhookVersion: v1

Such as we do when we scaffold a controller for a Core Type:

- controller: true
  group: apps
  kind: Deployment
  path: k8s.io/api/apps/v1 <- See

• We will need to either update the referent docs to let users know how to do that.
• By last add to the generate.sh a call as follows so that we get it tests under the generation of testdata samples.

    # Create webhook for core type
    $kb create webhook --group "" --version v1 --kind Pod --programmatic-validation --conversion --defaulting