docs: Marker docs about required fields are not fully accurate

[ahmetb]

What broke? What's expected?

In CRD validation documentation (https://book.kubebuilder.io/reference/markers/crd-validation) //+kubebuilder:validation:Required marker is advertised as "specifies that this field is required".

However, it seems for a struct field, empty struct in a YAML manifest (i.e. {}) or for a string field empty string "" bypasses this check.

I think it's somewhat misleading that this validation allows zero values (which the omitempty would've omitted) through just fine.

Reproducing this issue

1. Use package level //+kubebuilder:validation:Required
2. Do not specify ",omitempty" on a string field.
3. kubectl apply --validate=false your custom resource without specifying the field → observe the validation error
4. specify "" as the value for the string field and re-apply → no error.

KubeBuilder (CLI) Version

3.10.0

PROJECT version

3

Plugin versions

go.kubebuilder.io/v4

Other versions

sigs.k8s.io/controller-runtime v0.16.2
kube-apiserver 1.21.14
kubectl 1.21.14

Extra Labels

/kind documentation

[camilamacedo86]

Hi @ahmetb,

By defining a String spec with "" you are defining a string with an empty value.
So, it does not seem to be an error but the expected behaviour.

In your case scenario, seems that you want ensure that:
a) The String spec exist ( +kubebuilder:validation:Required )
b) If its value is bigger than X size ( +kubebuilder:validation:MinLength )

So you would need to use both.

However, if you think that the description or behaviour should be changed then can you please raise an issue against: https://github.com/kubernetes-sigs/controller-tools.

See that the markers are defined in this project. Kubebuilder uses controller-gen (controller-tools) to perform these validations. Indeed the doc is generated automatically from the descriptions added in controller-tools, see: https://github.com/kubernetes-sigs/controller-tools/blob/f185f4d8e8f1c0a006fee16fbb80c832594a1fcf/pkg/crd/markers/validation.go#L77

Therefore, I am closing this one.
But if you need, please feel free to reopen this one.