Handle deprecated fields during conversion from v1beta1 to v1

[lbernick]

This issue is for discussing how to implement conversion between v1beta1 and v1 CRDs, as proposed in TEP-0096. This conversation came up in tektoncd/community#587.

One question we will need to answer is how to handle the "resources" field of Task/TaskRun/Pipeline/PipelineRun, since these will be removed in v1.

Copying over a comment from @sbwsg:

We serialize the Finally section of a v1beta1 Pipeline into an annotation if a client requests the v1alpha1 version. When a client submits a v1alpha1 version of a Pipeline with that annotation present the process reverses and the v1beta1 object is recreated with the Finally section in-tact:

pipeline/pkg/apis/pipeline/v1alpha1/pipeline_conversion.go

Lines 142 to 177 in 7a0a988

	// serializeFinally serializes a list of Finally Tasks to the annotations
	// of an object's metadata section. This can then be used to re-instantiate
	// the Finally Tasks when converting back up to v1beta1 and beyond.
	func serializeFinally(meta *metav1.ObjectMeta, finally []v1beta1.PipelineTask) error {
	if len(finally) != 0 {
	b, err := json.Marshal(finally)
	if err != nil {
	return err
	}
	if meta.Annotations == nil {
	meta.Annotations = make(map[string]string)
	}
	meta.Annotations[finallyAnnotationKey] = string(b)
	}
	return nil
	}
	// deserializeFinally populates a PipelineSpec's Finally list
	// from an annotation found on resources that have been previously
	// converted down from v1beta1 to v1alpha1.
	func deserializeFinally(meta *metav1.ObjectMeta, spec *v1beta1.PipelineSpec) error {
	if meta.Annotations != nil {
	if str, ok := meta.Annotations[finallyAnnotationKey]; ok {
	finally := []v1beta1.PipelineTask{}
	if err := json.Unmarshal([]byte(str), &finally); err != nil {
	return fmt.Errorf("error converting finally annotation into beta field: %w", err)
	}
	delete(meta.Annotations, finallyAnnotationKey)
	if len(meta.Annotations) == 0 {
	meta.Annotations = nil
	}
	spec.Finally = finally
	}
	}
	return nil
	}

We don't do this for any other v1beta1-only fields. So, for example, when a v1alpha1 client requests a v1beta1 Pipeline with When Expressions, we simply drop them on the floor. If that client then re-applies the v1alpha1 version the stored v1beta1 version will be updated and the when expressions will be gone.

For a while we were working on an approach where we take the entire v1beta1 object and serialize it into an annotation when clients request v1alpha1, but it proved to be a complex and imperfect workaround.

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[vdemeester]

/lifecycle frozen

[abayer]

Should this be folded into #4983?

[vdemeester]

probably 🙃

[lbernick]

Added it to the linked issues in that epic! I think this still has value remaining open as a subtask, to discuss what we want to do when we update the stored version to v1 and need to implement conversion from v1beta1 to v1.

[lbernick]

@afrittoli if you have any context about past pitfalls we ran into when supporting deprecated fields on conversion from v1alpha1 -> v1beta1 this issue is probably the best place for it!

[vdemeester]

We don't do this for any other v1beta1-only fields. So, for example, when a v1alpha1 client requests a v1beta1 Pipeline with When Expressions, we simply drop them on the floor. If that client then re-applies the v1alpha1 version the stored v1beta1 version will be updated and the when expressions will be gone.

Note that this can happen no matter what we do 🙃. If the user / tool cleans the annotation(s), the situation is the same 👼🏼