Ignore diff created by helm when using --three-way-merge

[yuvalhnoga]

Hi,
Currently when using the --three-way-merge options it shows some changes that were made by helm and it would be nice if it didn't show them because they are irrelevant.

Example:

  apiVersion: apps/v1
  kind: Deployment
  metadata:
-   annotations:
-     deployment.kubernetes.io/revision: "5"
    creationTimestamp: "2021-04-08T14:16:14Z"
-   generation: 8
+   generation: 9

[mumoshu]

@yuvalhnoga Hey. deployment.kubernetes.io/revision: "5" does look irrelevant because it's added automatically by K8s. I want your insight about generation- what's the rationale of marking generation irrelevant, you think?

[yuvalhnoga]

Thanks for replying :)
generation seems irrelevant to me because it's added automatically too and will always show up when using diff

[mumoshu]

@yuvalhnoga I see. Thanks for validation 😄

[mumoshu]

We already have similar cleanup logics in

helm-diff/cmd/upgrade.go

Lines 546 to 572 in 9086688

	func deleteStatusAndTidyMetadata(obj []byte) (map[string]interface{}, error) {
	var objectMap map[string]interface{}
	err := jsoniterator.Unmarshal(obj, &objectMap)
	if err != nil {
	return nil, errors.Wrap(err, "could not unmarshal byte sequence")
	}
	delete(objectMap, "status")
	metadata := objectMap["metadata"].(map[string]interface{})
	delete(metadata, "managedFields")
	// See the below for the goal of this metadata tidy logic.
	// https://github.com/databus23/helm-diff/issues/326#issuecomment-1008253274
	if a := metadata["annotations"]; a != nil {
	annotations := a.(map[string]interface{})
	delete(annotations, "meta.helm.sh/release-name")
	delete(annotations, "meta.helm.sh/release-namespace")
	if len(annotations) == 0 {
	delete(metadata, "annotations")
	}
	}
	return objectMap, nil
	}

Could anyone contribute?