Is it possible to get a kubernetes object in json or yaml with all optional fields explicitly set to null?

I'm attempting to migrate a helm/kubernetes codebase to dhall-kubernetes. Dhall is typed, so I need to provide full records with optional fields set to null if there were not set. So I'm looking for something like kubectl get objname id -o yaml, but I need it to output all optional fields like fieldName: null. Is there a way to accomplish this? I don't know how to do it, so as a plan B I wrote dhall-default and I attempt to approach it in a different way.

Solution

I'll turn @sjakobi's solution into an answer like @dredozubov suggested

You can pass the desired type from dhall-kubernetes to yaml-to-dhall and it will generate the equivalent Dhall code, albeit without any simplifications.

As an example, suppose that you have the following Kubernetes resource:

# ./nginx.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      name: nginx
  template:
    metadata:
      name: nginx
    spec:
      containers:
        - image: nginx:1.15.3
          name: nginx
          ports:
            - containerPort: 80

... and the following Dhall type for a Kubernetes deployment:

-- ./Deployment.dhall

let kubernetes = https://raw.githubusercontent.com/dhall-lang/dhall-kubernetes/506d633e382872346927b8cb9884d8b7382e6cab/package.dhall

in  kubernetes.Deployment.Type

Then you can translate the YAML to Dhall by running:

$ yaml-to-dhall --file ./nginx.yaml ./Deployment.dhall

The output is a bit large (~1300 lines), because yaml-to-dhall doesn't yet take advantage of support for default values, so I won't include the output here.

If you pipe the result back into dhall-to-yaml then you will get the original Resource (albeit with fields sorted):

$ yaml-to-dhall --file ./nginx.yaml ./Deployment.dhall | dhall-to-yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      name: nginx
  template:
    metadata:
      name: nginx
    spec:
      containers:
        - image: nginx:1.15.3
          name: nginx
          ports:
            - containerPort: 80

... and if you supply the --preserve-null option to dhall-to-yaml it will preserve all null fields as the question requests:

$ yaml-to-dhall --file ./nginx.yaml ./Deployment.dhall | dhall-to-yaml --preserve-null 
apiVersion: apps/v1
kind: Deployment
metadata:
  annotations: null
  clusterName: null
  creationTimestamp: null
  deletionGracePeriodSeconds: null
  deletionTimestamp: null
  finalizers: null
  generateName: null
  generation: null
  labels: null
  managedFields: null
  name: nginx
  namespace: null
  ownerReferences: null
  resourceVersion: null
  selfLink: null
  uid: null
spec:
  minReadySeconds: null
  paused: null
  progressDeadlineSeconds: null
  replicas: 2
  revisionHistoryLimit: null
  selector:
    matchExpressions: null
    matchLabels:
      name: nginx
  strategy: null
  template:
    metadata:
      annotations: null
      clusterName: null
      creationTimestamp: null
      deletionGracePeriodSeconds: null
      deletionTimestamp: null
      finalizers: null
      generateName: null
      generation: null
      labels: null
      managedFields: null
      name: nginx
      namespace: null
      ownerReferences: null
      resourceVersion: null
      selfLink: null
      uid: null
    spec:
      activeDeadlineSeconds: null
      affinity: null
      automountServiceAccountToken: null
      containers:
        - args: null
          command: null
          env: null
          envFrom: null
          image: nginx:1.15.3
          imagePullPolicy: null
          lifecycle: null
          livenessProbe: null
          name: nginx
          ports:
            - containerPort: 80
              hostIP: null
              hostPort: null
              name: null
              protocol: null
          readinessProbe: null
          resources: null
          securityContext: null
          startupProbe: null
          stdin: null
          stdinOnce: null
          terminationMessagePath: null
          terminationMessagePolicy: null
          tty: null
          volumeDevices: null
          volumeMounts: null
          workingDir: null
      dnsConfig: null
      dnsPolicy: null
      enableServiceLinks: null
      ephemeralContainers: null
      hostAliases: null
      hostIPC: null
      hostNetwork: null
      hostPID: null
      hostname: null
      imagePullSecrets: null
      initContainers: null
      nodeName: null
      nodeSelector: null
      overhead: null
      preemptionPolicy: null
      priority: null
      priorityClassName: null
      readinessGates: null
      restartPolicy: null
      runtimeClassName: null
      schedulerName: null
      securityContext: null
      serviceAccount: null
      serviceAccountName: null
      shareProcessNamespace: null
      subdomain: null
      terminationGracePeriodSeconds: null
      tolerations: null
      topologySpreadConstraints: null
      volumes: null
status: null