Jsonnet - Apply mixin multiple times in for loop

I am using Jsonnet to render Kubernetes objects, I would like to use a mixin to apply multiple volume mounts to a deployment.

An example of what I've tried (k being the kausal library):

config: {
  mountConfig: [
    first: {
      mountPath: '/path/to/first',
      subPath: 'first',
      data: {},
    },
    second: {
      mountPath: '/path/to/second',
      subPath: 'second',
      data: {},
    },
  ],
}

configMap: configMap.new('config')
           + configMap.withData(
               { [config.mountPath]: config.data }
               for config in $.mountConfig
             ),

deployment: deployment.new(
              name='dep1',
              replicas='2',
              containers=[container.new('name', 'image')]
            )
            + k.util.configMapVolumeMount($.configMap, config.mountPath, config.subPath)
              for mount in $.config.mountConfig

The above creates a single configmap with a key for each config file and then attempts to mount the configmap multiple times for each config file defined within the configmap.

Obviously an incomplete example, I can't figure out the syntax to do a + mixin for something in somethings.

Afaicf subPath handling against a single configMap is more involved in kausal.libsonnet libs,as k.util.configMapVolumeMount() calls will end up adding the configmap entry to pod's volumes[] many times.

I think that the below snippet solves your question, mind that there are also other syntax fixes (besides the implementation mechanics).

source: foo.jsonnet

// foo.jsonnet
local k = import 'jsonnet-libs/ksonnet-util/kausal.libsonnet',
      deployment = k.apps.v1.deployment,
      container = k.core.v1.container,
      configMap = k.core.v1.configMap,
      volumeMount = k.core.v1.volumeMount;

local config = {
  mountConfig: [
    {
      mountPath: '/path/to/first',
      subPath: 'first',
      data: 'Data ONE',  // NOTE: must be a string
    },
    {
      mountPath: '/path/to/second',
      subPath: 'second',
      data: 'Data TWO',  // NOTE: must be a string
    },
  ],
};

{
  configMap:
    configMap.new('config')
    + configMap.withData({
      [e.subPath]: e.data
      for e in config.mountConfig
    }),

  deployment:
    local configVolName = $.configMap.metadata.name + '-volume';

    deployment.new(
      name='dep1',
      replicas=2,
      containers=[
        container.new('name', 'image')
        + container.withVolumeMountsMixin([
          volumeMount.new(configVolName, e.mountPath)
          + volumeMount.withSubPath(e.subPath)
          for e in config.mountConfig
        ]),

      ]
    )
    + deployment.spec.template.spec.withVolumesMixin([
      k.core.v1.volume.fromConfigMap(configVolName, $.configMap.metadata.name),
    ]),

}

shell run and output

## Initialize jsonnet-bundler
$ jb init

## Add jsonnet libs
$ jb install https://github.com/grafana/jsonnet-libs
GET https://github.com/grafana/jsonnet-libs/archive/5f8a166911d56d0402fd52cbbce47cadfee0e466.tar.gz 200

## Add Kube 1.27 underlying libs, see https://tanka.dev/known-issues
$ jb install github.com/jsonnet-libs/k8s-libsonnet/1.27@main
GET https://github.com/jsonnet-libs/k8s-libsonnet/archive/6ecbb7709baf27f44b2e48f3529741ae6754ae6a.tar.gz 200
$ mkdir -p lib; echo "import 'github.com/jsonnet-libs/k8s-libsonnet/1.27/main.libsonnet'" > lib/k.libsonnet

## Spit-out cm+deployment JSON, need to massage it a bit for `kubectl` to slurp it in
$ jsonnet -J lib -J vendor foo.jsonnet |jq -S '.[]' |kubectl apply --dry-run=server -f-
configmap/config created (server dry run)
deployment.apps/dep1 created (server dry run)

rendered YAML from manifested JSON

The output from jsonnet -J lib -J vendor foo.jsonnet| yq -y .

configMap:
  apiVersion: v1
  data:
    first: Data ONE
    second: Data TWO
  kind: ConfigMap
  metadata:
    name: config
deployment:
  apiVersion: apps/v1
  kind: Deployment
  metadata:
    name: dep1
  spec:
    minReadySeconds: 10
    replicas: 2
    revisionHistoryLimit: 10
    selector:
      matchLabels:
        name: dep1
    template:
      metadata:
        labels:
          name: dep1
      spec:
        containers:
          - image: image
            imagePullPolicy: IfNotPresent
            name: name
            volumeMounts:
              - mountPath: /path/to/first
                name: config-volume
                subPath: first
              - mountPath: /path/to/second
                name: config-volume
                subPath: second
        volumes:
          - configMap:
              name: config
            name: config-volume