why is double colon used instead of single colon

[LeoQuote]

In this part of code,

kube-prometheus/jsonnet/kube-prometheus/main.libsonnet

Line 16 in 4d81048

values:: {

double colon was used, but I cannot get any info about double colon in jsonnet except for this archived project https://github.com/ksonnet/ksonnet-lib/blob/master/docs/jsonnetIntro.md#functions is that obsolete or just typo?

[paulfantom]

double colon hides object during manifestation.

From https://jsonnet.org/learning/tutorial.html, section "Object-Orientation":

Hidden fields, defined with ::, which do not appear in generated JSON

[ArthurSens]

If you are using the examples in this repository, they explicit skip the values object when printing:

local kp =
  (import 'kube-prometheus/main.libsonnet') +
  {
    values+:: {
      common+: {
        namespace: 'monitoring',
      },
    },
  };

{ 'setup/0namespace-namespace': kp.kubePrometheus.namespace } +
{
  ['setup/prometheus-operator-' + name]: kp.prometheusOperator[name]
  for name in std.filter((function(name) name != 'serviceMonitor' && name != 'prometheusRule'), std.objectFields(kp.prometheusOperator))
} +
// serviceMonitor and prometheusRule are separated so that they can be created after the CRDs are ready
{ 'prometheus-operator-serviceMonitor': kp.prometheusOperator.serviceMonitor } +
{ 'prometheus-operator-prometheusRule': kp.prometheusOperator.prometheusRule } +
{ 'kube-prometheus-prometheusRule': kp.kubePrometheus.prometheusRule } +
{ ['alertmanager-' + name]: kp.alertmanager[name] for name in std.objectFields(kp.alertmanager) } +
{ ['blackbox-exporter-' + name]: kp.blackboxExporter[name] for name in std.objectFields(kp.blackboxExporter) } +
{ ['grafana-' + name]: kp.grafana[name] for name in std.objectFields(kp.grafana) } +
{ ['kube-state-metrics-' + name]: kp.kubeStateMetrics[name] for name in std.objectFields(kp.kubeStateMetrics) } +
{ ['kubernetes-' + name]: kp.kubernetesControlPlane[name] for name in std.objectFields(kp.kubernetesControlPlane) }
{ ['node-exporter-' + name]: kp.nodeExporter[name] for name in std.objectFields(kp.nodeExporter) } +
{ ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } +
{ ['prometheus-adapter-' + name]: kp.prometheusAdapter[name] for name in std.objectFields(kp.prometheusAdapter) }

Notice that it directly calls the child objects, e.g. kp.prometheus, kp.alertmanager, kp.nodeExporter, etc. Try this:

local kp =
  (import 'kube-prometheus/main.libsonnet') +
  {
    values+:: {
      common+: {
        namespace: 'monitoring',
      },
    },
   prometheus+:: {}
  };

{ ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } 

and

local kp =
  (import 'kube-prometheus/main.libsonnet') +
  {
    values+:: {
      common+: {
        namespace: 'monitoring',
      },
    },
   prometheus+: {}
  };

{ ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } 

The first one should not create any manifests because of the double double collon ::, while the other will generate because there is only one

[LeoQuote]

I'm still puzzled, so double colon :: hides some field and prevent this resource being created, why would I write it in the first place ? why dont I just delete it?

[ArthurSens]

Because it holds information used on other places of kube-prometheus. See: https://github.com/prometheus-operator/kube-prometheus/blob/main/jsonnet/kube-prometheus/main.libsonnet#L37-L134

On your jsonnet file that is consuming main.libsonnet, you can override some fields in the "values" object, and even though it is not turned into its own file, it will configure all the others

[LeoQuote]

Sorry, can I just ask a specific question, why is the example in https://github.com/prometheus-operator/kube-prometheus/blob/main/README.md#defining-the-servicemonitor-for-each-additional-namespace is using

    prometheus+:: {
      namespaces+: ['my-namespace', 'my-second-namespace'],
    },

while the example here https://github.com/prometheus-operator/kube-prometheus/blob/main/README.md#adding-additional-namespaces-to-monitor is using

    prometheus+: {
      namespaces+: ['my-namespace', 'my-second-namespace'],
    },

Are these two config all configring

kube-prometheus/jsonnet/kube-prometheus/components/prometheus.libsonnet

Line 12 in 4d81048

namespaces: ['default', 'kube-system', defaults.namespace],

this fields? if these two style works exactly the same, can I just use +: for all fields?

[LeoQuote]

#1174 (reply in thread) I tried the two examples you provided, these two example produce exactly the same manifests.

/kube-prom $ ls manifests/
prometheus-clusterRoleBinding.yaml   prometheus-roleBindingConfig.yaml              prometheus-serviceMonitor.yaml
prometheus-clusterRole.yaml          prometheus-roleBindingSpecificNamespaces.yaml  prometheus-service.yaml
prometheus-podDisruptionBudget.yaml  prometheus-roleConfig.yaml                     setup
prometheus-prometheusRule.yaml       prometheus-roleSpecificNamespaces.yaml
prometheus-prometheus.yaml           prometheus-serviceAccount.yaml