kubenix/lib/helm/chart2json.nix

{
  runCommand,
  lib,
  kubernetes-helm,
  yq,
}:
with lib;
  {
    # chart to template
    chart,
    # release name
    name,
    # namespace to install release into
    namespace ? null,
    # values to pass to chart
    values ? {},
    # kubernetes version to template chart for
    kubeVersion ? null,
    # whether to include CRD
    includeCRDs ? false,
    # whether to include hooks
    noHooks ? false,
  }: let
    valuesJsonFile = builtins.toFile "${name}-values.json" (builtins.toJSON values);
    # The `helm template` and YAML -> JSON steps are separate `runCommand` derivations for easier debuggability
    resourcesYaml = runCommand "${name}.yaml" {nativeBuildInputs = [kubernetes-helm];} ''
      helm template "${name}" \
          ${optionalString (kubeVersion != null) "--kube-version ${kubeVersion}"} \
          ${optionalString (namespace != null) "--namespace ${namespace}"} \
          ${optionalString (values != {}) "-f ${valuesJsonFile}"} \
          ${optionalString includeCRDs "--include-crds"} \
          ${optionalString noHooks "--no-hooks"} \
          ${chart} >$out
    '';
  in
    runCommand "${name}.json" {} ''
      # Remove null values
      ${yq}/bin/yq -Scs 'walk(
        if type == "object" then
          with_entries(select(.value != null))
        elif type == "array" then
          map(select(. != null))
        else
          .
        end)' ${resourcesYaml} >$out
    ''