ApplicationSet: accessing cluster list inside template without creating a single element per cluster

[OpenGuidou]

Summary

If we want to access a list of cluster used inside ArgoCD, we generally use the clusterGenerator

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: guestbook
  namespace: argocd
spec:
  goTemplate: true
  goTemplateOptions: ["missingkey=error"]
  generators:
  - clusters:       
      selector:
        matchLabels:
          staging: "true"
  template:
    metadata:
      name: '{{.name}}-guestbook' # 'name' field of the Secret
    spec:
      project: "my-project"
      source:
        repoURL: https://github.com/argoproj/argocd-example-apps/
        targetRevision: HEAD
        path: guestbook
      destination:
        server: '{{.server}}' # 'server' field of the secret
        namespace: guestbook

However, this ends up creating one Application per cluster selected.
It is useful to create one Application in each of those clusters, but sometimes we only need to get the clusters info without using them as destination.

Would there be a way to get the list of cluster matched, and use them as a value list inside a single Application ?

Something like:

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: guestbook
  namespace: argocd
spec:
  goTemplate: true
  goTemplateOptions: ["missingkey=error"]
  generators:
  - clusters:
      flatClusterMode: true #<------ Dummy option to use it flat
      selector:
        matchLabels:
          staging: "true"
  template:
    metadata:
      name: 'my-guestbook' 
    spec:
      project: "my-project"
      source:
        repoURL: https://github.com/argoproj/argocd-example-apps/
        targetRevision: HEAD
        path: guestbook
        helm:
          values: |
            clusters:
            {{ range .clusters }} #<--- access the cluster list
              - name: {{ .name }}
            {{ end }}
      destination:
        server: 'in-cluster' # <--- deploying it a single place
        namespace: guestbook