fix: list generator elements should be optional

[blakepettersson]

A bug was reported, where an applicationset with an empty elements array, when created with argocd appset create <filename>.yaml gets a ...list.elements: Required value error.

My hypothesis is that when calling the K8s API, golang JSON marshalling mangles the empty elements array to nil, rather than creating an empty array when submitting the POST.

Still need to figure out why the same setup seemingly works fine when the same appset is in an app-of-apps.

Fixes #17450

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[blakepettersson]

So, looking at this further the discrepancy between how this works in an app-of-apps setting and when invoked using argocd appset create seems to be the following:

1. When invoked from appset create .. the ApplicationSet gets marshaled as an ApplicationSet, without any indirection, causing elements to be nil.
2. When synced in SyncAppState, the ApplicationSet gets marshaled as an Unstructured, where there is a bunch of weird marshaling logic going on. This causes the marshaled JSON string to have an empty array of elements.

Thoughts?

[blakepettersson]

An example appset, which without this patch would fail with appset create .... If this appset is in an app-of-apps, it'd instead fail at a later stage (since there's no repo with that name, but that's another story).

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  annotations:
    argocd.argoproj.io/sync-wave: "0"
  name: some-random-app
  namespace: argocd
spec:
  goTemplate: true
  generators:
    - matrix:
        generators:
          - git:
              repoURL: git@github.com:blakepettersson/some-random-repo.git
              revision: main
              files:
                - path: some-random-file.yaml
          - list:
              elements: []
              elementsYaml: "{{ .clusters | toJson }}"

  syncPolicy: {}
  template:
    metadata:
      name: "some-random-app-{{.env}}"
    spec:
      project: default
      source:
        repoURL: git@github.com:blakepettersson/some-random-repo.git
        path: "some-random-path/{{.env}}"
        targetRevision: main
      destination:
        name: '{{.name}}'
        namespace: 'some-random-app-{{.env}}'
      ignoreDifferences:
        - group: argoproj.io
          jsonPointers:
            - /status
          kind: Application
      syncPolicy:
        automated:
          allowEmpty: true
          prune: true
          selfHeal: true
        syncOptions:
          - CreateNamespace=true
          - ApplyOutOfSyncOnly=true

[jannfis]

A bug was reported

Reported where? Care to link it, please?

[blakepettersson]

Reported where?

Internally by an Akuity customer - I cannot link to the reported bug sadly 😞

[jannfis]

I cannot link to the reported bug sadly

Care to open a bug on GitHub describing this problem? It would help others in the community who happen to stumble over it.

[blakepettersson]

Sure thing, here's the linked issue: #17450

[alexmt]

LGTM!

[blakepettersson]

/cherry-pick release-2.9

[blakepettersson]

/cherry-pick release-2.10

[blakepettersson]

/cherry-pick release-2.8