Chart versions prefixed with `v` aren't compatible with Flux semver ranges

[RedbackThomson]

Describe the bug
All of our controller charts are versioned, prefixed with a v before the semver. eg. public.ecr.aws/aws-controllers-k8s/ec2-chart:v1.0.1

The Flux Helm controller has support for Semver ranges:

The chart.spec.version can be a fixed semver, or any semver range (i.e. >=4.0.0 <5.0.0). It is ignored for HelmRelease resources that reference a GitRepository or Bucket source.

This support is not compatible with the v. Instead, the controller complains that it cannot find any images within that range.

Steps to reproduce
Create a Flux HelmRelease for one of the ACK OCI Helm charts, and use the chart.spec.version with a range (eg. >=1.0.0 <2.0.0).

Expected outcome
The controller should understand the chart versions and be able to use proper semver ranges and filtering.

[stefanprodan]

This is not a Flux issue, we conform with the Helm spec and we use the Helm Go SDK. Helm itself does not support the v prefix, charts should be versioned using strict semver format. Using the v prefix also breaks the Helm CLI helm/helm#11107.

[wallrj]

I regard it as a Helm bug. Helm does support the v prefix when interacting with non-oci registry. For example, the cert-manager Helm chart has a v prefix and helm install can calculate the latest semver release just fine.

$ helm repo add jetstack https://charts.jetstack.io
$ helm repo update jetstack

$ helm search repo jetstack
NAME                                    CHART VERSION   APP VERSION     DESCRIPTION
jetstack/cert-manager                   v1.11.1         v1.11.1         A Helm chart for cert-manager

$ helm install cert-manager jetstack/cert-manager --namespace cert-manager --set
installCRDs=true
NAME: cert-manager
LAST DEPLOYED: Thu Apr 27 16:58:08 2023
NAMESPACE: cert-manager
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
cert-manager v1.11.1 has been deployed successfully!