Argocd-cli app diff validation not working with multi-source application

[asifasido]

Checklist:

• I've searched in the docs and FAQ for my answer: https://bit.ly/argocd-faq.
• I've included steps to reproduce the bug.
• I've pasted the output of argocd version.

Describe the bug
When trying to validate changes in a multi-source application using argocd app diff or argocd app sync, Argo CD did not return any errors for invalid YAML files or other issues. It seems this functionality is not supported multi-source application.
The branch I provided for revision contains changes, but Argo CD did not notify about any changes.
To Reproduce

1. Create an ArgoCD application with multiple sources (for example, a Helm chart and a values file from a different repo)
2. Try to compare changes using different revisions for different sources:

argocd app sync <app-name> \
  --revisions <chart-version> --source-positions 1 \
  --revisions <pr-branch> --source-positions 2 \
  --dry-run \
  --preview-changes \
  --grpc-web

Expected behavior
I'm trying to use the following command to validate PRs before merging them to the main branch
When using with multiple sources and different revisions, I expect the command to perform thorough validation of the changes, similar to how Kubernetes admission controllers work. Specifically:

1. The command should validate the rendered manifests before reporting success
2. If a values.yaml file contains changes that would break the application (like missing quotes ' schedule: * */12 * * *
   ' , invalid configuration), the dry-run should fail

Screenshots

Version