Description

Kaniko accepts a --tarPath arg to write out to a tarball. I mistakenly passed this without a --destination and ended up with a tarball with only a manifest.json containing null.

I opened google/go-containerregistry#887 to fix the issue in go-containerregistry (calculating a manifest without refs doesn't make much sense), but we should also check for this on the kaniko side with kaniko specific details to help users do the right thing.

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Adds integration tests if needed.

There are no tests for the tarball write path as far as I can tell. Adding unit/integration tests to test this one check would be a substantial lift.

See the contribution guide for more details.

Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

Release Notes

Describe any changes here so maintainer can include it in the release notes, or delete this block.

- kaniko will error if `--tarPath` is specified without `--destination` instead of building an invalid image