align the behavior of recursive copying

[qweeah]

The behavior of recursive copying flag --rescursive/-r should be the same no matter the source is an OCI image layout folder or OCI registry.

Expected Behavior

Suppose we have below content:

graph TD
Z>v1] -..-> ML1
ML1 --linux/amd64--> M1
ML1 --linux/arm64--> M2
ML1 --linux/s390x--> M3

A1 --subject-->ML1
A2 --subject--> M1

Loading

Where ML1 is an index (manifest list) with images in multiple architectures. M1, M2 and M3 represents the manifest of images in each arch. A1 and A2 are the artifact manifests with subject pointing to ML1 and M1 respectively.

• oras cp -r [--from-oci-layout] $FROM:v1 $TO:v2: copy ML1, A1, M1, M2 and M3 to $TO and tag ML1 as v2.
• oras cp -r [--from-oci-layout] $FROM:v1 $TO: copy ML1, A1, M1, M2 and M3 to $TO without tagging.
• oras cp -r [--from-oci-layout] $FROM:v1 --platform linux/amd64 $TO:v2: copy M1 and A2 to $TO and tag M1 as v2.
• oras cp -r [--from-oci-layout] $FROM:v1 --platform linux/amd64 $TO: copy M1 and A2 to $TO without tagging.
• oras cp -r [--from-oci-layout] $FROM@$M1_DIGEST $TO:v2: copy M1 and A2 to $TO and tag M1 as v2
• oras cp -r [--from-oci-layout] $FROM@$M1_DIGEST $TO: copy M1 and A2 to $TO without tagging.

[qweeah]

Closing since #818 is merged.