feat: push an ORAS artifact manifest when no blob is specified

[yuehaoliang]

Resolve #466

Signed-off-by: Haoliang Yue yuehaoliang@microsoft.com

[qweeah]

LGTM

[codecov-commenter]

Codecov Report

Merging #486 (7ce7ec7) into main (d776a22) will not change coverage.
The diff coverage is n/a.

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[sajayantony]

@shizhMSFT @FeynmanZhou - it would be good to start discussing how the ORAS CLI and library can start thinking about using the OCI artifact manifest as well. Having it default to ORAS artifact might make it hard to switch to the OCI artifact manifest if that is approved.

Can we explore what options we have here

1. Maybe have a config file support in the CLI
2. Or a flag that that says something like oras push {ref} --oras-artifact
3. Or consider switching the default and drop the oras-artifact support from the CLI at some point.

All of these have pros and cons and starting that discussion might be useful before switching push to use the artifact spec as default.

[shizhMSFT]

@sajayantony This issue / PR is based on @SteveLasker 's feedback that OCI manifest does not support empty layer array in terms of spec. That's why ORAS artifact manifest becomes the only choice.

[sajayantony]

Yes I understand the decision. I’m asking how do we plan to change the default to use the OCI manifest if that would become the preferred way.

Basically consider how the we keep compatibility with ORAS manifest later.

[SteveLasker]

@sajayantony , are you asking about the pending OCI manifest changes?

[shizhMSFT]

Since we will support OCI manifest & OCI Artifact (opencontainers/image-spec#934), let's postpone this change.

[shizhMSFT]

Let's re-open this PR if needed later.

[SteveLasker]

The CLI IX is pretty important for the annotations, without blobs scenarios.

[shizhMSFT]

Closing again as oras-project/oras-go#271 is planned.