allow image index type for oci-layout

[panekj]

OCI specification allows either image.index or image.manifest for each manifest descriptor in OCI layout https://github.com/opencontainers/image-spec/blob/c05acf7eb327dae4704a4efe01253a0e60af6b34/image-layout.md?plain=1#L153

[AkihiroSuda]

How to test this?

[apostasie]

How to test this?

Generally speaking, wondering if we would need some tooling to manually author and push manifests - that would allow testing how we behave in the face of broken / unsupported / maliciously crafted manifests.

That would be a bit of work, but not completely unrealistic.

[apostasie]

(comment above does not imply support for this specific change here - I am scratching my head as to what the use-case for it is?)

[panekj]

How to test this?

I'm not going to provide anything specific for nerdctl as I don't know the project nor have found any testing that would apply for this, but building image using different tool (e.g. Docker) and try to load it with nerdctl should reveal any issues (i hope).

I am scratching my head as to what the use-case for it is?

I am scratching my head as to why I have to provide reasoning for adjusting project to a spec, but above described "test" may suffice?

[AkihiroSuda]

How did you actually test this PR?

[apostasie]

How to test this?

I'm not going to provide anything specific for nerdctl as I don't know the project nor have found any testing that would apply for this, but building image using different tool (e.g. Docker) and try to load it with nerdctl should reveal any issues (i hope).

I am scratching my head as to what the use-case for it is?

I am scratching my head as to why I have to provide reasoning for adjusting project to a spec, but above described "test" may suffice?

Did not mean this in any offensive nor dismissive way.
I am just trying to understand how to test this, what concrete use-cases are out there that we can codify as tests here to ensure this is working as expected.
Peace.