mergeop/diffop not working properly with Moby worker

[tonistiigi]

Description

Issue was reported in docker slack involving missing filecaps after using COPY --link:

Details

While the specific issue was fixed in moby/buildkit#3671 , the reason it appeared in Moby and not in regular buildkit is that there seems to be an issue with the way images are created from the merge/diff references. While the correct behavior is to export the original individual layers, Moby exports the merge base snapshot. This isn't correct and doesn't have the cache semantics that merge/diff is supposed to promise. I think it may also cause failed cache imports when using --cache-from with such images.

@sipsma

Reproduce

Use COPY --link with 23.0

Expected behavior

No response

docker version

-

docker info

-

Additional Info

No response

[neersighted]

PRs are merged to master and 23.0.

[tonistiigi]

We can leave this open for the actual fix for the issue, as the PRs were just a workaround.

cc @sipsma