crane: image argument is different for crane export and crane push

[reddaly]

Describe the bug

crane export "image" argument is different from crane push.

I'm using rules_oci to generate images. I want to list the contents of the output of a oci_image target. The oci_image target is a directory that is accepted by crane push through the loadImage codepath:

go-containerregistry/cmd/crane/cmd/push.go

Lines 89 to 129 in c195f15

	func loadImage(path string, index bool) (partial.WithRawManifest, error) {
	stat, err := os.Stat(path)
	if err != nil {
	return nil, err
	}
	if !stat.IsDir() {
	img, err := crane.Load(path)
	if err != nil {
	return nil, fmt.Errorf("loading %s as tarball: %w", path, err)
	}
	return img, nil
	}
	l, err := layout.ImageIndexFromPath(path)
	if err != nil {
	return nil, fmt.Errorf("loading %s as OCI layout: %w", path, err)
	}
	if index {
	return l, nil
	}
	m, err := l.IndexManifest()
	if err != nil {
	return nil, err
	}
	if len(m.Manifests) != 1 {
	return nil, fmt.Errorf("layout contains %d entries, consider --index", len(m.Manifests))
	}
	desc := m.Manifests[0]
	if desc.MediaType.IsImage() {
	return l.Image(desc.Digest)
	} else if desc.MediaType.IsIndex() {
	return l.ImageIndex(desc.Digest)
	}
	return nil, fmt.Errorf("layout contains non-image (mediaType: %q), consider --index", desc.MediaType)
	}

I'm using crane export to try to get a tarball of the file system of the image. However, crane export doesn't process its image argument the same way. There is no call to ImageIndexFromPath etc.

As a result I don't have an easy way to inspect the filesystem contents of the image rules_oci produces using crane.

To Reproduce

TODO

Expected behavior

TODO

Additional context

Add any other context about the problem here.

$ dist/code5/external/oci_crane_linux_amd64/crane version                                                                                                                                                                           
0.15.2        

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