imagetools: avoid trying to load attestations inline references

When creating resulting image index it is wasteful
to check for attestations for the descriptors in original
index what were already attestation for subject manifest.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

commands/imagetools/create.go

@@ -200,25 +200,37 @@ func runCreate(ctx context.Context, dockerCli command.Cli, in createOptions, arg
 	eg, _ := errgroup.WithContext(ctx)
 	pw := progress.WithPrefix(printer, "internal", true)
 
+	tagsByRepo := map[string][]reference.Named{}
 	for _, t := range tags {
+		repo := t.Name()
+		tagsByRepo[repo] = append(tagsByRepo[repo], t)
+	}
+
+	for repo, repoTags := range tagsByRepo {
 		eg.Go(func() error {
-			return progress.Wrap(fmt.Sprintf("pushing %s", t.String()), pw.Write, func(sub progress.SubLogger) error {
+			seed := repoTags[0]
+			return progress.Wrap(fmt.Sprintf("pushing %s", repo), pw.Write, func(sub progress.SubLogger) error {
 				ctx = withMediaTypeKeyPrefix(ctx)
 				eg2, _ := errgroup.WithContext(ctx)
 				for _, desc := range manifests {
 					eg2.Go(func() error {
-						sub.Log(1, fmt.Appendf(nil, "copying %s from %s to %s\n", desc.Digest.String(), desc.Source.Ref.String(), t.String()))
+						sub.Log(1, fmt.Appendf(nil, "copying %s from %s to %s\n", desc.Digest.String(), desc.Source.Ref.String(), repo))
 						return r.Copy(ctx, &imagetools.Source{
 							Ref:  desc.Source.Ref,
 							Desc: desc.Descriptor,
-						}, t)
+						}, seed)
 					})
 				}
 				if err := eg2.Wait(); err != nil {
 					return err
 				}
-				sub.Log(1, fmt.Appendf(nil, "pushing %s to %s\n", desc.Digest.String(), t.String()))
-				return r.Push(ctx, t, desc, dt)
+				for _, t := range repoTags {
+					sub.Log(1, fmt.Appendf(nil, "pushing %s to %s\n", desc.Digest.String(), t.String()))
+					if err := r.Push(ctx, t, desc, dt); err != nil {
+						return err
+					}
+				}
+				return nil
 			})
 		})
 	}

util/imagetools/create.go

@@ -429,6 +429,9 @@ func (r *Resolver) filterPlatforms(ctx context.Context, dt []byte, desc ocispecs
 	// try to pull in attestation manifest via referrer if one exists
 	addedRef := false
 	for d := range matchedManifests {
+		if _, ok := references[d]; ok { // manifest itself is already attestation
+			continue
+		}
 		hasRef := false
 		for _, subject := range references {
 			if subject.Digest == d {