@@ -631,7 +631,7 @@ func (p *puller) Snapshot(ctx context.Context, g session.Group) (cache.Immutable

 		ongoing.add(desc)

 		layers = append(layers, &layerDescriptor{

 			desc:    desc,

-			diffID:  layer.DiffID(img.RootFS.DiffIDs[i]),

+			diffID:  img.RootFS.DiffIDs[i],

 			fetcher: fetcher,

 			ref:     p.src.Reference,

 			is:      p.is,

@@ -147,7 +147,7 @@ func (s *snapshotter) chainID(key string) (layer.ChainID, bool) {

 		if err != nil {

 			return "", false

 		}

-		return layer.ChainID(dgst), true

+		return dgst, true

 	}

 	return "", false

 }

@@ -1,9 +1,13 @@

+// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:

+//go:build go1.23

+

 package mobyexporter

 import (

 	"bytes"

 	"context"

 	"fmt"

+	"slices"

 	"strings"

 	"github.com/containerd/containerd/v2/core/content"

@@ -151,10 +155,7 @@ func (e *imageExporterInstance) Export(ctx context.Context, inp *exporter.Source

 			return nil, nil, layersDone(err)

 		}

-		diffs = make([]digest.Digest, len(diffIDs))

-		for i := range diffIDs {

-			diffs[i] = digest.Digest(diffIDs[i])

-		}

+		diffs = slices.Clone(diffIDs)

 		_ = layersDone(nil)

 	}

@@ -369,7 +369,7 @@ func (w *Worker) GetRemotes(ctx context.Context, ref cache.ImmutableRef, createI

 	for i, dgst := range diffIDs {

 		descriptors[i] = ocispec.Descriptor{

 			MediaType: c8dimages.MediaTypeDockerSchema2Layer,

-			Digest:    digest.Digest(dgst),

+			Digest:    dgst,

 			Size:      -1,

 		}

 	}

@@ -439,7 +439,7 @@ func (w *Worker) FromRemote(ctx context.Context, remote *solver.Remote) (cache.I

 		// ongoing.add(desc)

 		layers = append(layers, &layerDescriptor{

 			desc:     l.Blob,

-			diffID:   layer.DiffID(l.Diff.Digest),

+			diffID:   l.Diff.Digest,

 			provider: remote.Provider,

 			w:        w,

 			pctx:     ctx,

@@ -178,7 +178,7 @@ func (l *MockRWLayer) Release() error { return nil }

 func (l *MockRWLayer) Root() string   { return "" }

 func (l *MockRWLayer) Commit() (builder.ROLayer, error) {

 	return &MockROLayer{

-		diffID: layer.DiffID(digest.Digest("sha256:1234")),

+		diffID: "sha256:1234",

 	}, nil

 }

@@ -159,7 +159,7 @@ func (c cacheAdaptor) Create(parent *image.Image, target image.Image, extraLayer

 	var layerDigest digest.Digest

 	if extraLayer != "" {

-		info, err := findContentByUncompressedDigest(ctx, c.is.client.ContentStore(), digest.Digest(extraLayer))

+		info, err := findContentByUncompressedDigest(ctx, c.is.client.ContentStore(), extraLayer)

 		if err != nil {

 			return "", fmt.Errorf("failed to find content for diff ID %q: %w", extraLayer, err)

 		}

@@ -387,7 +387,7 @@ func (rw *rwlayer) Commit() (_ builder.ROLayer, outErr error) {

 		key:                key,

 		c:                  rw.c,

 		snapshotter:        rw.snapshotter,

-		diffID:             layer.DiffID(diffID),

+		diffID:             diffID,

 		contentStoreDigest: desc.Digest,

 		lease:              &lease,

 	}, nil

@@ -1,13 +1,16 @@

+// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:

+//go:build go1.23

+

 package containerd

 import (

+	"slices"

+

 	"github.com/docker/docker/api/types/container"

 	"github.com/docker/docker/dockerversion"

 	"github.com/docker/docker/image"

-	"github.com/docker/docker/layer"

 	"github.com/docker/go-connections/nat"

 	imagespec "github.com/moby/docker-image-spec/specs-go/v1"

-	"github.com/opencontainers/go-digest"

 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"

 )

@@ -27,16 +30,12 @@ func dockerOciImageToDockerImagePartial(id image.ID, img imagespec.DockerOCIImag

 		Created:       img.Created,

 	}

-	rootFS := &image.RootFS{

-		Type: img.RootFS.Type,

-	}

-	for _, diffId := range img.RootFS.DiffIDs {

-		rootFS.DiffIDs = append(rootFS.DiffIDs, layer.DiffID(diffId))

-	}

-

 	out := image.NewImage(id)

 	out.V1Image = v1Image

-	out.RootFS = rootFS

+	out.RootFS = &image.RootFS{

+		Type:    img.RootFS.Type,

+		DiffIDs: slices.Clone(img.RootFS.DiffIDs),

+	}

 	out.History = img.History

 	out.OSFeatures = img.OSFeatures

 	out.OSVersion = img.OSVersion

@@ -44,14 +43,6 @@ func dockerOciImageToDockerImagePartial(id image.ID, img imagespec.DockerOCIImag

 }

 func dockerImageToDockerOCIImage(img image.Image) imagespec.DockerOCIImage {

-	rootfs := ocispec.RootFS{

-		Type:    img.RootFS.Type,

-		DiffIDs: []digest.Digest{},

-	}

-	for _, diffId := range img.RootFS.DiffIDs {

-		rootfs.DiffIDs = append(rootfs.DiffIDs, digest.Digest(diffId))

-	}

-

 	return imagespec.DockerOCIImage{

 		Image: ocispec.Image{

 			Created: img.Created,

@@ -63,7 +54,10 @@ func dockerImageToDockerOCIImage(img image.Image) imagespec.DockerOCIImage {

 				OSVersion:    img.OSVersion,

 				OSFeatures:   img.OSFeatures,

 			},

-			RootFS:  rootfs,

+			RootFS: ocispec.RootFS{

+				Type:    img.RootFS.Type,

+				DiffIDs: slices.Clone(img.RootFS.DiffIDs),

+			},

 			History: img.History,

 		},

 		Config: containerConfigToDockerOCIImageConfig(img.Config),

@@ -140,8 +140,7 @@ deleteImagesLoop:

 	// Compute how much space was freed

 	for _, d := range rep.ImagesDeleted {

 		if d.Deleted != "" {

-			chid := layer.ChainID(d.Deleted)

-			if l, ok := allLayers[chid]; ok {

+			if l, ok := allLayers[layer.ChainID(d.Deleted)]; ok {

 				rep.SpaceReclaimed += uint64(l.DiffSize())

 			}

 		}

@@ -117,7 +117,7 @@ func (serv *v2MetadataService) digestNamespace() string {

 }

 func (serv *v2MetadataService) diffIDKey(diffID layer.DiffID) string {

-	return string(digest.Digest(diffID).Algorithm()) + "/" + digest.Digest(diffID).Encoded()

+	return string(diffID.Algorithm()) + "/" + diffID.Encoded()

 }

 func (serv *v2MetadataService) digestKey(dgst digest.Digest) string {

@@ -145,11 +145,11 @@ func (serv *v2MetadataService) GetMetadata(diffID layer.DiffID) ([]V2Metadata, e

 // GetDiffID finds a layer DiffID from a digest.

 func (serv *v2MetadataService) GetDiffID(dgst digest.Digest) (layer.DiffID, error) {

 	if serv.store == nil {

-		return layer.DiffID(""), errors.New("no metadata storage")

+		return "", errors.New("no metadata storage")

 	}

 	diffIDBytes, err := serv.store.Get(serv.digestNamespace(), serv.digestKey(dgst))

 	if err != nil {

-		return layer.DiffID(""), err

+		return "", err

 	}

 	return layer.DiffID(diffIDBytes), nil

@@ -73,13 +73,13 @@ func TestV2MetadataService(t *testing.T) {

 	}

 	// Test GetMetadata on a nonexistent entry

-	_, err = metadataService.GetMetadata(layer.DiffID("sha256:82379823067823853223359023576437723560923756b03560378f4497753917"))

+	_, err = metadataService.GetMetadata("sha256:82379823067823853223359023576437723560923756b03560378f4497753917")

 	if err == nil {

 		t.Fatal("expected error looking up nonexistent entry")

 	}

 	// Test GetDiffID on a nonexistent entry

-	_, err = metadataService.GetDiffID(digest.Digest("sha256:82379823067823853223359023576437723560923756b03560378f4497753917"))

+	_, err = metadataService.GetDiffID("sha256:82379823067823853223359023576437723560923756b03560378f4497753917")

 	if err == nil {

 		t.Fatal("expected error looking up nonexistent entry")

 	}

@@ -15,6 +15,7 @@ import (

 	"github.com/docker/docker/layer"

 	"github.com/docker/docker/pkg/progress"

 	"github.com/opencontainers/go-digest"

+	"github.com/opencontainers/image-spec/identity"

 	"gotest.tools/v3/assert"

 )

@@ -63,18 +64,6 @@ type mockLayerStore struct {

 	layers map[layer.ChainID]*mockLayer

 }

-func createChainIDFromParent(parent layer.ChainID, dgsts ...layer.DiffID) layer.ChainID {

-	if len(dgsts) == 0 {

-		return parent

-	}

-	if parent == "" {

-		return createChainIDFromParent(layer.ChainID(dgsts[0]), dgsts[1:]...) // #nosec G602 -- false positive: slice bounds out of range

-	}

-	// H = "H(n-1) SHA256(n)"

-	dgst := digest.FromBytes([]byte(string(parent) + " " + string(dgsts[0]))) // #nosec G602 -- false positive: slice bounds out of range

-	return createChainIDFromParent(layer.ChainID(dgst), dgsts[1:]...)         // #nosec G602 -- false positive: slice bounds out of range

-}

-

 func (ls *mockLayerStore) Map() map[layer.ChainID]layer.Layer {

 	layers := map[layer.ChainID]layer.Layer{}

@@ -95,11 +84,13 @@ func (ls *mockLayerStore) RegisterWithDescriptor(reader io.Reader, parentID laye

 		err    error

 	)

+	var diffIDs []layer.DiffID

 	if parentID != "" {

 		parent, err = ls.Get(parentID)

 		if err != nil {

 			return nil, err

 		}

+		diffIDs = append(diffIDs, parentID)

 	}

 	l := &mockLayer{parent: parent}

@@ -107,8 +98,9 @@ func (ls *mockLayerStore) RegisterWithDescriptor(reader io.Reader, parentID laye

 	if err != nil {

 		return nil, err

 	}

-	l.diffID = layer.DiffID(digest.FromBytes(l.layerData.Bytes()))

-	l.chainID = createChainIDFromParent(parentID, l.diffID)

+	l.diffID = digest.FromBytes(l.layerData.Bytes())

+	diffIDs = append(diffIDs, l.diffID)

+	l.chainID = identity.ChainID(diffIDs)

 	ls.layers[l.chainID] = l

 	return l, nil

@@ -231,33 +223,33 @@ func downloadDescriptors(currentDownloads *atomic.Int32) []DownloadDescriptor {

 		&mockDownloadDescriptor{

 			currentDownloads: currentDownloads,

 			id:               "id1",

-			expectedDiffID:   layer.DiffID("sha256:68e2c75dc5c78ea9240689c60d7599766c213ae210434c53af18470ae8c53ec1"),

+			expectedDiffID:   "sha256:68e2c75dc5c78ea9240689c60d7599766c213ae210434c53af18470ae8c53ec1",

 		},

 		&mockDownloadDescriptor{

 			currentDownloads: currentDownloads,

 			id:               "id2",

-			expectedDiffID:   layer.DiffID("sha256:64a636223116aa837973a5d9c2bdd17d9b204e4f95ac423e20e65dfbb3655473"),

+			expectedDiffID:   "sha256:64a636223116aa837973a5d9c2bdd17d9b204e4f95ac423e20e65dfbb3655473",

 		},

 		&mockDownloadDescriptor{

 			currentDownloads: currentDownloads,

 			id:               "id3",

-			expectedDiffID:   layer.DiffID("sha256:58745a8bbd669c25213e9de578c4da5c8ee1c836b3581432c2b50e38a6753300"),

+			expectedDiffID:   "sha256:58745a8bbd669c25213e9de578c4da5c8ee1c836b3581432c2b50e38a6753300",

 		},

 		&mockDownloadDescriptor{

 			currentDownloads: currentDownloads,

 			id:               "id2",

-			expectedDiffID:   layer.DiffID("sha256:64a636223116aa837973a5d9c2bdd17d9b204e4f95ac423e20e65dfbb3655473"),

+			expectedDiffID:   "sha256:64a636223116aa837973a5d9c2bdd17d9b204e4f95ac423e20e65dfbb3655473",

 		},

 		&mockDownloadDescriptor{

 			currentDownloads: currentDownloads,

 			id:               "id4",

-			expectedDiffID:   layer.DiffID("sha256:0dfb5b9577716cc173e95af7c10289322c29a6453a1718addc00c0c5b1330936"),

+			expectedDiffID:   "sha256:0dfb5b9577716cc173e95af7c10289322c29a6453a1718addc00c0c5b1330936",

 			simulateRetries:  1,

 		},

 		&mockDownloadDescriptor{

 			currentDownloads: currentDownloads,

 			id:               "id5",

-			expectedDiffID:   layer.DiffID("sha256:0a5f25fa1acbc647f6112a6276735d0fa01e4ee2aa7ec33015e337350e1ea23d"),

+			expectedDiffID:   "sha256:0a5f25fa1acbc647f6112a6276735d0fa01e4ee2aa7ec33015e337350e1ea23d",

 		},

 	}

 }

@@ -91,7 +91,7 @@ func TestImageOSNotEmpty(t *testing.T) {

 func TestNewChildImageFromImageWithRootFS(t *testing.T) {

 	rootFS := NewRootFS()

-	rootFS.Append(layer.DiffID("ba5e"))

+	rootFS.Append("ba5e")

 	parent := &Image{

 		RootFS: rootFS,

 		History: []History{

@@ -109,7 +109,7 @@ func TestNewChildImageFromImageWithRootFS(t *testing.T) {

 	}

 	newImage := NewChildImage(parent, childConfig, "platform")

-	expectedDiffIDs := []layer.DiffID{layer.DiffID("ba5e"), layer.DiffID("abcdef")}

+	expectedDiffIDs := []layer.DiffID{"ba5e", "abcdef"}

 	assert.Check(t, is.DeepEqual(expectedDiffIDs, newImage.RootFS.DiffIDs))

 	assert.Check(t, is.Equal(childConfig.Author, newImage.Author))

 	assert.Check(t, is.DeepEqual(childConfig.Config, newImage.Config))

@@ -31,6 +31,8 @@ func TestRestore(t *testing.T) {

 	err = fsStore.SetMetadata(id2, "parent", []byte(id1))

 	assert.NilError(t, err)

+	// This produces an error log (trying to unmarshal the "invalid" value from above, but doesn't return an error;

+	// ERRO[0000] invalid image                                 digest="sha256:f1234d75178d892a133a410355a5a990cf75d2f33eba25d575943d4df632f3a4" err="invalid character 'i' looking for beginning of value: invalid"

 	imgStore, err := NewImageStore(fsStore, &mockLayerGetReleaser{})

 	assert.NilError(t, err)

@@ -284,7 +284,7 @@ func (s *saveSession) save(ctx context.Context, outStream io.Writer) error {

 			if _, ok := reposLegacy[familiarName]; !ok {

 				reposLegacy[familiarName] = make(map[string]string)

 			}

-			reposLegacy[familiarName][ref.Tag()] = digest.Digest(imageDescr.layers[len(imageDescr.layers)-1]).Encoded()

+			reposLegacy[familiarName][ref.Tag()] = imageDescr.layers[len(imageDescr.layers)-1].Encoded()

 			repoTags = append(repoTags, reference.FamiliarString(ref))

 			taggedManifest := untaggedMfstDesc

@@ -300,10 +300,9 @@ func (s *saveSession) save(ctx context.Context, outStream io.Writer) error {

 			manifestDescriptors = append(manifestDescriptors, untaggedMfstDesc)

 		}

-		for _, l := range imageDescr.layers {

+		for _, lDgst := range imageDescr.layers {

 			// IMPORTANT: We use path, not filepath here to ensure the layers

 			// in the manifest use Unix-style forward-slashes.

-			lDgst := digest.Digest(l)

 			layers = append(layers, path.Join(ocispec.ImageBlobsDir, lDgst.Algorithm().String(), lDgst.Encoded()))

 		}

@@ -530,11 +529,11 @@ func (s *saveSession) saveConfigAndLayer(ctx context.Context, id layer.ChainID,

 	}

 	lDiffID := l.DiffID()

-	lDgst := digest.Digest(lDiffID)

+	lDgst := lDiffID

 	if _, ok := s.savedLayers[lDiffID]; ok {

 		return s.savedLayers[lDiffID], nil

 	}

-	layerPath := filepath.Join(outDir, lDgst.Algorithm().String(), lDgst.Encoded())

+	layerPath := filepath.Join(outDir, lDiffID.Algorithm().String(), lDiffID.Encoded())

 	defer layer.ReleaseAndLog(s.lss, l)

 	if _, err = os.Stat(layerPath); err == nil {

@@ -9,7 +9,7 @@ import (

 // DigestSHA256EmptyTar is the canonical sha256 digest of empty tar file -

 // (1024 NULL bytes)

-const DigestSHA256EmptyTar = DiffID("sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef")

+const DigestSHA256EmptyTar DiffID = "sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef"

 type emptyLayer struct{}

@@ -19,7 +19,7 @@ var EmptyLayer = &emptyLayer{}

 func (el *emptyLayer) TarStream() (io.ReadCloser, error) {

 	buf := new(bytes.Buffer)

 	tarWriter := tar.NewWriter(buf)

-	tarWriter.Close()

+	_ = tarWriter.Close()

 	return io.NopCloser(buf), nil

 }

@@ -31,7 +31,7 @@ func (el *emptyLayer) TarStreamFrom(p ChainID) (io.ReadCloser, error) {

 }

 func (el *emptyLayer) ChainID() ChainID {

-	return ChainID(DigestSHA256EmptyTar)

+	return DigestSHA256EmptyTar

 }

 func (el *emptyLayer) DiffID() DiffID {

@@ -8,7 +8,7 @@ import (

 )

 func TestEmptyLayer(t *testing.T) {

-	if EmptyLayer.ChainID() != ChainID(DigestSHA256EmptyTar) {

+	if EmptyLayer.ChainID() != DigestSHA256EmptyTar {

 		t.Fatal("wrong ChainID for empty layer")

 	}

@@ -45,7 +45,7 @@ func TestEmptyLayer(t *testing.T) {

 		t.Fatalf("error hashing empty tar layer: %v", err)

 	}

-	if digester.Digest() != digest.Digest(DigestSHA256EmptyTar) {

+	if digester.Digest() != DigestSHA256EmptyTar {

 		t.Fatal("empty layer tar stream hashes to wrong value")

 	}

 }

@@ -46,8 +46,7 @@ func newFSMetadataStore(root string) (*fileMetadataStore, error) {

 }

 func (fms *fileMetadataStore) getLayerDirectory(layer ChainID) string {

-	dgst := digest.Digest(layer)

-	return filepath.Join(fms.root, string(dgst.Algorithm()), dgst.Encoded())

+	return filepath.Join(fms.root, string(layer.Algorithm()), layer.Encoded())

 }

 func (fms *fileMetadataStore) getLayerFilename(layer ChainID, filename string) string {

@@ -83,11 +82,11 @@ func (fm *fileMetadataTransaction) SetSize(size int64) error {

 }

 func (fm *fileMetadataTransaction) SetParent(parent ChainID) error {

-	return fm.ws.WriteFile("parent", []byte(digest.Digest(parent).String()), 0o644)

+	return fm.ws.WriteFile("parent", []byte(parent.String()), 0o644)

 }

 func (fm *fileMetadataTransaction) SetDiffID(diff DiffID) error {

-	return fm.ws.WriteFile("diff", []byte(digest.Digest(diff).String()), 0o644)

+	return fm.ws.WriteFile("diff", []byte(diff.String()), 0o644)

 }

 func (fm *fileMetadataTransaction) SetCacheID(cacheID string) error {

@@ -165,7 +164,7 @@ func (fms *fileMetadataStore) GetParent(layer ChainID) (ChainID, error) {

 		return "", err

 	}

-	return ChainID(dgst), nil

+	return dgst, nil

 }

 func (fms *fileMetadataStore) GetDiffID(layer ChainID) (DiffID, error) {

@@ -179,7 +178,7 @@ func (fms *fileMetadataStore) GetDiffID(layer ChainID) (DiffID, error) {

 		return "", err

 	}

-	return DiffID(dgst), nil

+	return dgst, nil

 }

 func (fms *fileMetadataStore) GetCacheID(layer ChainID) (string, error) {

@@ -249,7 +248,7 @@ func (fms *fileMetadataStore) SetMountParent(mount string, parent ChainID) error

 	if err := os.MkdirAll(fms.getMountDirectory(mount), 0o755); err != nil {

 		return err

 	}

-	return os.WriteFile(fms.getMountFilename(mount, "parent"), []byte(digest.Digest(parent).String()), 0o644)

+	return os.WriteFile(fms.getMountFilename(mount, "parent"), []byte(parent.String()), 0o644)

 }

 func (fms *fileMetadataStore) GetMountID(mount string) (string, error) {

@@ -297,7 +296,7 @@ func (fms *fileMetadataStore) GetMountParent(mount string) (ChainID, error) {

 		return "", err

 	}

-	return ChainID(dgst), nil

+	return dgst, nil

 }

 func (fms *fileMetadataStore) getOrphan() ([]roLayer, error) {

@@ -339,7 +338,7 @@ func (fms *fileMetadataStore) getOrphan() ([]roLayer, error) {

 			}

 			l := &roLayer{

-				chainID: ChainID(dgst),

+				chainID: dgst,

 				cacheID: cacheID,

 			}

 			orphanLayers = append(orphanLayers, *l)

@@ -366,7 +365,7 @@ func (fms *fileMetadataStore) List() ([]ChainID, []string, error) {

 				if err := dgst.Validate(); err != nil {

 					log.G(context.TODO()).Debugf("Ignoring invalid digest %s:%s", algorithm, fi.Name())

 				} else {

-					ids = append(ids, ChainID(dgst))

+					ids = append(ids, dgst)

 				}

 			}

 		}

@@ -392,7 +391,7 @@ func (fms *fileMetadataStore) List() ([]ChainID, []string, error) {

 // Remove layerdb folder if that is marked for removal

 func (fms *fileMetadataStore) Remove(layer ChainID, cache string) error {

-	dgst := digest.Digest(layer)

+	dgst := layer

 	files, err := os.ReadDir(filepath.Join(fms.root, string(dgst.Algorithm())))

 	if err != nil {

 		return err

@@ -17,7 +17,7 @@ import (

 func randomLayerID(seed int64) ChainID {

 	r := rand.New(rand.NewSource(seed)).Int63()

-	return ChainID(digest.FromBytes([]byte(strconv.FormatInt(r, 10))))

+	return digest.FromBytes([]byte(strconv.FormatInt(r, 10)))

 }

 func newFileMetadataStore(t *testing.T) (*fileMetadataStore, string) {

@@ -243,7 +243,7 @@ func (ls *layerStore) applyTar(tx *fileMetadataTransaction, ts io.Reader, parent

 	}

 	layer.size = applySize

-	layer.diffID = DiffID(digester.Digest())

+	layer.diffID = digester.Digest()

 	log.G(context.TODO()).Debugf("Applied tar %s to %s, size: %d", layer.diffID, layer.cacheID, applySize)

@@ -386,9 +386,8 @@ func (ls *layerStore) deleteLayer(layer *roLayer, metadata *Metadata) error {

 	// if ls.driver.Remove fails

 	var dir string

 	for {

-		dgst := digest.Digest(layer.chainID)

-		tmpID := fmt.Sprintf("%s-%s-removing", dgst.Encoded(), stringid.GenerateRandomID())

-		dir = filepath.Join(ls.store.root, string(dgst.Algorithm()), tmpID)

+		tmpID := fmt.Sprintf("%s-%s-removing", layer.chainID.Encoded(), stringid.GenerateRandomID())

+		dir = filepath.Join(ls.store.root, string(layer.chainID.Algorithm()), tmpID)

 		err := os.Rename(ls.store.getLayerDirectory(layer.chainID), dir)

 		if os.IsExist(err) {

 			continue

@@ -517,7 +517,7 @@ func TestTarStreamStability(t *testing.T) {

 func assertLayerDiff(t *testing.T, expected []byte, layer Layer) {

 	expectedDigest := digest.FromBytes(expected)

-	if digest.Digest(layer.DiffID()) != expectedDigest {

+	if layer.DiffID() != expectedDigest {

 		t.Fatalf("Mismatched diff id for %s, got %s, expected %s", layer.ChainID(), layer.DiffID(), expected)

 	}

@@ -698,8 +698,8 @@ func TestTarStreamVerification(t *testing.T) {

 	if err != nil {

 		t.Fatal(err)

 	}

-	id1 := digest.Digest(layer1.ChainID())

-	id2 := digest.Digest(layer2.ChainID())

+	id1 := layer1.ChainID()

+	id2 := layer2.ChainID()

 	// Replace tar data files

 	src, err := os.Open(filepath.Join(tmpdir, id1.Algorithm().String(), id1.Encoded(), "tar-split.json.gz"))

@@ -29,7 +29,7 @@ func (rl *roLayer) TarStream() (io.ReadCloser, error) {

 		return nil, err

 	}

-	vrc, err := newVerifiedReadCloser(rc, digest.Digest(rl.diffID))

+	vrc, err := newVerifiedReadCloser(rc, rl.diffID)

 	if err != nil {

 		return nil, err

 	}

@@ -48,7 +48,7 @@ func (rl *roLayer) TarStreamFrom(parent ChainID) (io.ReadCloser, error) {

 		}

 	}

-	if parent != ChainID("") && parentCacheID == "" {

+	if parent != "" && parentCacheID == "" {

 		return nil, fmt.Errorf("layer ID '%s' is not a parent of the specified layer: cannot provide diff to non-parent", parent)

 	}

 	return rl.layerStore.driver.Diff(rl.cacheID, parentCacheID)