commit: always set a parent ID

Always set a parent ID when we go to commit an image, whether it's as
part of build-using-dockerfile or our "commit" CLI.  Coerce the parent
image's ID directly into the value that we use instead of digesting it
again.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #1538
Approved by: vrothberg

commit.go

@@ -67,8 +67,6 @@ type CommitOptions struct {
 
 	// OnBuild is a list of commands to be run by images based on this image
 	OnBuild []string
-	// Parent is the base image that this image was created by.
-	Parent string
 
 	// OmitTimestamp forces epoch 0 as created timestamp to allow for
 	// deterministic, content-addressable builds.
@@ -169,7 +167,7 @@ func (b *Builder) Commit(ctx context.Context, dest types.ImageReference, options
 		}
 	}
 	// Build an image reference from which we can copy the finished image.
-	src, err := b.makeImageRef(options.PreferredManifestType, options.Parent, exportBaseLayers, options.Squash, options.BlobDirectory, options.Compression, options.HistoryTimestamp, options.OmitTimestamp)
+	src, err := b.makeImageRef(options.PreferredManifestType, exportBaseLayers, options.Squash, options.BlobDirectory, options.Compression, options.HistoryTimestamp, options.OmitTimestamp)
 	if err != nil {
 		return imgID, nil, "", errors.Wrapf(err, "error computing layer digests and building metadata for container %q", b.ContainerID)
 	}

image.go

@@ -184,7 +184,7 @@ func (i *containerImageRef) createConfigsAndManifests() (v1.Image, v1.Manifest,
 	if err := json.Unmarshal(i.dconfig, &dimage); err != nil {
 		return v1.Image{}, v1.Manifest{}, docker.V2Image{}, docker.V2S2Manifest{}, err
 	}
-	dimage.Parent = docker.ID(digest.FromString(i.parent))
+	dimage.Parent = docker.ID(i.parent)
 	// Always replace this value, since we're newer than our base image.
 	dimage.Created = created
 	// Clear the list of diffIDs, since we always repopulate it.
@@ -445,7 +445,7 @@ func (i *containerImageRef) NewImageSource(ctx context.Context, sc *types.System
 	}
 	dimage.History = append(dimage.History, dnews)
 	appendHistory(i.postEmptyLayers)
-	dimage.Parent = docker.ID(digest.FromString(i.parent))
+	dimage.Parent = docker.ID(i.parent)
 
 	// Sanity check that we didn't just create a mismatch between non-empty layers in the
 	// history and the number of diffIDs.
@@ -636,7 +636,7 @@ func (i *containerImageSource) GetBlob(ctx context.Context, blob types.BlobInfo,
 	return ioutils.NewReadCloserWrapper(layerFile, closer), size, nil
 }
 
-func (b *Builder) makeImageRef(manifestType, parent string, exporting bool, squash bool, blobDirectory string, compress archive.Compression, historyTimestamp *time.Time, omitTimestamp bool) (types.ImageReference, error) {
+func (b *Builder) makeImageRef(manifestType string, exporting bool, squash bool, blobDirectory string, compress archive.Compression, historyTimestamp *time.Time, omitTimestamp bool) (types.ImageReference, error) {
 	var name reference.Named
 	container, err := b.store.Container(b.ContainerID)
 	if err != nil {
@@ -674,6 +674,14 @@ func (b *Builder) makeImageRef(manifestType, parent string, exporting bool, squa
 		created = time.Unix(0, 0)
 	}
 
+	parent := ""
+	if b.FromImageID != "" {
+		parentDigest := digest.NewDigestFromEncoded(digest.Canonical, b.FromImageID)
+		if parentDigest.Validate() == nil {
+			parent = parentDigest.String()
+		}
+	}
+
 	ref := &containerImageRef{
 		store:                 b.store,
 		compression:           compress,

imagebuildah/build.go

@@ -1460,7 +1460,6 @@ func (s *StageExecutor) commit(ctx context.Context, ib *imagebuilder.Builder, cr
 		SystemContext:         s.executor.systemContext,
 		Squash:                s.executor.squash,
 		BlobDirectory:         s.executor.blobDirectory,
-		Parent:                s.builder.FromImageID,
 	}
 	imgID, _, manifestDigest, err := s.builder.Commit(ctx, imageRef, options)
 	if err != nil {