commit: set "parent" for docker format only when requested

Make setting the Parent field in the config blob of a docker format
image optional (yes, we're bringing it back!), since it no longer
appears to be set by newer versions of docker build.

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

commit.go

@@ -108,6 +108,10 @@ type CommitOptions struct {
 	// UnsetEnvs is a list of environments to not add to final image.
 	// Deprecated: use UnsetEnv() before committing instead.
 	UnsetEnvs []string
+	// CompatSetParent causes the "parent" field to be set when committing
+	// the image in Docker format.  Newer BuildKit-based builds don't set
+	// this field.
+	CompatSetParent types.OptionalBool
 }
 
 var (

define/build.go

@@ -316,4 +316,8 @@ type BuildOptions struct {
 	// value set in a base image will be preserved, so this does not
 	// frequently need to be set.
 	OSVersion string
+	// CompatSetParent causes the "parent" field to be set in the image's
+	// configuration when committing in Docker format.  Newer
+	// BuildKit-based docker build doesn't set this field.
+	CompatSetParent types.OptionalBool
 }

image.go

@@ -76,6 +76,7 @@ type containerImageRef struct {
 	blobDirectory         string
 	preEmptyLayers        []v1.History
 	postEmptyLayers       []v1.History
+	compatSetParent       types.OptionalBool
 }
 
 type blobLayerInfo struct {
@@ -230,6 +231,11 @@ 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
 	}
+	// Set the parent, but only if we want to be compatible with "classic" docker build.
+	if i.compatSetParent == types.OptionalBoolTrue {
+		dimage.Parent = docker.ID(i.parent)
+	}
+	// Set the container ID and containerConfig in the docker format.
 	dimage.Container = i.containerID
 	if dimage.Config != nil {
 		dimage.ContainerConfig = *dimage.Config
@@ -838,6 +844,7 @@ func (b *Builder) makeContainerImageRef(options CommitOptions) (*containerImageR
 		blobDirectory:         options.BlobDirectory,
 		preEmptyLayers:        b.PrependedEmptyLayers,
 		postEmptyLayers:       b.AppendedEmptyLayers,
+		compatSetParent:       options.CompatSetParent,
 	}
 	return ref, nil
 }

imagebuildah/executor.go

@@ -141,6 +141,7 @@ type Executor struct {
 	osVersion               string
 	osFeatures              []string
 	envs                    []string
+	compatSetParent         types.OptionalBool
 }
 
 type imageTypeAndHistoryAndDiffIDs struct {
@@ -293,6 +294,7 @@ func newExecutor(logger *logrus.Logger, logPrefix string, store storage.Store, o
 		osVersion:                      options.OSVersion,
 		osFeatures:                     append([]string{}, options.OSFeatures...),
 		envs:                           append([]string{}, options.Envs...),
+		compatSetParent:                options.CompatSetParent,
 	}
 	if exec.err == nil {
 		exec.err = os.Stderr

imagebuildah/stage_executor.go

@@ -2014,6 +2014,7 @@ func (s *StageExecutor) commit(ctx context.Context, createdBy string, emptyLayer
 		RetryDelay:            s.executor.retryPullPushDelay,
 		HistoryTimestamp:      s.executor.timestamp,
 		Manifest:              s.executor.manifest,
+		CompatSetParent:       s.executor.compatSetParent,
 	}
 	imgID, _, manifestDigest, err := s.builder.Commit(ctx, imageRef, options)
 	if err != nil {