Add debug statements to the extender

phase/extender.go

@@ -140,36 +140,46 @@
 		return fmt.Errorf("getting run image to extend: %w", err)
 	}
 
-	origTopLayer, err := topLayer(origBaseImage)
+	origTopLayer, err := topLayerDigest(origBaseImage, logger)
 	if err != nil {
 		return fmt.Errorf("getting original run image top layer: %w", err)
 	}
+	logger.Debugf("Original image top layer digest: %s", origTopLayer)
 
 	extendedImage, err := e.extend(buildpack.DockerfileKindRun, origBaseImage, logger)
 	if err != nil {
 		return fmt.Errorf("extending run image: %w", err)
 	}
 
-	if err = e.saveSparse(extendedImage, origTopLayer); err != nil {
-		return fmt.Errorf("copying extended image to output directory: %w", err)
+	if err = e.saveSparse(extendedImage, origTopLayer, logger); err != nil {
+		return fmt.Errorf("failed to copy extended image to output directory: %w", err)
 	}
 	return e.DockerfileApplier.Cleanup()
 }
 
-func topLayer(image v1.Image) (string, error) {
+func topLayerDigest(image v1.Image, logger log.Logger) (string, error) {
+	imageHash, err := image.Digest()
+	if err != nil {
+		return "", err
+	}
+
 	manifest, err := image.Manifest()
 	if err != nil {
 		return "", fmt.Errorf("getting image manifest: %w", err)
 	}
-	layers := manifest.Layers
-	if len(layers) == 0 {
+
+	allLayers := manifest.Layers
+	logger.Debugf("Found %d layers in original image with digest: %s", len(allLayers), imageHash)
+
+	if len(allLayers) == 0 {
 		return "", nil
 	}
-	layer := layers[len(layers)-1]
+
+	layer := allLayers[len(allLayers)-1]
 	return layer.Digest.String(), nil
 }
 
-func (e *Extender) saveSparse(image v1.Image, origTopLayerHash string) error {
+func (e *Extender) saveSparse(image v1.Image, origTopLayerHash string, logger log.Logger) error {
 	// save sparse image (manifest and config)
 	imageHash, err := image.Digest()
 	if err != nil {
@@ -189,6 +199,8 @@
 	if err != nil {
 		return fmt.Errorf("getting image layers: %w", err)
 	}
+	logger.Debugf("Found %d layers in extended image with digest: %s", len(allLayers), imageHash)
+
 	var (
 		currentHash  v1.Hash
 		needsCopying bool
@@ -205,13 +217,16 @@
 		switch {
 		case needsCopying:
 			currentLayer := currentLayer // allow use in closure
+			logger.Debugf("Copying top layer with digest: %s", currentHash)
 			group.Go(func() error {
 				return copyLayer(currentLayer, toPath)
 			})
 		case currentHash.String() == origTopLayerHash:
+			logger.Debugf("Found original top layer with digest: %s", currentHash)
 			needsCopying = true
 			continue
 		default:
+			logger.Debugf("Skipping base layer with digest: %s", currentHash)
 			continue
 		}
 	}
@@ -256,6 +271,12 @@
 		rebasable      = true // we don't require the initial base image to have io.buildpacks.rebasable=true
 		workingHistory []v1.History
 	)
+	digest, err := baseImage.Digest()
+	if err != nil {
+		return nil, err
+	}
+	logger.Debugf("Original image has digest: %s", digest)
+
 	// get config
 	baseImage, err = imgutil.OverrideHistoryIfNeeded(baseImage)
 	if err != nil {
@@ -284,6 +305,12 @@
 		); err != nil {
 			return nil, fmt.Errorf("applying Dockerfile to image: %w", err)
 		}
+		digest, err = baseImage.Digest()
+		if err != nil {
+			return nil, err
+		}
+		logger.Debugf("Intermediate image has digest: %s", digest)
+
 		// update rebasable, history in config, and user/group IDs
 		configFile, err = baseImage.ConfigFile()
 		if err != nil || configFile == nil {
@@ -320,10 +347,21 @@
 	if userID != origUserID {
 		logger.Warnf("The original user ID was %s but the final extension left the user ID set to %s.", origUserID, userID)
 	}
+	// build images don't mutate the config
 	if kind == buildpack.DockerfileKindBuild {
 		return baseImage, nil
 	}
-	return mutate.ConfigFile(baseImage, configFile)
+	// run images mutate the config
+	baseImage, err = mutate.ConfigFile(baseImage, configFile)
+	if err != nil {
+		return nil, err
+	}
+	digest, err = baseImage.Digest()
+	if err != nil {
+		return nil, err
+	}
+	logger.Debugf("Final extended image has digest: %s", digest)
+	return baseImage, nil
 }
 
 func userFrom(config v1.ConfigFile) (string, string) {