Returns an error if the condition is not met

image/descriptor.go

@@ -54,7 +54,7 @@ func listReferences(w walker) (map[string]*descriptor, error) {
 
 	if err := w.walk(func(path string, info os.FileInfo, r io.Reader) error {
 		if info.IsDir() || !strings.HasPrefix(path, "refs") {
-			return nil
+			return errors.New("no descriptors found")
 		}
 
 		var d descriptor

image/image.go

@@ -53,12 +53,6 @@ func validate(w walker, refs []string, out *log.Logger) error {
 	if err != nil {
 		return err
 	}
-	if len(refs) == 0 && len(ds) == 0 {
-		// TODO(runcom): ugly, we'll need a better way and library
-		// to express log levels.
-		// see https://github.com/opencontainers/image-spec/issues/288
-		out.Print("WARNING: no descriptors found")
-	}
 
 	if len(refs) == 0 {
 		for ref := range ds {