1 files changed, 25 insertions, 7 deletions
diff --git a/src/main/scala/firrtl/annotations/JsonProtocol.scala b/src/main/scala/firrtl/annotations/JsonProtocol.scala
index b09155d8..c3853650 100644
--- a/src/main/scala/firrtl/annotations/JsonProtocol.scala
+++ b/src/main/scala/firrtl/annotations/JsonProtocol.scala
@@ -9,6 +9,12 @@ import org.json4s.native.JsonMethods._
 import org.json4s.native.Serialization
 import org.json4s.native.Serialization.{read, writePretty}
 
+trait HasSerializationHints {
+  // For serialization of complicated constructor arguments, let the annotation
+  // writer specify additional type hints for relevant classes that might be
+  // contained within
+  def typeHints: Seq[Class[_]]
+}
 
 object JsonProtocol {
   class TransformClassSerializer extends CustomSerializer[Class[_ <: Transform]](format => (
@@ -74,7 +80,7 @@ object JsonProtocol {
   ))
 
   /** Construct Json formatter for annotations */
-  def jsonFormat(tags: Seq[Class[_ <: Annotation]]) = {
+  def jsonFormat(tags: Seq[Class[_]]) = {
     Serialization.formats(FullTypeHints(tags.toList)).withTypeHintFieldName("class") +
       new TransformClassSerializer + new NamedSerializer + new CircuitNameSerializer +
       new ModuleNameSerializer + new ComponentNameSerializer + new TargetSerializer +
@@ -87,7 +93,11 @@ object JsonProtocol {
   def serialize(annos: Seq[Annotation]): String = serializeTry(annos).get
 
   def serializeTry(annos: Seq[Annotation]): Try[String] = {
-    val tags = annos.map(_.getClass).distinct
+    val tags = annos.flatMap({
+      case anno: HasSerializationHints => anno.getClass +: anno.typeHints
+      case anno => Seq(anno.getClass)
+    }).distinct
+
     implicit val formats = jsonFormat(tags)
     Try(writePretty(annos))
   }
@@ -101,12 +111,20 @@ object JsonProtocol {
       case x => throw new InvalidAnnotationJSONException(
         s"Annotations must be serialized as a JArray, got ${x.getClass.getSimpleName} instead!")
     }
-    // Gather classes so we can deserialize arbitrary Annotations
-    val classes = annos.map({
-      case JObject(("class", JString(c)) :: tail) => c
-      case obj => throw new InvalidAnnotationJSONException(s"Expected field 'class' not found! $obj")
+    // Recursively gather typeHints by pulling the "class" field from JObjects
+    // Json4s should emit this as the first field in all serialized classes
+    // Setting requireClassField mandates that all JObjects must provide a typeHint,
+    // this used on the first invocation to check all annotations do so
+    def findTypeHints(classInst: Seq[JValue], requireClassField: Boolean = false): Seq[String] = classInst.flatMap({
+      case JObject(("class", JString(name)) :: fields) => name +: findTypeHints(fields.map(_._2))
+      case obj: JObject if requireClassField => throw new InvalidAnnotationJSONException(s"Expected field 'class' not found! $obj")
+      case JObject(fields) => findTypeHints(fields.map(_._2))
+      case JArray(arr) => findTypeHints(arr)
+      case oJValue => Seq()
     }).distinct
-    val loaded = classes.map(Class.forName(_).asInstanceOf[Class[_ <: Annotation]])
+
+    val classes = findTypeHints(annos, true)
+    val loaded = classes.map(Class.forName(_))
     implicit val formats = jsonFormat(loaded)
     read[List[Annotation]](in)
   }).recoverWith {