Add serialization support for LoadMemoryFileType in LoadMemoryAnnotation (#1056)

* Add serialization support for LoadMemoryFileType in LoadMemoryAnnotation
Add custom LoadMemoryFileTypeSerializer.
Add test to verify LoadMemoryAnnotation can be correctly serialized/deserialized.

* Simplify and focus LoadMemoryAnnotation serialization/deserialization.
Respond to comments on earlier implementations.

* Add type FileType definition for current chisel3 code.

2 files changed, 24 insertions, 8 deletions

diff --git a/src/main/scala/firrtl/annotations/JsonProtocol.scala b/src/main/scala/firrtl/annotations/JsonProtocol.scala
index acb2d957..ea29f090 100644
--- a/src/main/scala/firrtl/annotations/JsonProtocol.scala
+++ b/src/main/scala/firrtl/annotations/JsonProtocol.scala
@@ -45,7 +45,10 @@ object JsonProtocol {
       }},
     { case x: Transform => JString(x.getClass.getName) }
   ))
-
+  class LoadMemoryFileTypeSerializer extends CustomSerializer[MemoryLoadFileType](format => (
+    { case JString(s) => MemoryLoadFileType.deserialize(s) },
+    { case named: MemoryLoadFileType => JString(named.serialize) }
+  ))
 
   class TargetSerializer extends CustomSerializer[Target](format => (
     { case JString(s) => Target.deserialize(s) },
@@ -78,7 +81,8 @@ object JsonProtocol {
       new TransformClassSerializer + new NamedSerializer + new CircuitNameSerializer +
       new ModuleNameSerializer + new ComponentNameSerializer + new TargetSerializer +
       new GenericTargetSerializer + new CircuitTargetSerializer + new ModuleTargetSerializer +
-      new InstanceTargetSerializer + new ReferenceTargetSerializer + new TransformSerializer
+      new InstanceTargetSerializer + new ReferenceTargetSerializer + new TransformSerializer  +
+      new LoadMemoryFileTypeSerializer
   }
 
   /** Serialize annotations to a String for emission */
diff --git a/src/main/scala/firrtl/annotations/LoadMemoryAnnotation.scala b/src/main/scala/firrtl/annotations/LoadMemoryAnnotation.scala
index c5dae954..c52bf5f6 100644
--- a/src/main/scala/firrtl/annotations/LoadMemoryAnnotation.scala
+++ b/src/main/scala/firrtl/annotations/LoadMemoryAnnotation.scala
@@ -4,13 +4,25 @@ package firrtl.annotations
 
 import java.io.File
 
-/** Enumeration of the two types of `readmem` statements available in Verilog.
+import firrtl.FIRRTLException
+
+/** Representation of the two types of `readmem` statements available in Verilog.
   */
-object MemoryLoadFileType extends Enumeration {
-  type FileType = Value
+sealed abstract class MemoryLoadFileType(val value: String) {
+  def serialize: String = value
+}
 
-  val Hex:    Value = Value("h")
-  val Binary: Value = Value("b")
+object MemoryLoadFileType {
+  // purely for backwards compatibility with chisel3's ChiselLoadMemoryAnnotation
+  type FileType = MemoryLoadFileType
+
+  case object Hex extends MemoryLoadFileType("h")
+  case object Binary extends MemoryLoadFileType("b")
+  def deserialize(s: String): MemoryLoadFileType = s match {
+    case "h" => MemoryLoadFileType.Hex
+    case "b" => MemoryLoadFileType.Binary
+    case _ => throw new FIRRTLException(s"Unrecognized MemoryLoadFileType: $s")
+  }
 }
 
 /** Firrtl implementation for load memory
@@ -21,7 +33,7 @@ object MemoryLoadFileType extends Enumeration {
 case class LoadMemoryAnnotation(
   target: ComponentName,
   fileName: String,
-  hexOrBinary: MemoryLoadFileType.FileType = MemoryLoadFileType.Hex,
+  hexOrBinary: MemoryLoadFileType = MemoryLoadFileType.Hex,
   originalMemoryNameOpt: Option[String] = None
 ) extends SingleTargetAnnotation[Named] {