Use streams in HowToSerialize

This converts the HowToSerialize trait to use a Stream[Char] when
defining how an annotation should be serialized.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

src/main/scala/firrtl/Emitter.scala

@@ -106,7 +106,7 @@ sealed trait EmittedAnnotation[T <: EmittedComponent] extends NoTargetAnnotation
 }
 sealed trait EmittedCircuitAnnotation[T <: EmittedCircuit] extends EmittedAnnotation[T] {
 
-  override def howToSerialize: Option[String] = Some(value.value)
+  override def howToSerialize: Option[Stream[Char]] = Some(new StringBuilder(value.value).toStream)
 
   override def filename(annotations: AnnotationSeq): File = {
     val sopts = view[StageOptions](annotations)
@@ -117,7 +117,7 @@ sealed trait EmittedCircuitAnnotation[T <: EmittedCircuit] extends EmittedAnnota
 }
 sealed trait EmittedModuleAnnotation[T <: EmittedModule] extends EmittedAnnotation[T] {
 
-  override def howToSerialize: Option[String] = Some(value.value)
+  override def howToSerialize: Option[Stream[Char]] = Some(new StringBuilder(value.value).toStream)
 
   override def howToResume(file: File): Option[AnnotationSeq] = None
 

src/main/scala/firrtl/options/StageAnnotations.scala

@@ -23,7 +23,7 @@ trait HowToSerialize { this: Annotation =>
 
   protected def suffix: Option[String]
 
-  def howToSerialize: Option[String]
+  def howToSerialize: Option[Stream[Char]]
 
   def howToResume(file: File): Option[AnnotationSeq]
 

src/main/scala/firrtl/options/phases/WriteOutputAnnotations.scala

@@ -6,7 +6,7 @@ import firrtl.AnnotationSeq
 import firrtl.annotations.{DeletedAnnotation, JsonProtocol}
 import firrtl.options.{HowToSerialize, Phase, StageOptions, Unserializable, Viewer}
 
-import java.io.PrintWriter
+import java.io.{BufferedWriter, FileWriter, PrintWriter}
 
 /** [[firrtl.options.Phase Phase]] that writes an [[AnnotationSeq]] to a file. A file is written if and only if a
   * [[StageOptions]] view has a non-empty [[StageOptions.annotationFileOut annotationFileOut]].
@@ -22,9 +22,9 @@ class WriteOutputAnnotations extends Phase {
       case a: HowToSerialize    =>
         val filename = a.filename(annotations)
         a.howToSerialize.map { str =>
-          val pw = new PrintWriter(filename)
-          pw.write(str)
-          pw.close()
+          val w = new BufferedWriter(new FileWriter(filename))
+          str.foreach( w.write(_) )
+          w.close()
         }
         a.howToResume(filename) match {
           case Some(a) => a

src/test/scala/firrtlTests/options/phases/WriteOutputAnnotationsSpec.scala

@@ -144,7 +144,7 @@ private object WriteOutputAnnotationsSpec {
 
     override protected def suffix: Option[String] = Some(".Serialize")
 
-    override def howToSerialize: Option[String] = Some(value)
+    override def howToSerialize: Option[Stream[Char]] = Some(new StringBuilder(value).toStream)
 
     override def howToResume(file: File): Option[AnnotationSeq] = Some(Seq(HowToFindMe(file.toString)))