Merge pull request #73 from dwijnand/self-serialisable-attrkeys

Define OptJsonWriter & put it on AttributeKey

internal/util-collection/src/main/scala/sbt/internal/util/Attributes.scala

@@ -5,6 +5,7 @@ package sbt.internal.util
 
 import Types._
 import scala.reflect.Manifest
+import sbt.util.OptJsonWriter
 
 // T must be invariant to work properly.
 //  Because it is sealed and the only instances go through AttributeKey.apply,
@@ -39,6 +40,8 @@ sealed trait AttributeKey[T] {
 
   /** Identifies the relative importance of a key among other keys.*/
   def rank: Int
+
+  def optJsonWriter: OptJsonWriter[T]
 }
 private[sbt] abstract class SharedAttributeKey[T] extends AttributeKey[T] {
   override final def toString = label
@@ -50,32 +53,33 @@ private[sbt] abstract class SharedAttributeKey[T] extends AttributeKey[T] {
   final def isLocal: Boolean = false
 }
 object AttributeKey {
-  def apply[T](name: String)(implicit mf: Manifest[T]): AttributeKey[T] =
+  def apply[T](name: String)(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] =
     make(name, None, Nil, Int.MaxValue)
 
-  def apply[T](name: String, rank: Int)(implicit mf: Manifest[T]): AttributeKey[T] =
+  def apply[T](name: String, rank: Int)(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] =
     make(name, None, Nil, rank)
 
-  def apply[T](name: String, description: String)(implicit mf: Manifest[T]): AttributeKey[T] =
+  def apply[T](name: String, description: String)(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] =
     apply(name, description, Nil)
 
-  def apply[T](name: String, description: String, rank: Int)(implicit mf: Manifest[T]): AttributeKey[T] =
+  def apply[T](name: String, description: String, rank: Int)(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] =
     apply(name, description, Nil, rank)
 
-  def apply[T](name: String, description: String, extend: Seq[AttributeKey[_]])(implicit mf: Manifest[T]): AttributeKey[T] =
+  def apply[T](name: String, description: String, extend: Seq[AttributeKey[_]])(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] =
     apply(name, description, extend, Int.MaxValue)
 
-  def apply[T](name: String, description: String, extend: Seq[AttributeKey[_]], rank: Int)(implicit mf: Manifest[T]): AttributeKey[T] =
+  def apply[T](name: String, description: String, extend: Seq[AttributeKey[_]], rank: Int)(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] =
     make(name, Some(description), extend, rank)
 
-  private[this] def make[T](name: String, description0: Option[String], extend0: Seq[AttributeKey[_]], rank0: Int)(implicit mf: Manifest[T]): AttributeKey[T] = new SharedAttributeKey[T] {
+  private[this] def make[T](name: String, description0: Option[String], extend0: Seq[AttributeKey[_]], rank0: Int)(implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] = new SharedAttributeKey[T] {
     def manifest = mf
     val label = Util.hyphenToCamel(name)
     def description = description0
     def extend = extend0
     def rank = rank0
+    def optJsonWriter = ojw
   }
-  private[sbt] def local[T](implicit mf: Manifest[T]): AttributeKey[T] = new AttributeKey[T] {
+  private[sbt] def local[T](implicit mf: Manifest[T], ojw: OptJsonWriter[T]): AttributeKey[T] = new AttributeKey[T] {
     def manifest = mf
     def label = LocalLabel
     def description = None
@@ -83,6 +87,7 @@ object AttributeKey {
     override def toString = label
     def isLocal: Boolean = true
     def rank = Int.MaxValue
+    val optJsonWriter = ojw
   }
   private[sbt] final val LocalLabel = "$" + "local"
 }

internal/util-collection/src/main/scala/sbt/util/OptJsonWriter.scala

@@ -0,0 +1,22 @@
+package sbt.util
+
+import sjsonnew.JsonWriter
+
+sealed trait OptJsonWriter[A]
+final case class NoJsonWriter[A]() extends OptJsonWriter[A]
+final case class SomeJsonWriter[A](value: JsonWriter[A]) extends OptJsonWriter[A]
+
+trait OptJsonWriter0 {
+  implicit def fallback[A]: NoJsonWriter[A] = NoJsonWriter()
+}
+object OptJsonWriter extends OptJsonWriter0 {
+  implicit def lift[A](implicit z: JsonWriter[A]): SomeJsonWriter[A] = SomeJsonWriter(z)
+
+  trait StrictMode0 {
+    implicit def conflictingFallback1[A]: NoJsonWriter[A] = NoJsonWriter()
+    implicit def conflictingFallback2[A]: NoJsonWriter[A] = NoJsonWriter()
+  }
+  object StrictMode extends StrictMode0 {
+    implicit def lift[A](implicit z: JsonWriter[A]): SomeJsonWriter[A] = SomeJsonWriter(z)
+  }
+}