Deprecated the @serializable annotation, introd...

Deprecated the @serializable annotation, introduce a new trait
"scala.Serializable" which has to be extended instead (cross-platform).

Known issues:
 - Companion objects of serializable classes (including case classes) are automatically made serializable. However, they don't extend "Serializable" statically because of the known difficulty (should be done before typing, but hard).
 - Writing "case class C() extends Serializable" gives "error: trait Serializable is inherited twice"
 - Functions are serializable, but don't extend Serializable dynamically (could be fixed by making FunctionN Serializable - shouldn't we?)

Note that @SerialVersionUID continues to be an annotation; it generates
a static field, which is not possible otherwise in scala.

Review by dragos, extempore.

Question to dragos: in JavaPlatform.isMaybeBoxed, why is there a test
for "JavaSerializableClass"? Is that correct?

1 files changed, 11 insertions, 12 deletions

diff --git a/src/library/scala/collection/immutable/Set.scala b/src/library/scala/collection/immutable/Set.scala
index 30f0d86139..ffd41752a4 100644
--- a/src/library/scala/collection/immutable/Set.scala
+++ b/src/library/scala/collection/immutable/Set.scala
@@ -43,8 +43,7 @@ object Set extends ImmutableSetFactory[Set] {
   private val hashSeed = "Set".hashCode
 
   /** An optimized representation for immutable empty sets */
-  @serializable
-  private object EmptySet extends Set[Any] {
+  private object EmptySet extends Set[Any] with Serializable {
     override def size: Int = 0
     def contains(elem: Any): Boolean = false
     def + (elem: Any): Set[Any] = new Set1(elem)
@@ -53,8 +52,8 @@ object Set extends ImmutableSetFactory[Set] {
     override def foreach[U](f: Any =>  U): Unit = {}
   }
 
-  @serializable @deprecated("use `Set.empty' instead")
-  class EmptySet[A] extends Set[A] {
+  @deprecated("use `Set.empty' instead")
+  class EmptySet[A] extends Set[A] with Serializable {
     override def size: Int = 0
     def contains(elem: A): Boolean = false
     def + (elem: A): Set[A] = new Set1(elem)
@@ -64,8 +63,8 @@ object Set extends ImmutableSetFactory[Set] {
   }
 
   /** An optimized representation for immutable sets of size 1 */
-  @serializable @SerialVersionUID(1233385750652442003L)
-  class Set1[A](elem1: A) extends Set[A] {
+  @SerialVersionUID(1233385750652442003L)
+  class Set1[A](elem1: A) extends Set[A] with Serializable {
     override def size: Int = 1
     def contains(elem: A): Boolean =
       elem == elem1
@@ -83,8 +82,8 @@ object Set extends ImmutableSetFactory[Set] {
   }
 
   /** An optimized representation for immutable sets of size 2 */
-  @serializable @SerialVersionUID(-6443011234944830092L)
-  class Set2[A](elem1: A, elem2: A) extends Set[A] {
+  @SerialVersionUID(-6443011234944830092L)
+  class Set2[A](elem1: A, elem2: A) extends Set[A] with Serializable {
     override def size: Int = 2
     def contains(elem: A): Boolean =
       elem == elem1 || elem == elem2
@@ -103,8 +102,8 @@ object Set extends ImmutableSetFactory[Set] {
   }
 
   /** An optimized representation for immutable sets of size 3 */
-  @serializable @SerialVersionUID(-3590273538119220064L)
-  class Set3[A](elem1: A, elem2: A, elem3: A) extends Set[A] {
+  @SerialVersionUID(-3590273538119220064L)
+  class Set3[A](elem1: A, elem2: A, elem3: A) extends Set[A] with Serializable {
     override def size: Int = 3
     def contains(elem: A): Boolean =
       elem == elem1 || elem == elem2 || elem == elem3
@@ -124,8 +123,8 @@ object Set extends ImmutableSetFactory[Set] {
   }
 
   /** An optimized representation for immutable sets of size 4 */
-  @serializable @SerialVersionUID(-3622399588156184395L)
-  class Set4[A](elem1: A, elem2: A, elem3: A, elem4: A) extends Set[A] {
+  @SerialVersionUID(-3622399588156184395L)
+  class Set4[A](elem1: A, elem2: A, elem3: A, elem4: A) extends Set[A] with Serializable {
     override def size: Int = 4
     def contains(elem: A): Boolean =
       elem == elem1 || elem == elem2 || elem == elem3 || elem == elem4