SD-120 Non FunctionN lambdas should not be universally serializable

Instead, we follow the example set by javac, and predicate serializability
of bot anon-class and invokedynamic-based lambdas on whether or not the
SAM type extends java.io.Serializable.

Fixes https://github.com/scala/scala-dev/issues/120

1 files changed, 4 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Delambdafy.scala b/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
index 804bcddb7b..5e5b9fd250 100644
--- a/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
+++ b/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
@@ -28,7 +28,7 @@ abstract class Delambdafy extends Transform with TypingTransformers with ast.Tre
   /** the following two members override abstract members in Transform */
   val phaseName: String = "delambdafy"
 
-  final case class LambdaMetaFactoryCapable(target: Symbol, arity: Int, functionalInterface: Symbol, sam: Symbol)
+  final case class LambdaMetaFactoryCapable(target: Symbol, arity: Int, functionalInterface: Symbol, sam: Symbol, isSerializable: Boolean, addScalaSerializableMarker: Boolean)
 
   /**
     * Get the symbol of the target lifted lambda body method from a function. I.e. if
@@ -95,6 +95,8 @@ abstract class Delambdafy extends Transform with TypingTransformers with ast.Tre
 
       // no need for adaptation when the implemented sam is of a specialized built-in function type
       val lambdaTarget = if (isSpecialized) target else createBoxingBridgeMethodIfNeeded(fun, target, functionalInterface, sam)
+      val isSerializable = samUserDefined == NoSymbol || samUserDefined.owner.isNonBottomSubClass(definitions.JavaSerializableClass)
+      val addScalaSerializableMarker = samUserDefined == NoSymbol
 
       // The backend needs to know the target of the lambda and the functional interface in order
       // to emit the invokedynamic instruction. We pass this information as tree attachment.
@@ -102,7 +104,7 @@ abstract class Delambdafy extends Transform with TypingTransformers with ast.Tre
       // see https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/LambdaMetafactory.html
       //   instantiatedMethodType is derived from lambdaTarget's signature
       //   samMethodType is derived from samOf(functionalInterface)'s signature
-      apply.updateAttachment(LambdaMetaFactoryCapable(lambdaTarget, fun.vparams.length, functionalInterface, sam))
+      apply.updateAttachment(LambdaMetaFactoryCapable(lambdaTarget, fun.vparams.length, functionalInterface, sam, isSerializable, addScalaSerializableMarker))
 
       apply
     }