1 files changed, 126 insertions, 0 deletions
diff --git a/src/library/scala/runtime/LambdaDeserializer.scala b/src/library/scala/runtime/LambdaDeserializer.scala
new file mode 100644
index 0000000000..25f41fd049
--- /dev/null
+++ b/src/library/scala/runtime/LambdaDeserializer.scala
@@ -0,0 +1,126 @@
+package scala.runtime
+
+import java.lang.invoke._
+
+/**
+ * This class is only intended to be called by synthetic `$deserializeLambda$` method that the Scala 2.12
+ * compiler will add to classes hosting lambdas.
+ *
+ * It is not intended to be consumed directly.
+ */
+object LambdaDeserializer {
+  /**
+   * Deserialize a lambda by calling `LambdaMetafactory.altMetafactory` to spin up a lambda class
+   * and instantiating this class with the captured arguments.
+   *
+   * A cache may be provided to ensure that subsequent deserialization of the same lambda expression
+   * is cheap, it amounts to a reflective call to the constructor of the previously created class.
+   * However, deserialization of the same lambda expression is not guaranteed to use the same class,
+   * concurrent deserialization of the same lambda expression may spin up more than one class.
+   *
+   * Assumptions:
+   *  - No additional marker interfaces are required beyond `{java.io,scala.}Serializable`. These are
+   *    not stored in `SerializedLambda`, so we can't reconstitute them.
+   *  - No additional bridge methods are passed to `altMetafactory`. Again, these are not stored.
+   *
+   * @param lookup      The factory for method handles. Must have access to the implementation method, the
+   *                    functional interface class, and `java.io.Serializable` or `scala.Serializable` as
+   *                    required.
+   * @param cache       A cache used to avoid spinning up a class for each deserialization of a given lambda. May be `null`
+   * @param serialized  The lambda to deserialize. Note that this is typically created by the `readResolve`
+   *                    member of the anonymous class created by `LambdaMetaFactory`.
+   * @return            An instance of the functional interface
+   */
+  def deserializeLambda(lookup: MethodHandles.Lookup, cache: java.util.Map[String, MethodHandle],
+                        targetMethodMap: java.util.Map[String, MethodHandle], serialized: SerializedLambda): AnyRef = {
+    assert(targetMethodMap != null)
+    def slashDot(name: String) = name.replaceAll("/", ".")
+    val loader = lookup.lookupClass().getClassLoader
+    val implClass = loader.loadClass(slashDot(serialized.getImplClass))
+    val key = LambdaDeserialize.nameAndDescriptorKey(serialized.getImplMethodName, serialized.getImplMethodSignature)
+
+    def makeCallSite: CallSite = {
+      import serialized._
+      def parseDescriptor(s: String) =
+        MethodType.fromMethodDescriptorString(s, loader)
+
+      val funcInterfaceSignature = parseDescriptor(getFunctionalInterfaceMethodSignature)
+      val instantiated = parseDescriptor(getInstantiatedMethodType)
+      val functionalInterfaceClass = loader.loadClass(slashDot(getFunctionalInterfaceClass))
+
+      val implMethodSig = parseDescriptor(getImplMethodSignature)
+      // Construct the invoked type from the impl method type. This is the type of a factory
+      // that will be generated by the meta-factory. It is a method type, with param types
+      // coming form the types of the captures, and return type being the functional interface.
+      val invokedType: MethodType = {
+        // 1. Add receiver for non-static impl methods
+        val withReceiver = getImplMethodKind match {
+          case MethodHandleInfo.REF_invokeStatic | MethodHandleInfo.REF_newInvokeSpecial =>
+            implMethodSig
+          case _ =>
+            implMethodSig.insertParameterTypes(0, implClass)
+        }
+        // 2. Remove lambda parameters, leaving only captures. Note: the receiver may be a lambda parameter,
+        //    such as in `Function<Object, String> s = Object::toString`
+        val lambdaArity = funcInterfaceSignature.parameterCount()
+        val from = withReceiver.parameterCount() - lambdaArity
+        val to = withReceiver.parameterCount()
+
+        // 3. Drop the lambda return type and replace with the functional interface.
+        withReceiver.dropParameterTypes(from, to).changeReturnType(functionalInterfaceClass)
+      }
+
+      // Lookup the implementation method
+      val implMethod: MethodHandle = try {
+        if (targetMethodMap.containsKey(key)) {
+          targetMethodMap.get(key)
+        } else {
+          throw new IllegalArgumentException("Illegal lambda deserialization")
+        }
+      } catch {
+        case e: ReflectiveOperationException => throw new IllegalArgumentException("Illegal lambda deserialization", e)
+      }
+
+      val flags: Int = LambdaMetafactory.FLAG_SERIALIZABLE | LambdaMetafactory.FLAG_MARKERS
+      val isScalaFunction = functionalInterfaceClass.getName.startsWith("scala.Function")
+      val markerInterface: Class[_] = loader.loadClass(if (isScalaFunction) ScalaSerializable else JavaIOSerializable)
+
+      LambdaMetafactory.altMetafactory(
+        lookup, getFunctionalInterfaceMethodName, invokedType,
+
+        /* samMethodType          = */ funcInterfaceSignature,
+        /* implMethod             = */ implMethod,
+        /* instantiatedMethodType = */ instantiated,
+        /* flags                  = */ flags.asInstanceOf[AnyRef],
+        /* markerInterfaceCount   = */ 1.asInstanceOf[AnyRef],
+        /* markerInterfaces[0]    = */ markerInterface,
+        /* bridgeCount            = */ 0.asInstanceOf[AnyRef]
+      )
+    }
+
+    val factory: MethodHandle = if (cache == null) {
+      makeCallSite.getTarget
+    } else cache.synchronized{
+      cache.get(key) match {
+        case null =>
+          val callSite = makeCallSite
+          val temp = callSite.getTarget
+          cache.put(key, temp)
+          temp
+        case target => target
+      }
+    }
+
+    val captures = Array.tabulate(serialized.getCapturedArgCount)(n => serialized.getCapturedArg(n))
+    factory.invokeWithArguments(captures: _*)
+  }
+
+  private val ScalaSerializable = "scala.Serializable"
+
+  private val JavaIOSerializable = {
+    // We could actually omit this marker interface as LambdaMetaFactory will add it if
+    // the FLAG_SERIALIZABLE is set and of the provided markers extend it. But the code
+    // is cleaner if we uniformly add a single marker, so I'm leaving it in place.
+    "java.io.Serializable"
+  }
+}