1 files changed, 55 insertions, 0 deletions
diff --git a/test/junit/scala/tools/nsc/backend/jvm/IndyLambdaTest.scala b/test/junit/scala/tools/nsc/backend/jvm/IndyLambdaTest.scala
new file mode 100644
index 0000000000..f5f93fef5c
--- /dev/null
+++ b/test/junit/scala/tools/nsc/backend/jvm/IndyLambdaTest.scala
@@ -0,0 +1,55 @@
+package scala.tools.nsc.backend.jvm
+
+import org.junit.Assert._
+import org.junit.{Assert, Test}
+
+import scala.tools.asm.{Handle, Opcodes}
+import scala.tools.asm.tree.InvokeDynamicInsnNode
+import scala.tools.nsc.backend.jvm.AsmUtils._
+import scala.tools.nsc.backend.jvm.CodeGenTools._
+import scala.tools.testing.ClearAfterClass
+import scala.collection.JavaConverters._
+
+object IndyLambdaTest extends ClearAfterClass.Clearable {
+  var compiler = newCompiler(extraArgs = "-Ybackend:GenBCode")
+
+  def clear(): Unit = {
+    compiler = null
+  }
+}
+
+class IndyLambdaTest extends ClearAfterClass {
+  ClearAfterClass.stateToClear = IndyLambdaTest
+  val compiler = IndyLambdaTest.compiler
+
+  @Test def boxingBridgeMethodUsedSelectively(): Unit = {
+    def implMethodDescriptorFor(code: String): String = {
+      val method = compileMethods(compiler)(s"""def f = $code """).find(_.name == "f").get
+      val x = method.instructions.iterator.asScala.toList
+      x.flatMap {
+        case insn : InvokeDynamicInsnNode => insn.bsmArgs.collect { case h : Handle => h.getDesc }
+        case _ => Nil
+      }.head
+    }
+    // unspecialized functions that have a primitive in parameter or return position
+    // give rise to a "boxing bridge" method (which has the suffix `$adapted`).
+    // This is because Scala's unboxing of null values gives zero, whereas Java's throw a NPE.
+
+    // 1. Here we show that we are calling the boxing bridge (the lambda bodies here are compiled into
+    //    methods of `(I)Ljava/lang/Object;` / `(I)Ljava/lang/Object;` respectively.)
+    assertEquals("(Ljava/lang/Object;)Ljava/lang/Object;", implMethodDescriptorFor("(x: Int) => new Object"))
+    assertEquals("(Ljava/lang/Object;)Ljava/lang/Object;", implMethodDescriptorFor("(x: Object) => 0"))
+
+    // 2a. We don't need such adaptations for parameters or return values with types that differ
+    // from Object due to other generic substitution, LambdaMetafactory will downcast the arguments.
+    assertEquals("(Ljava/lang/String;)Ljava/lang/String;", implMethodDescriptorFor("(x: String) => x"))
+
+    // 2b. Testing 2a. in combination with 1.
+    assertEquals("(Ljava/lang/Object;)Ljava/lang/String;", implMethodDescriptorFor("(x: Int) => \"\""))
+    assertEquals("(Ljava/lang/String;)Ljava/lang/Object;", implMethodDescriptorFor("(x: String) => 0"))
+
+    // 3. Specialized functions, don't need any of this as they implement a method like `apply$mcII$sp`,
+    //    and the (un)boxing is handled in the base class in code emitted by scalac.
+    assertEquals("(I)I", implMethodDescriptorFor("(x: Int) => x"))
+  }
+}