1 files changed, 63 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..ac2aab01dc
--- /dev/null
+++ b/test/junit/scala/tools/nsc/backend/jvm/IndyLambdaTest.scala
@@ -0,0 +1,63 @@
+package scala.tools.nsc.backend.jvm
+
+import org.junit.Assert._
+import org.junit.Test
+
+import scala.collection.JavaConverters._
+import scala.tools.asm.Handle
+import scala.tools.asm.tree.InvokeDynamicInsnNode
+import scala.tools.testing.BytecodeTesting
+
+class IndyLambdaTest extends BytecodeTesting {
+  import compiler._
+
+  @Test def boxingBridgeMethodUsedSelectively(): Unit = {
+    def implMethodDescriptorFor(code: String): String = {
+      val method = compileAsmMethods(s"""def f = $code """).find(_.name == "f").get
+      val x = method.instructions.iterator.asScala.toList
+      x.flatMap {
+        case insn : InvokeDynamicInsnNode => insn.bsmArgs.collect { case h : Handle => h.getDesc }
+        case _ => Nil
+      }.head
+    }
+
+    val obj = "Ljava/lang/Object;"
+    val str = "Ljava/lang/String;"
+
+    // unspecialized functions that have a primitive in parameter or return position
+    // give rise to a "boxing bridge" method (which has the suffix `$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(s"($obj)$obj", implMethodDescriptorFor("(x: Int) => new Object"))
+    assertEquals(s"($obj)$obj", 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(s"($str)$str", implMethodDescriptorFor("(x: String) => x"))
+
+    // 2b. Testing 2a. in combination with 1.
+    assertEquals(s"($obj)$str", implMethodDescriptorFor("(x: Int) => \"\""))
+    assertEquals(s"($str)$obj", 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"))
+
+    // non-builtin sams are like specialized functions
+    compileToBytes("class VC(private val i: Int) extends AnyVal; trait FunVC { def apply(a: VC): VC }")
+    assertEquals("(I)I", implMethodDescriptorFor("((x: VC) => x): FunVC"))
+
+    compileToBytes("trait Fun1[T, U] { def apply(a: T): U }")
+    assertEquals(s"($obj)$str", implMethodDescriptorFor("(x => x.toString): Fun1[Int, String]"))
+    assertEquals(s"($obj)$obj", implMethodDescriptorFor("(x => println(x)): Fun1[Int, Unit]"))
+    assertEquals(s"($obj)$str", implMethodDescriptorFor("((x: VC) => \"\") : Fun1[VC, String]"))
+    assertEquals(s"($str)$obj", implMethodDescriptorFor("((x: String) => new VC(0)) : Fun1[String, VC]"))
+
+    compileToBytes("trait Coll[A, Repr] extends Any")
+    compileToBytes("final class ofInt(val repr: Array[Int]) extends AnyVal with Coll[Int, Array[Int]]")
+
+    assertEquals(s"([I)$obj", implMethodDescriptorFor("((xs: Array[Int]) => new ofInt(xs)): Array[Int] => Coll[Int, Array[Int]]"))
+  }
+}