Merge pull request scala#4139 from retronym/ticket/7965

SI-7965 Support calls to MethodHandle.{invoke,invokeExact}

Author: adriaanm

spec/06-expressions.md

@@ -410,6 +410,19 @@ The final result of the transformation is a block of the form
 }
 ```
 
+### Signature Polymorphic Methods
+
+For invocations of signature polymorphic methods of the target platform `$f$($e_1 , \ldots , e_m$)`,
+the invoked function has a different method type `($p_1$:$T_1 , \ldots , p_n$:$T_n$)$U$` at each call
+site. The parameter types `$T_ , \ldots , T_n$` are the types of the argument expressions
+`$e_1 , \ldots , e_m$` and `$U$` is the expected type at the call site. If the expected type is
+undefined then `$U$` is `scala.AnyRef`. The parameter names `$p_1 , \ldots , p_n$` are fresh.
+
+###### Note
+
+On the Java platform version 7 and later, the methods `invoke` and `invokeExact` in class
+`java.lang.invoke.MethodHandle` are signature polymorphic.
+
 ## Method Values
 
 ```ebnf

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -3281,6 +3281,22 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           }
           handleOverloaded
 
+        case _ if isPolymorphicSignature(fun.symbol) =>
+          // Mimic's Java's treatment of polymorphic signatures as described in
+          // https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.12.3
+          //
+          // One can think of these methods as being infinitely overloaded. We create
+          // a ficticious new cloned method symbol for each call site that takes on a signature
+          // governed by a) the argument types and b) the expected type
+          val args1 = typedArgs(args, forArgMode(fun, mode))
+          val pts = args1.map(_.tpe.deconst)
+          val clone = fun.symbol.cloneSymbol
+          val cloneParams = pts map (pt => clone.newValueParameter(currentUnit.freshTermName()).setInfo(pt))
+          val resultType = if (isFullyDefined(pt)) pt else ObjectTpe
+          clone.modifyInfo(mt => copyMethodType(mt, cloneParams, resultType))
+          val fun1 = fun.setSymbol(clone).setType(clone.info)
+          doTypedApply(tree, fun1, args1, mode, resultType).setType(resultType)
+
         case mt @ MethodType(params, _) =>
           val paramTypes = mt.paramTypes
           // repeat vararg as often as needed, remove by-name

src/reflect/scala/reflect/internal/Definitions.scala

@@ -514,6 +514,8 @@ trait Definitions extends api.StandardDefinitions {
     lazy val ScalaSignatureAnnotation = requiredClass[scala.reflect.ScalaSignature]
     lazy val ScalaLongSignatureAnnotation = requiredClass[scala.reflect.ScalaLongSignature]
 
+    lazy val MethodHandle = getClassIfDefined("java.lang.invoke.MethodHandle")
+
     // Option classes
     lazy val OptionClass: ClassSymbol   = requiredClass[Option[_]]
     lazy val OptionModule: ModuleSymbol = requiredModule[scala.Option.type]
@@ -1508,6 +1510,9 @@ trait Definitions extends api.StandardDefinitions {
 
       lazy val PartialManifestClass  = getTypeMember(ReflectPackage, tpnme.ClassManifest)
       lazy val ManifestSymbols = Set[Symbol](PartialManifestClass, FullManifestClass, OptManifestClass)
+
+      def isPolymorphicSignature(sym: Symbol) = PolySigMethods(sym)
+      private lazy val PolySigMethods: Set[Symbol] = Set[Symbol](MethodHandle.info.decl(sn.Invoke), MethodHandle.info.decl(sn.InvokeExact)).filter(_.exists)
     }
   }
 }

src/reflect/scala/reflect/internal/StdNames.scala

@@ -1147,6 +1147,7 @@ trait StdNames {
     final val GetClassLoader: TermName   = newTermName("getClassLoader")
     final val GetMethod: TermName        = newTermName("getMethod")
     final val Invoke: TermName           = newTermName("invoke")
+    final val InvokeExact: TermName      = newTermName("invokeExact")
 
     val Boxed = immutable.Map[TypeName, TypeName](
       tpnme.Boolean -> BoxedBoolean,

src/reflect/scala/reflect/runtime/JavaUniverseForce.scala

@@ -310,6 +310,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     definitions.QuasiquoteClass_api_unapply
     definitions.ScalaSignatureAnnotation
     definitions.ScalaLongSignatureAnnotation
+    definitions.MethodHandle
     definitions.OptionClass
     definitions.OptionModule
     definitions.SomeClass

test/files/run/t7965.scala

@@ -0,0 +1,54 @@
+// Test that scala doesn't apply boxing or varargs conversions to the
+// @PolymorphicSignature magical methods, MethodHandle#{invoke, invokeExact}
+object Test {
+  val code = """
+
+object O {
+  private def foo = "foo"
+  private def bar(x: Int): Int = -x
+  private def baz(x: Box): Unit = x.a = "present"
+  val lookup = java.lang.invoke.MethodHandles.lookup
+}
+
+import java.lang.invoke._
+class Box(var a: Any)
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    def lookup(name: String, params: Array[Class[_]], ret: Class[_]) = {
+      val mt = MethodType.methodType(ret, params)
+      O.lookup.findVirtual(O.getClass, name, mt)
+    }
+    val fooResult = (lookup("foo", Array(), classOf[String]).invokeExact(O): Int)
+    assert(fooResult == "foo")
+
+    val barResult = (lookup("bar", Array(classOf[Int]), classOf[Int]).invokeExact(O, 42): Int)
+    assert(barResult == -42)
+
+    val box = new Box(null)
+    (lookup("baz", Array(classOf[Box]), Void.TYPE).invokeExact(O, box) : Unit)
+    assert(box.a == "present")
+
+    // Note: Application in statement position in a block in Java also infers return type of Unit,
+    // but we don't support that, ascribe the type to Unit as above.
+    // as done in Java.
+    // lookup("baz", Array(classOf[Box]), Void.TYPE).invokeExact(O, box)
+    ()
+  }
+}
+
+"""
+  def main(args: Array[String]): Unit = {
+    if (util.Properties.isJavaAtLeast("1.7")) test()
+  }
+
+  def test() {
+    import scala.reflect.runtime._
+    import scala.tools.reflect.ToolBox
+
+    val m = currentMirror
+    val tb = m.mkToolBox()
+    import tb._
+    eval(parse(code))
+  }
+}