Fix CCE in code generated by Array.apply[T] optimization

Author: retronym

src/compiler/scala/tools/nsc/transform/CleanUp.scala

@@ -486,21 +486,26 @@ abstract class CleanUp extends Statics with Transform with ast.TreeDSL {
       // with just `ArrayValue(...).$asInstanceOf[...]`
       //
       // See scala/bug#6611; we must *only* do this for literal vararg arrays.
-      case Apply(appMeth, Apply(wrapRefArrayMeth, (arg @ StripCast(ArrayValue(_, _))) :: Nil) :: _ :: Nil)
-      if wrapRefArrayMeth.symbol == currentRun.runDefinitions.Predef_wrapRefArray && appMeth.symbol == ArrayModule_genericApply =>
-        super.transform(arg)
-      case Apply(appMeth, (ap1 @ Apply(wrapRefArrayMeth, (arg @ StripCast(ArrayValue(elemtpt, elems))) :: Nil)) :: classTagEvidence :: Nil)
-      if wrapRefArrayMeth.symbol == currentRun.runDefinitions.Predef_genericWrapRefArray && appMeth.symbol == ArrayModule_genericApply &&
+      case Apply(appMeth, Apply(wrapRefArrayMeth, (arg @ StripCast(ArrayValue(elemtpt, elems))) :: Nil) :: classTagEvidence :: Nil)
+      if (wrapRefArrayMeth.symbol == currentRun.runDefinitions.Predef_genericWrapRefArray || wrapRefArrayMeth.symbol ==  currentRun.runDefinitions.Predef_wrapRefArray) && appMeth.symbol == ArrayModule_genericApply &&
          !elemtpt.tpe.typeSymbol.isBottomClass =>
-        val arr = localTyper.typedPos(tree.pos)(gen.mkMethodCall(classTagEvidence, definitions.ClassTagClass.info.decl(nme.newArray), Nil, Literal(Constant(elems.size)) :: Nil))
-        localTyper.typedPos(tree.pos) {
-          gen.evalOnce(arr, currentOwner, unit) { arr =>
-            val stats = mutable.ListBuffer[Tree]()
-            foreachWithIndex(elems) { (elem, i) =>
-              stats += gen.mkMethodCall(gen.mkCast(arr(), definitions.arrayType(elemtpt.tpe)), definitions.Array_update, Nil, Literal(Constant(i)) :: elem :: Nil)
+        classTagEvidence.attachments.get[analyzer.MacroExpansionAttachment] match {
+          case Some(att) if att.expandee.symbol.name == nme.materializeClassTag && tree.isInstanceOf[ApplyToImplicitArgs] =>
+            super.transform(arg)
+          case None                                                    =>
+            localTyper.typedPos(tree.pos) {
+              gen.evalOnce(classTagEvidence, currentOwner, unit) { ev =>
+                val arr = localTyper.typedPos(tree.pos)(gen.mkMethodCall(classTagEvidence, definitions.ClassTagClass.info.decl(nme.newArray), Nil, Literal(Constant(elems.size)) :: Nil))
+                gen.evalOnce(arr, currentOwner, unit) { arr =>
+                  val stats = mutable.ListBuffer[Tree]()
+                  foreachWithIndex(elems) { (elem, i) =>
+                    stats += gen.mkMethodCall(gen.mkAttributedRef(definitions.ScalaRunTimeModule), currentRun.runDefinitions.arrayUpdateMethod,
+                                              Nil, arr() :: Literal(Constant(i)) :: elem :: Nil)
+                  }
+                  super.transform(Block(stats.toList, arr()))
+                }
+              }
             }
-            Block(stats.toList, arr())
-          }
         }
       case Apply(appMeth, elem0 :: Apply(wrapArrayMeth, (rest @ ArrayValue(elemtpt, _)) :: Nil) :: Nil)
       if wrapArrayMeth.symbol == Predef_wrapArray(elemtpt.tpe) && appMeth.symbol == ArrayModule_apply(elemtpt.tpe) =>

test/files/instrumented/t11882a.check

@@ -3,3 +3,5 @@ Method call statistics:
     1  OptimusSeq$.unsafeFromAnyArray1([Ljava/lang/Object;)LOptimusSeq;
     1  Test$.doIt$1()LOptimusSeq;
     1  scala/reflect/ClassTag$.AnyRef()Lscala/reflect/ClassTag;
+    1  scala/reflect/ManifestFactory$ObjectManifest.newArray(I)Ljava/lang/Object;
+    1  scala/reflect/ManifestFactory$ObjectManifest.newArray(I)[Ljava/lang/Object;

test/files/instrumented/t11882c.check

@@ -0,0 +1,2 @@
+Method call statistics:
+    1  Test$.doIt$1()[Ljava/lang/String;

test/files/instrumented/t11882c.scala

@@ -0,0 +1,14 @@
+import scala.reflect.ClassTag
+import scala.tools.partest.instrumented._
+import scala.tools.partest.instrumented.Instrumentation._
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    def doIt = Array[String](null, null, null, null)
+    doIt
+    startProfiling()
+    doIt
+    stopProfiling()
+    printStatistics()
+  }
+}

test/files/run/t11882-class-cast.scala

@@ -0,0 +1,8 @@
+object Test {
+  def test[T <: AnyRef: reflect.ClassTag](t: T) = Array(t)
+  def main(args: Array[String]): Unit = {
+    // was: java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;
+    val x: Array[String] = test[String]("x")
+    assert(x(0) == "x")
+  }
+}