SI-9702 Fix backend crash with classOf[T] annotation argument

This commit fixes various issues with classOf literals and Java
annotations.

  - Ensure that a Type within a ConstantType (i.e., a classOf literal)
    is erased, so `classOf[List[Int]]` becomes `classOf[List]`.
  - Ensure that no non-erased types are passed to `typeToBType` in the
    backend. This happens for Java annotations: the annotation type and
    `classOf` annotation arguments are not erased, the annotationInfos
    of a symbol are not touched in the compiler pipeline.
  - If T is an alias to a value class, ensure that `classOf[T]` erases
    to the value class by calling `dealiasWiden` in erasure.

Author: lrytz

src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala

@@ -469,13 +469,10 @@ abstract class BCodeBodyBuilder extends BCodeSkelBuilder {
         case NullTag    => emit(asm.Opcodes.ACONST_NULL)
 
         case ClazzTag   =>
-          val toPush: BType = {
-            typeToBType(const.typeValue) match {
-              case kind: PrimitiveBType => boxedClassOfPrimitive(kind)
-              case kind => kind
-            }
-          }
-          mnode.visitLdcInsn(toPush.toASMType)
+          val tp = typeToBType(const.typeValue)
+          // classOf[Int] is transformed to Integer.TYPE by CleanUp
+          assert(!tp.isPrimitive, s"expected class type in classOf[T], found primitive type $tp")
+          mnode.visitLdcInsn(tp.toASMType)
 
         case EnumTag   =>
           val sym       = const.symbolValue

src/compiler/scala/tools/nsc/backend/jvm/BCodeHelpers.scala

@@ -595,17 +595,6 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
       val classSym = if (sym.isJavaDefined && sym.isModuleClass) exitingPickler(sym.linkedClassOfClass) else sym
       classBTypeFromSymbol(classSym).internalName
     }
-
-    /**
-     * The jvm descriptor of a type.
-     */
-    final def descriptor(t: Type): String = typeToBType(t).descriptor
-
-    /**
-     * The jvm descriptor for a symbol.
-     */
-    final def descriptor(sym: Symbol): String = classBTypeFromSymbol(sym).descriptor
-
   } // end of trait BCInnerClassGen
 
   trait BCAnnotGen extends BCInnerClassGen {
@@ -614,6 +603,35 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
     private lazy val AnnotationRetentionPolicyClassValue   = AnnotationRetentionPolicyModule.tpe.member(TermName("CLASS"))
     private lazy val AnnotationRetentionPolicyRuntimeValue = AnnotationRetentionPolicyModule.tpe.member(TermName("RUNTIME"))
 
+    /**
+     * Annotations are not processed by the compilation pipeline like ordinary trees. Instead, the
+     * typer extracts them into [[AnnotationInfo]] objects which are attached to the corresponding
+     * symbol (sym.annotations) or type (as an AnnotatedType, eliminated by erasure).
+     *
+     * For Scala annotations this is OK: they are stored in the pickle and ignored by the backend.
+     * Java annoations on the other hand are additionally emitted to the classfile in Java's format.
+     *
+     * This means that [[Type]] instances within an AnnotaionInfo reach the backend non-erased. Examples:
+     *   - @(javax.annotation.Resource @annotation.meta.getter) val x = 0
+     *     Here, annotationInfo.atp is an AnnotatedType.
+     *   - @SomeAnnotation[T] val x = 0
+     *     In principle, the annotationInfo.atp is a non-erased type ref. However, this cannot
+     *     actually happen because Java annotations cannot be generic.
+     *   - @javax.annotation.Resource(`type` = classOf[List[_]]) val x = 0
+     *     The annotationInfo.assocs contains a LiteralAnnotArg(Constant(tp)) where tp is the
+     *     non-erased existential type.
+     */
+    def erasedType(tp: Type): Type = enteringErasure {
+      // make sure we don't erase value class references to the type that the value class boxes
+      // this is basically the same logic as in erasure's preTransform, case Literal(classTag).
+      tp.dealiasWiden match {
+        case tr @ TypeRef(_, clazz, _) if clazz.isDerivedValueClass => erasure.scalaErasure.eraseNormalClassRef(tr)
+        case tpe => erasure.erasure(tpe.typeSymbol)(tpe)
+      }
+    }
+
+    def descriptorForErasedType(tp: Type): String = typeToBType(erasedType(tp)).descriptor
+
     /** Whether an annotation should be emitted as a Java annotation
       * .initialize: if 'annot' is read from pickle, atp might be uninitialized
       */
@@ -650,7 +668,6 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
         ca(idx) = b.asInstanceOf[Char]
         idx += 1
       }
-
       ca
     }
 
@@ -713,9 +730,10 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
               case StringTag  =>
                 assert(const.value != null, const) // TODO this invariant isn't documented in `case class Constant`
                 av.visit(name, const.stringValue)  // `stringValue` special-cases null, but that execution path isn't exercised for a const with StringTag
-              case ClazzTag   => av.visit(name, typeToBType(const.typeValue).toASMType)
+              case ClazzTag   =>
+                av.visit(name, typeToBType(erasedType(const.typeValue)).toASMType)
               case EnumTag =>
-                val edesc  = descriptor(const.tpe) // the class descriptor of the enumeration class.
+                val edesc  = descriptorForErasedType(const.tpe) // the class descriptor of the enumeration class.
                 val evalue = const.symbolValue.name.toString // value the actual enumeration value.
                 av.visitEnum(name, edesc, evalue)
             }
@@ -740,7 +758,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
         case NestedAnnotArg(annInfo) =>
           val AnnotationInfo(typ, args, assocs) = annInfo
           assert(args.isEmpty, args)
-          val desc = descriptor(typ) // the class descriptor of the nested annotation class
+          val desc = descriptorForErasedType(typ) // the class descriptor of the nested annotation class
           val nestedVisitor = av.visitAnnotation(name, desc)
           emitAssocs(nestedVisitor, assocs)
       }
@@ -765,7 +783,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
       for(annot <- annotations; if shouldEmitAnnotation(annot)) {
         val AnnotationInfo(typ, args, assocs) = annot
         assert(args.isEmpty, args)
-        val av = cw.visitAnnotation(descriptor(typ), isRuntimeVisible(annot))
+        val av = cw.visitAnnotation(descriptorForErasedType(typ), isRuntimeVisible(annot))
         emitAssocs(av, assocs)
       }
     }
@@ -777,7 +795,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
       for(annot <- annotations; if shouldEmitAnnotation(annot)) {
         val AnnotationInfo(typ, args, assocs) = annot
         assert(args.isEmpty, args)
-        val av = mw.visitAnnotation(descriptor(typ), isRuntimeVisible(annot))
+        val av = mw.visitAnnotation(descriptorForErasedType(typ), isRuntimeVisible(annot))
         emitAssocs(av, assocs)
       }
     }
@@ -789,7 +807,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
       for(annot <- annotations; if shouldEmitAnnotation(annot)) {
         val AnnotationInfo(typ, args, assocs) = annot
         assert(args.isEmpty, args)
-        val av = fw.visitAnnotation(descriptor(typ), isRuntimeVisible(annot))
+        val av = fw.visitAnnotation(descriptorForErasedType(typ), isRuntimeVisible(annot))
         emitAssocs(av, assocs)
       }
     }
@@ -804,7 +822,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
            annot <- annots) {
         val AnnotationInfo(typ, args, assocs) = annot
         assert(args.isEmpty, args)
-        val pannVisitor: asm.AnnotationVisitor = jmethod.visitParameterAnnotation(idx, descriptor(typ), isRuntimeVisible(annot))
+        val pannVisitor: asm.AnnotationVisitor = jmethod.visitParameterAnnotation(idx, descriptorForErasedType(typ), isRuntimeVisible(annot))
         emitAssocs(pannVisitor, assocs)
       }
     }
@@ -988,7 +1006,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
 
       mirrorMethod.visitCode()
 
-      mirrorMethod.visitFieldInsn(asm.Opcodes.GETSTATIC, moduleName, strMODULE_INSTANCE_FIELD, descriptor(module))
+      mirrorMethod.visitFieldInsn(asm.Opcodes.GETSTATIC, moduleName, strMODULE_INSTANCE_FIELD, classBTypeFromSymbol(module).descriptor)
 
       var index = 0
       for(jparamType <- paramJavaTypes) {
@@ -1049,7 +1067,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
     def getExceptions(excs: List[AnnotationInfo]): List[String] = {
       for (ThrownException(tp) <- excs.distinct)
       yield {
-        val erased = enteringErasure(erasure.erasure(tp.typeSymbol)(tp))
+        val erased = erasedType(tp)
         internalName(erased.typeSymbol)
       }
     }

src/compiler/scala/tools/nsc/backend/jvm/BTypesFromSymbols.scala

@@ -177,7 +177,7 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
 
     /**
      * When compiling Array.scala, the type parameter T is not erased and shows up in method
-     * signatures, e.g. `def apply(i: Int): T`. A TyperRef to T is replaced by ObjectReference.
+     * signatures, e.g. `def apply(i: Int): T`. A TypeRef for T is replaced by ObjectRef.
      */
     def nonClassTypeRefToBType(sym: Symbol): ClassBType = {
       assert(sym.isType && isCompilingArray, sym)
@@ -190,39 +190,24 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
       case TypeRef(_, sym, _)                 => primitiveOrClassToBType(sym) // Common reference to a type such as scala.Int or java.lang.String
       case ClassInfoType(_, _, sym)           => primitiveOrClassToBType(sym) // We get here, for example, for genLoadModule, which invokes typeToBType(moduleClassSymbol.info)
 
-      /* AnnotatedType should (probably) be eliminated by erasure. However we know it happens for
-       * meta-annotated annotations (@(ann @getter) val x = 0), so we don't emit a warning.
-       * The type in the AnnotationInfo is an AnnotatedTpe. Tested in jvm/annotations.scala.
-       */
-      case a @ AnnotatedType(_, t) =>
-        debuglog(s"typeKind of annotated type $a")
-        typeToBType(t)
-
-      /* ExistentialType should (probably) be eliminated by erasure. We know they get here for
-       * classOf constants:
-       *   class C[T]
-       *   class T { final val k = classOf[C[_]] }
-       */
-      case e @ ExistentialType(_, t) =>
-        debuglog(s"typeKind of existential type $e")
-        typeToBType(t)
-
       /* The cases below should probably never occur. They are kept for now to avoid introducing
        * new compiler crashes, but we added a warning. The compiler / library bootstrap and the
        * test suite don't produce any warning.
        */
 
       case tp =>
-        currentUnit.warning(tp.typeSymbol.pos,
+        warning(tp.typeSymbol.pos,
           s"an unexpected type representation reached the compiler backend while compiling $currentUnit: $tp. " +
             "If possible, please file a bug on issues.scala-lang.org.")
 
         tp match {
-          case ThisType(ArrayClass)               => ObjectRef // was introduced in 9b17332f11 to fix SI-999, but this code is not reached in its test, or any other test
-          case ThisType(sym)                      => classBTypeFromSymbol(sym)
-          case SingleType(_, sym)                 => primitiveOrClassToBType(sym)
-          case ConstantType(_)                    => typeToBType(t.underlying)
-          case RefinedType(parents, _)            => parents.map(typeToBType(_).asClassBType).reduceLeft((a, b) => a.jvmWiseLUB(b).get)
+          case ThisType(ArrayClass)    => ObjectRef // was introduced in 9b17332f11 to fix SI-999, but this code is not reached in its test, or any other test
+          case ThisType(sym)           => classBTypeFromSymbol(sym)
+          case SingleType(_, sym)      => primitiveOrClassToBType(sym)
+          case ConstantType(_)         => typeToBType(t.underlying)
+          case RefinedType(parents, _) => parents.map(typeToBType(_).asClassBType).reduceLeft((a, b) => a.jvmWiseLUB(b).get)
+          case AnnotatedType(_, t)     => typeToBType(t)
+          case ExistentialType(_, t)   => typeToBType(t)
         }
     }
   }

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

@@ -1112,7 +1112,7 @@ abstract class Erasure extends AddInterfaces
 
         case Literal(ct) if ct.tag == ClazzTag
                          && ct.typeValue.typeSymbol != definitions.UnitClass =>
-          val erased = ct.typeValue match {
+          val erased = ct.typeValue.dealiasWiden match {
             case tr @ TypeRef(_, clazz, _) if clazz.isDerivedValueClass => scalaErasure.eraseNormalClassRef(tr)
             case tpe => specialScalaErasure(tpe)
           }

src/reflect/scala/reflect/internal/transform/Erasure.scala

@@ -112,8 +112,9 @@ trait Erasure {
     protected def eraseDerivedValueClassRef(tref: TypeRef): Type = erasedValueClassArg(tref)
 
     def apply(tp: Type): Type = tp match {
-      case ConstantType(_) =>
-        tp
+      case ConstantType(ct) =>
+        if (ct.tag == ClazzTag) ConstantType(Constant(apply(ct.typeValue)))
+        else tp
       case st: ThisType if st.sym.isPackageClass =>
         tp
       case st: SubType =>

src/reflect/scala/reflect/runtime/JavaMirrors.scala

@@ -1161,6 +1161,7 @@ private[scala] trait JavaMirrors extends internal.SymbolTable with api.JavaUnive
       propagatePackageBoundary(jmeth.javaFlags, meth)
       copyAnnotations(meth, jmeth)
       if (jmeth.javaFlags.isVarargs) meth modifyInfo arrayToRepeated
+      if (jmeth.getDefaultValue != null) meth.addAnnotation(AnnotationDefaultAttr)
       markAllCompleted(meth)
       meth
     }

test/junit/scala/issues/RunTest.scala

@@ -0,0 +1,143 @@
+package scala.issues
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.{AfterClass, BeforeClass, Test}
+import org.junit.Assert._
+
+import scala.reflect.runtime._
+import scala.tools.reflect.ToolBox
+import scala.tools.testing.ClearAfterClass
+
+object RunTest extends ClearAfterClass.Clearable {
+  var toolBox = universe.runtimeMirror(getClass.getClassLoader).mkToolBox()
+  override def clear(): Unit = { toolBox = null }
+
+  // definitions for individual tests
+
+  class VC(val x: Any) extends AnyVal
+}
+
+@RunWith(classOf[JUnit4])
+class RunTest extends ClearAfterClass {
+  ClearAfterClass.stateToClear = RunTest
+
+  def run[T](code: String): T = {
+    val tb = RunTest.toolBox
+    tb.eval(tb.parse(code)).asInstanceOf[T]
+  }
+
+  @Test
+  def classOfValueClassAlias(): Unit = {
+    val code =
+      """import scala.issues.RunTest.VC
+        |type aVC = VC
+        |type aInt = Int
+        |type aInteger = Integer
+        |classOf[VC] == classOf[aVC] &&
+        |  classOf[aInt] == classOf[Int] &&
+        |  classOf[aInteger] == classOf[Integer] &&
+        |  classOf[aInt] != classOf[aInteger]
+      """.stripMargin
+    assertTrue(run[Boolean](code))
+  }
+
+  @Test
+  def classOfFinalVal(): Unit = {
+    val code =
+      """class C {
+        |  final val a1 = classOf[Int]
+        |  final val b1 = classOf[List[_]]
+        |  final val c1 = classOf[List[String]]
+        |  final val d1 = classOf[Array[Int]]
+        |  final val e1 = classOf[Array[List[_]]]
+        |  final val f1 = classOf[Array[_]]
+        |
+        |  val a2 = classOf[Int]
+        |  val b2 = classOf[List[_]]
+        |  val c2 = classOf[List[String]]
+        |  val d2 = classOf[Array[Int]]
+        |  val e2 = classOf[Array[List[_]]]
+        |  val f2 = classOf[Array[_]]
+        |
+        |  val listC = Class.forName("scala.collection.immutable.List")
+        |
+        |  val compare = List(
+        |    (a1, a2, Integer.TYPE),
+        |    (b1, b2, listC),
+        |    (c1, c2, listC),
+        |    (d1, d2, Array(1).getClass),
+        |    (e1, e2, Array(List()).getClass),
+        |    (f1, f2, new Object().getClass))
+        |}
+        |(new C).compare
+      """.stripMargin
+    type K = Class[_]
+    val cs = run[List[(K, K, K)]](code)
+    for ((x, y, z) <- cs) {
+      assertEquals(x, y)
+      assertEquals(x, z)
+    }
+  }
+
+  @Test
+  def t9702(): Unit = {
+    val code =
+      """import javax.annotation.Resource
+        |import scala.issues.RunTest.VC
+        |class C {
+        |  type aList[K] = List[K]
+        |  type aVC = VC
+        |  type aInt = Int
+        |  type aInteger = Integer
+        |  @Resource(`type` = classOf[List[Int]])      def a = 0
+        |  @Resource(`type` = classOf[List[_]])        def b = 0
+        |  @Resource(`type` = classOf[aList[_]])       def c = 0
+        |  @Resource(`type` = classOf[Int])            def d = 0
+        |  @Resource(`type` = classOf[aInt])           def e = 0
+        |  @Resource(`type` = classOf[Integer])        def f = 0
+        |  @Resource(`type` = classOf[aInteger])       def g = 0
+        |  @Resource(`type` = classOf[VC])             def h = 0
+        |  @Resource(`type` = classOf[aVC])            def i = 0
+        |  @Resource(`type` = classOf[Array[Int]])     def j = 0
+        |  @Resource(`type` = classOf[Array[List[_]]]) def k = 0
+        |}
+        |val c = classOf[C]
+        |def typeArg(meth: String) = c.getDeclaredMethod(meth).getDeclaredAnnotation(classOf[Resource]).`type`
+        |('a' to 'k').toList.map(_.toString).map(typeArg)
+      """.stripMargin
+
+    val l = Class.forName("scala.collection.immutable.List")
+    val i = Integer.TYPE
+    val ig = new Integer(1).getClass
+    val v = new RunTest.VC(1).getClass
+    val ai = Array(1).getClass
+    val al = Array(List()).getClass
+
+    // sanity checks
+    assertEquals(i, classOf[Int])
+    assertNotEquals(i, ig)
+
+    assertEquals(run[List[Class[_]]](code),
+      List(l, l, l, i, i, ig, ig, v, v, ai, al))
+  }
+
+  @Test
+  def annotationInfoNotErased(): Unit = {
+    val code =
+      """import javax.annotation.Resource
+        |import scala.annotation.meta.getter
+        |class C {
+        |  type Rg = Resource @getter
+        |  @(Resource @getter)(`type` = classOf[Int]) def a = 0
+        |  @Rg(`type` = classOf[Int])                 def b = 0
+        |}
+        |val c = classOf[C]
+        |def typeArg(meth: String) = c.getDeclaredMethod(meth).getDeclaredAnnotation(classOf[Resource]).`type`
+        |List("a", "b") map typeArg
+        |""".stripMargin
+
+    val i = Integer.TYPE
+    assertEquals(run[List[Class[_]]](code), List(i, i))
+  }
+}