Fix #8349: Generic signatures of generic arrays

When T[] is erased to Object, it should get a Java generic signature of
Object and not of T<>. Fixed by reusing the same logic we have in
TypeErasure which replaces a bunch of weird code imported from scalac.

The new behavior differs in one case from scalac: `Array[_ <: Byte]`
gets a generic signature of `byte[]` instead of `Object`, but this is
consistent with how we handle erasure (which I think is OK because as
far as I can tell, we can't construct a value of type `Array[Nothing]`
with Dotty).

Author: smarter

compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala

@@ -9,7 +9,7 @@ import core.Flags._
 import core.Names.{DerivedName, Name, SimpleName, TypeName}
 import core.Symbols._
 import core.TypeApplications.TypeParamInfo
-import core.TypeErasure.erasure
+import core.TypeErasure.{erasure, isUnboundedGeneric}
 import core.Types._
 import core.classfile.ClassfileConstants
 import ast.Trees._
@@ -182,15 +182,16 @@ object GenericSignatures {
         case ref @ TypeParamRef(_: PolyType, _) =>
           typeParamSig(ref.paramName.lastPart)
 
+        case defn.ArrayOf(elemtp) =>
+          if (isUnboundedGeneric(elemtp))
+            jsig(defn.ObjectType)
+          else {
+            builder.append(ClassfileConstants.ARRAY_TAG)
+            jsig(elemtp)
+          }
+
         case RefOrAppliedType(sym, pre, args) =>
-          // If args isEmpty, Array is being used as a type constructor
-          if (sym == defn.ArrayClass && args.nonEmpty)
-            if (unboundedGenericArrayLevel(tp) == 1) jsig(defn.ObjectType)
-            else {
-              builder.append(ClassfileConstants.ARRAY_TAG)
-              args.foreach(jsig(_))
-            }
-          else if (sym == defn.PairClass && tp.tupleArity > Definitions.MaxTupleArity)
+          if (sym == defn.PairClass && tp.tupleArity > Definitions.MaxTupleArity)
             jsig(defn.TupleXXLClass.typeRef)
           else if (isTypeParameterInSig(sym, sym0)) {
             assert(!sym.isAliasType, "Unexpected alias type: " + sym)
@@ -368,17 +369,6 @@ object GenericSignatures {
     case tp => tp :: Nil
   }
 
-  /** Arrays despite their finality may turn up as refined type parents,
-    *  e.g. with "tagged types" like Array[Int] with T.
-    */
-  private def unboundedGenericArrayLevel(tp: Type)(implicit ctx: Context): Int = tp match {
-    case GenericArray(core, level) if !(core <:< defn.AnyRefType) =>
-      level
-    case AndType(tp1, tp2) =>
-      unboundedGenericArrayLevel(tp1) max unboundedGenericArrayLevel(tp2)
-    case _ =>
-      0
-  }
 
   // only refer to type params that will actually make it into the sig, this excludes:
   // * higher-order type parameters
@@ -420,53 +410,6 @@ object GenericSignatures {
     if (owner.is(PackageClass) || owner.isTerm) pre else cls.owner.info /* .tpe_* */
   }
 
-  object GenericArray {
-
-    /** Is `tp` an unbounded generic type (i.e. which could be instantiated
-      *  with primitive as well as class types)?.
-      */
-    private def genericCore(tp: Type)(implicit ctx: Context): Type = tp.widenDealias match {
-      /* A Java Array<T> is erased to Array[Object] (T can only be a reference type), where as a Scala Array[T] is
-       * erased to Object. However, there is only symbol for the Array class. So to make the distinction between
-       * a Java and a Scala array, we check if the owner of T comes from a Java class.
-       * This however caused issue scala/bug#5654. The additional test for EXISTENTIAL fixes it, see the ticket comments.
-       * In short, members of an existential type (e.g. `T` in `forSome { type T }`) can have pretty arbitrary
-       * owners (e.g. when computing lubs, <root> is used). All packageClass symbols have `isJavaDefined == true`.
-       */
-      case RefOrAppliedType(sym, tp, _) =>
-        if (sym.isAbstractOrParamType && (!sym.owner.is(JavaDefined) || sym.is(Scala2Existential)))
-          tp
-        else
-          NoType
-
-      case bounds: TypeBounds =>
-        bounds
-
-      case _ =>
-        NoType
-    }
-
-    /** If `tp` is of the form Array[...Array[T]...] where `T` is an abstract type
-      *  then Some((N, T)) where N is the number of Array constructors enclosing `T`,
-      *  otherwise None. Existentials on any level are ignored.
-      */
-    def unapply(tp: Type)(implicit ctx: Context): Option[(Type, Int)] = tp.widenDealias match {
-      case defn.ArrayOf(arg) =>
-        genericCore(arg) match {
-          case NoType =>
-            arg match {
-              case GenericArray(core, level) => Some((core, level + 1))
-              case _ => None
-            }
-          case core =>
-            Some((core, 1))
-        }
-      case _ =>
-        None
-    }
-  }
-
-
   private object RefOrAppliedType {
     def unapply(tp: Type)(implicit ctx: Context): Option[(Symbol, Type, List[Type])] = tp match {
       case TypeParamRef(_, _) =>

tests/generic-java-signatures/arrayBound.check

@@ -2,4 +2,7 @@ T <: java.lang.Object
 U <: T[]
 V <: java.util.List<T[]>
 W <: java.util.List<? extends java.util.Date>
-X <: java.util.HashMap<java.lang.Object, java.util.ArrayList<? extends java.util.Date>>
+X <: java.util.HashMap<java.lang.Object, java.util.ArrayList<? extends java.util.Date>>
+T1 <: java.lang.Object
+U1 <: java.lang.Object
+V1 <: java.lang.Object[]

tests/generic-java-signatures/arrayBound.scala

@@ -1,9 +1,18 @@
-class Foo[T <: Array[_], U <: Array[T], V <: java.util.List[Array[T]], W <: java.util.List[_ <: java.util.Date], X <: java.util.HashMap[Array[_], java.util.ArrayList[_ <: java.util.Date]]]
+class Foo[
+  T <: Array[_],
+  U <: Array[T],
+  V <: java.util.List[Array[T]],
+  W <: java.util.List[_ <: java.util.Date],
+  X <: java.util.HashMap[Array[_], java.util.ArrayList[_ <: java.util.Date]],
+  T1,
+  U1 <: Array[T1],
+  V1 <: Array[Array[T1]]
+]
 object Test {
   def main(args: Array[String]): Unit = {
-    val tParams = classOf[Foo[_, _, _, _, _]].getTypeParameters()
+    val tParams = classOf[Foo[_, _, _, _, _, _, _, _]].getTypeParameters()
     tParams.foreach { tp =>
       println(tp.getName + " <: " + tp.getBounds.map(_.getTypeName).mkString(", "))
     }
   }
-}
+}

tests/generic-java-signatures/primitives.check

@@ -6,4 +6,4 @@ E <: int[]
 F <: long[]
 G <: short[]
 H <: boolean[]
-I <: java.lang.Object
+I <: byte[]