Fix ClassCastException with Java primitive varargs

The class constant corresponding to the primitive type `int` is
represented in bytecode by `Integer.TYPE`, this is correctly handled
when calling `clsOf`, but so far `ElimRepeated` was manually creating a
constant instead which does not work (I've now changed the backend to
emit a failure instead of doing the wrong thing when someone does that,
I also plan to rework the way we handle classOf to make this less
error-prone).

Note: after this commit, tests/run/t1360.scala started failing, this is
fixed in the next commit.

Author: smarter

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

@@ -483,13 +483,10 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
         case NullTag    => emit(asm.Opcodes.ACONST_NULL)
 
         case ClazzTag   =>
-          val toPush: BType = {
-            toTypeKind(const.typeValue) match {
-              case kind: PrimitiveBType => boxedClassOfPrimitive(kind)
-              case kind => kind
-            }
-          }
-          mnode.visitLdcInsn(toPush.toASMType)
+          val tp = toTypeKind(const.typeValue)
+          // classOf[Int] is transformed to Integer.TYPE by ClassOf
+          assert(!tp.isPrimitive, s"expected class type in classOf[T], found primitive type $tp")
+          mnode.visitLdcInsn(tp.toASMType)
 
         case EnumTag   =>
           val sym       = const.symbolValue

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

@@ -99,7 +99,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
       ref(defn.DottyArraysModule)
         .select(nme.seqToArray)
         .appliedToType(elemType)
-        .appliedTo(tree, Literal(Constant(elemClass.typeRef)))
+        .appliedTo(tree, clsOf(elemClass.typeRef))
   }
 
   /** Convert Java array argument to Scala Seq */

tests/run/java-varargs/A_1.java

@@ -0,0 +1,4 @@
+class A_1 {
+  public static void foo(int... args) {
+  }
+}

tests/run/java-varargs/Test_2.scala

@@ -0,0 +1,6 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    A_1.foo(Array(1): _*)
+    A_1.foo(Seq(1): _*)
+  }
+}