Fix #1905: Duplicate bridge

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

@@ -600,6 +600,7 @@ object Erasure extends TypeTestsCasts{
     // this implementation doesn't check for bridge clashes with value types!
     def addBridges(oldStats: List[untpd.Tree], newStats: List[tpd.Tree])(implicit ctx: Context): List[tpd.Tree] = {
       val beforeCtx = ctx.withPhase(ctx.erasurePhase)
+      val afterCtx = ctx.withPhase(ctx.elimErasedValueTypePhase.next)
       def traverse(after: List[Tree], before: List[untpd.Tree],
                    emittedBridges: ListBuffer[tpd.DefDef] = ListBuffer[tpd.DefDef]()): List[tpd.DefDef] = {
         after match {
@@ -613,7 +614,7 @@ object Erasure extends TypeTestsCasts{
                   val newSymbol = member.symbol(ctx)
                   assert(oldSymbol.name(beforeCtx) == newSymbol.name,
                     s"${oldSymbol.name(beforeCtx)} bridging with ${newSymbol.name}")
-                  val newOverridden = oldSymbol.denot.allOverriddenSymbols.toSet // TODO: clarify new <-> old in a comment; symbols are swapped here
+                  val newOverridden = oldSymbol.denot.allOverriddenSymbols(afterCtx).toSet // TODO: clarify new <-> old in a comment; symbols are swapped here
                   val oldOverridden = newSymbol.allOverriddenSymbols(beforeCtx).toSet // TODO: can we find a more efficient impl? newOverridden does not have to be a set!
                   def stillInBaseClass(sym: Symbol) = ctx.owner derivesFrom sym.owner
                   val neededBridges = (oldOverridden -- newOverridden).filter(stillInBaseClass)

tests/run/iarray.scala

@@ -0,0 +1,20 @@
+import scala.reflect.ClassTag
+
+class Arr[T](private val underlying: scala.Array[T]) extends AnyVal {
+  def toList = underlying.toList
+}
+
+trait SeqMonoTransforms[+A, +Repr] extends Any {
+  protected[this] def fromIterableWithSameElemType(): Repr
+}
+
+class ArrOps[A](val xs: Arr[A]) extends AnyRef with SeqMonoTransforms[A, Arr[A]] {
+  def fromIterableWithSameElemType(): Arr[A] = xs
+}
+
+object Test {
+  def main(args: Array[String]) =
+    assert(new ArrOps(new Arr(Array(1, 2, 3))).fromIterableWithSameElemType.toList ==
+      List(1, 2, 3))
+}
+