Fix underlyingIfRepeated always assuming Scala repeated.

Author: DarkDimius

src/dotty/tools/dotc/core/TypeApplications.scala

@@ -283,9 +283,12 @@ class TypeApplications(val self: Type) extends AnyVal {
   /** If this is repeated parameter type, its underlying Seq type,
    *  or, if isJava is true, Array type, else the type itself.
    */
-  def underlyingIfRepeated(isJava: Boolean)(implicit ctx: Context): Type =
-    if (self.isRepeatedParam) translateParameterized(defn.RepeatedParamClass, defn.SeqClass)
+  def underlyingIfRepeated(isJava: Boolean)(implicit ctx: Context): Type = {
+    if (self.isRepeatedParam)
+      if (isJava) translateParameterized(defn.RepeatedParamClass, defn.ArrayClass)
+      else translateParameterized(defn.RepeatedParamClass, defn.SeqClass)
     else self
+  }
 
   /** If this is an encoding of a (partially) applied type, return its arguments,
    *  otherwise return Nil.

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

@@ -61,9 +61,10 @@ class ElimRepeated extends MiniPhaseTransform with InfoTransformer { thisTransfo
     case tp @ MethodType(paramNames, paramTypes) =>
       val resultType1 = elimRepeated(tp.resultType)
       val paramTypes1 =
-        if (paramTypes.nonEmpty && paramTypes.last.isRepeatedParam)
-          paramTypes.init :+ paramTypes.last.underlyingIfRepeated(tp.isJava)
-        else paramTypes
+        if (paramTypes.nonEmpty && paramTypes.last.isRepeatedParam) {
+          val last = paramTypes.last.underlyingIfRepeated(tp.isJava)
+          paramTypes.init :+ last
+        } else paramTypes
       tp.derivedMethodType(paramNames, paramTypes1, resultType1)
     case tp: PolyType =>
       tp.derivedPolyType(tp.paramNames, tp.paramBounds, elimRepeated(tp.resultType))