Convert lifted non-SeqLiteral vararg splices into Seqs

closes lampepfl#18233

Author: KacperFKorban

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

@@ -167,6 +167,22 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   private def arrayToSeq(tree: Tree)(using Context): Tree =
     wrapArray(tree, tree.tpe.elemType)
 
+  /**
+    * Wrap vararg splices that have been lifted to valdefs in a call to `arrayToSeq`.
+    * `SeqLiteral`s are not wrapped, since they are eliminated in their own phase see `SeqLiterals`.
+    */
+  override def transformValDef(tree: ValDef)(using Context): Tree =
+    if tree.tpt.typeOpt.isRepeatedParam then
+      tree.rhs match {
+        case Typed(expr, tpt)
+        if tpt.typeOpt.isRepeatedParam && expr.typeOpt.derivesFrom(defn.ArrayClass) && !expr.isInstanceOf[SeqLiteral] =>
+          cpy.ValDef(tree)(rhs = Typed(arrayToSeq(expr), tpt))
+        case _ =>
+          tree
+      }
+    else
+      tree
+
   /** Generate the method definitions for the varargs forwarders created in transform */
   override def transformDefDef(tree: DefDef)(using Context): Tree =
     // If transform reported an error, don't go further

tests/run/i18233-min.scala

@@ -0,0 +1,15 @@
+// scalac: -coverage-out:coverage
+
+def aList =
+  List(Array[String]()*)
+
+def arr =
+  Array("abc", "def")
+
+def anotherList =
+  List(arr*)
+
+object Test extends App {
+  println(aList)
+  println(anotherList)
+}

tests/run/i18233.scala

@@ -0,0 +1,11 @@
+// scalac: -coverage-out:coverage
+
+enum Foo:
+  case Bar, Baz
+
+object Foo:
+  def render = List(values.tail*).mkString
+
+object Test extends App {
+  println(Foo.render)
+}