Ensure conversion to imm.Seq is only done once

Author: lrytz

shared/src/main/scala/scala/xml/Group.scala

@@ -22,6 +22,10 @@ import scala.collection.Seq
  */
 // Note: used by the Scala compiler.
 final case class Group(nodes: Seq[Node]) extends Node {
+  // Ideally, the `immutable.Seq` would be stored as a field.
+  // But evolving the case class and remaining binary compatible is very difficult
+  // Since `Group` is used rarely, call `toSeq` on the field.
+  // In practice, it should not matter - the `nodes` field anyway contains an `immutable.Seq`.
   override def theSeq: ScalaVersionSpecific.SeqOfNode = nodes.toSeq
 
   override def canEqual(other: Any): Boolean = other match {

shared/src/main/scala/scala/xml/NodeSeq.scala

@@ -26,7 +26,7 @@ import scala.collection.Seq
 object NodeSeq {
   final val Empty: NodeSeq = fromSeq(Nil)
   def fromSeq(s: Seq[Node]): NodeSeq = new NodeSeq {
-    override def theSeq: ScalaVersionSpecific.SeqOfNode = s match {
+    override val theSeq: ScalaVersionSpecific.SeqOfNode = s match {
       case ns: ScalaVersionSpecific.SeqOfNode => ns
       case _ => s.toVector
     }