Make RuleTransformer fully recursive [#257]

shared/src/main/scala/scala/xml/transform/NestingTransformer.scala

@@ -0,0 +1,19 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2002-2020, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    (c) 2011-2020, Lightbend, Inc.       **
+** /____/\___/_/ |_/____/_/ | |    http://scala-lang.org/               **
+**                          |/                                          **
+\*                                                                      */
+
+package scala
+package xml
+package transform
+
+import scala.collection.Seq
+
+class NestingTransformer(rule: RewriteRule) extends BasicTransformer {
+  override def transform(n: Node): Seq[Node] = {
+    rule.transform(super.transform(n))
+  }
+}

shared/src/main/scala/scala/xml/transform/RuleTransformer.scala

@@ -13,6 +13,9 @@ package transform
 import scala.collection.Seq
 
 class RuleTransformer(rules: RewriteRule*) extends BasicTransformer {
-  override def transform(n: Node): Seq[Node] =
-    rules.foldLeft(super.transform(n)) { (res, rule) => rule transform res }
+  private val transformers = rules.map(new NestingTransformer(_))
+  override def transform(n: Node): Seq[Node] = {
+    if (transformers.isEmpty) n
+    else transformers.tail.foldLeft(transformers.head.transform(n)) { (res, transformer) => transformer.transform(res) }
+  }
 }

shared/src/test/scala-2.x/scala/xml/TransformersTest.scala

@@ -60,7 +60,7 @@ class TransformersTest {
   @Test
   def preserveReferentialComplexityInLinearComplexity = { // SI-4528
     var i = 0
- 
+
     val xmlNode = <a><b><c><h1>Hello Example</h1></c></b></a>
 
     new RuleTransformer(new RewriteRule {
@@ -77,4 +77,19 @@ class TransformersTest {
 
     assertEquals(1, i)
   }
+
+  @Test
+  def appliesRulesRecursivelyOnPreviousChanges = { // #257
+    def add(outer: Elem, inner: Node) = new RewriteRule {
+      override def transform(n: Node): Seq[Node] = n match {
+        case e: Elem if e.label == outer.label => e.copy(child = e.child ++ inner)
+        case other => other
+      }
+    }
+
+    def transformer = new RuleTransformer(add(<element/>, <new/>), add(<new/>, <thing/>))
+
+    assertEquals(<element><new><thing/></new></element>, transformer(<element/>))
+  }
 }
+