diff --git a/README.md b/README.md
index 68e555b88..39d5229f0 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,9 @@
Maintainer wanted!
==================
-[](https://gitter.im/scala/scala-xml?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
Would you like to maintain this project? (Please [get in touch](https://github.com/scala/scala#get-in-touch) with someone from the scala/scala core team!)
-scala-xml [
](https://travis-ci.org/scala/scala-xml) [
](http://search.maven.org/#search%7Cga%7C1%7Cg%3Aorg.scala-lang.modules%20a%3Ascala-xml_2.11) [
](http://search.maven.org/#search%7Cga%7C1%7Cg%3Aorg.scala-lang.modules%20a%3Ascala-xml_2.12*)
+scala-xml [](https://travis-ci.org/scala/scala-xml) [](http://search.maven.org/#search%7Cga%7C1%7Cg%3Aorg.scala-lang.modules%20a%3Ascala-xml_2.11) [](http://search.maven.org/#search%7Cga%7C1%7Cg%3Aorg.scala-lang.modules%20a%3Ascala-xml_2.12*) [](https://gitter.im/scala/scala-xml)
=========
The standard Scala XML library. Please file issues here instead of over at issues.scala-lang.org.
diff --git a/src/main/scala/scala/xml/transform/BasicTransformer.scala b/src/main/scala/scala/xml/transform/BasicTransformer.scala
index 8cad1ef22..ce7441ef8 100644
--- a/src/main/scala/scala/xml/transform/BasicTransformer.scala
+++ b/src/main/scala/scala/xml/transform/BasicTransformer.scala
@@ -32,11 +32,10 @@ abstract class BasicTransformer extends Function1[Node, Node] {
* otherwise a new sequence of concatenated results.
*/
def transform(ns: Seq[Node]): Seq[Node] = {
- val (xs1, xs2) = ns span (n => unchanged(n, transform(n)))
-
- if (xs2.isEmpty) ns
- else xs1 ++ transform(xs2.head) ++ transform(xs2.tail)
- }
+ val changed = ns flatMap transform
+ if (changed.length != ns.length || (changed, ns).zipped.exists(_ != _)) changed
+ else ns
+}
def transform(n: Node): Seq[Node] = {
if (n.doTransform) n match {
diff --git a/src/test/scala/scala/xml/ReuseNodesTest.scala b/src/test/scala/scala/xml/ReuseNodesTest.scala
new file mode 100644
index 000000000..5c61d0e3f
--- /dev/null
+++ b/src/test/scala/scala/xml/ReuseNodesTest.scala
@@ -0,0 +1,106 @@
+package scala.xml
+
+import scala.xml.transform._
+import org.junit.Test
+import org.junit.Assert.assertTrue
+import org.junit.Assert.assertEquals
+import org.junit.experimental.theories.Theories
+import org.junit.experimental.theories.Theory
+import org.junit.experimental.theories.DataPoints
+import org.junit.runner.RunWith
+/**
+ * This test verify that after the tranform, the resultant xml node
+ * uses as many old nodes as possible.
+ *
+ * Three transformers class for case -
+ * One for orginal, one for modified, and one proposed which shows
+ * all are equivalent when it comes to reusing as many nodes as possible
+ */
+object ReuseNodesTest {
+
+ class OriginalTranformr(rules: RewriteRule*) extends RuleTransformer(rules:_*) {
+ override def transform(ns: Seq[Node]): Seq[Node] = {
+ val xs = ns.toStream map transform
+ val (xs1, xs2) = xs zip ns span { case (x, n) => unchanged(n, x) }
+
+ if (xs2.isEmpty) ns
+ else (xs1 map (_._2)) ++ xs2.head._1 ++ transform(ns drop (xs1.length + 1))
+ }
+ override def transform(n:Node): Seq[Node] = super.transform(n)
+ }
+
+ class ModifiedTranformr(rules: RewriteRule*) extends RuleTransformer(rules:_*) {
+ override def transform(ns: Seq[Node]): Seq[Node] = {
+ val changed = ns flatMap transform
+
+ if (changed.length != ns.length || (changed, ns).zipped.exists(_ != _)) changed
+ else ns
+ }
+ override def transform(n:Node): Seq[Node] = super.transform(n)
+ }
+
+ class AlternateTranformr(rules: RewriteRule*) extends RuleTransformer(rules:_*) {
+ override def transform(ns: Seq[Node]): Seq[Node] = {
+ val xs = ns.toStream map transform
+ val (xs1, xs2) = xs zip ns span { case (x, n) => unchanged(n, x) }
+
+ if (xs2.isEmpty) ns
+ else (xs1 map (_._2)) ++ xs2.head._1 ++ transform(ns drop (xs1.length + 1))
+ }
+ override def transform(n:Node): Seq[Node] = super.transform(n)
+ }
+
+ def rewriteRule = new RewriteRule {
+ override def transform(n: Node): NodeSeq = n match {
+ case n if n.label == "change" => Elem(
+ n.prefix, "changed", n.attributes, n.scope, n.child.isEmpty, n.child : _*)
+ case _ => n
+ }
+ }
+
+ @DataPoints
+ def tranformers() = Array(
+ new OriginalTranformr(rewriteRule),
+ new ModifiedTranformr(rewriteRule),
+ new AlternateTranformr(rewriteRule))
+}
+
+@RunWith(classOf[Theories])
+class ReuseNodesTest {
+
+ @Theory
+ def transformReferentialEquality(rt:RuleTransformer) = {
+ val original =
+ val tranformed = rt.transform(original)
+ assertTrue(original eq tranformed)
+ }
+
+ @Theory
+ def transformReferentialEqualityOnly(rt:RuleTransformer) = {
+ val original =
+ val transformed = rt.transform(original)
+ recursiveAssert(original,transformed)
+ }
+
+ def recursiveAssert(original:Seq[Node], transformed:Seq[Node]):Unit = {
+ (original.toList,transformed.toList) match {
+ case (Nil, Nil) => {}
+ case (x::xs,y::ys) => {
+ recursiveAssert(x,y)
+ recursiveAssert(xs,ys)
+ }
+ }
+ }
+
+ def recursiveAssert(original:Node, transformed:Node):Unit = {
+ transformed.label match {
+ case "changed" => // do nothing expect this node to be changed
+ recursiveAssert(original.child,transformed.child)
+ case _ => {
+ assertTrue(original eq transformed)
+ // No need to check for childrens, node being immuatable
+ // childs can't be differnt if parents are refertially equal
+ }
+ }
+ }
+}
\ No newline at end of file