BasicTransformer exponential complexity

[note]

I am using 1.0.6. I just pasted code from https://issues.scala-lang.org/browse/SI-4528, namely:

var i = 0
  def translate(text: String): String = {
    println(i + " -> " + text)
    i += 1

    return "!%s!".format(text)
  }

  val xmlNode = <a><b><c><h1>Hello Example</h1></c></b></a>;

  new scala.xml.transform.RuleTransformer(new scala.xml.transform.RewriteRule {
    override def transform(n: Node): Seq[Node] = n match {
      case t: Text if !t.text.trim.isEmpty => Text(translate(t.text.trim))
      case _ => n
    }
  }).transform(xmlNode)

and the output is:

0 -> Hello Example
1 -> Hello Example
.
. (lines between left empty for sake of brevity)
30 -> Hello Example
31 -> Hello Example

It may seem it was covered by #59 but either in fact it does not or some regression was introduced.

[ashawley]

Seems it wasn't fixed in b2eef1f, see below. I had written a test in #88, but I guess it wasn't a good one. Can the test be fixed somehow to verify the bug still exists?

$ git checkout -b pr-58 b2eef1f
Switched to a new branch 'pr-58' 
$ sbt
> console
Welcome to Scala version 2.11.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_40).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.xml._

var i = 0;
def translate(text: String): String = {
    println(i + " -> " + text)
    i += 1
 
    return "!%s!".format(text)
}
 
val xmlNode = <a><b><c><h1>Hello Example</h1></c></b></a>;
 
new transform.RuleTransformer(new transform.RewriteRule {
    override def transform(n: Node): Seq[Node] = n match {
        case t: Text if !t.text.trim.isEmpty => Text(translate(t.text.trim))
        case _ => n
    }
}).transform(xmlNode);

// Exiting paste mode, now interpreting.

0 -> Hello Example
1 -> Hello Example
...
30 -> Hello Example
31 -> Hello Example
import scala.xml._
i: Int = 32
translate: (text: String)String
xmlNode: scala.xml.Elem = <a><b><c><h1>Hello Example</h1></c></b></a>
res0: Seq[scala.xml.Node] = <a><b><c><h1>!Hello Example!</h1></c></b></a>

[note]

OK, I found explanation. So bug is in fact gone but it take me some time to see correct behavior.

1. I pulled master and run example code on that code - I saw undesired 32 Hello Example messages.
2. I started to debug and then I noticed that debugger actually uses files from 1.0.5 jar.
3. I reminded myself that scala 2.12.1 pulled the most recent scala-xml. I changed build.sbt to use scala 2.12.1.
4. Now I saw desired behavior (just 1 message).

So because scala-xml is a dependency of scala-compiler it brings it to classpath and since 2.12.0-RC1 used 1.0.5 http://mvnrepository.com/artifact/org.scala-lang/scala-compiler/2.12.0-RC1 I was seeing incorrect behavior.

There's still open question for users of 2.11.8 how to get 1.0.6. I got scala-xml 1.0.6 explicitly in my build.sbt but it's not enough and I am little afraid it may be hard to accomplish because sbt may treat scala-compiler differently and simple exclude will not work.

To sum up - you can close the issue. Maybe scala version in build.sbt should be bumped to 2.12.1.

[note]

OK I guess I can find an answer in scala-xml's itself build.sbt (#20)

[SethTisue]

Maybe scala version in build.sbt should be bumped to 2.12.1

I have submitted #127 on this

[SethTisue]

There's still open question for users of 2.11.8 how to get 1.0.6.

a PR adding appropriate documentation on this to the README would be very welcome.

[ashawley]

@SethTisue I agree. The documentation could be better. The link to the example cross-building project is not enough.