scala.xml.PrettyPrinter to format shorter node when there is no text in it

Question

I use scala.xml.PrettyPrinter to format my XML in Scala. The problem is with nodes without text content. Instead of this:

<node></node>

I'd prefer to have this:

<node />

How can I make PrettyPrinter to format it my way?

Answer 1

This was a bug in scala-xml, but it was fixed in version 1.1.0 on Feb-20-2018. A new option minimizeEmpty was added to PrettyPrinter.

To use 1.1.0, add the following to your build.sbt:

libraryDependencies ++= Seq(
  "org.scala-lang.modules" %% "scala-xml" % "1.1.0"
)

Here's an example of how to make use of the new option in PrettyPrinter:

val pp = new xml.PrettyPrinter(80, 2, minimizeEmpty = true)
val x = <node><leaf></leaf></node>
println(pp.format(x))

This will output:

<node>
  <leaf/>
</node>

If the Scala compiler, complains:

java.lang.NoSuchMethodError: scala.xml.PrettyPrinter.<init>(IIZ)V

then you need to enable a forked JVM in sbt, so that Scala is using the new version of scala-xml. Just add the follow to your build.sbt:

fork := true

Previous to scala-xml 1.1.0, the method to create <node/>, leafTag(), is in the class, but unused. You can fix it like so:

import xml._
val p2 = new PrettyPrinter(120, 2) {
  override protected def traverse(node:Node, pscope:NamespaceBinding, ind:Int) = 
    node match {
      case n:Elem if n.child.size == 0 => makeBox(ind, leafTag(n))
      case _ => super.traverse(node, pscope, ind)
    }
}

There's no reason to use the override-hack if you can just upgrade to 1.1.0.