Scala example source code file (StackTracing.scala)

This example Scala source code file (StackTracing.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

array, arraybuffer, causedby, compiler, int, nsc, self, stacktraceelement, string, suppressed, throwable, tracerelation

The StackTracing.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 */

package scala.tools.nsc.util

private[util] trait StackTracing extends Any {

  /** Format a stack trace, returning the prefix consisting of frames that satisfy
   *  a given predicate.
   *  The format is similar to the typical case described in the JavaDoc
   *  for [[java.lang.Throwable#printStackTrace]].
   *  If a stack trace is truncated, it will be followed by a line of the form
   *  `... 3 elided`, by analogy to the lines `... 3 more` which indicate
   *  shared stack trace segments.
   *  @param e the exception
   *  @param p the predicate to select the prefix
   */
  def stackTracePrefixString(e: Throwable)(p: StackTraceElement => Boolean): String = {
    import collection.mutable.{ ArrayBuffer, ListBuffer }
    import compat.Platform.EOL
    import util.Properties.isJavaAtLeast

    val sb = ListBuffer.empty[String]

    type TraceRelation = String
    val Self       = new TraceRelation("")
    val CausedBy   = new TraceRelation("Caused by: ")
    val Suppressed = new TraceRelation("Suppressed: ")

    val suppressable = isJavaAtLeast("1.7")

    def clazz(e: Throwable)           = e.getClass.getName
    def because(e: Throwable): String = e.getCause match { case null => null ; case c => header(c) }
    def msg(e: Throwable): String     = e.getMessage match { case null => because(e) ; case s => s }
    def txt(e: Throwable): String     = msg(e) match { case null => "" ; case s => s": $s" }
    def header(e: Throwable): String  = s"${clazz(e)}${txt(e)}"

    val indent = "\u0020\u0020"

    val seen = new ArrayBuffer[Throwable](16)
    def unseen(t: Throwable) = {
      def inSeen = seen exists (_ eq t)
      val interesting = (t != null) && !inSeen
      if (interesting) seen += t
      interesting
    }

    def print(e: Throwable, r: TraceRelation, share: Array[StackTraceElement], indents: Int): Unit = if (unseen(e)) {
      val trace  = e.getStackTrace
      val frames = (
        if (share.nonEmpty) {
          val spare  = share.reverseIterator
          val trimmed = trace.reverse dropWhile (spare.hasNext && spare.next == _)
          trimmed.reverse
        } else trace
      )
      val prefix   = frames takeWhile p
      val margin   = indent * indents
      val indented = margin + indent
      sb append s"${margin}${r}${header(e)}"
      prefix foreach (f => sb append s"${indented}at $f")
      if (frames.size < trace.size) sb append s"$indented... ${trace.size - frames.size} more"
      if (r == Self && prefix.size < frames.size) sb append s"$indented... ${frames.size - prefix.size} elided"
      print(e.getCause, CausedBy, trace, indents)
      if (suppressable) {
        import scala.language.reflectiveCalls
        type Suppressing = { def getSuppressed(): Array[Throwable] }
        for (s <- e.asInstanceOf[Suppressing].getSuppressed) print(s, Suppressed, frames, indents + 1)
      }
    }
    print(e, Self, share = Array.empty, indents = 0)

    sb mkString EOL
  }
}