A utility function to summarize an exception.

Now when I start the repl and trigger an exception during
initialization, it offers a one line message like:

  uncaught exception during compilation:
    AssertionError("assertion failed: (14,13)")
    @ scala.reflect.internal.Symbols$Symbol.updateInfo(Symbols.scala:1309)

Which is a marked debugging improvement from RC1:

  uncaught exception during compilation: java.lang.AssertionError

1 files changed, 12 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/util/package.scala b/src/compiler/scala/tools/nsc/util/package.scala
index d34d4ee092..e9dcaa8e16 100644
--- a/src/compiler/scala/tools/nsc/util/package.scala
+++ b/src/compiler/scala/tools/nsc/util/package.scala
@@ -83,6 +83,18 @@ package object util {
   }
   def stackTraceString(ex: Throwable): String = stringFromWriter(ex printStackTrace _)
 
+  /** A one line string which contains the class of the exception, the
+   *  message if any, and the first non-Predef location in the stack trace
+   *  (to exclude assert, require, etc.)
+   */
+  def stackTraceHeadString(ex: Throwable): String = {
+    val frame = ex.getStackTrace.dropWhile(_.getClassName contains "Predef").head
+    val msg   = ex.getMessage match { case null | "" => "" ; case s => s"""("$s")""" }
+    val clazz = ex.getClass.getName.split('.').last
+
+    s"$clazz$msg @ $frame"
+  }
+
   lazy val trace = new SimpleTracer(System.out)
   lazy val errtrace = new SimpleTracer(System.err)