Merge pull request #975 from smarter/fix/logging

Better logging, especially of exceptions

Author: smarter

src/dotty/tools/dotc/Driver.scala

@@ -50,8 +50,13 @@ abstract class Driver extends DotClass {
     process(args, initCtx)
   }
 
-  def main(args: Array[String]): Unit =
+  def main(args: Array[String]): Unit = {
+    // Preload scala.util.control.NonFatal. Otherwise, when trying to catch a StackOverflowError,
+    // we may try to load it but fail with another StackOverflowError and lose the original exception,
+    // see <https://groups.google.com/forum/#!topic/scala-user/kte6nak-zPM>.
+    val _ = NonFatal
     sys.exit(if (process(args).hasErrors) 1 else 0)
+  }
 }
 
 class FatalError(msg: String) extends Exception

src/dotty/tools/dotc/reporting/Reporter.scala

@@ -152,7 +152,12 @@ trait Reporting { this: Context =>
       case _ => String.valueOf(res)
     }
     if (printer eq config.Printers.noPrinter) op
-    else traceIndented[T](s"==> $question?", (res: Any) => s"<== $question = ${resStr(res)}")(op)
+    else {
+      // Avoid evaluating question multiple time, since each evaluation
+      // may cause some extra logging output.
+      val q: String = question
+      traceIndented[T](s"==> $q?", (res: Any) => s"<== $q = ${resStr(res)}")(op)
+    }
   }
 
   def traceIndented[T](leading: => String, trailing: Any => String)(op: => T): T =