Don't suppress stacktraces when testing pickler

Author: odersky

compiler/src/dotty/tools/dotc/core/Mode.scala

@@ -81,10 +81,13 @@ object Mode {
   /** Read original positions when unpickling from TASTY */
   val ReadPositions = newMode(16, "ReadPositions")
 
+  /** Don't suppress exceptions thrown during show */
+  val PrintShowExceptions = newMode(17, "PrintShowExceptions")
+
   val PatternOrType = Pattern | Type
 
   /** We are elaborating the fully qualified name of a package clause.
    *  In this case, identifiers should never be imported.
    */
-  val InPackageClauseName = newMode(17, "InPackageClauseName")
+  val InPackageClauseName = newMode(18, "InPackageClauseName")
 }

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -31,7 +31,8 @@ object Formatting {
       case arg: Showable =>
         try arg.show
         catch {
-          case NonFatal(ex) => s"[cannot display due to $ex, raw string = $toString]"
+          case NonFatal(ex) if !ctx.mode.is(Mode.PrintShowExceptions) =>
+            s"[cannot display due to $ex, raw string = $toString]"
         }
       case _ => arg.toString
     }

compiler/src/dotty/tools/dotc/transform/Pickler.scala

@@ -79,7 +79,8 @@ class Pickler extends Phase {
           ctx.fresh
             .setPeriod(Period(ctx.runId + 1, FirstPhaseId))
             .setReporter(new ThrowingReporter(ctx.reporter))
-            .addMode(Mode.ReadPositions))
+            .addMode(Mode.ReadPositions)
+            .addMode(Mode.PrintShowExceptions))
     result
   }