Make sure that the stacktrace is shown with -Ydebug-unpickling

Author: nicolasstucki

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

@@ -26,6 +26,7 @@ abstract class TypeError(using creationContext: Context) extends Exception(""):
     || (cyclicErrors != noPrinter && this.isInstanceOf[CyclicReference] && !(ctx.mode is Mode.CheckCyclic))
     || ctx.settings.YdebugTypeError.value
     || ctx.settings.YdebugError.value
+    || ctx.settings.YdebugUnpickling.value
 
   override def fillInStackTrace(): Throwable =
     if computeStackTrace then super.fillInStackTrace().nn
@@ -191,3 +192,14 @@ object CyclicReference:
     ex
 end CyclicReference
 
+class UnpicklingError(denot: Denotation, where: String, cause: Throwable)(using Context) extends TypeError:
+  override def toMessage(using Context): Message =
+    val debugUnpickling = cause match
+      case cause: UnpicklingError => ""
+      case _ =>
+        if ctx.settings.YdebugUnpickling.value then
+          cause.getStackTrace().nn.mkString("\n    ", "\n    ", "")
+        else "\n\nRun with -Ydebug-unpickling to see full stack trace."
+    em"""Could not read definition $denot$where. Caused by the following exception:
+        |$cause$debugUnpickling"""
+end UnpicklingError

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -145,12 +145,7 @@ class TreeUnpickler(reader: TastyReader,
         def where =
           val f = denot.symbol.associatedFile
           if f == null then "" else s" in $f"
-        if ctx.settings.YdebugUnpickling.value then throw ex
-        else throw TypeError(
-          em"""Could not read definition of $denot$where
-              |An exception was encountered:
-              |  $ex
-              |Run with -Ydebug-unpickling to see full stack trace.""")
+        throw UnpicklingError(denot, where, ex)
       treeAtAddr(currentAddr) =
         try
           atPhaseBeforeTransforms {