Fix #6976: Improve macro exception stack handling

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

@@ -282,7 +282,7 @@ object Splicer {
 
       val name = getDirectName(fn.info.finalResultType, fn.name.asTermName)
       val method = getMethod(clazz, name, paramsSig(fn))
-      (args: List[Object]) => stopIfRuntimeException(method.invoke(inst, args: _*))
+      (args: List[Object]) => stopIfRuntimeException(method.invoke(inst, args: _*), method)
     }
 
     private def interpretModuleAccess(fn: Symbol)(implicit env: Env): Object =
@@ -339,7 +339,7 @@ object Splicer {
 
     private def extraMsg = ". The most common reason for that is that you apply macros in the compilation run that defines them"
 
-    private def stopIfRuntimeException[T](thunk: => T): T = {
+    private def stopIfRuntimeException[T](thunk: => T, method: Method): T = {
       try thunk
       catch {
         case ex: RuntimeException =>
@@ -352,13 +352,16 @@ object Splicer {
           throw new StopInterpretation(sw.toString, pos)
         case ex: InvocationTargetException =>
           val sw = new StringWriter()
-          sw.write("An exception occurred while executing macro expansion: ")
-          sw.write(ex.getTargetException.getMessage)
-          sw.write("\n")
-          for (stack <- ex.getTargetException.getStackTrace.iterator.takeWhile(_.getClassName != this.getClass.getName).drop(1)) {
-            sw.write(stack.toString)
-            sw.write("\n")
+          sw.write("Exception occurred while executing macro expansion.\n")
+          val targetException = ex.getTargetException
+          if (!ctx.settings.Ydebug.value) {
+            val end = targetException.getStackTrace.lastIndexWhere { x =>
+              x.getClassName == method.getDeclaringClass.getCanonicalName && x.getMethodName == method.getName
+            }
+            val shortStackTrace = targetException.getStackTrace.take(end + 1)
+            targetException.setStackTrace(shortStackTrace)
           }
+          targetException.printStackTrace(new PrintWriter(sw))
           sw.write("\n")
           throw new StopInterpretation(sw.toString, pos)
       }

tests/neg-macros/i6976.check

@@ -0,0 +1,9 @@
+
+-- Error: tests/neg-macros/i6976/Test_2.scala:5:44 ---------------------------------------------------------------------
+5 |  def main(args: Array[String]): Unit = mcr { 2 } // error
+  |                                        ^^^^^^^^^
+  |    Exception occurred while executing macro expansion.
+  |    scala.MatchError: Inlined(EmptyTree,List(),Literal(Constant(2))) (of class dotty.tools.dotc.ast.Trees$Inlined)
+  |    	at playground.macros$.mcrImpl(Macro_1.scala:12)
+  |    
+  | This location is in code that was inlined at Test_2.scala:5

tests/neg-macros/i6976/Macro_1.scala

@@ -0,0 +1,14 @@
+package playground
+
+import scala.quoted._, scala.quoted.matching._
+import delegate scala.quoted._
+import scala.tasty._
+
+object macros {
+  inline def mcr(x: => Any) = ${mcrImpl('x)}
+
+  def mcrImpl(body: Expr[Any]) given (ctx: QuoteContext): Expr[Any] = {
+    import ctx.tasty._
+    body.unseal match { case Block(_, _) => '{2} }
+  }
+}

tests/neg-macros/i6976/Test_2.scala

@@ -0,0 +1,6 @@
+
+import playground.macros._
+
+object Test {
+  def main(args: Array[String]): Unit = mcr { 2 } // error
+}