Failed evaluation in dotty

[adpi2]

In dotty dotty.tools.dotc.rewrites.Rewrites.scala, evaluation of pbuf(2).span fails with:

IllegalArgumentException@5626 "java.lang.IllegalArgumentException: object is not an instance of declaring class"

[iusildra]

Minimized code:

object Rewrites {
  private class Patch(val span: Span)
  
  def main(args: Array[String]): Unit = {
    val patch = Patch(Span(0))
    println("ok")
  }
}

class Span(start: Int) extends AnyVal

The problem seems to be with private classes having value classes as attributes

[iusildra]

Hum, I'm trying to print the trees generated by the compiler, but even when passing -Xprint:all in scalacOptions to DebugTools#loadExpressionCompiler, the trees are not printed...
So I compile the minimized code in a separate file, but could not find any difference between the private class Patch and class Patch versions, each with and without a val expr$19744 = patch.span after the val patch = ..., apart from a different ordering, but I don't thing it matters

[adpi2]

I think the IllegalArgumentException comes from one of the method in

scala-debug-adapter/modules/expression-compiler/src/main/scala-3/dotty/tools/dotc/evaluation/InsertExpression.scala

Lines 30 to 113 in 33e8272

	s"""|class ${exprCtx.expressionClassName}(names: Array[String], values: Array[Any]):
	| import java.lang.reflect.InvocationTargetException
	| val classLoader = getClass.getClassLoader.nn
	|
	| def evaluate(): Any =
	| ()
	|
	| def getLocalValue(name: String): Any =
	| val idx = names.indexOf(name)
	| if idx == -1 then throw new NoSuchElementException(name)
	| else values(idx)
	|
	| def setLocalValue(name: String, value: Any): Any =
	| val idx = names.indexOf(name)
	| if idx == -1 then throw new NoSuchElementException(name)
	| else values(idx) = value
	|
	| def callMethod(obj: Any, className: String, methodName: String, paramTypesNames: Array[String], returnTypeName: String, args: Array[Object]): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val method = clazz.getDeclaredMethods.nn
	| .map(_.nn)
	| .find { m =>
	| m.getName == methodName &&
	| m.getReturnType.nn.getName == returnTypeName &&
	| m.getParameterTypes.nn.map(_.nn.getName).toSeq == paramTypesNames.toSeq
	| }
	| .getOrElse(throw new NoSuchMethodException(methodName))
	| method.setAccessible(true)
	| unwrapException(method.invoke(obj, args*))
	|
	| def callConstructor(className: String, paramTypesNames: Array[String], args: Array[Object]): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val constructor = clazz.getConstructors.nn
	| .map(_.nn)
	| .find { c => c.getParameterTypes.nn.map(_.nn.getName).toSeq == paramTypesNames.toSeq }
	| .getOrElse(throw new NoSuchMethodException(s"new $$className"))
	| constructor.setAccessible(true)
	| unwrapException(constructor.newInstance(args*))
	|
	| def getField(obj: Any, className: String, fieldName: String): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val field = clazz.getDeclaredField(fieldName).nn
	| field.setAccessible(true)
	| field.get(obj)
	|
	| def setField(obj: Any, className: String, fieldName: String, value: Any): Unit =
	| val clazz = classLoader.loadClass(className).nn
	| val field = clazz.getDeclaredField(fieldName).nn
	| field.setAccessible(true)
	| field.set(obj, value)
	|
	| def getOuter(obj: Any, outerTypeName: String): Any =
	| val clazz = obj.getClass
	| val field = getSuperclassIterator(clazz)
	| .flatMap(_.getDeclaredFields.nn.toSeq)
	| .map(_.nn)
	| .find { field => field.getName == "$$outer" && field.getType.nn.getName == outerTypeName }
	| .getOrElse(throw new NoSuchFieldException("$$outer"))
	| field.setAccessible(true)
	| field.get(obj)
	|
	| def getStaticObject(className: String): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val field = clazz.getDeclaredField("MODULE$$").nn
	| field.setAccessible(true)
	| field.get(null)
	|
	| def getSuperclassIterator(clazz: Class[?] | Null): Iterator[Class[?]] =
	| Iterator.iterate(clazz)(_.nn.getSuperclass).takeWhile(_ != null).map(_.nn)
	|
	| // a fake method that is used between the extract-expression and the resolve-reflect-eval phases,
	| // which transforms them to calls of one of the methods defined above.
	| def reflectEval(qualifier: Object, term: String, args: Array[Object]): Any = ???
	|
	| private def unwrapException(f: => Any): Any =
	| try f
	| catch
	| case e: InvocationTargetException => throw e.getCause.nn
	|
	| extension [T] (x: T | Null)
	| private def nn: T =
	| assert(x != null)
	| x.asInstanceOf[T]
	|""".stripMargin

You should be able to get the stack trace of this exception by inspecting it in the debug console or by wrapping the debug console in a try catch. Then you can add println in the methods in

scala-debug-adapter/modules/expression-compiler/src/main/scala-3/dotty/tools/dotc/evaluation/InsertExpression.scala

Lines 30 to 113 in 33e8272

	s"""|class ${exprCtx.expressionClassName}(names: Array[String], values: Array[Any]):
	| import java.lang.reflect.InvocationTargetException
	| val classLoader = getClass.getClassLoader.nn
	|
	| def evaluate(): Any =
	| ()
	|
	| def getLocalValue(name: String): Any =
	| val idx = names.indexOf(name)
	| if idx == -1 then throw new NoSuchElementException(name)
	| else values(idx)
	|
	| def setLocalValue(name: String, value: Any): Any =
	| val idx = names.indexOf(name)
	| if idx == -1 then throw new NoSuchElementException(name)
	| else values(idx) = value
	|
	| def callMethod(obj: Any, className: String, methodName: String, paramTypesNames: Array[String], returnTypeName: String, args: Array[Object]): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val method = clazz.getDeclaredMethods.nn
	| .map(_.nn)
	| .find { m =>
	| m.getName == methodName &&
	| m.getReturnType.nn.getName == returnTypeName &&
	| m.getParameterTypes.nn.map(_.nn.getName).toSeq == paramTypesNames.toSeq
	| }
	| .getOrElse(throw new NoSuchMethodException(methodName))
	| method.setAccessible(true)
	| unwrapException(method.invoke(obj, args*))
	|
	| def callConstructor(className: String, paramTypesNames: Array[String], args: Array[Object]): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val constructor = clazz.getConstructors.nn
	| .map(_.nn)
	| .find { c => c.getParameterTypes.nn.map(_.nn.getName).toSeq == paramTypesNames.toSeq }
	| .getOrElse(throw new NoSuchMethodException(s"new $$className"))
	| constructor.setAccessible(true)
	| unwrapException(constructor.newInstance(args*))
	|
	| def getField(obj: Any, className: String, fieldName: String): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val field = clazz.getDeclaredField(fieldName).nn
	| field.setAccessible(true)
	| field.get(obj)
	|
	| def setField(obj: Any, className: String, fieldName: String, value: Any): Unit =
	| val clazz = classLoader.loadClass(className).nn
	| val field = clazz.getDeclaredField(fieldName).nn
	| field.setAccessible(true)
	| field.set(obj, value)
	|
	| def getOuter(obj: Any, outerTypeName: String): Any =
	| val clazz = obj.getClass
	| val field = getSuperclassIterator(clazz)
	| .flatMap(_.getDeclaredFields.nn.toSeq)
	| .map(_.nn)
	| .find { field => field.getName == "$$outer" && field.getType.nn.getName == outerTypeName }
	| .getOrElse(throw new NoSuchFieldException("$$outer"))
	| field.setAccessible(true)
	| field.get(obj)
	|
	| def getStaticObject(className: String): Any =
	| val clazz = classLoader.loadClass(className).nn
	| val field = clazz.getDeclaredField("MODULE$$").nn
	| field.setAccessible(true)
	| field.get(null)
	|
	| def getSuperclassIterator(clazz: Class[?] | Null): Iterator[Class[?]] =
	| Iterator.iterate(clazz)(_.nn.getSuperclass).takeWhile(_ != null).map(_.nn)
	|
	| // a fake method that is used between the extract-expression and the resolve-reflect-eval phases,
	| // which transforms them to calls of one of the methods defined above.
	| def reflectEval(qualifier: Object, term: String, args: Array[Object]): Any = ???
	|
	| private def unwrapException(f: => Any): Any =
	| try f
	| catch
	| case e: InvocationTargetException => throw e.getCause.nn
	|
	| extension [T] (x: T | Null)
	| private def nn: T =
	| assert(x != null)
	| x.asInstanceOf[T]
	|""".stripMargin

to get some info.

[iusildra]

Here's what I get when try-catching in the debug console 🙃

$ try { patch.span } catch { case e => e.getStackTrace() }
> 0
$ patch.span
> IllegalArgumentException@1232 "java.lang.IllegalArgumentException: object is not an instance of declaring class"
$ try { patch.span } catch { case e => println(e.getStackTrace()) }
> 0

[adpi2]

Huh that's weird.

Is 0 the expected span?

[iusildra]

Yes