Compiler exception in innocent code.

[scabug]

In trunk:

case class Property[T](private var t: T) {
 var beforeChanges: List[(T, T) => Unit] = Nil
 var afterChanges: List[T => Unit] = Nil
 def apply = t
 def update(t2: T) = {
  beforeChanges foreach (_(t, t2))
  t = t2
  afterChanges foreach (_(t2))
 }
}

causes:

Exception in thread "main" java.lang.Error: symbol value t$$1$$1 does not exist in line3$$object$$$$iw$$$$iw$$Property.equals
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:918)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.genLoadArguments(GenICode.scala:1109)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:826)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.genCond(GenICode.scala:1401)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:432)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:945)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:945)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:945)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:455)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:945)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:945)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.genCond(GenICode.scala:1401)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.scala$$tools$$nsc$$backend$$icode$$GenICode$$ICodePhase$$$$genLoad(GenICode.scala:764)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:114)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase$$$$anonfun$$gen$$1.apply(GenICode.scala:71)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase$$$$anonfun$$gen$$1.apply(GenICode.scala:71)
        at scala.collection.generic.LinearSequenceTemplate$$class.foreach(LinearSequenceTemplate.scala:81)
        at scala.collection.immutable.List.foreach(List.scala:26)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:71)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:136)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:90)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase$$$$anonfun$$gen$$1.apply(GenICode.scala:71)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase$$$$anonfun$$gen$$1.apply(GenICode.scala:71)
        at scala.collection.generic.LinearSequenceTemplate$$class.foreach(LinearSequenceTemplate.scala:81)
        at scala.collection.immutable.List.foreach(List.scala:26)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:71)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:81)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.gen(GenICode.scala:67)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.apply(GenICode.scala:63)
        at scala.tools.nsc.Global$$GlobalPhase.applyPhase(Global.scala:311)
        at scala.tools.nsc.Global$$GlobalPhase$$$$anonfun$$run$$1.apply(Global.scala:289)
        at scala.tools.nsc.Global$$GlobalPhase$$$$anonfun$$run$$1.apply(Global.scala:289)
        at scala.collection.Iterator$$class.foreach(Iterator.scala:500)
        at scala.collection.mutable.ListBuffer$$$$anon$$1.foreach(ListBuffer.scala:280)
        at scala.tools.nsc.Global$$GlobalPhase.run(Global.scala:289)
        at scala.tools.nsc.backend.icode.GenICode$$ICodePhase.run(GenICode.scala:56)
        at scala.tools.nsc.Global$$Run.compileSources(Global.scala:787)
        at scala.tools.nsc.Interpreter$$Request.compile(Interpreter.scala:712)
        at scala.tools.nsc.Interpreter.interpret(Interpreter.scala:426)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:329)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:339)
        at scala.tools.nsc.InterpreterLoop.command(InterpreterLoop.scala:306)
        at scala.tools.nsc.InterpreterLoop.processLine$$1(InterpreterLoop.scala:203)
        at scala.tools.nsc.InterpreterLoop.repl(InterpreterLoop.scala:221)
        at scala.tools.nsc.InterpreterLoop.main(InterpreterLoop.scala:377)
        at scala.tools.nsc.MainGenericRunner$$.main(MainGenericRunner.scala:126)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-2175?orig=1
Reporter: Ricky Clarkson (ricky_clarkson)

[scabug]

@lrytz said:
can you have a look at it and find out what part of the compiler is causing it?

[scabug]

@TiarkRompf said:
sorry, I'm swamped with exam stuff at the moment. Iuli, can you have a look?

[scabug]

@dragos said:
This is a bug in the pattern matcher. It generates a reference to a synthetic local val which is not defined.

[scabug]

@paulp said:
Replying to [comment:5 dragos]:

This is a bug in the pattern matcher. It generates a reference to a synthetic local val which is not defined.

I think this is another variation on the many bugs which swirl around private in case classes. Some I have hacked around unpleasantly, some are still outstanding (especially when you kick it up a notch to private[this]) and I'm not at all sure they can be dealt with sanely.

I really wonder why someone would want "private var" as a case class field anyway... I would like to propose off the cuff that neither "private" nor "var" be allowed in the first parameter list to a case class. Put anything you want in the second. OK, so multiple parameter lists to case classes are totally broken right now, but if fixed that would offer some measure of sanity.

Not that this doesn't still need to be fixed, but I'm afraid it will end up being another ugly band-aid around the dancing privates.

FWIW neither of these crashes:

case class Property[T]()(private var t: Int)
case class Property[T](var t: Int)

[scabug]

Ricky Clarkson (ricky_clarkson) said:
Though I'm the reporter I'd agree that Scala probably shouldn't support this. The code dates from a time when I was 'case class happy'. I wouldn't use private or var with case classes today.

[scabug]

@paulp said:
Couldn't tell you when this domino fell, but fall it did. Test case in r18927.