Compiler crash: assignment inside anonymous class inside value class

[allanrenucci]

class StringOps(val s: String) extends AnyVal {
  def lines: Iterator[String] = new collection.AbstractIterator[String] {
    private[this] var index = 0
    def hasNext: Boolean = false
    def next(): String = {
      index = 1 // I'm causing the crash
      ""
    }
  }
}

> dotc Test.scala
Exception in thread "main" java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:204)
	at dotty.tools.dotc.ast.tpd$TreeOps$.$anonfun$becomes$1(tpd.scala:864)
	at dotty.tools.dotc.core.Symbols$Symbol.orElse(Symbols.scala:554)
	at dotty.tools.dotc.ast.tpd$TreeOps$.becomes$extension(tpd.scala:863)
	at dotty.tools.dotc.transform.Getters.transformAssign(Getters.scala:75)
	at dotty.tools.dotc.transform.MegaPhase.goAssign(MegaPhase.scala:667)

[allanrenucci]

Setters are generated during Desugar. At this time Local flags are not removed yet. However during Getter the flag has been removed and can't be recovered inside value classes. Not seeing the Local flag, Getter expects a setter to be generated but can't find it.