scala编译期间的合成值

Question

何时生成合成值？它们用于什么？在哪个编译器阶段被删除？在制作scala编译器插件时，我一直遇到有关合成值的错误。这是错误：

  

错误：scala.reflect.internal.FatalError：     符号值x $ 3＃33790在scala.collection.immutable.Stream.scala $ collection中不存在$ immutable $ Stream $$ advance $ 1，其中包含locals值newvalue＃39255，value newvalue＃39254，value rest＃33601，value stub1 ＃33600，值stub0＃33599。

Method code: def advance(stub0: List[A], stub1: List[A], rest: Stream[A]): Stream[A] = if (rest.isEmpty())
  Stream.empty()
else
  {
    if (stub0.isEmpty())
      {
        val newvalue: scala#27.collection#2835.immutable#5932.Stream#8383 = Stream.this.scala$collection$immutable$Stream$$advance$1(stub1.reverse(), Nil, rest);
        newvalue
      }
    else
      {
        val newvalue: collection#2835.immutable#5932.Stream$Cons#11078 = scala.collection.immutable.Stream$cons.apply(stub0.head(), {
          ((new <$anon: Function0#2069>(Stream.this, stub0, stub1, rest, x$3)): Function0#2069)
        });
        newvalue
      }
  }