Subtle change in outer capture under -Ydelambdafy:method

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// test.scala
class C {
  def test {
    println({() => class D; classOf[D].getDeclaredFields.mkString(",")}.apply())
  }
}

object Test {
  def main(args: Array[String]): Unit = {
    new C().test
  }

}

% scalac-hash v2.11.7 test.scala  && scala-hash v2.11.7 Test
public final C$$anonfun$test$1 C$$anonfun$test$1$D$1.$outer

% scalac-hash v2.11.7 -Ydelambdafy:method test.scala  && scala-hash v2.11.7 -Ydelambdafy:method Test
public final C C$D$1.$outer

This difference is observable via a change in memory retention, or a change in the serializability of D (as seen in the wild in Shapeless: milessabin/shapeless@ac12155)

I'm not really sure why we need an outer pointer at all for a local class such as D.

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Imported From: https://issues.scala-lang.org/browse/SI-9408?orig=1
Reporter: @retronym
Affected Versions: 2.11.7
See #4440, #1419

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@retronym said:
See also the discussion bewteen me and @milessabin on on the shapeless commit: milessabin/shapeless@ac12155

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@milessabin said (edited on Jul 19, 2015 10:39:25 AM UTC):
See eventual fix in shapeless here.

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@retronym said:
Here's an attempt to infer the finality of local classes with respect to the outer pointer elision optimization: scala/scala@2.12.x...retronym:ticket/9408

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@retronym said:
scala/scala#4652

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@milessabin said:
Awesome ... thanks :-)