partial function defined in value class method results in spurious implementation restriction

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{code}
scala> class Foo(val a: Int) extends AnyVal { def foo = { {case x => x}: PartialFunction[Int, Int]; () }}
:7: error: implementation restriction: nested class is not allowed in value class
This restriction is planned to be removed in subsequent releases.
class Foo(val a: Int) extends AnyVal { def foo = { {case x => x}: PartialFunction[Int, Int]; () }}{code}

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Imported From: https://issues.scala-lang.org/browse/SI-7571?orig=1
Reporter: @ijuma
Affected Versions: 2.10.0

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@paulp said:
It's "spurious" in the sense that you shouldn't have to know that partial functions are implemented with anonymous objects; but it's genuine in the sense that partial functions are implemented with anonymous objects.

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@retronym said:
I'm trying to remember exactly why the restriction exists (5d9cde105e); I suspect it is because we can't define an $outer pointer. But I don't think that is relevant for this case.

class Foo extends AnyVal {
  def foo = () => 0 // okay
  def bar = {case x => x} : PartialFunction[Int, Int] // should also be okay IMO
}

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@retronym said:
scala/scala#2648

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@paulp said:

I'm trying to remember exactly why the restriction exists (5d9cde105e); I suspect it is because we can't define an $outer pointer.

Yes, that's why.