NoSuchMethodError for field accessor of local class

[LPTK]

The following code generates a NoSuchMethodError at runtime when using Scala 2.12 but not when using Scala 2.11:

  def transformer(rec_pf: (Tree => Tree) => PartialFunction[Tree, Tree]) =
    new Transformer {
      val pf: PartialFunction[Tree, Tree] = rec_pf(transform) // on Scala 2.12, this raises: java.lang.NoSuchMethodError: squid.utils.meta.UniverseHelpers$$anon$5.pf()Lscala/PartialFunction
      // ^ solved if we make it a def
      override def transform(x: Tree) = pf.applyOrElse(x, super.transform)
    } transform _

Here is the crash reproduced in the REPL:

Welcome to Scala 2.12.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_65).
Type in expressions for evaluation. Or try :help.

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> def transformer(...

scala> transformer(k => { case q"0" => q"1" })
res0: reflect.runtime.universe.Tree => reflect.runtime.universe.Tree = $$Lambda$15192/118067290@3ec611bc

scala> res0(q"Some(0).get")
java.lang.NoSuchMethodError: $anon$1.pf()Lscala/PartialFunction;
  at $anon$1.transform(<console>:18)
  at .$anonfun$transformer$1(<console>:19)
  ... 38 elided

[howtonotwin]

This can be simplified to some more basic types:

def f[A](v: A) = x => {
    (new Function1[A, A] {
      val u = v
      override def apply(x: A) = u
    }).apply(x)
  }
f("")("a")

And the eerie thing is that adding a type signature fixes it:

def f[A](v: A): A => A = ???

[lrytz]

Fixed by scala/scala@9614c3a / scala/scala#7340