AbstractMethodError or IllegalAccessError exception calling member of a specialized class in another module

[OndrejSpanel]

reproduction steps

using Scala 2.13.3, 2.12.2, 2.11.12 or 2.10.7 (other versions not tested)

Clone https://github.com/OndrejSpanel/SpecRepro or use the files as below:

Buffer.scala:

trait ABuffer[@specialized(Float)T] {
  def count: Int
}

class Buffer[@specialized(Float) T](array_par: Array[T]) extends ABuffer[T] {
  var array: Array[T] = array_par

  var count: Int = 0
}

class Float32Buffer(array_par: Array[Float]) extends Buffer[Float](array_par)

Main.scala:

object Main extends App {

  val vertices = Array[Float]()

  val attribute = new Float32Buffer(vertices)
  println(attribute.count)

}

build.sbt:

name := "SpecRepro"

val commonSettings = Seq(scalaVersion := "2.13.3")

lazy val root = (project in file(".")).settings(commonSettings)

lazy val examples = (project in file("examples")).dependsOn(root).settings(commonSettings)

problem

When running Main, an exception java.lang.AbstractMethodError is thrown.

Notes

This is extracted from a real-life problem, where the module root is in fact a library used in a different sbt project.

• the issue cannot be seen if both sources are located in the same SBT module
• the issue goes away if you change var count to def count
• the issue goes away if you change var array to var array: Array[T] = _
• the issue goes away if you remove any of the two @specialized annotations
• if you change var count to val count, an exception java.lang.IllegalAccessError si thrown instead

I was unable to reproduce the issue with Dotty 0.27.0-RC1

[SethTisue]

I was unable to reproduce the issue with Dotty 0.27.0-RC1

Dotty simply ignores @specialized

[OndrejSpanel]

It seems the issue was already described in http://aleksandar-prokopec.com/2013/11/03/specialization-quirks.html:

Specialization in 2.10 has a problem of specializing constructors in some cases

With explanation and a workaround:

I won’t get into why the above fails the way it fails - suffices to say that the specialization creates specialized fields in the specialized variants of the class and does not properly rewire the bridges for the field accessor methods in the constructor body correctly. Here is the pattern to solve the above issues - create a method init in which you initialize the troublesome fields:

[joroKr21]

Looks like the names are mangled for some reason:

scala> typeOf[Buffer[_]].decls.toList.map(_.name).foreach(println)
array_par
<init>
array
array_$eq
array
$line3$$read$$iw$Buffer$$count
$line3$$read$$iw$Buffer$$count_$eq
$line3$$read$$iw$Buffer$$count