AbstractMethodError when implementing abstract @varargs method

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import scala.annotation.varargs

abstract class VarargAbstractClass {
  @varargs
  def x(els: String*): Int
}
class ClassImplementsClass extends VarargAbstractClass {
  override def x(els: String*): Int = els.length
}

fails with an AbstractMethodError when the method is called from Java like this:

VarargAbstractClass i = new ClassImplementsClass();
i.x("a", "b", "c");

See more examples in this file:

https://github.com/jrudolph/scala-broken-java-varargs/blob/master/src/test/java/example/Test.java

I first thought that this was related to #1459 but I know think it is a separate issue. It seems the main problem is that the forwarder in VarargAbstractClass is created as abstract because in Uncurry flags from the original method are just copied to the forwarder method. Clearing the DEFERRED flag for the forwarder method seems to fix this issue for me (but I didn't run the complete test suite to look for other problems).

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Imported From: https://issues.scala-lang.org/browse/SI-9013?orig=1
Reporter: @jrudolph
Affected Versions: 2.10.4, 2.11.4
See #1459, #3899

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Joseph K Bradley (jkbradley) said:
Are there any known workarounds for this yet? (Thanks in advance for any help!)

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@retronym said:
Related: #3899 / #1459

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@retronym said (edited by @adriaanm on Jun 11, 2015 12:50:41 PM UTC):
WIP: https://github.com/retronym/scala/tree/ticket/9220

(scala/scala@53bc6d2)

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Reynold Xin (rxin) said:
Any idea when we might be able to fix this in a Scala 2.10.x release? If we can't fix this, we would be forced to rewrite the DataFrame APIs in Spark in Java, in order to support streaming functionality, which would require defining abstract vararg methods.

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@adriaanm said:
We should fix this in 2.11, but we're not planning to release further 2.10.x releases. https://github.com/scala/scala/releases/tag/v2.10.5 was the last one.

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Michael Rüegg (mrueegg) said:
I've just stumbled over this issue. With my Gist, I was able to verify that this actually worked in Scala 2.10.4 but now I get an AbstractMethodError in 2.11.7. See here: https://gist.github.com/mrueegg/f191e547bee6a24a6bcf

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Reid Spencer (reactific) said:
This issue bit me today. In my case it comes from attempting to implement OrientDB's OBinarySerializer class with a Scala implementation. I have tried several ways to fix this except implementing it in Java which I will try next. I'm looking forward to this being fixed in 2.11.9.

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@adriaanm said:
scala/scala#5631