AbstractMethodError when overriding java method with default implementation which implementation is "muted" in inherited interface

[unkarjedy]

reproduction steps

using Scala (2.13.3),

public interface BaseRootJava {
    default boolean startInWriteAction() {
        return true;
    }
}

public interface BaseIntermidiateJava extends BaseRootJava {
    String getText();

    @Override
    boolean startInWriteAction();
}

class ChildScala extends BaseIntermidiateJava {
  override def getText: String = ""
}

object Main {
  def main(args: Array[String]): Unit = {
    val action = new ChildScala
    println(action.startInWriteAction())
  }
}

problem

This code compiles but throws an error at runtime:

Exception in thread "main" java.lang.AbstractMethodError: Method MyIntentionActionScala.startInWriteAction()Z is abstract
	at MyIntentionActionScala.startInWriteAction(MyIntentionActionScala.scala)
	at Main$.main(Main.scala:5)
	at Main.main(Main.scala)

java analog will not compile

public class ChildJava implements BaseIntermidiateJava {
    @Override
    public String getText() { return null; }
}

[unkarjedy]

related: https://youtrack.jetbrains.com/issue/SCL-18412

[Jasper-M]

Is getText necessary to reproduce?

[dwijnand]

I think it should "do the right thing" (return true), but if javac doesn't compile it perhaps it does so for a good reason, worth following.

[Jasper-M]

I think it should "do the right thing"

There doesn't seem to be agreement on what the right thing is.

Scala 2.13

scala> trait Foo { def foo = "foo" }
     | trait Bar extends Foo { override def foo: String }
     | class Baz extends Bar
trait Foo
trait Bar
class Baz

Dotty (lampepfl/dotty#4770)

scala> trait Foo { def foo = "foo" }                                            
     | trait Bar extends Foo { override def foo: String }
     | class Baz extends Bar
3 |class Baz extends Bar
  |      ^
  |  class Baz needs to be abstract, since override def foo: => String is not defined 

I've never quite understood the reasoning behind Scala 2's behavior actually...