Kotlin interop: reporting wrong type for inner classes appearing in Kotlin method types

[jbwheatley]

Compiler version

3.0.0-RC2

Minimized code

I'm working with a library that is written in kotlin, and running into a compilation error on 3.0.0-RC2 that doesn't happen on 2.13.5. The decompiled .class file looks like:

public abstract class VerificationResult {
  public static final class Ok extends VerificationResult {...}
  public static final class Failed extends VerificationResult {...}
  ...
}

and then there is a method on another class like:

public void displayFailures(@NotNull List<Failed> failures)

I then get this compiler error when calling the method:

Output

[error] 16 |            verifier.displayFailures(List(failed).asJava)
[error]    |                                     ^^^^^^^^^^^^^^^^^^^
[error]    |Found:    java.util.List[au.com.dius.pact.provider.VerificationResult.Failed]
[error]    |Required: java.util.List[au.com.dius.pact.provider.VerificationResult$Failed]

Expectation

Should compile.

[smarter]

We need a way (ideally minimized) to reproduce the problem, otherwise there's not much we can do about it.

[jbwheatley]

Foo.java as:

package foo;
import foo.Foo.Bar1;
import java.util.List;

public abstract class Foo {
    public static final class Bar1 extends Foo {}
    public static final class Bar2 extends Foo {}
}

class Baz {
    public void bars(List<Bar1> bs) {
        bs.clear();
    }
}

FooScala.scala as:

package foo
import Foo._
import scala.jdk.CollectionConverters._

object FooScala {
  def doThings(foo: Foo): Unit =
    foo match {
      case b: Foo.Bar1 => new Baz().bars(List(b).asJava)
      case _: Foo.Bar2 => ()
    }
}

will recreate the issue

[smarter]

Thank you for the minimization, I just tried it but I can't reproduce the issue (the code compiles fine), can you list the steps you use to reproduce the problem and the version of javac you have?

[jbwheatley]

Running sbt +compile at my project route. sbt is using java 14.0.1, presumably that is the issue?

[smarter]

I don't have java 14 here, but I can't reproduce with either java 8 or 15 locally, could you try using a different version?

[jbwheatley]

oh I'm an idiot, I was getting my errors all mixed up (sorry, end of the day here in UK). My minimized example isn't causing the error for me 🤦 I'm stuck for a way to reproduce this for you besides having you try it with the library I am using

[smarter]

I know that feeling :). if you can minimize it to a scala file that depends on a publicly available library that would be useful already.

[jbwheatley]

Finally got something for you! 😁 https://scastie.scala-lang.org/e4TAeoEISaeDFNE4HqbrnQ

[smarter]

Thank you! This can be reproduced using coursier with:

scalac -classpath "$(cs fetch -p au.com.dius.pact:provider:4.2.0)" Test.scala

@prolativ You've worked on inner classes recently, so you might be able to figure out what's going on here