[java-interop] Compilation error "incompatible type in overriding" when inheriting from a Java subclass with different field type to parent class (regression in 2.13)

[hughsimpson]

Minimal to reproduce:

public class Base {
    long[] counts;
}

public class Cover extends Base {
    int[] counts;
}

Extending in Scala:

class LocalImpl extends Cover

throws incompatible type in overriding in 2.13.0 (compiles for 2.10.7, 2.11.12, 2.12.7)

[SethTisue]

Nicely minimized.

At first I thought this might be an access thing, but it's not, it's a method-vs-field thing. Make the fields public, javac still accepts it. But make the fields into methods, and javac of course says counts() in Cover cannot override counts() in Base, regardless of whether they're public-access or default-access.

It seems sad that this is even legal Java...

@retronym @adriaanm scala/scala#7671 ? scala/scala#7929 ?

[adriaanm]

Yeah, looks like another victim of the stricter refchecks in scala/scala#7439.
We'll need to add a few exemptions in the logic for when we're dealing with Java pairs

[hughsimpson]

For posterity, the workaround in my case was to use a delegate pattern and not subclass directly. cf kamon-io/Kamon@4ca896d