IssueTracker

Sealed classes and interfaces cannot be extended directly outside their module. Intuitively this implies they are effectively final, and therefore otherwise incompatible changes would be allowed, such as adding a new abstract method.

Unfortunately, it's possible to extend a sealed class with an abstract class as below and inadvertently expose a new abstract method (funFromSealed() in the example below). We should figure out how we want to model this behavior in Metalava, figure out if there's any other considerations to sealed classes, and then maybe update ClassItem.isEffectivelyFinal() to match.

sealed class Sealed {
    abstract fun funFromSealed()
}

abstract class Abstract : Sealed()

class Concrete : Abstract() {
    override fun funFromSealed()
}