Exposing internal types check is too strict

Language Design
1

There are cases where internal types are not leaked, but the compiler complains regardless.

Example:

internal class InternalClass()

sealed class SealedClass() {

    protected fun ExposesInternal(): InternalClass {
        ...
    }
}

In this case the compiler complains that the ExposesInternal function exposes InternalClass, but given that the class that is using it is a sealed class and the function has protected visibility this is not the case.