“Leaking ‘this’ in constructor” warning should apply to final classes as well as open ones?

tl;dr: https://youtrack.jetbrains.com/issue/KT-22044 is a good fit regarding this issue.

I will cite what Intellij IDEAs inspection called “Leaking ‘this’ in constructor” says about this:

This inspection reports dangerous operations inside constructors including:

• Accessing a non-final property in constructor
• Calling a non-final function in constructor
• Using this as a function argument in a constructor of a non-final class

These operations are dangerous because your class can be inherited, and a derived class is not yet initialized at this moment. Typical example:

abstract class Base {
    val code = calculate()
    abstract fun calculate(): Int
}

class Derived(private val x: Int) : Base() {
    override fun calculate() = x
}

fun testIt() {
    println(Derived(42).code) // Expected: 42, actual: 0
}

I think that there should be warning nonetheless as you were able to access a non-initialized variable. The reason: the compiler already disallows direct access to uninitialized variables, i.e. the following will not compile:

class Demo {
  val some : Int
  init {
    println(some) // Variable 'some' must be initialized

but accessing it indirectly compiles and shows the default value of the variable type:

class Demo2 {
  val some : Int
  val someString : String
  init {
    fun Demo2.indirectSome() = some
    fun Demo2.indirectSomeString() = someString
    println(indirectSome()) // prints 0
    println(indirectSomeString()) // prints null; and yes.. this can lead to NullPointerExceptions

and there we also have a “leak”, basically accessing some before it should 😉