I'm experiencing some unreal `"Unreachable Code"` with K2 Mode active. Has anyone got the same issue...

# k2-adopters

[Giorgio Vespucci]

I'm experiencing some unreal "Unreachable Code" with K2 Mode active.
Has anyone got the same issue?

[dmitriy.novozhilov]

Providing some code examples would be helpfull

[Giorgio Vespucci]

Eh! It's proprietary code, in my case, I don't know whether I can arrange a public showcase... :(

[Giorgio Vespucci]

const val DASH_PREFIXED_INPUT_EXPECTED_RESULT = "I am reachable for any input prefixed by `-`"
const val NULL_INPUT_EXPECTED_RESULT = "I am reachable for any null input"
val ANY_OTHER_INPUT_EXPECTED_RESULT = null

fun main() {
    check(unreachable("-hello") == DASH_PREFIXED_INPUT_EXPECTED_RESULT)
    check(unreachable(null) == NULL_INPUT_EXPECTED_RESULT)
    check(unreachable("goodbye") == null)
    println("All good")
}

fun unreachable(input: String?): String? {
    return input?.let {
        return if (it.startsWith("-")) {  
           DASH_PREFIXED_INPUT_EXPECTED_RESULT
        } else {
            ANY_OTHER_INPUT_EXPECTED_RESULT
        }
    } ?: NULL_INPUT_EXPECTED_RESULT
}

[Giorgio Vespucci]

It should raise the alert

[Giorgio Vespucci]

unreachable-k2-mode.png

[dmitriy.novozhilov]

Thanks. I believe it's a KTIJ-32807.

You can workaround it by removing the return inside let, as it's effectively unused (at least in the example you've provided)

[Giorgio Vespucci]

I believe the inner return is necessary, otherwise the Elvis would kick in

The let expression would output a null, and the Elvis operator will return the fallback value

Is that right?

[Giorgio Vespucci]

We leveraged what we found here https://medium.com/google-developer-experts/the-hidden-pitfalls-of-the-elvis-operator-da536ba68161

[dmitriy.novozhilov]

Ah, you are right indeed.

[Roman Golyshev]

JIC: This false positive “unreachable code” does not reproduce in K2 Mode anymore, at least in the current Nightly, so it should be fixed for you in 252 release

Could you please share your IDEA version?

[Giorgio Vespucci]

Sure