Hey, what's wrong here? I don't get any syntax err...

# announcements

[Sebastian Krajewski]

Hey, what's wrong here? I don't get any syntax error but compilator crashes with this message:

Cause: Label wasn't found during iterating through instructions
Element is unknownThe root cause was thrown at: LabelNormalizationMethodTransformer.kt:148

-.kt

[Sebastian Krajewski]

Oh, this also causes a compilator crash:

class foo(var bar : String)

fun main() {    
    var baz : foo? = foo("test")
    baz?.bar += "test"
}

[streetsofboston]

Is it because may be trying to assign a value to a null property…?
baz?.bar could be null. Then you may wind up with null += test.
This should not compile. But instead of a compiler error you get a compiler crash…

[streetsofboston]

I get the same error

[Sebastian Krajewski]

But ?. operator ensures that you work on an instance

[streetsofboston]

What you’d want is baz?.let { it.bar += test }

[streetsofboston]

This is a simplified version of the bug you found:

class Container(
    var value : String = ""
)

fun bug() {
    val container : Container? = null
    container?.value += "2"
}

It seems to come from the += operator with an optional/nullable left-hand side expression

[Sebastian Krajewski]

Yep, because ?.plus() seems to work

[Sebastian Krajewski]

But if value is non nullable and property is called safely, why it needs safe call?

[streetsofboston]

I think since a String is a immutable class, the += is not a plusAssign. It probably rewrites it a object = object + param, which may fail….

[streetsofboston]

Rewriting it manually works….

class Container(
    var value : String = ""
)

fun bug() {
    val container : Container? = null
    container?.value = container?.value + "2"
}

You should file a bug.

[Sebastian Krajewski]

It is already filled

[streetsofboston]

Do you have the link to the bug? I’d love to share it with my teams here. Thank you!

[Sebastian Krajewski]

It was filled by my friend: https://youtrack.jetbrains.com/issue/KT-31135