> Leaked in-place lambda: block: suspend (T) -&...

# k2-adopters

[Oliver.O]

Leaked in-place lambda: block: suspend (T) -> R

What is the compiler trying to tell me? (Code in 🧵)

[Oliver.O]

suspend fun <T : ExecutorCoroutineDispatcher, R> T.useWithBlockHound(block: suspend (T) -> R): R {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    var exception: Throwable? = null
    try {
        return block(this)
    } catch (e: Throwable) {
        exception = e
        throw e
    } finally {
        withContext(NonCancellable) {
            withBlockHoundMode(BlockHoundMode.DISABLED) {
                closeFinally(exception)
            }
        }
    }
}

One warning message is referring to the line contract {.
A second one refers to return block(this).

[Oliver.O]

And then there's

block: suspend (T) -> R has wrong invocation kind: given EXACTLY_ONCE case, but ZERO case is possible

warning at line contract {, but for that I've already filed KT-63414.

[dmitriy.novozhilov]

Usually this diagnostic means that lambda declared as calls-in-place is leaked into some not in-place context (e.g. send to some executor or saved into variable)
But this particular case seems like a bug, so n please report another issue

[Oliver.O]

Thanks for the explanation. It seems the warning is basically addressing KT-15514. Will report the above case.

[Oliver.O]

Seems that the compiler has a point, though: The docs say that functions declaring callsInPlace must be inline. If I change the above accordingly, the "leaked in-place lambda" warnings disappear. Created KT-63416.