I've recently enabled the new inference algorithm ...

# compiler

[rocketraman]

I've recently enabled the new inference algorithm with the Kotlin 1.4 nightly (1.4.0-dev-6071) compiler. I have an inline function that calls some Java code with signature:

public <T> T deserialize(..., final Type type)

like this:

inline fun <reified T: Set<Any?>> deser(...): T? = deserialize(..., object : TypeToken<T>() {}.type)

and this used to work fine with 1.4-M1 / old inference. However, now I get a runtime error when the java code attempts to return its value to the Kotlin code:

Caused by: java.lang.ClassCastException: class java.util.LinkedHashSet cannot be cast to class java.lang.Void (java.util.LinkedHashSet and java.lang.Void are in module java.base of loader 'bootstrap')

I can "solve" this by explicitly adding the T type to the deserialize call i.e. deserialize<T>(...), but I'm wondering if this is a bug with the new type inference? The compiler does not report any errors if the <T> is left off.

[mikhail.zarechenskiy]

Thanks! At first glance, it seems like a bug to me, is there any chance we can get your project for testing?

[rocketraman]

@mikhail.zarechenskiy Upon further investigation I see that it appears to be this issue here: https://youtrack.jetbrains.com/issue/KT-25345. Not sure why this wasn't happening on 1.3.x or 1.4-M1 though because this issue is marked as affecting 1.2.41.

[rocketraman]

I've added a simple reproducer to that issue.

[rocketraman]

Maybe not, see my next post in #compiler ...

[mikhail.zarechenskiy]

Speaking about https://youtrack.jetbrains.com/issue/KT-38427 it's intended behavior, more details in https://youtrack.jetbrains.com/issue/KT-36776
But we're going to reconsider it as found several problematic examples

[rocketraman]

Ah, thanks for that background information.