Kotlin K2 Support

[mgroth0]

Testing Problem

I am testing with Kotlin K2 (Kotlin version 2.0.0-Beta2). I just discovered jqwik and wanted to play around with it and consider integrating it into my projects. The docs for kotlin say to include these compiler arguments:

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf(
            "-Xjsr305=strict", // For strict type warnings
            "-Xemit-jvm-type-annotations" // Required for annotations on type variables
        )
        jvmTarget = "11" // 1.8 or above
        javaParameters = true // Required to get correct parameter names in reporting
    }
}

I tried to add the two compiler arguments above, but then got the following warnings:

w: Flag is not supported by this version of the compiler: -Xjsr305=strict
w: Flag is not supported by this version of the compiler: -Xemit-jvm-type-annotations

This signals to me that jqwik does not yet have first class support for Kotlin 2, so I am hesitating to use it for now.

Suggested Solution

I suggest to add support for Kotlin 2. The documentation could be updated to say how the user should configure kotlin if they use K2, which would also reasure the user that K2 is supported.

[vlsi]

I guess the mentioned flags are outdated, and they should be removed

[jlink]

K2 is still in beta with the latest Kotlin release (1.9.22), isn't it.
My plan is to update to K2 as soon as it is the default, which I assume will be in Kotlin 2.0.

What if we use this issue to document the problems with K2 and the stuff that has to be changes, like dropping some compiler flags - and maybe adding others.

BTW, @mgroth0 What's the correct way to use K2 from Gradle with the current Kotlin release?

[vlsi]

See https://kotlinlang.org/docs/whatsnew19.html#try-the-k2-compiler-in-your-project

./gradlew -Pkotlin.experimental.tryK2=true ...

[jlink]

Thanks @vlsi .
A first try leads to many compilation errors. Arrgh.

[vlsi]

The majority of compilation errors are caused by jsr305 annotations.

WDYT of completely removing jsr305 from jqwik?
For instance, https://github.com/jqwik-team/jqwik/blob/main/api/src/main/java/net/jqwik/api/NonNullApi.java effectively marks everything as non-null no matter if you specify it with jspecify.

[vlsi]

I think you should be able to drop @NonNullApi (along with jsr305 dependency), and add @NullMarked at the package level: https://jspecify.dev/docs/user-guide#java-variables-are-references

[jlink]

At least worth a try.

[mgroth0]

Thank you both for looking into this and for giving K2 a shot.

I've been working with K2 for a month or so now. It's still unstable, and I've had to create workarounds for many issues. Sorry for dumping this on you guys. It might be smart to wait a few more months at least. I expect Jetbrains will have resolved many more issues by then.

[vlsi]

jsr305 removal makes sense even without K2