Moving to Kotlin 2 (once 2.0.20 is released)

[ftomassetti]

Kotlin 2 is coming, bringing benefits to the multi-platform projects.

Current versions of Kotlin 2 (Kotlin 2.0.0-Beta3 as of now) cannot be used in production, but we may start running experiments to see if there are issues with the Kotlin 2 compiler. In my experience with other projects the migration was rather smooth, but this is a project supporting many platforms and perhaps there could be more suprises.

[lppedd]

Probably in 3/4 months?
Left is Beta4, and a couple of RCs at least.

We can already try out K2 tho.

[lppedd]

Just compiled/tested with K2, all good!

[ftomassetti]

Just compiled/tested with K2, all good!

Great!

[ftomassetti]

I guess with Kotlin 2, the K2 compiler is enabled by default, right?

[lppedd]

Yes, exactly.

K1 will be available for some minor versions IIRC (e.g., 2.2), so there is no rush in case of issues (which we don't have anyway).

[sschuberth]

Will the generated code improve with K2? This comment seems to hint at it.

[lppedd]

@sschuberth in this specific case we might benefit of future language capabilities, but the main improvement is a bit of speed up when building.

No changes for generated code, but in case you can be more specific and I can try to answer.

[lppedd]

I've tested Beta4 today with the K2 IDE.
Still not ready imo, especially the IDE plugin (you can't work in non-JVM or non-Common source sets). We can definitely update to Kotlin 2.0, but we will need to keep the API version at the 1.9 level, as that's where most users will be at for quite some time.

[ftomassetti]

Now Kotlin 2.0.0 has been released, so we could check the situation and decide if we want to move to K2 using API 1.9

[lppedd]

I've been observing the situation since beta versions. My advice is to wait until 2.0.20. That's what most issues, and they are a lot, are targeting.

[ftomassetti]

Noted, thank you

[lppedd]

Like, stuff like KT-68538 needs to be fixed before considering an update to 2.0+.
It's too risky.

[lppedd]

2.0.20-Beta1 should be out mid next week.

[JesusMcCloud]

2.0.20 stable is here

[lppedd]

@JesusMcCloud I'm going to verify the project compiled on 2.0.20 will be consumable by 1.9.24 without issues on Monday, and then I'll open a PR.

[lppedd]

Note that I want to deliver one last potentially breaking change before releasing 1.0.0 on Kotlin 2.0.20.

[JesusMcCloud]

thanks! I just stumbled upon this issue here, because the dependency on an incompatible kotlin-reflect messes with one of our (rather complex) projects on kotlin 2.0.0

[lppedd]

@JesusMcCloud I guess the dependency you're mentioning is this one:

antlr-kotlin/antlr-kotlin-runtime/build.gradle.kts

Line 32 in 7951a3f

implementation(kotlin("reflect"))

I'm not sure why it was added, but given we don't depend on reflect features, I'll get rid of it.
Good catch.

[ftomassetti]

Should we move to a newer version of Gradle? here it says that:

Support has been added for Gradle versions 8.6–8.8

perhaps as part of this task we should move to the gradle wrapper 8.8

[lppedd]

Seems reasonable. I'll do that too, we should get slightly better build times too.

[JesusMcCloud]

Would it be possible to publish one last intermed. snapshot release before the final one (not talking about RC, but a real snapshot)?

[ftomassetti]

Would it be possible to publish one last intermed. snapshot release before the final one (not talking about RC, but a real snapshot)?

I am not sure we can publish snapshots or how to do that, but if you want I can do another RC

[lppedd]

My idea is the following.

1. Merge all remaining open PRs
2. Release 1.0.0 on Kotlin 1.9.24
3. Bump to 1.1.0 and move to Kotlin 2.0.20 on K2

[JesusMcCloud]

Would it be possible to publish one last intermed. snapshot release before the final one (not talking about RC, but a real snapshot)?

I am not sure we can publish snapshots or how to do that, but if you want I can do another RC

Another RC is fine too. Getting rid of reflection is more important to us than K2 at the moment. Would be very much appreciated!

[ftomassetti]

I released RC5 right now.

We can now proceed with the plan suggested by @lppedd and release 1.0.0 and then 1.1.0 however @JesusMcCloud can use RC5 right away.

[lemcoder]

Hello, Can you please tell what is the state of migrating to Kotlin 2? I'd also be glad to help with migration

[lppedd]

@lemcoder I'm waiting for KT-66125 to be addressed.
1.9.x artifacts will still be consumable by 2.1.x tho, so there is no real pressure as of now, unless some unknown breaking change comes up.

[lppedd]

KT-73130 is another one that could mess up the JS parser.

[lemcoder]

Hey @lppedd it seems like both issues had been fixed now 🙌

[lppedd]

All in all it looks like 2.1.20 will be the version to update to.
Looking at YouTrack I don't see any other important issue.

[lppedd]

I'd like to understand this first.

See https://youtrack.jetbrains.com/issue/KT-74067