Support the K2 Compiler

[JoelWilcox]

For now this is just a placeholder to track future K2 support, and to document that Anvil is currently incompatible with K2 as folks start testing it out in projects that may be using Anvil.

[joshfriend]

Can the k2 warning be disabled (or shown only once)? It shows up literally thousands of times in build logs when K2 is enabled.

[chrisjenx]

With 1.9.20 out and 2.0 next, is there an ETA for K2 support, as would love to start testing and sending feedback to the KT team.

[ZacSweers]

No ETA currently, we more or less have to get #751 and #704 done first

[matejdro]

K2 seems to be out and stable now. As far as I can see, there is no way of disabling it for Kotlin 2.0? So all Anvil projects are stuck at 1.9 for now.

[ZacSweers]

As far as I can see, there is no way of disabling it for Kotlin 2.0?

You can force language version 1.9 while still using Kotlin 2.0.0.

You can get fairly far with the 2.5.0 betas. I wrote some instructions here: https://www.zacsweers.dev/preparing-for-k2/#anvil. The TL;DR is that yes, projects with component merging will require language version 1.9, but any projects using just factory gen can use KSP instead.

We're working on it, we didn't expect the IR APIs we use to break in 2.0 as they weren't annotated as obsolete in the compiler.