[KSP2] Dagger codegen is super slow on KSP2

[mar3kk]

In our Android project with dagger+hilt the kspDebugKotlin task of the biggest module in our project is taking almost 2x the time on KSP2 than on KSP1. Checked with dagger 2.57, Kotlin 2.2.0, KSP 2.2.0-2.0.2. It feels like there already was performance regression when switching from KAPT to KSP, and with KSP2 it got incredibly bad.
I don't have a proof that this is purely a dagger ksp processor issue but there is a big chance it is. We know that in general dagger is the most time consuming ksp processor in our project. Now Kotlin 1.9 is deprecated so I assume in one of the future Kotlin releases it will be removed and we will be forced to use KSP2. What is the dagger team take on that? Is there any ongoing effort to make it more efficient? Is there any roadmap to follow?

I can run some benchmarks or get some more detailed numbers, but don't really know how to measure time spent in each KSP processor.

[bcorso]

Yes, we have heard from other users of KSP2 being slower that KSP1 (e.g. google/ksp#2282)

Note that from Dagger's perspective KSP1 and KSP2 are just two implementations of the same API, so Dagger itself doesn't do anything special for KSP2. That is, I think the root cause of these performance issues will lie in KSP2's implementation rather than Dagger itself. We have plans to do some performance investigations within Google to find and investigate Dagger KSP2 performance regressions, but this will take some time and are for Bazel not Gradle builds. Any Gradle repro projects demonstrating the performance difference between KSP1 and KSP2 would helpful so that we can pass these to the KSP team to investigate.