Feature request: Support KSP

[davidjwiner]

For Kotlin projects, Dagger currently makes use of KAPT. This is generally quite slow since it requires generating Java stubs before the annotation processing step.

KSP offers an alternative to this by making it easier for annotation processors like Dagger to more directly use Kotlin's compiler plugin infrastructure. Based on initial benchmarks, using KSP can speed up build times by as much as 2x.

[Chang-Eric]

Just updating this to give a sense of where we are at. This is a priority for us that we are looking into. There are some complications though mostly due to the SPI plugins which expose the JSR-269 APIs through our public interface. There’s also the fact that our annotation processor code base is huge.

Because we still need to support our javac users, we cannot switch entirely to the KSP APIs which leaves us in a bit of a pickle since the places these are exposed are deep in our core model classes. I don’t think there is a possible way to get around this being a breaking API change, but we’ll need to figure out the right API to switch to that can support both KSP and javac SPI users.

Anyway, all this is to say, this is a high priority and we are working on this, but it is also a complicated thing to rollout for a codebase our size.

[ZacSweers]

Can you use compiler-processing from Room to simultaneously support both? SPI users can, for now at least, be told they're unsupported in KSP (which seems fair considering the SPI API is javac-based anyway).

[Chang-Eric]

Thanks for the pointer, we are already in discussion with that team about that as a possibility =)

[CoreFloDev]

Hi any update on this? Thanks!

[Chang-Eric]

Still working on it. We're preparing a new model that will wrap both javac and KSP types like in this recent change: 30fa0f3

[Jeffset]

SPI users can, for now at least, be told they're unsupported in KSP

I've opened a separate issue #2802 for that to track status and discuss possible solutions as my team is concerned about KSP support in SPI.

[bcorso]

@Jeffset, once we're ready to support KSP in Dagger, we will likewise support KSP in the SPI plugins as well. I think we can probably close #2802 , as this issue should track both.

Just to give you more details on our plans for the SPI plugin:

The new SPI model currently exists, and we are beginning to use it internally in Dagger. However, it is not yet available for users to write their own plugins.

The new model will be a thin wrapper around the javac/ksp types. For example, DaggerElement is a wrapper around Element in javac and KSDeclaration in KSP. If you need access to the javac or KSP types directly in your plugin, you will be able to call .compiler() to get which environment you're currently in (i.e. javac or KSP), and then call .javac() or .ksp() respectively to get access to the types.

Feel free to let us know if you have any concerns.

[ColtonIdle]

KSP is officially 1.0!
https://android-developers.googleblog.com/2021/09/accelerated-kotlin-build-times-with.html

My last dep that uses kapt is dagger + hilt! Do we have any estimated timeline? Just curious if this is a "likely by the end of 2021" type of feature request, or a "likely by the end of 2022" type of feature request. 😅

[ZacSweers]

Dagger maintainers are pretty good about posting updates, let's trust a push system rather than nagging about something they are obviously aware of and working on.

[Chang-Eric]

Updating here since it has been some time. We've been making progress on the KSP migration, which includes making changes to Room's xprocessing libraries which we are using. Things were recently delayed for a while as the migration uncovered and exacerbated an existing issue which is the main change of the 2.41 release we just did. This issue caused a large delay not only in pulling people off the migration but also because we were afraid of making the problem worse by continuing the migration.

For that reason, it is still hard to give any sort of estimate as it is really the unknowns that we're going to hit that will take the bulk of the time. Just that one issue discovered set us back a couple months. With that said, now that the 2.41 release is finally out, we are now unblocked to continue the migration work.

[johnnycrq]

any news here?