From the `fir-plugins.md` doc file and the `fir-pl...

# k2-adopters

[Tadeas Kriz]

From the fir-plugins.md doc file and the fir-plugin-prototype it seems like there's no support for running a visitor/transformer similar to IrGenerationExtension. Is that a current limitation, or am I just missing something? I'd like to run a transformer visitor on FIR in any of the FIR phases. Is it supported and if not, will it be? Thanks!

Or maybe if it'll still be through extensions like it is now, will there be support for more predicates, so we're not limited to annotations? For example a predicate like "all classes implementing an interface" or "all sealed interfaces", or even "all functions returning a type".

[Javier]

we were modifying function bodies with FirBodyResolveTransformer if I remember correctly

[Javier]

Have you checked all classes that implement

abstract class FirTransformer<in D> : FirVisitor<FirElement, D>()

[semoro]

Hi! IrGenerationExtension is still supported in K2, note that FIR is a Compiler Frontend of K2, while IR is a backend part
Take a look at Parcelize implementation, which supports both K1 and K2 compilers and uses IrGenerationExtension
https://github.com/JetBrains/kotlin/blob/5802bf85878029ce840d0897d29ad5c4829c10e6/[…]c/org/jetbrains/kotlin/parcelize/ParcelizeComponentRegistrar.kt

[semoro]

Javier [8:49 PM]

we were modifying function bodies with FirBodyResolveTransformer if I remember correctly

Javier [8:49 PM]

> Have you checked all classes that implement

abstract class FirTransformer<in D> : FirVisitor<FirElement, D>()

Note that FirTransformer and FirBodyResolveTransformer is actually a core internal API of FIR, that is highly-likely to change without prior notice
Not sure how you can use it to change bodies, since its only usage is to resolve raw FIR

[Tadeas Kriz]

Thanks, I'll check the FirBodyResolveTransformer. I'm looking to edit the FIR so that there's new declarations visible to the source code, so IrGenerationExtension is too late for me

[semoro]

FIR part of a compiler plugin only needed if you want to generate user-visible declarations
In order to do so, you will have to use FirDeclarationGenerationExtension

[Tadeas Kriz]

Yeah, that's the one I played around with, but I haven't found how to generate anything out of nowhere, or how to predicate match something like "all interfaces"

[semoro]

Exactly! The problem is that the FIR actually runs in the IDE as well
In order to match "all interfaces" you would need to be able to build FIR for every file in project, that would require substantial amount of time to complete

[Tadeas Kriz]

Yeah, but I don't need all of them at once, I can run for the current one, similar to how I can run for certain annotated types

[Tadeas Kriz]

Or maybe I'm misunderstanding the predicates altogether

[semoro]

Only if your plugin generates top-level callable declarations
Otherwise, at the time when you generate say class, interfaces are not resolved yet

[Tadeas Kriz]

Interesting. I'm gonna dig deeper into the Kotlin codebase and possibly IDEA as well to see how that all works together, to see if what I'm trying to achieve is possible with today's APIs, or if there'd be something else needed. Thanks a lot for your help!

[semoro]

Let's imagine we have a predicate like type that implements interface X that is used to generate other classes, let's say typeSome

interface X {}

class My : MySome(), X {}

/* generated class MySome { ... } */

Here, in order to determine if X is really that interface X that we are looking for, we need to resolve the super-type list
In order to do so, we need to query FirDeclarationGenerationExtension for a name MySome , which, in turn, will call predicate matching to find classes that implement interface X, and here we have a cycle

[semoro]

There are also good talks from KotlinConf that are explaining how FIR plugins work:

https://www.youtube.com/watch?v=Pl-89n9wDqo▾

https://www.youtube.com/watch?v=wUGfuWHCqrc▾