Hello again! how do you get a `KClass` out from an annotation argument? Given the annotation: ```@Re...

# ksp

[Lamberto Basti]

Hello again! how do you get a KClass out from an annotation argument?
Given the annotation:

@Retention(AnnotationRetention.SOURCE)
@Target(AnnotationTarget.PROPERTY)
annotation class Reference(val table: KClass<out Table>, val columnName: String)

// usage
@Reference(MyTable::class, "id")

I am trying to preocess it with:

val reference = kSPropertyDeclaration.getAnnotationsByType(Reference::class).first()

But when i access reference.table it errors with:

[ksp] com.google.devtools.ksp.KSTypeNotPresentException: java.lang.ClassNotFoundException: com.github.lamba92.ktor.restrepositories.tests.Cities
	at com.google.devtools.ksp.UtilsKt.asClass(utils.kt:509)
	at com.google.devtools.ksp.UtilsKt.createInvocationHandler$lambda$8(utils.kt:385)
	at jdk.proxy5/jdk.proxy5.$Proxy29.table(Unknown Source)

I believe the returned class has some kind of lazy behaviour because it errors only when accessing table , but it is kinda weird.

Also, com.github.lamba92.ktor.restrepositories.tests.Cities is one of the source files.

[Lamberto Basti]

It apperas to be this issue here

[jw]

KSP is running on the JVM with the compiler classpath. You cannot load classes which are in the code that is being compiled.

[jw]

https://kotlinlang.org/docs/ksp-additional-details.html

[jw]

Any type references in the code that is being compiled need to be held as symbolic references. If you try to load them in the current classloader it almost certainly will fail.

[Lamberto Basti]

Uhm I see. And is there a way to just get the fqn of the class written in the annotation parameter?

[jw]

I haven't used KSP but it looks like maybe KSType is what you want

[jw]

if the declaration is a KSClassDecalaration it'll have qualifiedName

[Lamberto Basti]

Indeed, but there was some magic involved:

propertyDeclaration.annotations
    .firstOrNull { 
        it.annotationType.resolve().toClassName() == Reference::class.asClassName()     
    }
    ?.arguments
    ?.first()
    ?.value // <-- this is type Any?
    ?.let { it as? KSType }
    ?.declaration
    ?.qualifiedName
    ?.asString()

So basically, somehow, automagically, the KSP runtime fills value with a KSType. I had to print out quite some stuff before figuring that out!

[Jiaxiang]

yeah, when dealing with KClass as class literals, KSP will try to convert it to KSType , we should probably note it in documents.