I am making an annotation processor that generates...

# kapt

[Fudge]

I am making an annotation processor that generates Kotlin source files using Kotlin poet, however I am unsure how can I make incremental processing work properly. The problem is that outdated source files don't get deleted. How can I "mark" generated Kotlin source file as being outdated and that they need to be deleted?
Example:

@NbtSerializable
class Foo // --> Generates source file named "FooUtil"

Now I remove @NbtSerializable and need FooUtil to be deleted as well.

[Sergey Chelombitko]

You need to call addOriginatingElement on every TypeSpec/FunSpec/etc. builder and pass the corresponding element.
Also make sure you use only FileSpec.writeTo(Filer) for writing files.