KSPHelloWorldProcessor.kt

/**
 * This is simple processor that use KSP API to generate
 * extension function for annotated classes with [HelloWorldAnnotation]
 */
class HelloWorldProcessor(
    private val logger: KSPLogger,
    private val codeGenerator: CodeGenerator
) : SymbolProcessor {

    override fun process(resolver: Resolver): List<KSAnnotated> {
        val symbols = resolver.getSymbolsWithAnnotation(HelloWorldAnnotation::class.qualifiedName!!)
        val returnList = symbols.filter { !it.validate() }.toList()
        symbols.filter { it is KSClassDeclaration && it.validate() }
            .forEach { it.accept(HelloWorldAnnotatedClassVisitor(), Unit) }
        return returnList
    }


    inner class HelloWorldAnnotatedClassVisitor : KSVisitorVoid() {
        override fun visitClassDeclaration(classDeclaration: KSClassDeclaration, data: Unit) {
            super.visitClassDeclaration(classDeclaration, data)

            val packageName = classDeclaration.qualifiedName?.getQualifier() ?: kotlin.run {
                logger.error("packageName is empty")
                return
            }

            val className = classDeclaration.simpleName.getShortName()

            codeGenerator.createNewFile(
                Dependencies(
                    true,
                    classDeclaration.containingFile!!
                ),
                packageName,
                "${className}_Generated"
            ).use { file ->
                file.write("""
                    package $packageName\n
                    fun ${packageName}.${className}.printHelloWorld() {
                        println("Hello world!")
                    }
                """.trimIndent().toByteArray())
            }
        }
    }
}