Completing the processor

ListedProcessor.kt

internal class ListedProcessor(
    private val environment: SymbolProcessorEnvironment,
) : SymbolProcessor {

    private fun Resolver.findAnnotations(
        kClass: KClass<*>,
    ) = getSymbolsWithAnnotation(
        kClass.qualifiedName.toString())
        .filterIsInstance<KSFunctionDeclaration>().filter {
            it.parameters.isEmpty()
        }
    override fun process(resolver: Resolver): List<KSAnnotated> {

        val listedFunctions: Sequence<KSFunctionDeclaration> =
            resolver.findAnnotations(Listed::class)
        if(!listedFunctions.iterator().hasNext()) return emptyList()

        // gathering the required imports
        val imports = listedFunctions.mapNotNull { it.qualifiedName?.asString() }.toSet()

        // group functions based on their given list-name
        val lists = listedFunctions.groupBy { it.annotations.first { it.shortName.asString()  == "Listed" }.arguments.first().value.toString() }

        val sourceFiles = listedFunctions.mapNotNull { it.containingFile }
        
        val fileText = buildString {
            append("package your.desired.packagename")

            newLine()
            newLine()

            imports.forEach {
                append("import $it")
                newLine()
            }
            
            newLine()
            
            lists.forEach { (listName, functions) ->
                val functionNames = functions.map { it.simpleName.asString() + "()" }.joinToString(", ")
                
                append("val $listName = listOf($functionNames)")
                newLine()
                
            }

        }

        createFileWithText(sourceFiles, fileText)
        return (listedFunctions).filterNot { it.validate() }.toList()
    }

    private fun createFileWithText(
        sourceFiles: Sequence<KSFile>,
        fileText: String,
    ) {
        val file = environment.codeGenerator.createNewFile(
            Dependencies(
                false,
                *sourceFiles.toList().toTypedArray(),
            ),
            "your.generated.file.package",
            "GeneratedLists"
        )

        file.write(fileText.toByteArray())
    }

    private fun StringBuilder.newLine(count: Int = 1) {
        repeat(count){
            append("\n")
        }
    }
}