Signature.kt

import java.lang.reflect.*
import java.lang.reflect.Array
import kotlin.reflect.jvm.javaConstructor
import kotlin.reflect.jvm.javaMethod

fun main() {
    val clazz: Class<*> = Long::class.java
    val method = Long::inc

    val className = clazz.name
    val methodName = (method.javaMethod ?: method.javaConstructor ?: throw IllegalStateException("$method is neither a method nor a constructor")).name

    for (executable in Class.forName(className).let { it.methods.toList() + it.constructors }) {
        if (executable.name == methodName) {
            val name = when (executable) {
                is Constructor<*> -> "<init>"
                is Method -> methodName
                else -> throw IllegalStateException("Unknown type ${executable.javaClass.name}")
            }

            println("${className.replace('.', '/')} $name ${getSignature(executable)}")
        }
    }
}

fun getSignature(e: Executable): String {
    try {
        val gSig: Field = when (e) {
            is Constructor<*> -> Constructor::class.java.getDeclaredField("signature")
            is Method -> Method::class.java.getDeclaredField("signature")
            else -> throw IllegalStateException("Unknown type ${e.javaClass.name}")
        }

        gSig.isAccessible = true
        val sig = gSig.get(e) as String?
        if (sig != null)
            return sig
    } catch (e: IllegalAccessException) {
        e.printStackTrace()
    } catch (e: NoSuchFieldException) {
        e.printStackTrace()
    }

    val sb = StringBuilder("(")
    for (type in e.parameterTypes) {
        sb.append(Array.newInstance(type, 0).toString().substring(1).substringBefore('@').replace('.', '/'))
    }

    sb.append(')')
    val returnType = when (e) {
        is Constructor<*> -> e.declaringClass
        is Method -> e.returnType
        else -> throw IllegalStateException("Unknown type ${e.javaClass.name}")
    }

    if (returnType === Void.TYPE) {
        sb.append("V")
    } else {
        sb.append(Array.newInstance(returnType, 0).toString().substring(1).substringBefore('@').replace('.', '/'))
    }

    return sb.toString()
}