Make some sense of JVM access modifiers

JvmAccessModifiers.kt

import org.objectweb.asm.Opcodes

data class AccessModifier(val code: Int, val name: String)

enum class ClassPart {
  CLASS,
  METHOD,
  FIELD,
  MODULE,
  MODULE_REQUIRES
}

/**
 * Unmasks an integer and pairs it with a string of human readable JVM access modifiers.
 */
fun Int.toAccessModifier(part: ClassPart = ClassPart.CLASS): AccessModifier {
  val modifier = buildString {
    var remaining = this@toAccessModifier
    var bit: Int
    while (remaining != 0) {
      bit = Integer.lowestOneBit(remaining)
      when (bit) {
        Opcodes.ACC_PUBLIC -> append("public")
        Opcodes.ACC_PRIVATE -> append("private")
        Opcodes.ACC_PROTECTED -> append("protected")
        Opcodes.ACC_STATIC -> append("static")
        Opcodes.ACC_FINAL -> append("final")
        0x0020 -> {
          // ACC_SUPER, ACC_SYNCHRONIZED, ACC_OPEN, and ACC_TRANSITIVE all share this value.
          when (part) {
            ClassPart.CLASS -> append("super")
            ClassPart.METHOD -> append("synchronized")
            ClassPart.MODULE_REQUIRES -> append("transitive")
            ClassPart.MODULE -> append("open")
            else -> throw IllegalStateException("Encountered unexpected opcode: 0x0020")
          }
        }
        0x0040 -> {
          // ACC_VOLATILE, ACC_BRIDGE, ACC_STATIC_PHASE all share this value.
          when (part) {
            ClassPart.METHOD -> append("bridge")
            ClassPart.FIELD -> append("volatile")
            ClassPart.MODULE_REQUIRES -> append("(requires static)")
            else -> throw IllegalStateException("Encountered unexpected opcode: 0x0040")
          }
        }
        0x0080 -> {
          // ACC_VARARGS, ACC_TRANSIENT share this value.
          when (part) {
            ClassPart.METHOD -> append("varargs")
            ClassPart.FIELD -> append("transient")
            else -> throw IllegalStateException("Encountered unexpected opcode: 0x0080")
          }
        }
        Opcodes.ACC_NATIVE -> append("native")
        Opcodes.ACC_INTERFACE -> append("interface")
        Opcodes.ACC_ABSTRACT -> append("abstract")
        Opcodes.ACC_STRICT -> append("strictfp")
        Opcodes.ACC_SYNTHETIC -> append("synthetic")
        Opcodes.ACC_ANNOTATION -> append("annotation")
        Opcodes.ACC_ENUM -> append("enum")
        0x8000 -> {
          // ACC_MANADATED and ACC_MODULE share this value.
          when (part) {
            ClassPart.MODULE -> append("mandated")
            ClassPart.CLASS -> append("module")
            else -> throw IllegalStateException("Encountered unexpected opcode: 0x8000")
          }
        }
        Opcodes.ACC_DEPRECATED -> append("DEPRECATED")
      }
      remaining -= bit
      append(" ")
    }
    trim()
    if (isEmpty()) {
      append("package-private")
    }
  }
  return AccessModifier(this, modifier.trim())
}