Turns a Kotlin Data class toString() into formatted JSON-like output

strings.kt

fun Any?.toIndentString(): String {
  val notFancy = toString()
  return buildString(notFancy.length) {
    var indent = 0
    fun StringBuilder.line() {
      appendln()
      repeat(2 * indent) { append(' ') }
    }

    for (char in notFancy) {
      if (char == ' ') continue

      when (char) {
        ')', ']' -> {
          indent--
          line()
        }
      }

      if (char == '=') append(' ')
      append(char)
      if (char == '=') append(' ')

      when (char) {
        '(', '[', ',' -> {
          if (char != ',') indent++
          line()
        }
      }
    }
  }
}

refactored version

fun String.toIndentString(): String = buildString(length) {
    var indent = 0

    fun line() {
        appendLine()
        repeat(2 * indent) { append(' ') }
    }

    this@toIndentString.filter { it != ' ' }.forEach { char ->
        when (char) {
            ')', ']', '}' -> {
                indent--
                line()
                append(char)
            }
            '=' -> append(" = ")
            '(', '[', '{', ',' -> {
                append(char)
                if (char != ',') indent++
                line()
            }
            else -> append(char)
        }
    }
}