import java.io.File

fun File.toPrettyTreeString(): String {
  return walk().joinToString("\n") { file ->
    val relativeFile = file.relativeTo(this)
    val depth = relativeFile.invariantSeparatorsPath.count { it == '/' }

    file.name.prependIndent(" ".repeat(depth))
  }
}

html
    index.html
    -basic -project
     it.protected
      index.html
      -protected-class
       index.html
       protected-fun.html
       -protected-class.html

`
└── site
    ├── styles
    │   └── site.css
    ├── images
    │   └── icon.png
    └── index.html

val entries = dir.listDirectoryEntries()

val entries = dir.toFile().walk().maxDepth(1).toList()

val entries = dir.toFile().walk().maxDepth(1).filter { it != dir.toFile() }