Str.join throws NegativeArraySizeException given an empty Seq and a nonempty separator

[akouryy]

scala> Nil.mkString(",")
val res0: String = ""
                                                                                                                                                                                                                    
scala> fansi.Str.join(Nil, "")
val res1: fansi.Str = 
                                                                                                                                                                                                                    
scala> fansi.Str.join(Nil, ",")
java.lang.NegativeArraySizeException: -1
  at fansi.Str$.join(Fansi.scala:370)
  ... 66 elided

I'm not sure if it's a bug, but allowing (Nil, ",") sounds more consistent.

Scala 3.1.3, fansi 0.3.1

[bwbecker]

Same thing with Scala 2.13.10:

    val s2 = Vector[fansi.Str](fansi.Color.Blue("blue"))
    println("nonEmpty: " + fansi.Str.join(s2, ", ").render)
    val s3 = Vector[fansi.Str]()
    println("empty: " + fansi.Str.join(s3, ", ").render)

Running it:

nonEmpty: blue
[error] java.lang.NegativeArraySizeException: -2
[error] 	at fansi.Str$.join(Fansi.scala:370)

[bwbecker]

Yup, lines 368 and following of Fansi.scala:

  def join(args: Iterable[Str], sep: fansi.Str = fansi.Str("")) = {
    val length = args.iterator.map(_.length + sep.length).sum - sep.length
    val chars = new Array[Char](length)

If the args iterable is empty, length becomes negative by the length of sep, which causes a problem in the next line.