Fix os.write.outputStream with perms for Scala 3

[kiendang]

On Scala 3

os.write.outputStream(os.pwd / "text", perms = os.PermSet(420))

java.lang.ClassCastException: class [Ljava.nio.file.attribute.FileAttribute; cannot be cast to class scala.collection.immutable.Seq ([Ljava.nio.file.attribute.FileAttribute; is in module java.base of loader 'bootstrap'; scala.collection.immutable.Seq is in unnamed module of loader java.net.URLClassLoader @4520ebad)
  os.write$.outputStream(ReadWriteOps.scala:35)
  ammonite.$sess.cmd0$.<clinit>(cmd0.sc:1)

[lihaoyi]

Looks reasonable, but do you know why it only fails on Scala 3? I would expect it behave the same on all versions of Scala

[kiendang]

@lihaoyi It's because the type here is wrong. It should be Array[FileAttribute[java.util.Set[PosixFilePermission]]] instead. I don't know how this compiles or why it runs on Scala 2 though.

[kiendang]

I don't know the details, but looks like Scala 3 handles varargs differently https://docs.scala-lang.org/scala3/reference/changed-features/vararg-splices.html

[kiendang]

Also looks like on Scala 2.13 using : _* with Array is a bit inefficient

val arr = Array(0, 1, 2, 3)
val lst = List(arr: _*)

Passing an explicit array value to a Scala varargs method is deprecated (since 2.13.0) and will result in a defensive copy; Use the more efficient non-copying ArraySeq.unsafeWrapArray or an explicit toIndexedSeq call
val lst = List(arr: _*)

Looks Scala 3 doesn't have the problem, but have to use the new syntax unavailable in Scala 2

val arr = Array(0, 1, 2, 3)
val lst = List(arr*) 

For Scala 2, these would not lead to copying

val arr = Seq(0, 1, 2, 3)
val lst = List(arr: _*)

import scala.collection.immutable.ArraySeq.unsafeWrapArray

val arr = Array(0, 1, 2, 3)
val lst = List(unsafeWrapArray(arr): _*)

[lihaoyi]

Thanks @kiendang !