Top level packages can't be aliased in import declaration

[scabug]

scala> import _root_.{scala => xxx}
<console>:7: error: _root_ cannot be imported
       import _root_.{scala => xxx}
              ^

It doesn't work in both the REPL and the IDE.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9125?orig=1
Reporter: @sschaef
Affected Versions: 2.10.5

[SethTisue]

was reported again at #12329 — I've changed the issue title to reflect that all top level packages are affected, not just the scala package

[som-snytt]

Relatedly createdly scala/scala3#11296

[Jasper-M]

This was once disabled as part of the fix for #283. For any interested archaeologists.

[som-snytt]

Thanks, I did dig that up yesterday. It was right before the winter holidays, 2007. Probably there was not a lot of discussion about imposing the limitation as a stop-gap.

[Jasper-M]

Maybe back then import aliasing didn't exist yet? In that case it would make sense to disallow import _root_.foo.

[som-snytt]

Relatedly, my linked ticket was due to my own partial understanding. You want an import to shadow an enclosing package name. Using mutable would be an actual use case, but here is scala, showing that root import is useful without rename.

package example {
  package scala {
    object X {
      import _root_.scala
      def empty = scala.collection.mutable.ListBuffer.empty[Int]
    }
  }
}

Recently I was toying in this area because of the question whether it's possible to shadow scala in an enclosing package, for purposes of cross-compilation. (That only works if you don't want to write scala.Int and other things.) It wasn't obvious to me that writing package scala.collection here also shadows scala.