Add support for _root_ package syntax

[sfiruch]

Scala uses _root_ to mark the start of the namespace:
https://docs.scala-lang.org/style/naming-conventions.html#root

Stainless stumbles over it with the following error message: _root_ cannot be imported

[jad-hamza]

I think the error message comes from the Scala compiler (for instance it appears in scala/bug#6217 and scala/bug#9125)

Could you try running scalac on your example as shown here: https://epfl-lara.github.io/stainless/installation.html#running-code-with-stainless-dependencies

scalac -d ~/.scala_objects $(find /path/to/Stainless/frontends/library/stainless/ -name "*.scala") File1.scala ... File_n.scala

[sfiruch]

My bad. You can't actually import things from the root namespace directly in scala. Sorry :)