Add generated sources to published source artifact

[armanbilge]

This is an easy gotcha. Found in the cats build, and I recently added something like this to one of my own projects.

lazy val includeGeneratedSrc: Setting[_] = {
  Compile / packageSrc / mappings ++= {
    val base = (Compile / sourceManaged).value
    (Compile / managedSources).value.map { file =>
      file -> file.relativeTo(base).get.getPath
    }
  }
}

I am genuinely curious if there's a situation where you don't want this.