Scala star pattern varargs matching error about sbt-assembly

[eed3si9n]

I can't reproduce the error in my environment. Are you using the latest 0.8.5? I noticed that you're using *.scala build file. Is PathList in the scope?

[polymorphic]

Hmm, I am getting the same error with 0.8.6 and Scala 2.9.2/sbt 0.12. Here are the settings:

  mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
    {
      case PathList("org", "apache", "commons", "collections", "bidimap", xs @ _*) => MergeStrategy.first
      case x => old(x)
    }
  }

and here's the error:

[info] Compiling 1 Scala source to /Users/dragos.manolescu/Repos/monitoring-pipeline/xml-stats-poller/project/target/scala-2.9.2/sbt-0.12/classes...
[error] /Users/dragos.manolescu/Repos/monitoring-pipeline/xml-stats-poller/project/XmlStatsPollerBuild.scala:36: star patterns must correspond with varargs parameters
[error] Error occurred in an application involving default arguments.
[error]           case PathList("org", "apache", "commons", "collections", "bidimap", xs @ _*) => MergeStrategy.first
[error]                                                                                     ^
[error] one error found

[eed3si9n]

when @kul originally reported this bug I probably only tested this using build.sbt, and trusted that if a setting works in build.sbt, it would always work in build.scala.
it turns out that's not always the case! there's a bug in the pattern matcher pre-2.10 (SI-3488) that blows up when default parameters are used in conjunction with _*. In this case, the default parameters are coming likely from Project.apply.

The workaround is to separate out the settings into a method:

  lazy val lib = Project("lib", file("lib"), settings = Defaults.defaultSettings ++ assemblySettings) settings(
      mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
        {
          case PathList("org", "apache", "commons", "collections", "bidimap", xs @ _*) => MergeStrategy.first
          case x => old(x)
        }
      }
    )