FilesInfo.exists(...) is typed incorrectly

[eed3si9n]

steps

scala> FilesInfo.exists(file("/tmp/target").globRecursive("*.js").get.toSet)
res42: sbt.util.FilesInfo[_1.F] forSome { val _1: sbt.util.FileInfo.Style } = FilesInfo(Set())

problem

FilesInfo.exists(...) returns an existential type argument sbt.util.FilesInfo[_1.F] forSome { val _1: sbt.util.FileInfo.Style }.

expectation

It should return FilesInfo[PlainFileInfo] otherwise it's useless.

note

scala> import sbt._, sbt.util.CacheImplicits._
import sbt._
import sbt.util.CacheImplicits._

// use streams.value.cacheStoreFactory
scala> val cacheFactory = sbt.util.CacheStoreFactory(file("/tmp/cache"))
cacheFactory: sbt.util.CacheStoreFactory = sbt.util.DirectoryStoreFactory@3a3d3778

scala> def doCompile(source: File): File = {
         println("working...")
         val out = file("/tmp/target/hello.js")
         IO.touch(out)
         out
       }
doCompile: (source: sbt.File)sbt.File

scala> val cachedCompile = Tracked.inputChanged(cacheFactory.make("input")) {
         (inChanged: Boolean, in: FilesInfo[ModifiedFileInfo]) =>
           val tracker = Tracked.outputChanged(cacheFactory.make("output")) {
             (outChanged: Boolean, outputs: FilesInfo[PlainFileInfo]) =>
               if (inChanged || outChanged) in.files.toList map { info => doCompile(info.file) }
               else outputs.files.toList map { _.file }
           }
           tracker(() => FilesInfo.exists(file("/tmp/target").globRecursive("*.js").get.toSet))
       }
<console>:26: error: type mismatch;
 found   : sbt.util.FilesInfo[_1.F] where val _1: sbt.util.FileInfo.Style
 required: sbt.FilesInfo[sbt.PlainFileInfo]
    (which expands to)  sbt.util.FilesInfo[sbt.util.PlainFileInfo]
                  tracker(() => FilesInfo.exists(file("/tmp/target").globRecursive("*.js").get.toSet))
                                                ^

workaround

Cast it to FilesInfo[PlainFileInfo] using asInstanceOf[FilesInfo[PlainFileInfo]] or use Seq[PlainFileInfo].