sbt assembly for Finatra application

Build.scala

import sbt._
import sbt.Keys._
import sbtassembly.Plugin.{MergeStrategy, assemblySettings, defaultMergeStrategy}
import sbtassembly.Plugin.AssemblyKeys.{assembly, mergeStrategy}
import sbtassembly.AssemblyUtils
 
object AppBuild extends Build {
  lazy val app = Project(
    id = "app",
    base = file("app"),
    settings = Project.defaultSettings ++ assemblySettings
  ).settings(
    libraryDependencies ++= Seq(
      "com.twitter" %% "finatra" % "1.5.3"
    ),
    mergeStrategy in assembly <<= (mergeStrategy in assembly) {
      val discardJar = new MergeStrategy {
        val name = "discard_jar"
        def apply(tempDir: File, path: String, files: Seq[File]): Either[String, Seq[(File, String)]] = {
          Right(
            for {
              // collects not jar-origined
              f <- files if !AssemblyUtils.sourceOfFileForMerge(tempDir, f)._4
            } yield {
              f -> path
            }
          )
        }
      }
 
      (old) => { x: String =>
        val sep = System.getProperty("file.separator")
        if (x.endsWith(".mustache") || x.startsWith("public" + sep)) {
          // discards files from other jars. only accepts files from app/*.
          discardJar
        } else {
          old(x)
        }
      }
    }
  )
}