scala.MatchError when creating fat jar using sbt assembly - scala

Question

I am trying to create a jar file for my project. I am using sbt assembly command to generate one.
But getting error when it starts merging files:
scala.MatchError:
spray\http\parser\ProtocolParameterRules$$anonfun$DeltaSeconds$1.class
(of class java.lang.String)
My build.sbt looks like this:
lazy val commonSettings = Seq(
name := "SampleSpray",
version := "1.0",
scalaVersion := "2.11.7",
organization := "com.test"
)
mainClass in assembly := Some("com.example.Boot")
lazy val root = (project in file(".")).
settings(commonSettings: _*).
settings(
name := "test",
resolvers += "spray repo" at "http://repo.spray.io",
libraryDependencies ++= {
val akkaV = "2.3.9"
val sprayV = "1.3.3"
Seq(
"io.spray" %% "spray-can" % sprayV,
"io.spray" %% "spray-routing" % sprayV,
"io.spray" %% "spray-json" % "1.3.2",
"io.spray" %% "spray-testkit" % sprayV % "test",
"com.typesafe.akka" %% "akka-actor" % akkaV,
"com.typesafe.akka" %% "akka-testkit" % akkaV % "test",
"org.specs2" %% "specs2-core" % "2.3.11" % "test",
"com.sksamuel.elastic4s" %% "elastic4s-core" % "2.1.0",
"com.sksamuel.elastic4s" %% "elastic4s-jackson" % "2.1.0",
"net.liftweb" %% "lift-json" % "2.6+"
)
}
)
assemblyOption in assembly := (assemblyOption in assembly).value.copy(cacheUnzip = false)
assemblyMergeStrategy in assembly := {
case "BaseDateTime.class" => MergeStrategy.first
}
Don't know why the error is coming.

Answer 1

The setting assemblyMergeStrategy in assembly has the type String => MergeStrategy.
In your sbt file you are using the partial function
{
case "BaseDateTime.class" => MergeStrategy.first
}
which is syntactic sugar for
(s:String) => {
s match {
case "BaseDateTime.class" => MergeStrategy.first
}
}
This representation shows that the given function will not exhaustively match all passed strings. In your case sbt-assembly tried to merge the file named spray\http\parser\ProtocolParameterRules$$anonfun$DeltaSeconds$1.class into the fat jar, but could not find any matching merge strategy. You need a "default" case also:
(s:String) => {
s match {
case "BaseDateTime.class" => MergeStrategy.first
case x =>
val oldStrategy = (assemblyMergeStrategy in assembly).value
oldStrategy(x)
}
}
Or written as partial function:
{
case "BaseDateTime.class" => MergeStrategy.first
case x =>
val oldStrategy = (assemblyMergeStrategy in assembly).value
oldStrategy(x)
}
I also ran into the same issue when sbt-assembly's assembly task failed to create a fat jar due to a name conflict in the elasticsearch and its transitive joda-time dependencies. Elasticsearch redefines the class org.joda.time.base.BaseDateTime which is already implemented in the joda-time library. I've followed your approach to tell sbt-assembly how resolve this conflict using the following assemblyMergeStrategy:
assemblyMergeStrategy in assembly := {
case "org/joda/time/base/BaseDateTime.class" => MergeStrategy.first
case x =>
val oldStrategy = (assemblyMergeStrategy in assembly).value
oldStrategy(x)
}