scala - assembly-merge-strategy issues using sbt-assembly

Question

I am trying to convert a scala project into a deployable fat jar using sbt-assembly. When I run my assembly task in sbt I am getting the following error:

Merging 'org/apache/commons/logging/impl/SimpleLog.class' with strategy 'deduplicate'
    :assembly: deduplicate: different file contents found in the following:
    [error] /Users/home/.ivy2/cache/commons-logging/commons-logging/jars/commons-logging-1.1.1.jar:org/apache/commons/logging/impl/SimpleLog.class
    [error] /Users/home/.ivy2/cache/org.slf4j/jcl-over-slf4j/jars/jcl-over-slf4j-1.6.4.jar:org/apache/commons/logging/impl/SimpleLog.class

Now from the sbt-assembly documentation:

If multiple files share the same relative path (e.g. a resource named application.conf in multiple dependency JARs), the default strategy is to verify that all candidates have the same contents and error out otherwise. This behavior can be configured on a per-path basis using either one of the following built-in strategies or writing a custom one:

• MergeStrategy.deduplicate is the default described above
• MergeStrategy.first picks the first of the matching files in classpath order
• MergeStrategy.last picks the last one
• MergeStrategy.singleOrError bails out with an error message on conflict
• MergeStrategy.concat simply concatenates all matching files and includes the result
• MergeStrategy.filterDistinctLines also concatenates, but leaves out duplicates along the way
• MergeStrategy.rename renames the files originating from jar files
• MergeStrategy.discard simply discards matching files

Going by this I setup my build.sbt as follows:

import sbt._
import Keys._
import sbtassembly.Plugin._
import AssemblyKeys._
name := "my-project"
version := "0.1"
scalaVersion := "2.9.2"
crossScalaVersions := Seq("2.9.1","2.9.2")

//assemblySettings
seq(assemblySettings: _*)

resolvers ++= Seq(
    "Typesafe Releases Repository" at "http://repo.typesafe.com/typesafe/releases/",
    "Typesafe Snapshots Repository" at "http://repo.typesafe.com/typesafe/snapshots/",
    "Sonatype Repository" at "http://oss.sonatype.org/content/repositories/releases/"
)

libraryDependencies ++= Seq(
    "org.scalatest" %% "scalatest" % "1.6.1" % "test",
    "org.clapper" %% "grizzled-slf4j" % "0.6.10",
    "org.scalaz" % "scalaz-core_2.9.2" % "7.0.0-M7",
    "net.databinder.dispatch" %% "dispatch-core" % "0.9.5"
)

scalacOptions += "-deprecation"
mainClass in assembly := Some("com.my.main.class")
test in assembly := {}
mergeStrategy in assembly := mergeStrategy.first

In the last line of the build.sbt, I have:

mergeStrategy in assembly := mergeStrategy.first

Now, when I run SBT, I get the following error:

error: value first is not a member of sbt.SettingKey[String => sbtassembly.Plugin.MergeStrategy]
    mergeStrategy in assembly := mergeStrategy.first

Can somebody point out what I might be doing wrong here?

Thanks

Answer 1

As for the current version 0.11.2 (2014-03-25), the way to define the merge strategy is different.

This is documented here, the relevant part is:

NOTE: mergeStrategy in assembly expects a function, you can't do

mergeStrategy in assembly := MergeStrategy.first

The new way is (copied from the same source):

mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
  {
    case PathList("javax", "servlet", xs @ _*)         => MergeStrategy.first
    case PathList(ps @ _*) if ps.last endsWith ".html" => MergeStrategy.first
    case "application.conf" => MergeStrategy.concat
    case "unwanted.txt"     => MergeStrategy.discard
    case x => old(x)
  }
}

This is possibly applicable to earlier versions as well, I don't know exactly when it has changed.