CODEWITHSUNDEEP
javascalasbtsbt-assembly
Make42
Make42

Reputation: 13108

sbt assembly works, but still "no main manifest attribute"

I am using sbt 1.0.2. My build.sbt is

name := "myprogram"

version := "0.1"

scalaVersion := "2.12.3"

libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.1" % "test"

// https://mvnrepository.com/artifact/net.sf.py4j/py4j
libraryDependencies += "net.sf.py4j" % "py4j" % "0.10.6"

scalacOptions ++= Seq(
  "-unchecked",
  "-deprecation",
  "-feature",
  "-encoding", "UTF-8",
  "-Xfuture",
  "-Xlint:unsound-match",      // Pattern match may not be typesafe.
  "-Yno-adapted-args",         // Do not adapt an argument list (either by inserting () or creating a tuple) to match the receiver.
  "-Ypartial-unification",     // Enable partial unification in type constructor inference
  "-Ywarn-dead-code",          // Warn when dead code is identified.
  "-Ywarn-inaccessible",       // Warn about inaccessible types in method signatures.
  "-Ywarn-infer-any",          // Warn when a type argument is inferred to be `Any`.
  "-Ywarn-nullary-override",   // Warn when non-nullary `def f()' overrides nullary `def f'.
  "-Ywarn-nullary-unit",       // Warn when nullary methods return Unit.
  "-Ywarn-unused",             // Warn if a method or value is unused.
  "-Ywarn-unused:implicits",   // Warn if an implicit parameter is unused.
  "-Ywarn-unused:imports",     // Warn if an import selector is not referenced.
  "-Ywarn-unused:locals",      // Warn if a local definition is unused.
  "-Ywarn-unused:params",      // Warn if a value parameter is unused.
  "-Ywarn-unused:patvars",     // Warn if a variable bound in a pattern is unused.
  "-Ywarn-unused:privates",    // Warn if a private member is unused.
  "-Ywarn-value-discard"       // Warn when non-Unit expression results are unused.
)

javacOptions ++= Seq("-source", "1.8", "-target", "1.8")

test in assembly := {}
assemblyJarName in assembly := "myprogram.jar"

exportJars := true

mainClass in Compile := Some("com.company.MyClass")
mainClass in assembly := Some("com.company.MyClass")
mainClass in(Compile, run) := Some("com.company.MyClass")
mainClass in(Compile, packageBin) := Some("com.company.MyClass")

and it seems to compile ok with sbt assembly, where some of the output is

[warn] Multiple main classes detected.  Run 'show discoveredMainClasses' to see the list
[info] Including: py4j-0.10.6.jar
[info] Including: scala-library.jar
[info] Checking every *.class/*.jar file's SHA-1.
[info] Merging files...
[warn] Merging 'META-INF/MANIFEST.MF' with strategy 'discard'
[warn] Merging 'META-INF/maven/net.sf.py4j/py4j/pom.properties' with strategy 'discard'
[warn] Merging 'META-INF/maven/net.sf.py4j/py4j/pom.xml' with strategy 'discard'
[warn] Strategy 'discard' was applied to 3 files

Once I go into command line I get

$ java -jar myprogram.jar
no main manifest attribute, in myprogram.jar

I opened up my jar and looked at MANIFEST.MF and could not find the main there:

Manifest-Version: 1.0
Implementation-Title: myprogram
Implementation-Version: 0.1
Specification-Vendor: default
Specification-Title: myprogram
Implementation-Vendor-Id: default
Specification-Version: 0.1
Implementation-Vendor: default

It might be worth mentioning that my program is mainly in Scala, except for my main class which is in Java.

What do I have to change?

Upvotes: 2

Views: 1353

Answers (1)

Frederic A.
Frederic A.

Reputation: 3514

From the logs you show, my guess is that - in the content of one of the included jars - there's already a META-INF/MANIFEST.MF, and yours/the one created by sbt assembly - where your main class is declared - gets discarded (I'm not 100% sure though because the content of the manifest you show seems to include stuff that come from your code).

I think this is the indication that your manifest gets discarded:

[warn] Merging 'META-INF/MANIFEST.MF' with strategy 'discard'

I bet there's already a 'META-INF/MANIFEST.MF' in py4j-0.10.6.jar.

How to fix that?

  1. avoid fat jar, for example using http://www.scala-sbt.org/sbt-native-packager, but I guess that's not the point here
  2. tweak the merge strategy, see details at https://github.com/sbt/sbt-assembly#merge-strategy. More specifically, you could try to set the MergeStrategy.concat strategy for merging META-INF/MANIFEST.MF.

roughly:

assemblyMergeStrategy in assembly := {
  case PathList("META-INF", "MANIFEST.MF")         => MergeStrategy.concat
  case x =>
    val oldStrategy = (assemblyMergeStrategy in assembly).value
    oldStrategy(x)
}

Upvotes: 2

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