Why is there no Main-Class attribute in generated manifest?

Question

I have a build.sbt file that includes the assembly plugin. Up until the most recent build, the Main-Class attribute was being included in the assembled far jar, but all of a sudden, this is no longer the case.

When I attempt to run the jar, I get the inimitable:

no main manifest attribute, in ./target/scala-2.10/foo-0.3.0-SNAPSHOT.jar

but using run from the sbt console, works fine.

My build.sbt currently looks like this (the mainClass in assembly added in an attempt to force indicate to the assembly plugin that it really should include, though I noticed in the plugin source code, it looks like it's checking the one specified for run anyway).

import AssemblyKeys._

name := "foo"

version := "0.3.0-SNAPSHOT"

organization := "com.mycompany.myproduct"

scalaVersion := "2.10.4"

mainClass in (Compile, run) := Some("ProcessRelogger")

mainClass in assembly := Some("ProcessRelogger")

assemblySettings

libraryDependencies ++= Seq(
  "org.scalatest" % "scalatest_2.10" % "1.9.2" % "test",
  "ch.qos.logback" % "logback-classic" % "1.0.9",
  "com.typesafe.akka" %% "akka-actor" % "2.2.4",
  "joda-time" % "joda-time" % "2.3",
  "com.rabbitmq" % "amqp-client" % "3.3.4",
  "org.scalaz" % "scalaz-core_2.10" % "7.0.6",
  "com.typesafe.slick" %% "slick" % "2.0.2",
  "postgresql" % "postgresql" % "9.1-901.jdbc4",
  "com.escalatesoft.subcut" %% "subcut" % "2.0"
)

and when I unzip the jar file, and check META-INF/MANIFEST.MF, there's no Main-Class: attribute included.

Answer 1

This is an attempt to reproduce the issue with the latest version of sbt-assembly 0.11.2.

project/build.properties

sbt.version=0.13.7-M3

project/assembly.sbt

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.11.2")

build.sbt

import AssemblyKeys._

assemblySettings

scalaVersion := "2.11.2"

src/main/scala/Main.scala

object HelloApp extends App {
  println("Hello")
}

With all the files above in a single project:

> about
[info] Updating {file:/Users/jacek/sandbox/sbt-assembly/}sbt-assembly...
[info] Resolving jline#jline;2.12 ...
[info] Done updating.
[info] This is sbt 0.13.7-M3
[info] The current project is {file:/Users/jacek/sandbox/sbt-assembly/}sbt-assembly 0.1-SNAPSHOT
[info] The current project is built against Scala 2.11.2
[info] Available Plugins: sbt.plugins.IvyPlugin, sbt.plugins.JvmPlugin, sbt.plugins.CorePlugin, sbt.plugins.JUnitXmlReportPlugin, com.typesafe.sbteclipse.plugin.EclipsePlugin, net.virtualvoid.sbt.graph.Plugin, com.github.tototoshi.sbt.musical.Plugin, com.timushev.sbt.updates.UpdatesPlugin, sbtassembly.Plugin
[info] sbt, sbt plugins, and build definitions are using Scala 2.10.4

> assembly
[info] Updating {file:/Users/jacek/sandbox/sbt-assembly/}sbt-assembly...
[info] Resolving jline#jline;2.12 ...
[info] Done updating.
[info] Compiling 1 Scala source to /Users/jacek/sandbox/sbt-assembly/target/scala-2.11/classes...
[info] Including: scala-library-2.11.2.jar
[info] Checking every *.class/*.jar file's SHA-1.
[info] Merging files...
[warn] Merging 'META-INF/MANIFEST.MF' with strategy 'discard'
[warn] Strategy 'discard' was applied to a file
[info] SHA-1: a5c09d7626fe19f4e3cd98d709966a77f127b048
[info] Packaging /Users/jacek/sandbox/sbt-assembly/target/scala-2.11/sbt-assembly-assembly-0.1-SNAPSHOT.jar ...
[info] Done packaging.
[success] Total time: 4 s, completed Oct 8, 2014 9:27:41 AM

> eval "unzip -p target/scala-2.11/sbt-assembly-assembly-0.1-SNAPSHOT.jar META-INF/MANIFEST.MF" !
Manifest-Version: 1.0
Implementation-Title: sbt-assembly
Implementation-Version: 0.1-SNAPSHOT
Specification-Vendor: default
Specification-Title: sbt-assembly
Implementation-Vendor-Id: default
Specification-Version: 0.1-SNAPSHOT
Main-Class: HelloApp
Implementation-Vendor: default

[info] ans: Int = 0