scala - Suppress main class in sbt-assembly -

in multi-project sbt build, how should 1 explicitly suppress mainclass attribute in sbt-assembly?

i've searched extensively cannot seem find out how prevent main class being set in jar built sbt-assembly in multi-project build.

in single-project build, seems work long there @ least 2 classes might potentially invoked command line:

import sbt._ import keys._  import sbtassembly.plugin._ import sbtassembly.assemblyutils._ import assemblykeys._  object testbuild extends build {   lazy val buildsettings = defaults.defaultsettings ++ assemblysettings ++ seq(     version := "0.1-snapshot",     organization := "com.organization",     scalaversion := "2.10.2",     mergestrategy in assembly := mergefirst   )    lazy val root = project(id = "test-assembly",     base = file("."),     settings = buildsettings) settings(     mainclass in assembly := none   )   lazy val mergefirst: string => mergestrategy = {      case "reference.conf" | "rootdoc.txt" => mergestrategy.concat     case pathlist("meta-inf", xs @ _*) =>     (xs map {_.tolowercase}) match {       case ("manifest.mf" :: nil) | ("index.list" :: nil) | ("dependencies" :: nil) =>       mergestrategy.discard       case ps @ (x :: xs) if ps.last.endswith(".sf") || ps.last.endswith(".dsa") =>       mergestrategy.discard       case "plexus" :: xs =>       mergestrategy.discard       case "services" :: xs =>       mergestrategy.filterdistinctlines       case ("spring.schemas" :: nil) | ("spring.handlers" :: nil) =>       mergestrategy.filterdistinctlines       case _ => mergestrategy.first     }     case _ => mergestrategy.first   } } 

however, appears mainclass := none isn't necessary. in fact, if left there, main class still set in manifest if there 1 candidate class.

unforunately, in multi-project build, not prevent main class being set including additional class dummy entry-point.

after lot of fiddling around, found prevent main class being set setting mainclass none in several scopes independently. in particular, trick:

mainclass in assembly := none mainclass in packagebin := none nainclass in compile := none mainclass in run := none 

i not find requirement stated in documentation , cannot figure out why necessary. setting mainclass in (compile, run) := none not work. need scoped separately.

is proper way manually suppress main class or missing something? if not bug, think should documented somewhere, given behavior not consistent between single- , multi-project builds.

main-class , other attributes in jar determined packageoptions in assembly, remove package.mainclass follows:

lazy val root = project(id = "test-assembly",   base = file("."),   settings = buildsettings) settings(   packageoptions in assembly ~= { os => os filternot {_.isinstanceof[package.mainclass]} } ) 

this should work multi-project builds too.

note: sbt-assembly caches output jar based on metadata of source input, testing settings around assembly requires clearing cache calling clean.