Calling a task from a plug-in that may be not present - scala

Question

Depending on a setting I need to call either package or assembly but obviously the assembly task is from sbt-assembly plugin that may not be added. My task looks something like this
lazy val useAssembly = settingKey[Boolean]("Use assembly")
lazy val myTask = Def.task {
val file = if (useAssembly.value) {
// somehow call assembly here
} else {
(`package` in Compile).value
}
// Do other stuff
}

Answer 1

PluginsDebug.autoPluginMap may be used to get available auto plugins. Create project/AssemblyIsAvailable.scala like so
package sbt.internal
/** If sbt-assembly is loaded, then it should be listed as sbtassembly.AssemblyPlugin **/
object AssemblyIsAvailable {
def apply(state: sbt.State): Boolean = {
PluginsDebug
.autoPluginMap(state)
.values
.toList
.map(_.label)
.exists(_.contains("ssembly"))
}
}
then define dynamic task assemblyOrDefaultPackage to be able to use conditional task evaluation within a task:
lazy val assemblyOrDefaultPackage = Def.taskDyn {
if (AssemblyIsAvailable(state.value))
Def.task { assembly.value }
else
Def.task { (Compile / Keys.`package`).value }
}
Now assemblyOrDefaultPackage can be evaluated within another task like so
lazy val myTask = Def.task {
val file = assemblyOrDefaultPackage.value
// Do other stuff
}
Alternatively, define custom command assemblyOrDefaultPackage in build.sbt like so
commands += Command.command("assemblyOrDefaultPackage") { state =>
(if (AssemblyIsAvailable(state)) "assembly" else "package") :: state
}
Now executing sbt assemblyOrDefaultPackage should package with sbt-assembly if available, otherwise fallback to default packaging.