How can I make a task depend on another task? - sbt

Question

I'm new to sbt and I try to create a script for either deploy my application or to deploy and run the application.
What already works for me is
sbt deploy
which will successfully deploy the final .jar file to the remove location.
However, I don't know how to make deployAndRunTask dependent on deployTask. I've tried several things but none of them worked so far.
My last hope was
deployAndRunTask := {
val d = deployTask.value
}
However, this does not seem to work.
This is the script that I'm currently at but sbt deploy-run will only execute the deployAndRunTask task but not the deyployTask.
// DEPLOYMENT
val deployTask = TaskKey[Unit]("deploy", "Copies assembly jar to remote location")
deployTask <<= assembly map { (asm) =>
val account = "user#example.com"
val local = asm.getPath
val remote = account + ":" + "/home/user/" + asm.getName
println(s"Copying: $local -> $account:$remote")
Seq("scp", local, remote) !!
}
val deployAndRunTask = TaskKey[Unit]("deploy-run", "Deploy and run application.")
deployAndRunTask := {
val d = deployTask.value
}
deployAndRunTask <<= assembly map { (asm) =>
println(s"Running the script ..")
}
What is the problem here?

Answer 1

The problem is that you define your task and then redefine it. So only the latter definition is taken into account. You cannot separate task definition and its dependency on another task. Also you're using a couple of outdated things in sbt:
use taskKey macro and you don't need to think about task name, because it's the same as the key name:
val deploy = taskKey[Unit]("Copies assembly jar to remote location")
val deployAndRun = taskKey[Unit]("Deploy and run application.")
Then you can refer to them as deploy and deployAndRun both in build.sbt and in the sbt shell
replace <<= with := and keyname map { (keyvalue) => ... } with just keyname.value. Things are more concise and easier to write.
You can read more about Migrating from sbt 0.13.x.
So here's your deployAndRun task definition with these changes:
deployAndRun := {
val d = deploy.value
val asm = assembly.value
println(s"Running the script ..")
}
It's dependent both on deploy and assembly tasks and will run them both before doing anything else. You can also use dependsOn, but I think it's unnecessary here.
You may also be interested in looking into Defining a sequential task with Def.sequential and Defining a dynamic task with Def.taskDyn.