Write Tasks in dedicated file, when writing SBT AutoPlugins - scala

Question

I have written an SBT auto plugin MyPlugin.scala:
package com.abhi
import sbt._
import sbt.Keys._
object MyPlugin extends AutoPlugin {
object autoImport {
val helloTask = taskKey[Unit]("says hello")
val byeTask = taskKey[Unit]("bye task")
}
import autoImport._
override lazy val projectSettings = Seq(
helloTask := {
val dir = sourceManaged.value
val cp = (dependencyClasspath in Compile).value
val r = (runner in Compile).value
val s = streams.value
val rd = (resourceDirectory in Compile).value
val sd = (sourceDirectory in Compile).value
println(s"Here to say hello $dir $cp $r $s $rd $sd")
},
byeTask := {
val dir = sourceManaged.value
val cp = (dependencyClasspath in Compile).value
val r = (runner in Compile).value
val s = streams.value
val rd = (resourceDirectory in Compile).value
val sd = (sourceDirectory in Compile).value
println(s"Here to say bye $dir $cp $r $s $rd $sd")
}
)
}
This works and I am able to use this plugin. However the implementation of helloTask and byeTask will be a little long, so I don't want to write the implementation inside MyPlugin.scala.
Instead, I want to create two separate files HelloTask.scala and ByeTask.scala and then write the respective implementations there.
I looked at the SBT documentation for Custom Settings and all examples always implement the tasks inside of the plugin itself.
How can I write the implementation of helloTask and byeTask outside of the MyPlugin.scala file? also how to share some logic between HelloTask and ByeTask.
The following lines are common between the two tasks and I want to write these only once
val dir = sourceManaged.value
val cp = (dependencyClasspath in Compile).value
val r = (runner in Compile).value
val s = streams.value
val rd = (resourceDirectory in Compile).value
val sd = (sourceDirectory in Compile).value

Answer 1

Separating tasks implementation is a common good practice. It is mentioned in the Tasks documentation. You can write an implementation using Def.task macro:
def taskImpl(args: ...): Def.Initialize[Task[...]] = Def.task {
...
}
And then use it with different arguments to set different task keys:
override def projectSettings = Seq(
taskA := taskImpl("A").value,
taskB := taskImpl("B").value,
)
In your case you could do something like this:
def saySmthImpl(msg: String): Def.Initialize[Task[Unit]] = Def.task {
val dir = sourceManaged.value
val cp = (dependencyClasspath in Compile).value
val r = (runner in Compile).value
val s = streams.value
val rd = (resourceDirectory in Compile).value
val sd = (sourceDirectory in Compile).value
println(s"$msg $dir $cp $r $s $rd $sd")
}
You can keep this implementation in a separate file if you want. The in the plugin definition you can use it like this:
override def projectSettings = Seq(
helloTask := saySmthImpl("Here to say hello").value,
byeTask := saySmthImpl("Here to say bye").value,
)
You should keep in mind though, that accessing other settings or tasks with .value can be done only in certain scopes, like that Def.task or Def.setting or when setting keys with :=. This limits (or rather directs) the ways you can share logic between different tasks implementations.