Best place to declare own settings so I can access them from sbt shell and my .sbt and .scala build files? - sbt

Question

My settings are declared in project/Utils.scala in an object BuildSupport and are made available in .sbt and .scala files with import BuildSupport._.
However, this doesn't work for sbt shell as seen in above screenshot since I can't import them there. For completeness sake, I have tried eval import BuildSupport._ but all that got me was <eval>:1: error: illegal start of simple expression.
How do I have to define own settings and tasks so I can access them from:
project/*.scala,
*.sbt and
sbt shell?
I assume defining them in an AutoPlugin would work, but I'd rather not have to go to that length. Is there any other way?

Answer 1

Declaring an adhoc AutoPlugin (https://www.scala-sbt.org/1.x/docs/Plugins.html) is the way to go.
Auto plugins ...
can define autoImport object, which is automatically included into build.sbt. This can be used for keys.
can define globalSettings, buildSettings, or projectSettings to inject settings and tasks either at the build-level or at the subproject level. This should become available in sbt shell.
A plugin doesn't have to be a published on its own. You can declare one inside project/*.scala like any other Scala object.
The plugin in the linked documentation is great for copy-pasting:
package sbthello
import sbt._
import Keys._
object HelloPlugin extends AutoPlugin {
override def trigger = allRequirements
object autoImport {
val helloGreeting = settingKey[String]("greeting")
val hello = taskKey[Unit]("say hello")
}
import autoImport._
override lazy val globalSettings: Seq[Setting[_]] = Seq(
helloGreeting := "hi",
)
override lazy val projectSettings: Seq[Setting[_]] = Seq(
hello := {
val s = streams.value
val g = helloGreeting.value
s.log.info(g)
}
)
}