Use sbt settingKey in function call - scala

Question

We have a build.sbt file like this, which is working fine:
name := "Foo"
version := "0.1"
scalaVersion := "2.12.8"
def aws(module: String): ModuleID = "com.amazonaws" % module % "1.11.250"
lazy val Core = project
.settings(
libraryDependencies ++= Seq(
aws("aws-java-sdk-s3"),
aws("aws-java-sdk-dynamodb"),
)
)
Basically, the project has a few AWS SDK library dependencies and we want to avoid typing the groupID (e.g. "com.amazonaws") and the revision (e.g. "1.11.250") multiple times and that's why we have this line:
def aws(module: String): ModuleID = "com.amazonaws" % module % "1.11.250"
However, since we have many repos like this and we want to move this definition to a custom sbt-plugin. To begin with, we try this:
name := "Foo"
version := "0.1"
scalaVersion := "2.12.8"
val awsVersion = settingKey[String]("The version of aws SDK used for building.") // line 5
def aws(module: String): ModuleID = "com.amazonaws" % module % awsVersion.value // line 6
awsVersion := "1.11.250"
lazy val Core = project
.settings(
libraryDependencies ++= Seq(
aws("aws-java-sdk-s3"),
aws("aws-java-sdk-dynamodb"),
)
)
However, line 6 is producing an error:
error: value can only be used within a task or setting macro, such as :=, +=, ++=, Def.task, or Def.setting.
The idea is that we'll move line 5 and 6 above to our plugin eventually so that we can use it like this:
name := "Foo"
version := "0.1"
scalaVersion := "2.12.8"
awsVersion := "1.11.250"
lazy val Core = project
.settings(
libraryDependencies ++= Seq(
aws("aws-java-sdk-s3"),
aws("aws-java-sdk-dynamodb"),
)
)
Any solution or work around for the error above?
We've also tried this:
def aws(module: String, version: String): ModuleID = "com.amazonaws" % module % version
... which is then used like this:
awsVersion := "1.11.250"
lazy val Core = project
.settings(
libraryDependencies ++= Seq(
aws("aws-java-sdk-s3", awsVersion.value),
aws("aws-java-sdk-dynamodb", awsVersion.value),
)
)
That works fine though a bit annoying to use and it defeats the purpose of using a settingKey to begin with.

Answer 1

You cannot use setting or task values in locally defined methods like aws. The values can be used only within other setting or task definitions, ie the error message such as :=, +=, ++=, Def.task, or Def.setting.
This is what you could do.
Create AutoPlugin in project folder.
import sbt.{AutoPlugin, Def, ModuleID, settingKey}
import sbt.PluginTrigger.AllRequirements
import sbt._
object AwsPlugin extends AutoPlugin {
override def trigger = AllRequirements
type GetAWS = String => ModuleID
object autoImport {
val awsVersion =
settingKey[String]("The version of aws SDK used for building.")
val awsLibrary = settingKey[GetAWS]("Builds given AWS library")
}
import autoImport._
override def projectSettings: Seq[Def.Setting[_]] = Seq(
awsLibrary := { id =>
"com.amazonaws" % id % awsVersion.value
}
)
}
Use it in this way in build.sbt
awsVersion in ThisBuild := "1.11.250"
lazy val Core = project
.settings(
libraryDependencies ++= Seq(
awsLibrary.value("aws-java-sdk-s3"),
awsLibrary.value("aws-java-sdk-dynamodb"),
)
)