Is it possible to parse Json in build.sbt? - scala

Question

I want to validate a downloaded Json file from server during build time and failed the build, if there are any errors.
Is it possible to parse/validate Json in build.sbt?

Answer 1

Your build.sbt is scala code so it can do everything you can do with other scala code.
You should be able to add dependencies (e.g. a json parsing library) of your build.sbt code in project/build.sbt since sbt is recursive.

Answer 2

Here is an example to supplement Jasper-M's answer.
For example, add liahoy's requests-scala HTTP client library, and upickle JSON deserialisation library to project/builds.sbt
libraryDependencies ++= List(
"com.lihaoyi" %% "requests" % "0.6.0",
"com.lihaoyi" %% "upickle" % "1.1.0"
)
Then under project/Preconditions.scala add the following object which will contain assertions you want to check before running the build
object Preconditions {
import scala.util.Try
import requests._
import upickle.default._
case class User(login: String, id: Int)
implicit val userRW: ReadWriter[User] = macroRW
def validateUserJson() = {
val result = Try(read[User](get("https://api.github.com/users/lihaoyi").text)).isSuccess
assert(result, "User JSON should be valid")
}
}
Now these facilities will be available to build.sbt under the root project. Lets create a task in build.sbt to run the assertions
lazy val checkPreconditions = taskKey[Unit]("Validate pre-conditions before building")
checkPreconditions := {
Preconditions.validateUserJson()
println("All preconditions passed!")
}
and finally lets make compile task dependant on checkPreconditions task using dependsOn like so
Compile / compile := (Compile / compile).dependsOn(checkPreconditions).value
Now executing sbt compile should check pre-conditions before proceeding with compilation.