How can scala-js integrate with sbt-web? - scala

Question

I would like to use scala-js with sbt-web in such a way that it can be compiled to produce javascript assets that are added to the asset pipeline (e.g. gzip, digest). I am aware of lihaoyi's workbench project but I do not believe this affects the asset pipeline. How can these two projects be integrated as an sbt-web plugin?

Answer 1

Scala-js produces js files from Scala files. The sbt-web documentation calls this a Source file task.
The result would look something like this:
val compileWithScalaJs = taskKey[Seq[File]]("Compiles with Scala js")
compileWithScalaJs := {
// call the correct compilation function / task on the Scala.js project
// copy the resulting javascript files to webTarget.value / "scalajs-plugin"
// return a list of those files
}
sourceGenerators in Assets <+= compileWithScalaJs
Edit
To create a plugin involves a bit more work. Scala.js is not yet an AutoPlugin, so you might have some problems with dependencies.
The first part is that you add the Scala.js library as a dependency to your plugin. You can do that by using code like this:
libraryDependencies += Defaults.sbtPluginExtra(
"org.scala-lang.modules.scalajs" % "scalajs-sbt-plugin" % "0.5.5",
(sbtBinaryVersion in update).value,
(scalaBinaryVersion in update).value
)
Your plugin would look something like this:
object MyScalaJsPlugin extends AutoPlugin {
/*
Other settings like autoImport and requires (for the sbt web dependency),
see the link above for more information
*/
def projectSettings = scalaJSSettings ++ Seq(
// here you add the sourceGenerators in Assets implementation
// these settings are scoped to the project, which allows you access
// to directories in the project as well
)
}
Then in a project that uses this plugin you can do:
lazy val root = project.in( file(".") ).enablePlugins(MyScalaJsPlugin)

Answer 2

Have a look at sbt-play-scalajs. It is an additional sbt plugin that helps integration with Play / sbt-web.
Your build file will look something like this (copied from README):
import sbt.Project.projectToRef
lazy val jsProjects = Seq(js)
lazy val jvm = project.settings(
scalaJSProjects := jsProjects,
pipelineStages := Seq(scalaJSProd)).
enablePlugins(PlayScala).
aggregate(jsProjects.map(projectToRef): _*)
lazy val js = project.enablePlugins(ScalaJSPlugin, ScalaJSPlay)