Misdetection of common JS modules in the sbt build

[tindzk]

While working on #634, I noticed that the sbt plug-in fails to detect CommonJS modules. I could trace it down to this function in SbtBloop.scala:

  lazy val findOutScalaJsModuleKind: Def.Initialize[Option[String]] = Def.settingDyn {
    try {
      val stageClass = Class.forName("core.tools.linker.backend.ModuleKind")
      val stageSetting = proxyForSetting("scalaJSModuleKind", stageClass)
      Def.setting {
        stageSetting.value.toString match {
          case "Some(NoModule)" => Some(NoJSModule)
          case "Some(CommonJSModule)" => Some(CommonJSModule)
          case _ => None
        }
      }
    } catch {
      case _: ClassNotFoundException => Def.setting(None)
    }
  }

A ClassNotFoundException gets triggered. When I changed stageClass to classOf[AnyRef], stageSetting.value would always be None.

[jvican]

Good catch. I don't really understand what you mean by changed stageClass to classOf[AnyRef]. Also, I struggle to see how this is related to common js, would you mind elaborating on that point? 😄

On commonjs, will we need to work on support for commonJSName too? https://www.scala-js.org/doc/project/dependencies.html

[tindzk]

Sorry, I pasted the wrong function. It should have been findOutScalaJsModuleKind.

I presumed core.tools.linker.backend.ModuleKind was not on the class path. Using classOf[AnyRef] could work then since all we need is a string representation.

commonJSName is only used for jsDependencies which we do not need to support in Bloop.

[jvican]

commonJSName is only used for jsDependencies which we do not need to support in Bloop.

How is the linker able to detect that a certain jar is mapped to a commonJSName to create the prelude explained in the docs? https://www.scala-js.org/doc/project/dependencies.html

[tindzk]

commonJSName was originally part of the Scala.js sbt plug-in, but was moved into a separate project called jsdependencies. You can find the implementation here.

Please note that the README states the following:

sbt-jsdependencies is not particularly recommended for new projects. Most projects should use scalajs-bundler instead, which provides saner dependencies through npm.

[jvican]

I think this is partially solved by https://github.com/scalacenter/bloop/pull/714/files which hasn't yet been picked up for me since I abandoned the PR a few weeks ago. I will probably continue the work I started in a matter of weeks as other work items have more priority.