When using sbt, is there a way to define sub projects as intransitive dependencies in a multi-project build?

[tahakonuk]

Hi,
I'm trying to create a layered project structure by defining multiple projects in my build.sbt as below;

lazy val root = (project in file("."))
  .aggregate(
    model,
    service,
    gui
  )
  .settings(...)
  )

lazy val model = (project in file("model"))
  .settings(...)

lazy val service = (project in file("service"))
  .settings(...)
  .dependsOn(model)

lazy val gui = (project in file("gui"))
  .settings(...)
  .dependsOn(service)

And I want to be able to hide model from gui. I asked this question in sbt repository and was advised that I should update the gui definition as follows;

lazy val gui = (project in file("gui"))
  .dependsOn(service)
  .settings(
    Compile / internalDependencyClasspath --= (model / Compile / exportedProducts).value
  )

I'm using metals in visual studio code. And this works if I compile the root from sbt or I choose sbt as a build server in metals. But it doesn't work if I try it with bloop. Is there a way to make it work with bloop?

The way I'm testing this is that I'm using a class from model in gui. Compilation fails with sbt but passes with bloop.

[tgodzik]

I think this might be too specific to how sbt works, which is why when Bloop's sbt plugin extracts the structure it does not exclude the model subproject. This might be fixable in the plugin itself, but not a 100% sure.

[tahakonuk]

Thank you for your response. Is there another way to achieve isolation other than that the one I've shown above? I mean does sbt plugin support that sort of behaviour at all?

[tgodzik]

From what I've seen this is just not really possible currently. And since it is a bit custom workaround, it might also not interact well with IDEs.

[tahakonuk]

OK then, thanks again.

[Arthurm1]

@tahakonuk Isn't this what SBT's Optional configuration is for?

e.g.

lazy val service = (project in file("service"))
  .dependsOn(model % Optional)

lazy val gui = (project in file("gui"))
  .dependsOn(service)

Although I'm not that familiar with SBT and looking through the Bloop Plugin code it seems that for some reason Optional is not a supported configuration so the classpaths are correct but service lacks a project dependency on model so ordering of compile will go wrong.
@tgodzik can you think of why Optional isn't supported?

There's also the Provided scope (which is supported by Bloop plugin) if you don't want to include model on gui runtime classpath either. But since the plugin doesn't yet export SBT runtime classpath it doesn't really matter.

Explanation of Provided and Optional scopes are here.

[tgodzik]

I can't figure out why optional was not supported, but I think #1540 fixes the issue properly.

[tahakonuk]

@Arthurm1 I wasn't aware of the Optional. Thank you for bringing that to my attention. I've just read the docs about it and I think you are right. It can be done using Optional.