BSP's dependencyModules do not return transitive libraries

[tgodzik]

While investigating scalameta/metals#6419 I realized that dependencyModules returns only the Scala 3 library for a simple Scala 3 project. It's missing the Scala 2.13 library.

My guess is that no transitive dependencies are being returned.

I can work around it by not requesting dependencyModules from Mill BSP server, but I wanted to mention it before doing a workaround.

[lefou]

You are right, there is no resolution step in the current implementation. It's probably an oversight.

P.S. I've planned to touch that code as part of a fix for #3148, but that will no happen in the near next days.

[tgodzik]

There is no hurry, unless this will take more than a month I don't think I need to add a workaround. Thanks!

[tgodzik]

Or did I misunderstand and it would be better to add it for now?

[lefou]

The fix in the right place, e.g. call resolveDeps, should be easier than any workaround.

mill/bsp/worker/src/mill/bsp/worker/MillBuildServer.scala

Lines 402 to 431 in 27ff770

	override def buildTargetDependencyModules(params: DependencyModulesParams)
	: CompletableFuture[DependencyModulesResult] =
	completableTasks(
	hint = "buildTargetDependencyModules",
	targetIds = _ => params.getTargets.asScala.toSeq,
	tasks = { case m: JavaModule =>
	T.task { (m.transitiveCompileIvyDeps(), m.transitiveIvyDeps(), m.unmanagedClasspath()) }
	}
	) {
	case (
	ev,
	state,
	id,
	m: JavaModule,
	(transitiveCompileIvyDeps, transitiveIvyDeps, unmanagedClasspath)
	) =>
	val ivy = transitiveCompileIvyDeps ++ transitiveIvyDeps
	val deps = ivy.map { dep =>
	// TODO: add data with "maven" data kind using a ...
	// MavenDependencyModule
	new DependencyModule(dep.dep.module.repr, dep.dep.version)
	}
	val unmanged = unmanagedClasspath.map { dep =>
	new DependencyModule(s"unmanaged-${dep.path.last}", "")
	}
	new DependencyModulesItem(id, (deps ++ unmanged).iterator.toSeq.asJava)
	} {
	new DependencyModulesResult(_)
	}

[megri]

Any updates on this? Perhaps I can help (I reported the original issue here: scalameta/metals#6419)

[lefou]

@megri Go ahead, I haven't started yet.

[megri]

The fix in the right place, e.g. call resolveDeps, should be easier than any workaround.

mill/bsp/worker/src/mill/bsp/worker/MillBuildServer.scala

Lines 402 to 431 in 27ff770

	override def buildTargetDependencyModules(params: DependencyModulesParams)
	: CompletableFuture[DependencyModulesResult] =
	completableTasks(
	hint = "buildTargetDependencyModules",
	targetIds = _ => params.getTargets.asScala.toSeq,
	tasks = { case m: JavaModule =>
	T.task { (m.transitiveCompileIvyDeps(), m.transitiveIvyDeps(), m.unmanagedClasspath()) }
	}
	) {
	case (
	ev,
	state,
	id,
	m: JavaModule,
	(transitiveCompileIvyDeps, transitiveIvyDeps, unmanagedClasspath)
	) =>
	val ivy = transitiveCompileIvyDeps ++ transitiveIvyDeps
	val deps = ivy.map { dep =>
	// TODO: add data with "maven" data kind using a ...
	// MavenDependencyModule
	new DependencyModule(dep.dep.module.repr, dep.dep.version)
	}
	val unmanged = unmanagedClasspath.map { dep =>
	new DependencyModule(s"unmanaged-${dep.path.last}", "")
	}
	new DependencyModulesItem(id, (deps ++ unmanged).iterator.toSeq.asJava)
	} {
	new DependencyModulesResult(_)
	}

Perhaps I'm misunderstanding the proposed solution but wouldn't it be weird to call m.resolveDeps in this method? That is, shouldn't these dependencies be resolved elsewhere?

[lefou]

Perhaps I'm misunderstanding the proposed solution but wouldn't it be weird to call m.resolveDeps in this method? That is, shouldn't these dependencies be resolved elsewhere?

@megri There is some resolution needed, that's for sure. Of course we already have a target which resolves all ivy dependencies used for compilation (JavaModule.resolvedIvyDeps), but it is only returning some jars, not the full Maven coordinates, which are clearly needed for the dependencyModules request. So we have multiple options here:

1. Refactor JavaModule to also return the coordinates for each jar, which isn't trivial since there is no API in coursier to get that easily. You either get some resolved metadata without the jar location or some jar location without the metadata. At least from what I have discovered about the API.

2. Just run the resolution locally in this BSP request (by doing something like what resolvedIvyDeps does). Since coursier has a cache and is fast, it should not impose much overhead. Otherwise, we have the same limitations regarding the coursier API, so it's probably easier to resolve and assemble the dependency data locally and only refactor after we have found a nice way to assemble it.