VSCode: Unused imports not highlighted

[dekiesel]

Hi,

metals doesn't highlight unused imports in vscode (probably a config error on my side).

Let's say I have two imports

import org.apache.spark.sql.Column
import org.apache.spark.sql.DataFrame

DataFrame is used, Column isn't. Metals doesn't highlight that unused column.

The "bloop sbt already installed"-checkbox is unticked:

I read somewhere that I should create projects/build.sbt, but that seems sbt specific and I assume metals would create that file if needed.

Organize Imports does organize the imports but doesn't remove the unused import.

Could somebody tell me how I can get highlighting working?

Thanks!

[tgodzik]

Metals uses the compiler option for that, so you would need to add it to scalac options if you want to see unused imports.

The options are -Ywarn-unused (or -Wunused in 2.13).

[tgodzik]

It's Bloop building the project yeah, but it can also be a number of other build servers. You usually have to import the build from an existing build tool such as Gradle, Mill, Maven or sbt. Some can also be used as the server themselves. By default we will suggest to import your project into Bloop and to do that we run a plugin for the specific build tool. What does exist in your workspace? build.gradle, build.sbt, build.sc or pom.xml ? Each of those have a bit different methods of adding scalac options, it might be useful for use to set up a guide for that actually, but it should be simple enough to do it.

We decided against enabling unused imports by default for everyone and are more "build tool centric" so that whatever you set up is set up for all the users and can be verified in CI.

[dekiesel]

We are using maven (and all the projects have a pom.xml). I see it is possible to add the option there, but I'd need to do that for every repo and I am the only one in my team using metals so I'll probably meet some resistance. Can this be enabled globally?

[tgodzik]

Can this be enabled globally?

Unfortunately not, you can create a feature request for that. There might be more people who would prefer it this way, thoughit might be hard to achieve.

We are using maven (and all the projects have a pom.xml). I see it is possible to add the option there, but I'd need to do that for every repo and I am the only one in my team using metals so I'll probably meet some resistance.

It's a normal linting option that should actually be useful for other people and can be verified on CI. It's good practice to add linting options irrelevant of the project.

You can see how it's done in maven here: https://davidb.github.io/scala-maven-plugin/example_compile.html under Compiler Arguments

[dekiesel]

Thank you. I guess part of my problem is that I am running scala3 locally, which doesn't seem to have the unused-flag

https://docs.scala-lang.org/scala3/guides/migration/options-lookup.html

I couldn't get it working at all.

import scala.math.sqrt
val unus = 2
@main def run() =
  val ages = Seq(42, 75, 29, 64)
  println(s"The oldest person is ${ages.max}")

C:\Users\user>scalac -Wunused:all scalatest.scala

C:\Users\user>

I'll consider downgrading or using intellij before pushing. Thank you very much for your help!

[dekiesel]

Since you need one flag for 2.12 and another one for 2.13 (and there is no flag for 3) the team declined adding anything to the pom.xml. So for unused imports I am stuck with Intellij.

Thank you for your support again :)