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sbt

sbt is the most commonly used build tool in the Scala community and works with Metals out-of-the-box.

Automatic installation​

The first time you open Metals in a new sbt workspace you will be prompted to import the build. Select "Import Build" to start the automatic installation. This will create all the needed Bloop config files. You should then be able to edit and compile your code utilizing all of the features.

Import build

The Automatic build import process for sbt happens through Bloop, a build server for Scala. Bloop implements the Build Server Protocol (BSP) that Metals uses to learn the directory structure of your project, its library dependencies, and to build or run your code.

Manual installation​

It's recommended to use automatic installation over manual installation since manual installation requires several independent steps that make it harder to stay up-to-date with the latest Metals version.

Instead of using automatic build import, you can manually install sbt-bloop and generate the Bloop JSON files directly from your sbt shell. This approach may speed up build import by avoiding Metals from starting sbt in a separate process.

First, install the Bloop plugin globally or inside your project directory:

// One of:
//   ~/.sbt/0.13/plugins/plugins.sbt
//   ~/.sbt/1.0/plugins/plugins.sbt
resolvers += Resolver.sonatypeRepo("snapshots")
addSbtPlugin("ch.epfl.scala" % "sbt-bloop" % "2.0.6")

Next, run:

sbt -Dbloop.export-jar-classifiers=sources bloopInstall

to generate the Bloop JSON configuration files. You can also set the bloopExportJarClassifiers setting inside your main build.sbt file, but using the above command will do it automatically for you in the current sbt session.

Finally, once bloopInstall is finished, execute the "Connect to build server" command (id: build.connect) command to tell Metals to establish a connection with the Bloop build server.

sbt Build Server​

As of sbt 1.4.1, Metals has integrated support for the sbt BSP server. If you'd like to use the sbt server as an alternative to Bloop (which is the default), then at any time while in an sbt workspace you can choose to switch in multiple ways.

Note: that if you are unfamiliar with the features that the different build servers may offer, then simply stick with the default (Bloop), which has great integrated stable support in Metals.

Generating a .bsp/sbt.json file if one doesn't exist​

More than likely if you're using sbt >= 1.4.1, you'll have already seen this file exist. However, if you're in a fresh workspace or it doesn't exist for some reason, you can execute a metals.generate-bsp-config command via the command palette, which will automatically detect that you're in a sbt workspace and generate the necessary file. After the file generation, Metals will then automatically connect to sbt. From this point on, you'll be using sbt instead of Bloop as your build server.

Connect to sbt build server​

If your workspace already has a .bsp/sbt.json file, then you can switch from using Bloop to sbt as a build server by executing a metals.bsp-switch command from the command palette. This command will recognize the .bsp/sbt.json file, and then connect to the sbt build server. After the connection is made, you'll be using sbt instead of Bloop as your build server.

Switching back to Bloop​

If you'd like to switch back to using Bloop as your build server, there are multiple ways for you to do this.

  1. Using the same metals.bsp-switch command as up above, and select "bloop".
  2. Use the metals.reset-choice functionality and choose to reset the "Build Server Selection". Then follow this with the metals.build-restart command which will disconnect you from the sbt build server, and then connect you back to the default Bloop server.

Troubleshooting​

Before reporting an issue, check if your problem is solved with one of the following tips.

Waiting for lock on .ivy2/.sbt.ivy.lock​

Metals run sbt in a separate process and this error happens where there are two sbt processes resolving dependencies at the same time.

Not valid key: metalsEnable​

This error might indicate that you have an old version of sbt-metals installed in your project.

[error] Not a valid key: metalsEnable (similar: scalafixEnabled)
[error] metalsEnable
[error]             ^

Try to remove any usage of sbt-metals in your build.