Scala CLI is an experimental tool to run/compile/test Scala that aims at being a better scala command. It shares some similarities with build tools, but doesn't aim at supporting multi-module projects, nor to be extended via a task system.

User-facing documentation can be found on our website: scala-cli.virtuslab.org.

Building Scala CLI requires a JVM 17 to work properly.

In theory, our build is able to download and install for its own needs JVM 17 on some OSes however it may not work in Intellij / Metals out of the box.

The Scala CLI sources ship with Mill launchers, so that Mill itself doesn't need to be installed on your system.

./mill -i scala …arguments…

./mill 'build-module.test'

./mill integration.test.jvm

Filter test suites with

./mill integration.test.jvm 'scala.cli.integration.RunTestsDefault.*'
./mill integration.test.jvm 'scala.cli.integration.RunTestsDefault.Multiple scripts'

Pass the --debug option to debug integration tests:

./mill integration.test.jvm 'scala.cli.integration.RunTestsDefault.*' --debug

The debug option uses 5005 port by default. It is possible to change it as follows:

./mill integration.test.jvm 'scala.cli.integration.RunTestsDefault.*' --debug:5006

(generating the launcher can take several minutes)

./mill integration.test.native

Build native packagers:

• deb for linux
• msi for windows
• dmg and pkg for macOS

(generating native packager for specified format)

./mill -i scala package ..arguments... --deb --output 'path.deb'
./mill -i scala package ..arguments... --dmg --output 'path.dmg'
./mill -i scala package ..arguments... --pkg --output 'path.pkg'

./mill mill.contrib.Bloop/install

Then run the command "Metals: Connect to build server".

(Recommended over the Metals import project functionality.)

Whenever the build is updated, just do these two steps again.

./mill mill.scalalib.GenIdea/idea

Then open the scala-cli directory in IntelliJ.

(Recommended over the IntelliJ import project functionality.)

Whenever the build is updated, run the command above again. IntelliJ should then pick up the new changes.

./mill -i show cli.nativeImage

This prints the path to the generated native image. The file named scala at the root of the project should also be a link to it. (Note that the link is committed and is always there, whether the files it points at exists or not.)

./mill -i show cli.launcher

This prints the path to the generated launcher. This launcher is a JAR, that directly re-uses the class directories of the modules of the project (so that cleaning up those classes will break the launcher). If this is a problem (if you wish to run the launcher on another machine or from a Docker image for example), use a native launcher (see above) or a standalone JVM one (see below).

./mill -i show cli.standaloneLauncher

This prints the path to the generated launcher. This launcher is a JAR, that embeds JARs of the scala-cli modules, and downloads their dependencies from Maven Central upon first launch (using the coursier cache, just like a coursier bootstrap).

A number of features of Scala CLI are managed from external projects, living under the scala-cli organization on GitHub. These projects can be used by Scala CLI as libraries pulled before it's compiled, but also as binaries. In the latter case, Scala CLI downloads on-the-fly binaries from these repositories' GitHub release assets, and runs them as external processes.

For example, here are a few external projects used by Scala CLI:

• scala-js-cli-native-image: provides a binary running the Scala.js linker
• scala-cli-signing: provides both libraries and binaries to handle PGP concerns in Scala CLI
• libsodiumjni: provides minimal JNI bindings for libsodium, that is used by Scala CLI to encrypt secrets uploaded as GitHub repository secrets in the publish setup sub-command

For the full list of those projects and their description, see the scala-cli repository list and the READMEs of each of these projects.

The use of external binaries allows to make the Scala CLI binary slimmer and faster to generate, but also allow to lower memory requirements to generate it (allowing to generate these binaries on the GitHub-provided GitHub actions hosts).

The Scala CLI website is built with Docusaurus and uses Infima for styling.

Ensure you are using Node >= 14.

cd website
yarn
yarn build
npm run serve

cd website
yarn
yarn run start

We have a built-in tool to validate .md files called Sclicheck. All Sclicheck tests can be run with Mill munit: (and this is what we run on the CI, too)

./mill -i docs-tests.test

The former also includes testing gifs and Sclicheck itself. To just check the documents, run:

./mill -i docs-tests.test 'sclicheck.DocTests.*'

You can also check all root docs, commands, reference docs, guides or cookbooks:

./mill -i docs-tests.test 'sclicheck.DocTests.root*'
./mill -i docs-tests.test 'sclicheck.DocTests.guide*'
./mill -i docs-tests.test 'sclicheck.DocTests.command*'
./mill -i docs-tests.test 'sclicheck.DocTests.cookbook*'
./mill -i docs-tests.test 'sclicheck.DocTests.reference*'

Similarly, you can check single files:

./mill -i docs-tests.test 'sclicheck.DocTests.<category> <doc-name>'

For example, to run the check on compile.md

./mill -i docs-tests.test 'sclicheck.DocTests.command compile'

Package with various logos for scala-cli can be found on google drive

There is a script scala-cli-src in the repository root that is intended to work exactly like released scala-cli, but using a binary compiled the worktree. Just add it to your PATH to get the already-released-scala-cli experience.

Instructions on how to release - Release Procedure

The easiest way to debug BSP sever is using scala-cli-src script with --bsp-debug-port 5050 flag (the port should be unique to the workspace where BSP will be debugged). In such case BSP will be launched using local source and will run on JVM. It will also expects a debugger running in the listen mode using provided port (so the initialization of the connection can be debugged). In such case we recommend to have option to auto rerun debugging session off (so there is always a debugger instance ready to be used).