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Mill

Getting Started

You can use Mill together with Bloop to speed up your development workflow and better integrate your build with your IDE.

Mill has built-in support for Bloop via mill-contrib, so follow the instructions below to install the mill-bloop module.

Export your build

The following mill command automatically downloads the required plugin and exports your mill build to bloop:

mill --import ivy:com.lihaoyi::mill-contrib-bloop: mill.contrib.bloop.Bloop/install

The mill plugin generates a configuration file per every compile and test sources in your build definition. For example, a build with a single Scala project foo generates two configuration files by default:

$ mill --import ivy:com.lihaoyi::mill-contrib-bloop: mill.contrib.bloop.Bloop/install
(...)
[120/123] MillBuildRootModule.bloop.writeConfigFile
[120] Wrote /disk/foo/.bloop/mill-build-.json
[121/123] foo.bloop.writeConfigFile
[121] Wrote /disk/foo/.bloop/foo.json
[122/123] foo.test.bloop.writeConfigFile
[122] Wrote /disk/foo/.bloop/foo.test.json
[123/123] =================== mill.contrib.bloop.Bloop/install =================== 10s

where:

  1. foo comes from the compile source set; and,
  2. foo.test comes from the test source set and depends on foo

Verify installation and export

If you haven't installed bloop and its CLI yet, follow these instructions before proceeding.

Verify your installation by running bloop projects in the root of the mill workspace directory.

$ bloop projects
mill-build-
foo
foo.test

If the results of bloop projects is empty, check that:

  1. You are running the command-line invocation in the root base directory (e.g. /disk/foo).
  2. The mill build export process completed successfully.
  3. The .bloop/ configuration directory contains bloop configuration files.

If you suspect bloop is loading the configuration files from somewhere else, run --verbose:

$ bloop projects --verbose
[D] Projects loaded from '/my-project/.bloop':
mill-build-
foo
foo.test

Here's a list of bloop commands you can run next to start playing with bloop:

  1. bloop compile --help: shows the help section for compile.
  2. bloop compile foo.test: compiles foo's src/main and src/test.
  3. bloop test foo.test -w: runs foo tests repeatedly with file watching enabled.

After verifying the export, you can continue using Bloop's command-line application or any build client integrating with Bloop, such as Metals.

Next steps after installation

Use an IDE such as Metals or IntelliJ to write code or play with the CLI if you want to explore what CLI options are available.

If you need help, you can always come over our Discord channel.

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