Edit

Installation

You can use Scalafmt from your editor, build tool or terminal.

IntelliJ

The Scala plugin compatible with recent versions of IntelliJ IDEA has built-in support for Scalafmt (see Note below). DO NOT install the deprecated Scalafmt plugin unless you have an older version of Intellij.

When opening a project that contains a .scalafmt.conf file, you will be prompted to use it:

IntelliJ scalafmt formatter

Choose the scalafmt formatter and IntelliJ's Reformat Code action will then use Scalafmt when formatting files. See below for shortcuts.

Note: IntelliJ 2019.1 or later is required in order for the Scala plugin to support Scalafmt and the dynamic version set in your .scalafmt.conf. If you must use an older version, see the FAQ for an alternative.

Format current file

  • Opt + Cmd + L (macOS)
  • Ctrl + Alt + L (other)

To re-configure the shortcut:

  • Open Preferences > Keymap
  • Search for "Reformat Code"

Range formatting

Scalafmt is primarily designed to operate on entire text files—formatting selected ranges of code may produce undesirable results. For this reason, IntelliJ uses its own formatter for ranges by default. It is not recommended to change this, and is instead recommended to format files when saving.

Format on save

  • for the current project (recommended): Preferences > Editor > Code Style > Scala
  • for all new projects: File > Other Settings > Preferences for New Projects… > Editor > Code Style > Scala

Enable format on save in IntelliJ

Resume using IntelliJ formatter

To reset the formatter to IntelliJ for an existing project that uses the Scalafmt formatter:

  • Open Preferences > Editor > Code Style > Scala
  • Switch "Formatter" value to "IntelliJ"

It is not possible to reset this setting for all existing projects.

VS Code

You can use the Metals language server to format code with Scalafmt in VS Code. For more details, refer to the Metals documentation.

Vim

You can use the Metals language server to format code with Scalafmt in Vim and NeoVim. For more details, refer to the Metals documentation.

Emacs

You can use the Metals language server to format code with Scalafmt in Emacs. For more details, refer to the Metals documentation.

The externally maintained format-all extension to Emacs also supports scalafmt as one of its formatters.

Sublime Text

You can use the Metals language server to format code with Scalafmt in Sublime Text. For more details, refer to the Metals documentation.

Eclipse

You can use the Metals language server to format code with Scalafmt in Eclipse. For more details, refer to the Metals documentation.

Metals

Metals automatically uses Scalafmt to respond to formatting requests from the editor, according to the configuration defined in .scalafmt.conf.

In most editors, if you there is no .scalafmt.conf, upon receiving the first format request Metals will create the .scalafmt.conf file for you.

You can find more information on triggering a format request for individual editors in their respective parts of the Metals site.

sbt

NB: keep in mind that versions of scalafmt-core and sbt-scalafmt are released independently, their versions do not align. The version of scalafmt-core is defined in the .scalafmt.conf configuration file and downloaded dynamically.

// In project/plugins.sbt. Note, does not support sbt 0.13, only sbt 1.x.
addSbtPlugin("org.scalameta" % "sbt-scalafmt" % SBT_PLUGIN_VERSION)

Latest published version of the sbt plugin: sbt-scalafmt Scala version support

To configure the scalafmt version add the following line into .scalafmt.conf:

version = 3.8.4-RC2

Task keys

  • myproject/scalafmt: Format main sources of myproject project
  • myproject/Test/scalafmt: Format test sources of myproject project
  • scalafmtCheck: Check if the scala sources under the project have been formatted.
  • scalafmtSbt: Format *.sbt and project/*.scala files.
  • scalafmtSbtCheck: Check if the files have been formatted by scalafmtSbt.
  • scalafmtOnly <file>...: Format specified files listed.
  • scalafmtAll or scalafmtCheckAll: Execute the scalafmt or scalafmtCheck task for all configurations in which it is enabled (since v2.0.0-RC5)

Settings

  • scalafmtConfig: File: The location of the .scalafmt.conf configuration file. Defaults to the .scalafmt.conf file at the root of the project.
  • scalafmtOnCompile: Boolean: Defines if the sbt-scalafmt should run scalafmt on compile. Default false.
    • ⚠️ This option is discouraged since it messes up undo buffers in the editor and it slows down compilation. It is recommended to use "format on save" in the editor instead.
  • [since v2.4.5] scalafmtFilter: String (default ""): optionally limits the set of files considered for formatting:
    • diff-dirty: only the files modified in the git working tree (git status)
    • diff-ref=<spec>: only the tracked files modified since <spec> (git diff)
    • [since v2.4.6] none: no restrictions
    • otherwise if project.git = true (.scalafmt.conf): only files tracked by git (git ls-tree)
    • otherwise, no restrictions
  • [since v2.4.3] scalafmtDetailedError: Boolean: if set, when handling a specific error (whether logging or throwing an exception), include the stacktrace as well
  • [since v2.4.5] scalafmtLogOnEachError: Boolean: if set, plugin will log errors
  • [since v2.4.5] scalafmtFailOnErrors: Boolean: if set, plugin will fail on errors
    • depending on scalafmtLogOnEachError, fail on the first error or only at the end
  • [since v2.4.6] scalafmtPrintDiff: Boolean: if set, check will display the differences for incorrectly formatted files

Enable IntegrationTest

Unnecessary since v2.4.4.

The sbt plugin is enabled by default for the Test and Compile configurations. Use scalafmtConfigSettings to enable the plugin for integration tests and then use it:scalafmt to format.

inConfig(IntegrationTest)(org.scalafmt.sbt.ScalafmtPlugin.scalafmtConfigSettings)

Share configuration between builds

To share configuration across different sbt builds, create a custom sbt plugin that generates .scalafmt-common.conf on build reload, then include the generated file from .scalafmt.conf

// project/MyScalafmtPlugin.scala
import sbt._
object MyScalafmtPlugin extends AutoPlugin {
  override def trigger = allRequirements
  override def requires = plugins.JvmPlugin
  override def buildSettings: Seq[Def.Setting[_]] = {
    SettingKey[Unit]("scalafmtGenerateConfig") :=
      IO.write(
        // writes to file once when build is loaded
        file(".scalafmt-common.conf"),
        "maxColumn = 100".stripMargin.getBytes("UTF-8")
      )
  }
}

// .scalafmt.conf
include ".scalafmt-common.conf"

Limit parallelism

You can limit formatting parallelism for projects with multiple subprojects in your build.sbt:

import org.scalafmt.sbt.ConcurrentRestrictionTags

Global / concurrentRestrictions += Tags.limit(org.scalafmt.sbt.ConcurrentRestrictionTags.Scalafmt, 4)

CLI

The recommended way to install the scalafmt command line tool is with Coursier.

Coursier

To install Coursier see here

install

If you're using a recent version of coursier which supports direct installation of packages, the simplest approach is by running

cs install scalafmt
scalafmt --version # should be 3.8.4-RC2

standalone

Alternatively, you can create a complete standalone executable (40+ MB in 2022) with:

coursier bootstrap org.scalameta:scalafmt-cli_2.13:3.8.4-RC2 \
  -r sonatype:snapshots --main org.scalafmt.cli.Cli \
  --standalone \
  -o scalafmt
./scalafmt --version # should be 3.8.4-RC2

slim

Finally, you can choose to obtain a slim bootstrap script (100+ KB in 2022) instead with:

coursier bootstrap org.scalameta:scalafmt-cli_2.13:3.8.4-RC2 \
  -r sonatype:snapshots --main org.scalafmt.cli.Cli \
  -o scalafmt
./scalafmt --version # should be 3.8.4-RC2

If a version is defined in .scalafmt.conf, the CLI binary will honor it by automatically resolving and downloading the corresponding artifacts if it does not match its own version. Otherwise, it is recommended to put this bootstrap script in your code repository to make sure everyone on your team, as well as CI, uses the same scalafmt version.

To configure which files to format, see project.

To customize the JVM options, use the Coursier option --java-opt, more info with

coursier bootstrap --help | grep -A 1 "\-\-java-opt"

Pre-release

Our CI publishes a pre-release version of scalafmt to Sonatype Snapshots on every merge into master. To use a pre-release, replace 3.8.4-RC2 with the version here:

Sonatype Snapshots

If you use coursier to install a pre-release, be sure to include the flag -r sonatype:snapshots so that the artifact can be resolved.

If you use sbt to install a pre-release, be sure to add the following setting:

resolvers += Resolver.sonatypeRepo("snapshots")

Native image

For macOS and Linux, it's possible to download pre-built GraalVm native binaries with instant startup and fast performance for short-lived Scalafmt runs.

VERSION=3.8.4-RC2
INSTALL_LOCATION=/usr/local/bin/scalafmt-native
curl https://raw.githubusercontent.com/scalameta/scalafmt/master/bin/install-scalafmt-native.sh | \
  bash -s -- $VERSION $INSTALL_LOCATION
scalafmt-native --help # should show version 3.8.4-RC2

The native image binaries have the limitation of working only with one version of Scalafmt. The native binaries fail when the version setting in .scalafmt.conf does not match the version of the native binary. It's recommended to use the JVM binary if you expect to use Scalafmt in multiple projects with different Scalafmt versions.

Please see issue #1569 if you'd like to contribute support for building native images for Windows!

Nailgun

Nailgun is recommended if you want to integrate scalafmt with a text editor like vim/Emacs/Atom/Sublime/VS Code.

  • Make sure you have a nailgun client installed. For example with brew install nailgun.
  • Create a standalone executable in /usr/local/bin/scalafmt_ng with (sudo if necessary)
coursier bootstrap --standalone org.scalameta:scalafmt-cli_2.13:3.8.4-RC2 \
  -r sonatype:snapshots -f --main com.martiansoftware.nailgun.NGServer \
  -o /usr/local/bin/scalafmt_ng
scalafmt_ng & // start nailgun in background
ng ng-alias scalafmt org.scalafmt.cli.Cli
ng scalafmt --version # should be 3.8.4-RC2

Nailgun keeps scalafmt running on a local server to avoid the JVM startup penalty and also so scalafmt can benefit from JIT. This makes scalafmt up to 10x faster when formatting a single file from the CLI. The downside to Nailgun is that the setup is complicated and the long-running server needs to be restarted once in awhile.

Homebrew

The recommended way to install the scalafmt command line tool is with Coursier, itself available via Homebrew.

brew install coursier/formulas/coursier
coursier install scalafmt
scalafmt --version // should be 3.8.4-RC2

If necessary, make sure to follow the Coursier instructions for updating $PATH so that the scalafmt binary becomes available in your terminal.

Arch Linux

You can install scalafmt for Arch Linux from AUR. There is the scalafmt-native-bin package that installs scalafmt binary built with GraalVM. GraalVM native binary provides instant startup without Nailgun.

yaourt -S scalafmt-native-bin
scalafmt --version // should be 3.8.4-RC2

--help

build commit: 8b1faed25915262bdc2e6e261526c15473f6ddfe
build time: Wed Nov 20 18:51:45 UTC 2024

scalafmt 3.8.4-RC2+10-8b1faed2-SNAPSHOT
Usage: scalafmt [options] [<file>...]

  -h, --help               prints this usage text
  -v, --version            print version 
  <file>...                file, or directory (in which all *.scala files are to be formatted);
                           if starts with '@', refers to path listing files to be formatted
                           (with "@-" referring to standard input as a special case)
  --stdout                 write formatted files to stdout
  --exclude <value>        file or directory, when missing all *.scala files are formatted.
  --respect-project-filters
                           use project filters even when specific files to format are provided
  -c, --config <value>     a file path to .scalafmt.conf.
  --config-str <value>     configuration defined as a string
  --stdin                  read from stdin and print to stdout
  --no-stderr              don't use strerr for messages, output to stdout
  --assume-filename <value>
                           when using --stdin, use --assume-filename to hint to scalafmt that the input is an .sbt file.
  --reportError            exit with status 1 if any mis-formatted code found.
  --test                   test for mis-formatted code only, exits with status 1 on failure.
  --check                  test for mis-formatted code only, exits with status 1 on first failure.
  --mode <value>           Sets the files to be formatted fetching mode.
                           Options:
                              diff-ref=xxx: format files listed in `git diff` against gitref `xxx`
                              diff: format files listed in `git diff` against gitref `master`
                              changed: format files listed in `git status` (latest changes against previous commit)
                              any: format any files found in current directory
                              anygit: format any git-tracked files found in current directory
  --diff                   Format files listed in `git diff` against master.
                           Deprecated: use --mode diff instead
  --diff-branch <value>    Format files listed in `git diff` against given git ref.
                           Deprecated: use --mode diff-ref=<ref> instead
  --build-info             prints build information
  --quiet                  don't print out stuff to console.
  --debug                  print out diagnostics to console.
  --non-interactive        disable fancy progress bar, useful in ci or sbt plugin.
  --list                   list files that are different from scalafmt formatting
Examples:
scalafmt # Format all files in the current project, configuration is determined in this order:
         # 1. .scalafmt.conf file in current directory
         # 2. .scalafmt.conf inside root directory of current git repo
         # 3. no configuration, default style
scalafmt --test # throw exception on mis-formatted files, won't write to files.
scalafmt --mode diff # Format all files that were edited in git diff against master branch.
scalafmt --mode changed # Format files listed in `git status` (latest changes against previous commit.
scalafmt --diff-branch 2.x # same as --diff, except against branch 2.x
scalafmt --stdin # read from stdin (doesn't imply --stdout)
scalafmt --stdin --assume-filename foo.sbt < foo.sbt # required when using --stdin to format .sbt files.
scalafmt Code1.scala A.scala       # write formatted contents to file.
scalafmt --stdout Code.scala       # print formatted contents to stdout.
scalafmt --exclude target          # format all files in directory excluding target
scalafmt --config .scalafmt.conf   # read custom style from file.
scalafmt --config-str "style=IntelliJ" # define custom style as a flag, must be quoted.
Please file bugs to https://github.com/scalameta/scalafmt/issues

Using custom repositories with CLI

Under the hood, scalafmt uses the scalafmt-dynamic library and, in turn, coursier, to download the version (of scalafmt-core) specified in .scalafmt.conf file.

By default, coursier will download from a few standard repositories (including sonatype, both public and snapshot). However, if you'd like to use instead some custom repositories within your environment, please specify them using the COURSIER_REPOSITORIES environment variable.

Repository credentials

Additionally, if your repositories require credentials, please specify them in the COURSIER_CREDENTIALS environment variable.

Keep in mind that coursier credential format is not the same as, say, sbt, and since multiple entries are allowed and expected, each requires a unique prefix of your choosing.

Others have also reported needing to include in their credentials settings such as

<prefix>.pass-on-redirect=true
<prefix>.auto=true

Gradle

It is possible to use scalafmt in gradle with the following externally maintained plugins:

Maven

It is possible to use scalafmt in Maven with the following externally maintained plugin:

Mill

Mill has scalafmt support built-in:

Standalone library

Use the scalafmt-dynamic module to integrate with Scalafmt.

libraryDependencies += "org.scalameta" %% "scalafmt-dynamic" % "3.8.4-RC2"

First, create an instance of Scalafmt and get paths for the file to format along with it's configuration file.

import java.nio.file._
import org.scalafmt.interfaces.Scalafmt
val scalafmt = Scalafmt.create(this.getClass.getClassLoader)
val config = Paths.get(".scalafmt.conf")
val file = Paths.get("Main.scala")

Use the format method to format a string with the given config and filename.

println(scalafmt.format(config, file, "object A  {  }"))
// object A {}
//

Binary compatibility guarantees

Stable public APIs:

  • org.scalafmt.interfaces (recommended): pure Java APIs with no external dependencies. Can be loaded via the scalafmt-dynamic module.
  • org.scalafmt.Scalafmt (discouraged): old public API that is stable and will remain stable but has several limitations.
    • no support for version in .scalafmt.conf
    • does not respect project.excludeFilters in .scalafmt.conf
    • doesn't automatically handle *.sbt and *.sc files
    • no caching of .scalafmt.conf

Internal APIs that are subject to binary breaking changes in any release:

  • org.scalafmt.dynamic: private implementation of scalafmt-interfaces. These classes can be used via the static method org.scalafmt.interfaces.Scalafmt.create(ClassLoader).
  • org.scalafmt.config: case classes for .scalafmt.conf configuration that that are only intended for internal usage.
  • org.scalafmt.cli: private implementation of the command-line interface.

*.sbt and *.sc files

It's possible to format *.sbt and *.sc files.

println(scalafmt.format(config, Paths.get("build.sbt"), "lazy    val   x =   project"))
// lazy val x = project
// 
println(scalafmt.format(config, Paths.get("build.sc"), "def  main(  ) = println()"))
// def main() = println()
//

The scalafmt instance automatically picks the correct parser depending on the provided filename.

Version handling

By default, the scalafmt instance automatically downloads the Scalafmt version declared in .scalafmt.conf. If the version setting is not declared, the original file contents are returned unchanged and an error is reported with instructions how to fix the problem.

Error reporting

By default, Scalafmt errors are reported to System.err. Extend org.scalafmt.interfaces.ScalafmtReporter to customize error reporting to handle parse and config errors.

Here is an example how to extend ScalafmtReporter.

File: ConsoleScalafmtReporter.scala

package org.scalafmt.dynamic

import org.scalafmt.interfaces.ScalafmtReporter

import java.io.OutputStreamWriter
import java.io.PrintStream
import java.io.PrintWriter
import java.nio.file.Path

object ConsoleScalafmtReporter extends ConsoleScalafmtReporter(System.err)

class ConsoleScalafmtReporter(out: PrintStream) extends ScalafmtReporter {
  override def error(file: Path, e: Throwable): Unit = {
    out.print(s"error: $file: ")
    trimStacktrace(e)
    e.printStackTrace(out)
  }

  override def error(path: Path, message: String): Unit = out
    .println(s"error: $path: $message")

  override def excluded(filename: Path): Unit = out
    .println(s"file excluded: $filename")

  override def parsedConfig(config: Path, scalafmtVersion: String): Unit = out
    .println(s"parsed config (v$scalafmtVersion): $config")

  override def downloadWriter(): PrintWriter = new PrintWriter(out)

  override def downloadOutputStreamWriter(): OutputStreamWriter =
    new OutputStreamWriter(out)

  protected def trimStacktrace(e: Throwable): Unit = ()
}

Use withReporter(reporter) to pass in your custom reporter.

import java.io._
import org.scalafmt.dynamic._
val myOut = new ByteArrayOutputStream()
val myReporter = new ConsoleScalafmtReporter(new PrintStream(myOut))
val customReporterScalafmt = scalafmt.withReporter(myReporter)

Project filters

By default, scalafmt only formats files that match the project.{excludeFilters,includeFilters} settings in .scalafmt.conf. Use withRespectExcludeFilters(false) to disable this behavior.

val scalafmtThatIgnoresProjectSettings = scalafmt.withRespectProjectFilters(false)

Alternate repositories and credentials

scalafmt uses some default repositories to download the version specified in .scalafmt.conf; these repositories could be hardcoded or potentially specified via the environment variables.

In order to specify explicit repositories as well, one could use

val scalafmtWithRepos = scalafmt.withMavenRepositories(
  "https://repo-1/snapshots",
  "https://repo-2/public"
)

In addition, if some of the default or custom repositories require access credentials, they could be specified via

import org.scalafmt.interfaces._

val scalafmtWithCreds = scalafmtWithRepos match {
  case x: RepositoryCredential.ScalafmtExtension =>
    x.withRepositoryCredentials(
      new RepositoryCredential("repo-1", "username", "password")
    )
  case x => x
}

This capability was added to the public interface as an extension method, accessible via a separate sub-interface.

Clearing resources

Use the clear() method to clear up resources of the scalafmt instance.

scalafmt.clear()

Calling from Java

It's possible to call Scalafmt from Java without depending directly on Scala libraries.

First, depend on the scalafmt-interfaces module, which is a pure Java library with no external dependencies.

<dependency>
    <groupId>org.scalameta</groupId>
    <artifactId>scalafmt-interfaces</artifactId>
    <version>3.8.4-RC2</version>
</dependency>

Next, obtain a classloader with the scalafmt-dynamic_2.12 classpath.

import java.net.URLClassLoader;
// this package contains only Java APIs.
import org.scalafmt.interfaces.*;

// ClassLoader that shares only org.scalafmt.interfaces from this classloader.
ClassLoader sharedParent = new ScalafmtClassLoader(this.getClass.getClassLoader)

// Jars to org.scalameta:scalafmt-dynamic_2.12:3.8.4-RC2 classpath. Obtain
// these from your build tool or programmatically with ivy/coursier.
URL[] jars = // ...
ClassLoader scalafmtDynamic = new URLClassLoader(jars, sharedParent)

Finally, create an instance of Scalafmt with the scalafmt-dynamic classloader.

Scalafmt scalafmt = Scalafmt.create(scalafmtDynamic)
String formatted = scalafmt.format(config, file, "object A   { }")
Configuration →