Scalafmt hook for pre-commit

Overview

This is pre-commit hook that runs scalafmt on changed .scala and .sbt files each time you commit them.

Getting Started

You need to have pre-commit, Nailgun (for installation guidelines please see the respective sites) and Bash installed first.

Next, you should place the hook inside the .pre-commit-hooks.yaml. Minimal version can looks like this:

- repo: git@github.com:coyainsurance/pre-commit-scalafmt.git
  sha: master # you probably do not want to use latest version, but rather pin it to specific commit and update manually
  hooks:
  - id: scalafmt
    args: [ -p9090, -t ] # run in server mode on port 9090 and pass `--test` to scalafmt; alternatively you can place here other supported cmdline arguments

After that, you should run

pre-commit install -f --install-hooks

or equivalent to install and/or update your hooks file.

Then you should be ready to enjoy automatic checks if your Scala files are formatted accordingly.

Details

Script has several options than can be passed using args array for the pre-commit hook configuration.

• -c $scalafmtConfig sets the scalafmt config (default=.scalafmt.conf).

• -d $bootstrapDirectory sets the bootstrap directory (default=$HOME/.scalafmt).

  It is used to place coursier and scalafmt binaries for the first time this hook is run.

• -p $port - binds nailgun to the specified port. Implies the -s option.

• -s - starts scalafmt in background using nailgun.

  That should significantly speedup checking your files, as scalafmt is then already running in background and JVM processes can take quite significant time to initialize. The tradeoff is that you may sometimes need to commit again, as hook may fail due to connection problems (apparently happens with long-enough running nailgun service).

  You should also make sure to have recent enough nailgun version (0.9.1 should do). In case of older version you may simply get no response back.

  Default port is specified by $NAILGUN_PORT environment variable if it exists. If not, 2113 is taken. Alternatively one can use -p option to override the port.

• -S allows you to set the Scala version for scalafmt, e.g. -S2.12 or -S2.13 (the default).

• -t - passes --test to scalafmt, that implies no mis-formatted file will be changed instead of returning 1 exit code on any.

• -v $version - forces to use specific (default=2.6.3) scalafmt version.

• -o $organisation - forces to use specific scalafmt organisation (default=org.scalameta). (The organisation before the release of 2.0 was com.geirsson.)

It was successfully tested both on Linux distributions and MacOS.