Pre-commit/Pre-push hooks for Scala

What for?

To make your code go smoother while still maintaining high code quality.

Why?

Scala has a quite rich build ecosystem, and a myriad of tools to help you writ good code. However, the build system(s) are relatively slow, so any helpers executed via those build system run the risk of interrupting the flow of a developer.

Moreover, some of the code quality tools/features (like unused import checks) are actively in opposition to a "run-often" coding approach.

Moving relevant checks to the pre-commit/pre-push phases partially alleviates those two issues.

How?

This is a set of hooks defined in the excellent pre-commit library.

Currently, they include the following:

sbt-fatal-warnings - turns on -Xfatal-warnings, runs a clean compilation on the given scope.
sbt-unused-imports - as above, but also adds the "unused imports" warning.
sbt-scalafmt - runs scalafmtCheckAll.
sbt-wartremover - runs the wartremover plugin.

To add one or more of the hooks into your repo:

Have everyone on your team install pre-commit.

Add a .pre-commit-config.yaml file to your repository, with the following syntax:

.pre-commit-config.yaml

repos:
-   repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v0.3.0
    default_phase: push #change to commit if desired
    hooks: #mix and match any of the following:
    -   id: sbt-fatal-warnings #arguments optional
        args: [--scope=test:compile]
    -   id: sbt-unused-imports #includes fatal warnings, arguments optional
        args: [--scope=test:compile]
    -   id: sbt-scalafmt
    -   id: sbt-wartremover #arguments are optional
        args: [--warts=Warts.unsafe, --scope=test:compile]

Run pre-commit install to apply your hooks to the repo.

Note	All hooks except for `sbt-scalafmt` have the optional `scope` argument, which allows to define what source scopes are relevant for the hook’s check. The default is `test:compile`.

Important

Steps 1-2 are only really required for the person setting up the pre-commit library integration. pre-commit library plugins, once installed, are normal Git hooks and are thus "visible" to everyone using the repo.

How to control hook run time

By default, the hooks defined here run on both pre-commit and pre-push. They do, however, require some time to get running on large codebases, especially since each hook’s execution is essentially a clean build.

To limit hook runs to e.g. pre-push, you need to add a stages argument with the relevant value:

.pre-commit-config.yaml

repos:
-   repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v0.3.0
    hooks:
    -   id: sbt-fatal-warnings
        stages: [push] #or [commit, push] etc.

I want more hooks/found a problem!

Thanks for noticing that! Please create an issue.

I want to add a hook!

Excellent, please create a PR. See the contribution guide for more details.