Overcommit

A gem to install and manage a configurable (but opinionated) set of Git hooks. Originally written for use at Causes.

In addition to supporting global hooks, it also allows teams to define plugins specific to a repository (installed in the .githooks directory).

Read more about overcommit on our engineering blog.

Installation

The overcommit is installed as a binary via rubygems:

gem install overcommit

You can then run the overcommit command to install hooks into repositories:

mkdir important-project
cd important-project
git init
overcommit .

overcommit also accepts a handful of arguments, which can be enumerated by running overcommit --help.

At Causes, we install all of the hooks via the --all flag. In absence of this flag, you will be given the default template. For more information, try overcommit --list-templates.

Dependencies

Some of the lints have third-party dependencies. For example, to lint your SCSS files, you're going to need our scss-lint gem:

gem install scss-lint

Other useful utilities include jshint, which can be installed via npm:

npm install -g jshint

Built-in hooks

There are two types of hooks installed by this utility. post-checkout, post-merge, and prepare-commit-msg are all simple shell scripts rolled by hand for use at Causes. We think other people may find them useful.

The second, more interesting type is the Ruby-based, extensible checks. These are currently pre-commit and commit-msg. These are used for checking the validity of the code to be committed and checking the content of the commit message, respectively.

You can see the various sub-hooks available in the lib/overcommit/plugins directory:

>> tree lib/overcommit/plugins
lib/overcommit/plugins
├── commit_msg
│   ├── change_id.rb
│   ├── release_note.rb
│   ├── russian_novel.rb
│   ├── text_width.rb
│   └── trailing_period.rb
└── pre_commit
    ├── author_name.rb
    ├── causes_email.rb
    ├── coffee_lint.rb
    ├── css_linter.rb
    ├── erb_syntax.rb
    ├── haml_syntax.rb
    ├── js_console_log.rb
    ├── js_syntax.rb
    ├── python_flake8.rb
    ├── restricted_paths.rb
    ├── ruby_syntax.rb
    ├── scss_lint.rb
    ├── test_history.rb
    ├── whitespace.rb
    └── yaml_syntax.rb

Most of them are straightforward lints, with an easter egg or two thrown in for good measure. Because some of these are Causes-specific (for instance, we insert a 'Change-Id' at the end of each commit message for Gerrit code review), the default installation will skip loading some of these checks.

Repo-specific hooks

Out of the box, overcommit comes with a set of hooks that enforce a variety of styles and lints. However, some hooks only make sense in the context of a given repository.

At Causes, for example, we have a repository for managing our Chef cookbooks. Inside this repository, we have a few additional lints we run before commits are pushed:

>> tree .githooks
.githooks
└── pre_commit
    ├── berksfile_source.rb
    ├── cookbook_version.rb
    └── food_critic.rb

food_critic.rb contains a subclass of HookSpecificCheck that runs Foodcritic against the cookbooks about to be committed (if any).

The meat of it looks like this:

module Overcommit::GitHook
  class FoodCritic < HookSpecificCheck
    include HookRegistry
    COOKBOOKS = 'cookbooks'
    @@options = { :tags => %w[~readme ~fc001] }

    def run_check
      begin
        require 'foodcritic'
      rescue LoadError
        return :stop, 'run `bundle install` to install the foodcritic gem'
      end

      changed_cookbooks = modified_files.map do |file|
        file.split('/')[0..1].join('/') if file.start_with? COOKBOOKS
      end.compact.uniq

      linter = ::FoodCritic::Linter.new
      review = linter.check(changed_cookbooks, @@options)
      return (review.warnings.any? ? :bad : :good), review
    end
  end
end

Other functionality

In addition to the Ruby-based plugin system, overcommit also ships with a few handy shell scripts:

• post-checkout runs ctags after checkouts to aid in tag-based navigation. We use this in combination with Vim by adding .git/tags to the tags configuration:

    set tags=.git/tags,.tags
  

• post-merge checks for updated submodules and prompts you to update them.

• prepare-commit-msg sets up your commit message to include additional author information and note submodule changes when updating.

Uninstallation

If you'd like to remove the hooks from a repository, just pass the --uninstall flag:

overcommit --uninstall important-project

Contributing

Pull requests and issues are welcome. New features should ship with tests so that we can avoid breaking them in the future.

License

Released under the MIT License.