"I know who you are and because of that I know what you do." This knowledge is a dependency that raises the cost of change.
-- Sandi Metz, Practical Object-Oriented Design in Ruby
Packwerk is a Ruby gem used to enforce boundaries and modularize Rails applications.
Packwerk can be used to:
- Combine groups of files into packages
- Define package-level constant visibility (i.e. have publicly accessible constants)
- Help existing codebases to become more modular without obstructing development
Prerequisites
Packwerk needs Zeitwerk enabled, which comes with Rails 6.
Packwerk supports MRI versions 2.7 and above.
Demo
Watch a 1-minute video demo on how Packwerk works.
Installation
- Add this line to your application's Gemfile:
gem 'packwerk'
- Install the gem
Execute:
$ bundle install
Or install it yourself as:
$ gem install packwerk
- Run
bundle binstub packwerk
to generate the binstub - Run
bin/packwerk init
to generate the configuration files
Usage
Read USAGE.md for usage once Packwerk is installed on your project.
Pronunciation
"Packwerk" is pronounced [ˈpakvɛʁk].
Ecosystem
Various third parties have built tooling on top of packwerk. Here's a selection of some that might prove useful:
- https://github.com/bellroy/graphwerk draws a graph of your package dependencies
- https://github.com/rubyatscale/packwerk-vscode integrates packwerk into Visual Studio Code so you can see violations right in your editor
- https://github.com/vinted/packwerk-intellij integrates packwerk into RubyMine so you can see violations right in your editor
- https://github.com/rubyatscale/packs-rails sets up Rails autoloading, as well as
rspec
andFactoryBot
integration, for packages arranged in a flat list. packs-rails is quite convenient, but for autoloading we recommend to useRails::Engine
s instead. - https://github.com/rubyatscale/danger-packwerk integrates packwerk with danger.systems to provide packwerk feedback as Github inline PR comments
- https://github.com/rubyatscale/packwerk-extensions contains extensions for packwerk, including a checker for packwerk that allows you to enforce public API boundaries. This was originally extracted from
packwerk
itself. - https://github.com/alexevanczuk/packs is a Rust implementation of packwerk that has experimental support for non-Rails, non-Zeitwerk applications.
Development
After checking out the repo, run bin/setup
to install dependencies. Then, run rake test
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
Limitations
With Ruby being a very dynamic language, static analysis tools such as Packwerk are bound to have limitations. To reduce the impact of those limitations, Packwerk is designed to avoid false positives (reporting references as violations that are actually fine) at any cost, and we pay the cost by accepting a small number of false negatives (failing to report actual violations).
- Packwerk can only resolve references to constants that are defined in code loaded by the application's Zeitwerk autoloader.
This is because we rely on Zeitwerk's conventions, and code that is loaded differently (like through an explicit
require
) often doesn't follow these conventions. - Method calls and objects passed around the application are completely ignored. Packwerk only cares about static constant references. That said, if you want Packwerk to analyze parameters of a method, you can use Sorbet to define a type signature. Sorbet signatures are pure Ruby code and use constants to express types, and Packwerk understands that.
- Support for custom Zeitwerk configuration is limited. If custom ActiveSupport inflections are used, Packwerk will understand that and everything is fine. However, if Zeitwerk is directly configured with custom Zeitwerk inflections or to collapse directories, Packwerk will get confused and produce false positives.
Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/Shopify/packwerk.
Read and follow the guidelines in CONTRIBUTING.md.
License
The gem is available as open source under the terms of the MIT License.