Extracting a Gem from your Rails app

Montreal.rb 2018

So you got that big pile of useful code.

Benefits of extracting

open-source code

Cleaner code and architecture
External collaborators
Fresh and new ideas
Reusable and sharable code
Test in isolation
Give back to the community

First gem?

Knowledge on requirement, use cases and edge cases
Implementation already exists
You already have an app to test it
Focus on the interface

Where to find useful code to extract?

About anywhere!

Are you solving common problems?
Have some cool scripts?

Where to find useful code to extract?

Custom validations
Test matchers
Wrapper around an external API
Additions or changes to Rails
PORO modeling common things
And many more!

This talk is a step by step guide to extract a gem from existing code

Step 1:

Identify and move the key parts of your code.

Problem solved

Scope

Interface

Step 2:

Refactor your code to move as much as possible to lib/

Decouple

Test in isolation

Break dependencies

Step 3:

Setup of the gem

Bundle gem [gemname]

Code of conduct
RSpec (minitest available)
Travis-CI ready

Rails plugin new [gemname]

Dummy rails app
Minitest only
Rake tasks setup
Useful for Rails Engines

VS.

Small number of variations Gemspec, licence, readme, etc

I did both commands

# Make dir and git init commands

> bundle gem has_prerequisite


> cd has_prerequisite

> git commit -Am "init the gem"

> cd ..


> rails plugin new has_prerequisite --skip-test --dummy-path=spec/dummy

> cd has_prerequisite


> git add -p

> git commit -m "init the rails specific setup of the gem"

Checklist:

Edit the Gemspec with the gems info
Tests are running?
Online Git repository

Gemspec structure

Gem::Specification.new do |s|
  s.name        = 'hola'
  s.version     = '0.0.0'
  s.date        = '2010-04-28'
  s.summary     = "Hola!"
  s.description = "A simple hello world gem"
  s.authors     = ["Nick Quaranto"]
  s.email       = 'nick@quaran.to'
  s.files       = ["lib/hola.rb"]
  s.homepage    = 'http://rubygems.org/gems/hola'
  s.license     = 'MIT'
end

Step 4:

Move the code!

Move one test first

Make sure required dev and test dependencies are in the Gemspec (rspec-rails, shoulda-matchers, its, etc)
Some minor changes to the test setup are expected
Make sure they run
Make sure they fail properly

Move the implementation

If step 2 was skipped, you might have broken dependencies
Add them to the gemfile and require
Implement components you don't want to be dependent on
Make sure to not move any secrets

Decisions

I decided to keep the dependency on Active Support but not Devise.

So I have to implement similar methods

Failures:

  1) HasPrerequisite redirection it redirects to the path when the prerequisite is not met
     Failure/Error: store_location_for(:user, request.fullpath)
     
     NoMethodError:
       undefined method `store_location_for' for #<#<Class:0x007f9d98a359e8>:0x007f9d9b931238>
     # ./lib/has_prerequisite.rb:36:in `perform_checks'
     # ./spec/has_prerequisite_spec.rb:43:in `block (2 levels) in <top (required)>'
     # ./spec/has_prerequisite_spec.rb:55:in `block (3 levels) in <top (required)>'

Refactor

Add features

Refactor again

Railties

Hooks for initialisation

Railties

Extend core classes
Initialisers
Set generators

Railties

module HasPrerequisite
  class Railtie > ::Rails::Railtie
    initializer "has_prerequisite.configure_view_controller" do |app|
      ActiveSupport.on_load :action_controller do
        include HasPrerequisite
      end
    end
  end
end

Step 5:

Test locally

Test again?

Yes.
Integration test (I have a dummy app!)
Pack the gem locally
Reference it from your application

Method 1: Reference from a path

gem 'has_prerequisite', path: '~/dev/has_prerequisite'

> bundle install
=> It will use your gem 

> rspec

Method 2: Pack and install locally

gem 'has_prerequisite'

> gem build has_prerequisite.gemspec
Successfully built RubyGem
Name: has_prerequisite
Version: 0.0.0
File: has_prerequisite-0.0.0.gem

> gem install ./has_prerequisite-0.0.0.gem
Successfully installed has_prerequisite-0.0.0
1 gem installed

Step 6:

Publish!

Version number

I recommend following Semantic Versioning

MAJOR . MINOR . PATCH

Version number

Production ready?
Stable API?

When to publish 1.0.0 ?

Tip: you can always use the labels (1.0.0.beta, 1.0.0.rc.1, 1.0.0.pre, 1.0.0.racecar-1)

Licence

choosealicense.com

Code of conduct

contributor-covenant.org

Use Git/Github features

Readme for documentation
Push hooks to test
Issue tracker
Projects
Releases automatically tagged
Use branches to merge and deploy bugfixes across versions

Rubygems.org

Where gems magically come from
Create an account

Private servers

Run your own with `gem server`
Gemfurry
Note: configure .gemspec to avoid accidental pushes to Rubygems.org

Publish!

→ bundle exec rake release   
has_prerequisite 0.0.1 built to pkg/has_prerequisite-0.0.1.gem.
Tagged v0.0.1.
Pushed git commits and tags.
Pushed has_prerequisite 0.0.1 to rubygems.org.