Upgrading Rails at scale 

gem ‘rails’, ‘5.2.0.rc2’ 

Edouard Chin https://github.com/Edouard-chin @DaroudeDudek 

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+ 

$ bundle-stats 

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gem 'rails', github: 'rails/rails', branch: 'master' 

Ran 83.838 tests 

source 'https://rubygems.org' gem 'rails', '~> 5.1.0' 

source 'https://rubygems.org' if ENV[‘SHOPIFY_NEXT’] bundler_monkey_patch end if ENV['SHOPIFY_NEXT'] gem 'rails', '~> 5.2.0' else gem 'rails', '~> 5.1.0' end 

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Fix all issues that might happen on boot 

2868 errors 

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Lessons learnt: Stop the bleeding first 

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gem 'rails', github: 'rails/rails', branch: 'master' 

1. Prepare app for dual-booting 2. Fix issues happening on boot 3. Enable CI 

Make CI fail only when new broken code is introduced Existing broken tests will be marked and allowed to fail 

mark_as :failing_on_rails_next test 'example test' do raise StandardError, 'This test fails but will be considered as passing' end 

mark_as :failing_on_rails_next test 'example test' do raise StandardError, 'This test fails but will be considered as passing' end # What's the difference between both test 'example test' do skip('This test is failing lets not run it') if running_on_rails_next? raise StandardError, 'This test fails but will be skipped' end 

mark_as :failing_on_rails_next test 'example test' do raise StandardError, 'This test fails but will be considered as passing' end desc 'This task is great' task :great_task do # ... end desc 'Another cool task' task :cool_task do # ... end 

# frozen_string_literal: true included do class_attribute :metadata, instance_accessor: false self.metadata = Hash.new { |hash, key| hash[key] = [] } end tags.each do |tag| next if method_defined?("#{tag}?") define_method "#{tag}?" do self.class.metadata[tag].include?(name.to_sym) end define_singleton_method :method_added do |name| tags.each do |tag| metadatas[tag] << name end singleton_class.send(:remove_method, :method_added) end module MarkingModule extend ActiveSupport::Concern module ClassMethods def mark_as(*tags) end end end 

# frozen_string_literal: true class MyTest < MiniTest::Test end mark_as :failing_on_rails_next def test_example end mark_as :slow def another_example end include MarkingModule # The `metadata` hash will look like this { failing_on_rails_next: ['test_example'], slow: ['another_example'] } puts MyTest.new('test_example').failing_on_rails_next? # true 

Minitest Reporter 

ProgressReporter SummaryReporter 

# Snippet taken from minitest.rb at_exit { exit exit_code || false } exit_code = Minitest.run ARGV 

module Minitest module Reporters class RailsNextReporter < BaseReporter ALLOWED = :allowed FIXED = :fixed attr_writer :state def after_test(test) return unless test_will_fail?(test) @state = else ALLOWED end end def test_will_fail?(test) return false unless options[:rails_next] test.respond_to?(:failing_on_rails_next?) && test.failing_on_rails_next? end if test.failures.none? FIXED def record(result) case @state when ALLOWED result.failures.clear end end when FIXED make_ci_fail end end end 

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Side advantage on stopping the bleeding: Getting help from other developers. 

Workforce ()*+,(- *+-()- )*+*+-+- ()*+,(- *+-()- )*+*+-+- 

Componentization 

Componentization Before After 

Natural way to identify which code belongs to which component. 

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⛵ * * Actually … 

Enable deprecation logging in Production 

Rails 5.0 ➡ Rails 5.1 0 new exceptions 

Rails.configuration.active_support.deprecation = :log 

Rails.configuration.active_support.deprecation = :notify 

class Subscriber < ActiveSupport::Subscriber cattr_accessor(:deprecations) { [] } def deprecation(event) message = event.payload[:message] deprecations << message unless exists?(message) end private def exists?(message) message && deprecations.any? { |deprecation| deprecation == message } end end Subscriber.attach_to :rails Notification name: “rails.deprecation” 

class Output < ActiveSupport::Subscriber def process_action(*) Subscriber.deprecations.each do |deprecation| Rails.logger.warn "[DEPRECATION WARNING] #{deprecation}" end Subscriber.deprecations.clear end end Output.attach_to :action_controller 

⛵ 

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source 'https://rubygems.org' if ENV['SHOPIFY_NEXT'] && File.exist?("#{Bundler::SharedHelpers.default_gemfile}_next.lock") module Bundler::SharedHelpers def default_lockfile=(path) @default_lockfile = path end def default_lockfile @default_lockfile ||= Pathname.new("#{default_gemfile}.lock") end end Bundler::SharedHelpers.default_lockfile = Pathname.new("#{Bundler::SharedHelpers.default_gemfile}_next.lock") class Bundler::Dsl unless self.method_defined? :to_definition_unpatched alias_method :to_definition_unpatched, :to_definition end def to_definition(bad_lockfile, unlock) to_definition_unpatched(Bundler::SharedHelpers.default_lockfile, unlock) end end end if ENV['SHOPIFY_NEXT'] else gem 'rails', '~> 5.1.0' end gem 'rails', '~> 5.2.0' 

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The less deprecations, the easier it will be to upgrade 

You have introduced new deprecations in the codebase 

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— test_foo: - DEPRECATION WARNING: This code is deprecated - DEPRECATION WARNING: Another deprecation test_bar - DEPRECATION WARNING: This code is deprecated class MyTest < MiniTest::Test def test_foo ActiveSupport::Deprecation.warn(‘This code is deprecated') ActiveSupport::Deprecation.warn(‘Another deprecation’) end def test_bar ActiveSupport::Deprecation.warn(‘This code is deprecated’) end end 

Small but quick upgrades 

Usable for any gem upgrade 

Edouard Chin https://github.com/Edouard-chin @DaroudeDudek Thanks!