Adds a generator to create an initializer with new defaults

Following the work done in #4064, this commits introduces a Rails
generator that creates a new initializer called, by default,
`new_solidus_defaults.rb`.

This initializer works in a very similar way that
[`new_framework_defaults.rb` does in
Rails](https://guides.rubyonrails.org/upgrading_ruby_on_rails.html#configure-framework-defaults).
It allows users to preview the defaults that have changed on a new
Solidus version, as they are printed one by one on a commented line.
Users can then keep enabling them while updating their application code.

We're adding the `load_defaults` call with the old version value to the
generated initializer. Users can remove the file altogether when they're
done with the process. At that point, we require them to add
`load_defaults` with the new version to the main initializer file
(`spree.rb`). Even if there's no actual need for that, as
`loaded_defaults` on the configuration class defaults to the current
Solidus version, we want to enforce that so that users are on the safe
side for the next version upgrade. If they don't add it, we emit a
warning.

For now, we're leaving this as a generator, but we could reference it
from a rake task, although probably there's no need.

Be aware that users need to provide the version from which they are
updating. It's an option that offers more flexibility, as users can
update from versions different from the latest one. It also plays well
with our system's flexibility, for instance, to change defaults between
a pre-release and a release. However, we can add some code to default to
the latest minor version, but we should keep that information in our
code, and that's a small burden for our update process.

api/Rakefile

@@ -12,6 +12,6 @@ task default: :spec
 DummyApp::RakeTasks.new(
   gem_root: File.expand_path(__dir__),
   lib_name: 'solidus_api'
-)
+) { Spree::Api::Config.load_defaults(Spree.solidus_version) }
 
 task test_app: 'db:reset'

api/lib/spree/api/engine.rb

@@ -11,6 +11,10 @@ class Engine < Rails::Engine
       # Leave initializer empty for backwards-compatibility. Other apps
       # might still rely on this event.
       initializer "spree.api.environment", before: :load_config_initializers do; end
+
+      config.after_initialize do
+        Spree::Api::Config.check_load_defaults_called('Spree::Api::Config')
+      end
     end
   end
 end

api/spec/spec_helper.rb

@@ -13,7 +13,7 @@
 DummyApp.setup(
   gem_root: File.expand_path('..', __dir__),
   lib_name: 'solidus_api'
-)
+) { Spree::Api::Config.load_defaults(Spree.solidus_version) }
 
 require 'rails-controller-testing'
 require 'rspec/rails'

backend/Rakefile

@@ -14,7 +14,10 @@ task default: [:spec, 'spec:js']
 DummyApp::RakeTasks.new(
   gem_root: File.expand_path(__dir__),
   lib_name: 'solidus_backend'
-)
+) do
+  Spree::Backend::Config.load_defaults(Spree.solidus_version)
+  Spree::Api::Config.load_defaults(Spree.solidus_version)
+end
 
 task :teaspoon do
   require 'teaspoon'

backend/lib/spree/backend/engine.rb

@@ -8,6 +8,10 @@ class Engine < ::Rails::Engine
       # Leave initializer empty for backwards-compatability. Other apps
       # might still rely on this event.
       initializer "spree.backend.environment", before: :load_config_initializers do; end
+
+      config.after_initialize do
+        Spree::Backend::Config.check_load_defaults_called('Spree::Backend::Config')
+      end
     end
   end
 end

backend/spec/spec_helper.rb

@@ -14,7 +14,10 @@
 DummyApp.setup(
   gem_root: File.expand_path('..', __dir__),
   lib_name: 'solidus_backend'
-)
+) do
+  Spree::Backend::Config.load_defaults(Spree.solidus_version)
+  Spree::Api::Config.load_defaults(Spree.solidus_version)
+end
 
 require 'rails-controller-testing'
 require 'rspec-activemodel-mocks'

backend/spec/teaspoon_env.rb

@@ -48,5 +48,8 @@
     gem_root: File.expand_path('..', __dir__),
     lib_name: 'solidus_backend',
     auto_migrate: false
-  )
+  ) do
+    Spree::Backend::Config.load_defaults(Spree.solidus_version)
+    Spree::Api::Config.load_defaults(Spree.solidus_version)
+  end
 end

core/lib/generators/solidus/update/templates/config/initializers/new_solidus_defaults.rb.tt

@@ -0,0 +1,29 @@
+# This initializer lets you preview the defaults that have changed on the new
+# Solidus version.
+#
+# It allows you to enable them one by one while you adapt your application.
+# When you're done with all of them, you can safely remove this file and add
+# the updated `load_defaults` calls to the top of the config blocks in your
+# Solidus main initializer.
+
+Spree.config do |config|
+  <%= @core_changes %>
+end
+
+<% if defined?(Spree::Frontend::Engine) -%>
+Spree::Frontend::Config.configure do |config|
+  <%= @frontend_changes %>
+end
+<% end -%>
+
+<% if defined?(Spree::Backend::Engine) -%>
+Spree::Backend::Config.configure do |config|
+  <%= @backend_changes %>
+end
+<% end -%>
+
+<% if defined?(Spree::Api::Engine) -%>
+Spree::Api::Config.configure do |config|
+  <%= @api_changes %>
+end
+<% end -%>

core/lib/generators/solidus/update/update_generator.rb

@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+require 'spree/core/preference_changes_between_solidus_versions'
+require 'rails/generators'
+
+module Solidus
+  class UpdateGenerator < ::Rails::Generators::Base
+    desc 'Generates a new initializer to preview the new defaults for current Solidus version'
+
+    source_root File.expand_path('templates', __dir__)
+
+    class_option :from,
+                 type: :string,
+                 banner: 'The version your are updating from. E.g. 2.11.10'
+
+    class_option :initializer_basename,
+                 type: :string,
+                 default: 'new_solidus_defaults',
+                 banner: 'The name for the new initializer'
+
+    class_option :to,
+                 type: :string,
+                 default: Spree.solidus_version,
+                 hide: true
+
+    class_option :initializer_directory,
+                 type: :string,
+                 default: 'config/initializers/',
+                 hide: true
+
+    def create_new_defaults_initializer
+      from = options[:from]
+      to = options[:to]
+      @from = from
+      @core_changes = core_changes_template(from, to)
+      @frontend_changes = frontend_changes_template(from, to)
+      @backend_changes = backend_changes_template(from, to)
+      @api_changes = api_changes_template(from, to)
+
+      template 'config/initializers/new_solidus_defaults.rb.tt',
+               File.join(options[:initializer_directory], "#{options[:initializer_basename]}.rb")
+    end
+
+    private
+
+    def core_changes_template(from, to)
+      changes_template_for(Spree::AppConfiguration, from, to)
+    end
+
+    def frontend_changes_template(from, to)
+      return '' unless defined?(Spree::Frontend::Engine)
+
+      changes_template_for(Spree::FrontendConfiguration, from, to)
+    end
+
+    def backend_changes_template(from, to)
+      return '' unless defined?(Spree::Backend::Engine)
+
+      changes_template_for(Spree::BackendConfiguration, from, to)
+    end
+
+    def api_changes_template(from, to)
+      return '' unless defined?(Spree::Api::Engine)
+
+      changes_template_for(Spree::ApiConfiguration, from, to)
+    end
+
+    def changes_template_for(klass, from, to)
+      changes = Spree::Core::PreferenceChangesBetweenSolidusVersions.new(klass).call(from: from, to: to)
+      return '# No changes' if changes.empty?
+
+      [
+        ["config.load_defaults('#{from}')"] +
+          changes.map do |pref_key, change|
+            "  # config.#{pref_key} = #{change[:to]}"
+          end.flatten
+      ].join("\n")
+    end
+  end
+end

core/lib/generators/spree/dummy/templates/rails/application.rb.tt

@@ -7,4 +7,3 @@ Bundler.require(*Rails.groups(assets: %w(development test)))
 require '<%= lib_name %>'
 
 <%= application_definition %>
-

core/lib/spree/core.rb

@@ -52,6 +52,13 @@ def self.config(&_block)
   end
 
   module Core
+    def self.solidus_installed?
+      (Rails.env.test? && Rails.application.class.name == 'DummyApp::Application') ||
+        Rails.application.paths['config/initializers'].paths.any? do |path|
+          File.exist?(path.join('spree.rb'))
+        end
+    end
+
     class GatewayError < RuntimeError; end
   end
 end

core/lib/spree/core/engine.rb

@@ -63,6 +63,10 @@ class Engine < ::Rails::Engine
         app.config.action_mailer.preview_path = "{#{original_preview_path},#{solidus_preview_path}}"
         ActionMailer::Base.preview_path = app.config.action_mailer.preview_path
       end
+
+      config.after_initialize do
+        Spree::Config.check_load_defaults_called('Spree::Config')
+      end
     end
   end
 end

core/lib/spree/core/preference_changes_between_solidus_versions.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module Spree
+  module Core
+    class PreferenceChangesBetweenSolidusVersions
+      attr_reader :config_class
+
+      def initialize(config_class)
+        @config_class = config_class
+      end
+
+      def call(from:, to:)
+        preferences_from = config_class.new.load_defaults(from)
+        preferences_to = config_class.new.load_defaults(to)
+        preferences_from.reduce({}) do |changes, (pref_key, value_from)|
+          value_to = preferences_to[pref_key]
+          if value_from == value_to
+            changes
+          else
+            changes.merge(
+              pref_key => { from: value_from, to: value_to }
+            )
+          end
+        end
+      end
+    end
+  end
+end

core/lib/spree/preferences/configuration.rb

@@ -38,18 +38,35 @@ class Configuration
     #     defaults. Set via {#load_defaults}
     attr_reader :loaded_defaults
 
+    attr_reader :load_defaults_called
+
     def initialize
       @loaded_defaults = Spree.solidus_version
+      @load_defaults_called = false
     end
 
     # @param [String] Solidus version from which take defaults when not
     # overriden.
     # @see #load_defaults
     def load_defaults(version)
       @loaded_defaults = version
+      @load_defaults_called = true
       reset
     end
 
+    def check_load_defaults_called(instance_constant_name = nil)
+      return if load_defaults_called || !Spree::Core.solidus_installed?
+
+      target_name = instance_constant_name || "#{self.class.name}.new"
+      Spree::Deprecation.warn <<~MSG
+        Please, indicate wich Solidus version defaults the application must use.
+        The method `#{target_name}.load_defaults` must be called from the Solidus initializer. E.g.:
+
+          config.load_defaults('#{Spree.solidus_version}')
+
+      MSG
+    end
+
     # @yield [config] Yields this configuration object to a block
     def configure
       yield(self)

core/lib/spree/testing_support/dummy_app.rb

@@ -34,9 +34,10 @@ module ApplicationHelper
 
 # @private
 module DummyApp
-  def self.setup(gem_root:, lib_name:, auto_migrate: true)
+  def self.setup(gem_root:, lib_name:, auto_migrate: true, &block)
     ENV["LIB_NAME"] = lib_name
     DummyApp::Application.config.root = File.join(gem_root, 'spec', 'dummy')
+    block.call if block_given?
 
     DummyApp::Application.initialize!
 
@@ -127,6 +128,7 @@ class Application < ::Rails::Application
 
 Spree.user_class = 'Spree::LegacyUser'
 Spree.config do |config|
+  config.load_defaults(Spree.solidus_version)
   config.mails_from = "[email protected]"
 
   if ENV['DISABLE_ACTIVE_STORAGE']

core/lib/spree/testing_support/dummy_app/rake_tasks.rb

@@ -4,15 +4,16 @@ module DummyApp
   class RakeTasks
     include Rake::DSL
 
-    def initialize(gem_root:, lib_name:)
+    def initialize(gem_root:, lib_name:, &block)
       task :dummy_environment do
         ENV['RAILS_ENV'] = 'test'
         require lib_name
         require 'spree/testing_support/dummy_app'
         DummyApp.setup(
           gem_root: gem_root,
           lib_name: lib_name,
-          auto_migrate: false
+          auto_migrate: false,
+          &block
         )
       end
     end