Deprecate solidus_frontend & allow installing solidus_starter_frontend

We're recommending new stores use solidus_starter_frontend [1] as their
storefront. However, we still want to give the option to install
solidus_frontend for now, as some extensions rely on it. We're modifying
the Solidus installer to allow installing one or the other.

Nonetheless, solidus_frontend is part of the solidus meta-gem [2], which
is what is usually bundled in a new installation. At this point, we
can't remove solidus_frontend from the meta-gem, as users upgrading from
old Solidus versions could see their storefronts suddenly gone. As that
will be a breaking change, we're deferring it until v4.0.

Until that happens, we must prevent users choosing the new frontend from
pulling solidus_frontend. Because of that, we're breaking down the
solidus gem into solidus_core, solidus_api, solidus_backend &
solidus_sample. We leverage Bundler's injector [3] to add dependencies
matching the main solidus gem constraints in the Gemfile. We also use it
to remove the meta-gem. Still, we need to extend the upstream injector
to support the `path:` option, which is required for local testing
(e.g., the sandbox application). We also must break down the meta-gem
when solidus_frontend is installed until we remove the frontend
directory from this repo. That prevents Bundler from resolving it from
there when `path:` or `git:` are used as sources.

As per the logic to detect which frontend gets installed, the first of
the following conditions met wins:

- It's explicitly selected with the `FRONTEND` environment variable
  (useful for sandbox applications).
- It's explicitly selected with the `frontend` option.
- If `solidus_frontend` is in the Gemfile, that's the one used.
- If the `auto_accept` option is given, `solidus_starter_frontend` is
  chosen.
- The user is prompted to select one or the other.

Extensions have been modified to explicitly depend on `solidus_frontend`
on their Gemfile, so the dummy app generator used for testing will work
OOO matching the third condition. As per its sandbox application,
they'll default to `solidus_starter_frontend` because they use
`auto_accept`, but they can select `solidus_frontend` through the
`FRONTEND` variable.

[1] - https://github.com/solidusio/solidus_starter_frontend
[2] - https://github.com/solidusio/solidus/blob/a22723079f88387f53f72b503db875b9d97aa3f5/solidus.gemspec#L27
[3] - https://github.com/rubygems/bundler/blob/master/lib/bundler/injector.rb

core/lib/generators/solidus/install/install_generator.rb

@@ -2,12 +2,23 @@
 
 require 'rails/generators'
 require 'rails/version'
+require_relative 'install_generator/bundler_context'
+require_relative 'install_generator/support_solidus_frontend_extraction'
+require_relative 'install_generator/install_frontend'
 
 module Solidus
   # @private
   class InstallGenerator < Rails::Generators::Base
     CORE_MOUNT_ROUTE = "mount Spree::Core::Engine"
 
+    LEGACY_FRONTEND = 'solidus_frontend'
+    DEFAULT_FRONTEND = 'solidus_starter_frontend'
+    FRONTENDS = [
+      DEFAULT_FRONTEND,
+      LEGACY_FRONTEND,
+      'none'
+    ].freeze
+
     class_option :migrate, type: :boolean, default: true, banner: 'Run Solidus migrations'
     class_option :seed, type: :boolean, default: true, banner: 'Load seed data (migrations must be run)'
     class_option :sample, type: :boolean, default: true, banner: 'Load sample data (migrations must be run)'
@@ -19,6 +30,11 @@ class InstallGenerator < Rails::Generators::Base
     class_option :lib_name, type: :string, default: 'spree'
     class_option :with_authentication, type: :boolean, default: true
     class_option :enforce_available_locales, type: :boolean, default: nil
+    class_option :frontend,
+                 type: :string,
+                 enum: FRONTENDS,
+                 default: nil,
+                 desc: "Indicates which frontend to install."
 
     def self.source_paths
       paths = superclass.source_paths
@@ -74,15 +90,9 @@ def setup_assets
       empty_directory 'app/assets/images'
 
       %w{javascripts stylesheets images}.each do |path|
-        empty_directory "vendor/assets/#{path}/spree/frontend" if defined?(Spree::Frontend) || Rails.env.test?
         empty_directory "vendor/assets/#{path}/spree/backend" if defined?(Spree::Backend) || Rails.env.test?
       end
 
-      if defined?(Spree::Frontend) || Rails.env.test?
-        template "vendor/assets/javascripts/spree/frontend/all.js"
-        template "vendor/assets/stylesheets/spree/frontend/all.css"
-      end
-
       if defined?(Spree::Backend) || Rails.env.test?
         template "vendor/assets/javascripts/spree/backend/all.js"
         template "vendor/assets/stylesheets/spree/backend/all.css"
@@ -112,6 +122,9 @@ def install_auth_plugin
         Solidus has a default authentication extension that uses Devise.
         You can find more info at https://github.com/solidusio/solidus_auth_devise.
 
+        Regardless of what you answer here, it'll be installed if you choose
+        solidus_starter_frontend as your storefront in a later step.
+
         Would you like to install it? (Y/n)"))
 
         @plugins_to_be_installed << 'solidus_auth_devise'
@@ -142,14 +155,30 @@ def run_bundle_install_if_needed_by_plugins
         gem plugin_name
       end
 
-      bundle_cleanly{ run "bundle install" } if @plugins_to_be_installed.any?
+      BundlerContext.bundle_cleanly { run "bundle install" } if @plugins_to_be_installed.any?
       run "spring stop" if defined?(Spring)
 
       @plugin_generators_to_run.each do |plugin_generator_name|
         generate "#{plugin_generator_name} --skip_migrations=true"
       end
     end
 
+    def install_frontend
+      return if options[:frontend] == 'none'
+
+      bundler_context = BundlerContext.new
+
+      frontend = detect_frontend_to_install(bundler_context)
+
+      support_solidus_frontend_extraction(bundler_context)
+
+      say_status :installing, frontend
+
+      InstallFrontend.
+        new(bundler_context: bundler_context, generator_context: self).
+        call(frontend, installer_adds_auth: @plugins_to_be_installed.include?('solidus_auth_devise'))
+    end
+
     def run_migrations
       if @run_migrations
         say_status :running, "migrations"
@@ -218,8 +247,26 @@ def complete
 
     private
 
-    def bundle_cleanly(&block)
-      Bundler.respond_to?(:with_unbundled_env) ? Bundler.with_unbundled_env(&block) : Bundler.with_clean_env(&block)
+    def detect_frontend_to_install(bundler_context)
+      ENV['FRONTEND'] ||
+        options[:frontend] ||
+        (bundler_context.component_in_gemfile?(:frontend) && LEGACY_FRONTEND) ||
+        (options[:auto_accept] && DEFAULT_FRONTEND) ||
+        ask(<<~MSG.indent(8), limited_to: FRONTENDS, default: DEFAULT_FRONTEND)
+
+          Which frontend would you like to use? solidus_starter_frontend is
+          recommended. However, some extensions are still only compatible with
+          the now deprecated solidus_frontend.
+
+        MSG
+    end
+
+    def support_solidus_frontend_extraction(bundler_context)
+      say_status "break down", "solidus"
+
+      SupportSolidusFrontendExtraction.
+        new(bundler_context: bundler_context).
+        call
     end
   end
 end

core/lib/generators/solidus/install/install_generator/bundler_context.rb

@@ -0,0 +1,101 @@
+# frozen_string_literal: true
+
+module Solidus
+  class InstallGenerator < Rails::Generators::Base
+    # Bundler context during the install process.
+    #
+    # This class gives access to information about the bundler context in which
+    # the install generator is run. I.e., which solidus components are present
+    # in the user's Gemfile. It also allows modifying the Gemfile to add or
+    # remove gems.
+    #
+    # @api private
+    class BundlerContext
+      # Write and remove into a Gemfile, supporting the `path: ` option.
+      #
+      # This custom injector adds support for path sources, which is missing in
+      # bundler's upstream injector.
+      #
+      # @api private
+      class InjectorWithPathSupport < Bundler::Injector
+        private def build_gem_lines(conservative_versioning)
+          @deps.map do |d|
+            name = d.name.dump
+            local = d.source.is_a?(Bundler::Source::Path)
+
+            requirement = if local
+                            ", path: \"#{d.source.path}\""
+                          elsif conservative_versioning
+                            ", \"#{conservative_version(@definition.specs[d.name][0])}\""
+                          else
+                            ", #{d.requirement.as_list.map(&:dump).join(", ")}"
+                          end
+
+            if d.groups != Array(:default)
+              group = d.groups.size == 1 ? ", :group => #{d.groups.first.inspect}" : ", :groups => #{d.groups.inspect}"
+            end
+
+            source = ", :source => \"#{d.source}\"" unless local || d.source.nil?
+            git = ", :git => \"#{d.git}\"" unless d.git.nil?
+            branch = ", :branch => \"#{d.branch}\"" unless d.branch.nil?
+
+            %(gem #{name}#{requirement}#{group}#{source}#{git}#{branch})
+          end.join("\n")
+        end
+      end
+
+      attr_reader :dependencies, :injector
+
+      def self.bundle_cleanly(&block)
+        Bundler.respond_to?(:with_unbundled_env) ? Bundler.with_unbundled_env(&block) : Bundler.with_clean_env(&block)
+      end
+
+      def initialize
+        @dependencies = Bundler.locked_gems.dependencies
+        @injector = InjectorWithPathSupport
+      end
+
+      def solidus_in_gemfile?
+        !solidus_dependency.nil?
+      end
+
+      def component_in_gemfile?(name)
+        !@dependencies["solidus_#{name}"].nil?
+      end
+
+      def break_down_components(components)
+        raise <<~MSG  unless solidus_in_gemfile?
+          solidus meta gem needs to be present in the Gemfile to build the component dependency
+        MSG
+
+        @injector.inject(
+          components.map { |component| dependency_for_component(component) }
+        )
+      end
+
+      def remove(*args, **kwargs, &block)
+        @injector.remove(*args, **kwargs, &block)
+      end
+
+      private
+
+      def dependency_for_component(component)
+        Bundler::Dependency.new(
+          "solidus_#{component}",
+          solidus_dependency.requirement,
+          {
+            "groups" => solidus_dependency.groups,
+            "source" => solidus_dependency.source,
+            "git" => solidus_dependency.git,
+            "branch" => solidus_dependency.branch,
+            "autorequire" => solidus_dependency.autorequire
+          }
+        )
+      end
+
+      def solidus_dependency
+        @dependencies['solidus']
+      end
+    end
+  end
+end

core/lib/generators/solidus/install/install_generator/install_frontend.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module Solidus
+  class InstallGenerator < Rails::Generators::Base
+    class InstallFrontend
+      attr_reader :bundler_context,
+                  :generator_context
+
+      def initialize(bundler_context:, generator_context:)
+        @bundler_context = bundler_context
+        @generator_context = generator_context
+      end
+
+      def call(frontend, installer_adds_auth:)
+        case frontend
+        when 'solidus_frontend'
+          install_solidus_frontend
+        when 'solidus_starter_frontend'
+          install_solidus_starter_frontend(installer_adds_auth)
+        end
+      end
+
+      private
+
+      def install_solidus_frontend
+        unless @bundler_context.component_in_gemfile?(:frontend)
+          BundlerContext.bundle_cleanly do
+            `bundle add solidus_frontend --source=https://rubygems.org`
+            `bundle install`
+          end
+        end
+
+        @generator_context.generate('solidus_frontend:install')
+      end
+
+      def install_solidus_starter_frontend(installer_adds_auth)
+        @bundler_context.remove(['solidus_frontend']) if @bundler_context.component_in_gemfile?(:frontend)
+
+        # TODO: Move installation of solidus_auth_devise to the
+        # solidus_starter_frontend template
+        BundlerContext.bundle_cleanly { `bundle add solidus_auth_devise` } unless auth_present?(installer_adds_auth)
+        `LOCATION="https://raw.githubusercontent.com/solidusio/solidus_starter_frontend/main/template.rb" bin/rails app:template`
+      end
+
+      def auth_present?(installer_adds_auth)
+        installer_adds_auth || @bundler_context.component_in_gemfile?(:auth_devise)
+      end
+    end
+  end
+end

core/lib/generators/solidus/install/install_generator/support_solidus_frontend_extraction.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module Solidus
+  class InstallGenerator < Rails::Generators::Base
+    # Helper for extracting solidus_frontend from solidus meta-gem
+    #
+    # We're recommending users use newer solidus_starter_frontend. However,
+    # we're still shipping solidus_frontend as part of the solidus meta-gem. The
+    # reason is that we don't want users updating previous versions to see its
+    # storefront gone suddenly.
+    #
+    # In future solidus releases, solidus_frontend won't be a component anymore.
+    # However, until that happens:
+    #
+    # - For users of the new frontend, we need to prevent pulling
+    # solidus_frontend.
+    # - For users of the legacy frontend, we need to prevent Bundler from
+    # resolving it from the mono-repo while it's still there.
+    #
+    # This class is a needed companion during the deprecation
+    # path. It'll modify the user's Gemfile, breaking the solidus gem down into
+    # its components but solidus_frontend.
+    class SupportSolidusFrontendExtraction
+      attr_reader :bundler_context
+
+      def initialize(bundler_context:)
+        @bundler_context = bundler_context
+      end
+
+      def call
+        return unless needs_to_break_down_solidus_meta_gem?
+
+        break_down_solidus_meta_gem
+      end
+
+      private
+
+      def break_down_solidus_meta_gem
+        @bundler_context.break_down_components(%w[core backend api sample])
+        @bundler_context.remove(['solidus'])
+      end
+
+      def needs_to_break_down_solidus_meta_gem?
+        @bundler_context.solidus_in_gemfile?
+      end
+    end
+  end
+end

core/lib/generators/solidus/install/templates/config/initializers/spree.rb.tt

@@ -31,15 +31,6 @@ Spree.config do |config|
   # to a custom users role:
   # config.roles.assign_permissions :role_name, ['Spree::PermissionSets::CustomPermissionSet']
 
-  # Frontend:
-
-  # Custom logo for the frontend
-  # config.logo = "logo/solidus.svg"
-
-  # Template to use when rendering layout
-  # config.layout = "spree/layouts/spree_application"
-
-
   # Admin:
 
   # Custom logo for the admin
@@ -61,12 +52,6 @@ Spree.config do |config|
   # )
 end
 
-<% if defined?(Spree::Frontend::Engine) -%>
-Spree::Frontend::Config.configure do |config|
-  config.locale = 'en'
-end
-<% end -%>
-
 <% if defined?(Spree::Backend::Engine) -%>
 Spree::Backend::Config.configure do |config|
   config.locale = 'en'