Fix the install generator

ref solidusio#3775

Fixes the issues with the install generator by bundling after adding the
extensions to the gemfile, stopping spring, and then running the install
generators for each of the installed extensions.

Currently this works a bit wonky as the extensions will ask if you want
to run migrations, and that's not desirable as migrations are already run
after these extensions are installed. Will fix and update shortly, just
wanted to get this into a PR!

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

@@ -111,14 +111,20 @@ def configure_application
       end
     end
 
-    def install_default_plugins
+    def plugin_install_preparation
+      @plugins_to_be_installed = []
+      @plugin_generators_to_run = []
+    end
+
+    def install_auth_plugin
       if options[:with_authentication] && (options[:auto_accept] || !no?("
-  Solidus has a default authentication extension that uses Devise.
-  You can find more info at https://github.com/solidusio/solidus_auth_devise.
+        Solidus has a default authentication extension that uses Devise.
+        You can find more info at https://github.com/solidusio/solidus_auth_devise.
 
-  Would you like to install it? (y/n)"))
+        Would you like to install it? (y/n)"))
 
-        gem 'solidus_auth_devise'
+        @plugins_to_be_installed << 'solidus_auth_devise'
+        @plugin_generators_to_run << 'solidus:auth:install'
       end
     end
 
@@ -135,7 +141,10 @@ def install_payment_method
 
       gem_name = PAYMENT_METHODS.fetch(name)
 
-      gem gem_name if gem_name
+      if gem_name
+        @plugins_to_be_installed << gem_name
+        @plugin_generators_to_run << "#{gem_name}:install"
+      end
     end
 
     def include_seed_data
@@ -156,6 +165,19 @@ def create_database
       rake 'db:create'
     end
 
+    def run_bundle_install_if_needed_by_plugins
+      @plugins_to_be_installed.each do |plugin_name|
+        gem plugin_name
+      end
+
+      bundle_cleanly{ run "bundle install" } if @plugins_to_be_installed.any?
+      run "spring stop"
+
+      @plugin_generators_to_run.each do |plugin_generator_name|
+        generate "#{plugin_generator_name} --skip_migrations=false"
+      end
+    end
+
     def run_migrations
       if @run_migrations
         say_status :running, "migrations"
@@ -221,5 +243,11 @@ def complete
         puts "Enjoy!"
       end
     end
+
+    private
+
+    def bundle_cleanly(&block)
+      Bundler.respond_to?(:with_unbundled_env) ? Bundler.with_unbundled_env(&block) : Bundler.with_clean_env(&block)
+    end
   end
 end