Fix plugin generation inside applications

Previously, generating a plugin inside an application would throw an
error when trying to create a dummy_app due to the generator trying to
reuse the application's name.

This is fixed by extracting the logic used to determine the source of an
application's name, and then only using the existing name as the source
for the app:update task.

Author: skipkayhil

railties/lib/rails/app_updater.rb

@@ -21,6 +21,7 @@ def app_generator
       private
         def generator_options
           options = { api: !!Rails.application.config.api_only, update: true }
+          options[:name]                = Rails.application.class.name.chomp("::Application").underscore
           options[:skip_active_job]     = !defined?(ActiveJob::Railtie)
           options[:skip_active_record]  = !defined?(ActiveRecord::Railtie)
           options[:skip_active_storage] = !defined?(ActiveStorage::Engine)

railties/lib/rails/generators/app_name.rb

@@ -11,22 +11,11 @@ def app_name
         end
 
         def original_app_name
-          @original_app_name ||= defined_app_const_base? ? defined_app_name : (options[:name] || File.basename(destination_root))
+          @original_app_name ||= (options[:name] || File.basename(destination_root))
         end
 
-        def defined_app_name
-          defined_app_const_base.underscore
-        end
-
-        def defined_app_const_base
-          Rails.respond_to?(:application) && defined?(Rails::Application) &&
-            Rails.application.is_a?(Rails::Application) && Rails.application.class.name.chomp("::Application")
-        end
-
-        alias :defined_app_const_base? :defined_app_const_base
-
         def app_const_base
-          @app_const_base ||= defined_app_const_base || app_name.gsub(/\W/, "_").squeeze("_").camelize
+          @app_const_base ||= app_name.gsub(/\W/, "_").squeeze("_").camelize
         end
         alias :camelized :app_const_base
 

railties/test/application/generators_test.rb

@@ -35,6 +35,11 @@ def with_bare_config
       assert File.exist?(File.join(rails_root, "vendor/plugins/bukkits/test/dummy/config/application.rb"))
     end
 
+    test "allow generating plugin inside Rails app directory" do
+      rails "generate", "plugin", "vendor/plugins/bukkits"
+      assert File.exist?(File.join(rails_root, "vendor/plugins/bukkits/test/dummy/config/application.rb"))
+    end
+
     test "generators default values" do
       with_bare_config do |c|
         assert_equal(true, c.generators.colorize_logging)

railties/test/generators/db_system_change_generator_test.rb

@@ -36,7 +36,7 @@ class ChangeGeneratorTest < Rails::Generators::TestCase
 
             assert_file("config/database.yml") do |content|
               assert_match "adapter: postgresql", content
-              assert_match "database: test_app", content
+              assert_match "database: tmp_production", content
             end
 
             assert_file("Gemfile") do |content|
@@ -50,7 +50,7 @@ class ChangeGeneratorTest < Rails::Generators::TestCase
 
             assert_file("config/database.yml") do |content|
               assert_match "adapter: mysql2", content
-              assert_match "database: test_app", content
+              assert_match "database: tmp_production", content
             end
 
             assert_file("Gemfile") do |content|
@@ -79,7 +79,7 @@ class ChangeGeneratorTest < Rails::Generators::TestCase
 
             assert_file("config/database.yml") do |content|
               assert_match "adapter: mysql2", content
-              assert_match "database: test_app", content
+              assert_match "database: tmp_production", content
             end
 
             assert_file("Gemfile") do |content|