Fix generator command for nested (namespaced) rails engine (take 2)

Rewrite https://github.com/rails/rails/pull/27550

085546df45 was reverted (b6ffb5efcb) because it change the return of `namespaced_path` from String to Array.

----------------

If we create nested (namespaced) rails engine such like bukkits-admin,
`bin/rails g scaffold User name:string age:integer`
will create
`bukkits-admin/app/controllers/bukkits/users_controller.rb`
but it should create
`bukkits-admin/app/controllers/bukkits/admin/users_controller.rb`.

In #6643, we changed `namespaced_path` as root path
because we supposed application_controller is always in root
but nested rails engine's application_controller will not.

1 files changed, 20 insertions, 0 deletions

diff --git a/railties/test/generators/scaffold_generator_test.rb b/railties/test/generators/scaffold_generator_test.rb
index 6b7e2c91d7..e2b2acab0f 100644
--- a/railties/test/generators/scaffold_generator_test.rb
+++ b/railties/test/generators/scaffold_generator_test.rb
@@ -492,6 +492,26 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
     end
   end
 
+  def test_scaffold_tests_pass_by_default_inside_namespaced_mountable_engine
+    Dir.chdir(destination_root) { `bundle exec rails plugin new bukkits-admin --mountable` }
+
+    engine_path = File.join(destination_root, "bukkits-admin")
+
+    Dir.chdir(engine_path) do
+      quietly do
+        `bin/rails g scaffold User name:string age:integer;
+        bin/rails db:migrate`
+      end
+
+      assert_file "bukkits-admin/app/controllers/bukkits/admin/users_controller.rb" do |content|
+        assert_match(/module Bukkits::Admin/, content)
+        assert_match(/class UsersController < ApplicationController/, content)
+      end
+
+      assert_match(/8 runs, 10 assertions, 0 failures, 0 errors/, `bin/rails test 2>&1`)
+    end
+  end
+
   def test_scaffold_tests_pass_by_default_inside_full_engine
     Dir.chdir(destination_root) { `bundle exec rails plugin new bukkits --full` }