Support searching for rubocop/config.yml in compliance with dot-config

Follow rubocop#12700 (comment)

This PR supports searching for `rubocop/config.yml` in compliance with dot-config.

This PR adds `project_root/.config/rubocop/config.yml` to the list of paths to search,
matching XDG path format of the already targeted `~/.config/rubocop/config.yml`.

However, support for `~/.config/rubocop.yml` is not included in this PR,
as the outcome of inquiry dot-config/dot-config.github.io#17
regarding it is still pending.

changelog/new_support_dot_config.md

@@ -1 +1 @@
-* [#12699](https://github.com/rubocop/rubocop/issues/12699): Support searching for `.rubocop.yml` in compliance with dot-config. ([@koic][])
+* [#12699](https://github.com/rubocop/rubocop/issues/12699): Support searching for `.rubocop.yml` and `rubocop/config.yml` in compliance with dot-config. ([@koic][])

docs/modules/ROOT/pages/configuration.adoc

@@ -34,7 +34,7 @@ and the user's global config locations. The user's global config locations consi
 dotfile or a config file inside the https://specifications.freedesktop.org/basedir-spec/latest/index.html[XDG Base Directory
 specification].
 
-* `.config/.rubocop.yml` of the project root
+* `.config/.rubocop.yml` or `.config/rubocop/config.yml` at the project root
 * `~/.rubocop.yml`
 * `$XDG_CONFIG_HOME/rubocop/config.yml` (expands to `~/.config/rubocop/config.yml`
 if `$XDG_CONFIG_HOME` is not set)
@@ -49,6 +49,7 @@ files:
 * `/path/to/project/lib/.rubocop.yml`
 * `/path/to/project/.rubocop.yml`
 * `/path/to/project/.config/.rubocop.yml`
+* `/path/to/project/.config/rubocop/config.yml`
 * `/.rubocop.yml`
 * `~/.rubocop.yml`
 * `~/.config/rubocop/config.yml`

lib/rubocop/config_finder.rb

@@ -44,9 +44,11 @@ def find_project_dotfile(target_dir)
       def find_project_root_dot_config
         return unless project_root
 
-        file = File.join(project_root, '.config', DOTFILE)
+        dotfile = File.join(project_root, '.config', DOTFILE)
+        return dotfile if File.exist?(dotfile)
 
-        file if File.exist?(file)
+        xdg_config = File.join(project_root, '.config', 'rubocop', XDG_CONFIG)
+        xdg_config if File.exist?(xdg_config)
       end
 
       def find_user_dotfile

spec/rubocop/config_loader_spec.rb

@@ -29,29 +29,64 @@
 
       before { create_empty_file('dir/example.rb') }
 
-      context 'but a config file exists in .config directory of the project root' do
+      context 'but a config file exists in .config/.rubocop.yml of the project root' do
         before do
           create_empty_file('Gemfile')
           create_empty_file('.config/.rubocop.yml')
         end
 
-        it 'returns the path to the file in home directory' do
+        it 'returns the path to the file in .config directory' do
           expect(configuration_file_for).to end_with('.config/.rubocop.yml')
         end
       end
 
-      context 'but a config file exists in both .config of the project root and home directories' do
+      context 'but a config file exists in both .config/.rubocop.yml of the project root and home directory' do
         before do
           create_empty_file('Gemfile')
           create_empty_file('.config/.rubocop.yml')
           create_empty_file('~/.rubocop.yml')
         end
 
-        it 'returns the path to the file in home directory' do
+        it 'returns the path to the file in .config directory' do
+          expect(configuration_file_for).to end_with('.config/.rubocop.yml')
+        end
+      end
+
+      context 'but a config file exists in .config/rubocop/config.yml of the project root' do
+        before do
+          create_empty_file('Gemfile')
+          create_empty_file('.config/rubocop/config.yml')
+        end
+
+        it 'returns the path to the file in .config/rubocop directory' do
+          expect(configuration_file_for).to end_with('.config/rubocop/config.yml')
+        end
+      end
+
+      context 'but a config file exists in both .config/.rubocop.yml and .config/rubocop/config.yml of the project root' do
+        before do
+          create_empty_file('Gemfile')
+          create_empty_file('.config/.rubocop.yml')
+          create_empty_file('.config/rubocop/config.yml')
+        end
+
+        it 'returns the path to the file in .config directory' do
           expect(configuration_file_for).to end_with('.config/.rubocop.yml')
         end
       end
 
+      context 'but a config file exists in both .config//rubocop/config.yml of the project root and home directory' do
+        before do
+          create_empty_file('Gemfile')
+          create_empty_file('.config/rubocop/config.yml')
+          create_empty_file('~/.rubocop.yml')
+        end
+
+        it 'returns the path to the file in .config/rubocop directory' do
+          expect(configuration_file_for).to end_with('.config/rubocop/config.yml')
+        end
+      end
+
       context 'but a config file exists in home directory' do
         before { create_empty_file('~/.rubocop.yml') }