Enable auto parallel inspection when config file is specified

changelog/change_enable_auto_parallel_inspection_when_config_file.md

@@ -0,0 +1 @@
+* [#12235](https://github.com/rubocop/rubocop/pull/12235): Enable auto parallel inspection when config file is specified. ([@aboutNisblee][])

lib/rubocop/cli.rb

@@ -11,7 +11,7 @@ class CLI
     STATUS_ERROR       = 2
     STATUS_INTERRUPTED = Signal.list['INT'] + 128
     DEFAULT_PARALLEL_OPTIONS = %i[
-      color debug display_style_guide display_time display_only_fail_level_offenses
+      color config debug display_style_guide display_time display_only_fail_level_offenses
       display_only_failed except extra_details fail_level fix_layout format
       ignore_disable_comments lint only only_guide_cops require safe
       autocorrect safe_autocorrect autocorrect_all

spec/rubocop/cli_spec.rb

@@ -220,7 +220,7 @@ def and_with_args
     #       In other words, even if no option is specified, it will be parallelized by default.
     describe 'when parallel static by default' do
       context 'when specifying `--debug` option only`' do
-        it 'fails with an error message' do
+        it 'uses parallel inspection' do
           create_file('example1.rb', <<~RUBY)
             # frozen_string_literal: true
 
@@ -231,6 +231,19 @@ def and_with_args
         end
       end
 
+      context 'when specifying configuration file' do
+        it 'uses parallel inspection' do
+          create_file('example1.rb', <<~RUBY)
+            # frozen_string_literal: true
+
+            puts 'hello'
+          RUBY
+          create_empty_file('.rubocop.yml')
+          expect(cli.run(['--debug', '--config', '.rubocop.yml'])).to eq(0)
+          expect($stdout.string.include?('Use parallel by default.')).to be(true)
+        end
+      end
+
       context 'when specifying `--debug` and `-a` options`' do
         it 'uses parallel inspection when correcting the file' do
           create_file('example1.rb', <<~RUBY)
@@ -249,7 +262,7 @@ def and_with_args
       end
 
       context 'when setting `UseCache: true`' do
-        it 'fails with an error message' do
+        it 'uses parallel inspection' do
           create_file('example.rb', <<~RUBY)
             # frozen_string_literal: true
 
@@ -265,7 +278,7 @@ def and_with_args
       end
 
       context 'when setting `UseCache: false`' do
-        it 'fails with an error message' do
+        it 'does not use parallel inspection' do
           create_file('example.rb', <<~RUBY)
             # frozen_string_literal: true