--no-parallel (-P/--parallel can not be combined with --auto-correct)

changelog/change_add_no_parallel_option.md

@@ -0,0 +1 @@
+* [#7544](https://github.com/rubocop/rubocop/pull/7544): Add --no-parallel (-P/--parallel can not be combined with --auto-correct). ([@kwerle][])

lib/rubocop/options.rb

@@ -186,7 +186,7 @@ def add_boolean_flags(opts)
 
       option(opts, '-v', '--version')
       option(opts, '-V', '--verbose-version')
-      option(opts, '-P', '--parallel')
+      option(opts, '-P', '--[no-]parallel')
     end
     # rubocop:enable Metrics/MethodLength, Metrics/AbcSize
 
@@ -498,7 +498,7 @@ module OptionsHelp
       version:                          'Display version.',
       verbose_version:                  'Display verbose version.',
       parallel:                         ['Use available CPUs to execute inspection in',
-                                         'parallel.'],
+                                         'parallel. Default is false.'],
       stdin:                            ['Pipe source from STDIN, using FILE in offense',
                                          'reports. This is useful for editor integration.'],
       init:                             'Generate a .rubocop.yml file in the current directory.'

spec/rubocop/options_spec.rb

@@ -137,8 +137,8 @@ def abs(path)
                   --[no-]color                 Force color output on or off.
               -v, --version                    Display version.
               -V, --verbose-version            Display verbose version.
-              -P, --parallel                   Use available CPUs to execute inspection in
-                                               parallel.
+              -P, --[no-]parallel              Use available CPUs to execute inspection in
+                                               parallel. Default is false.
               -l, --lint                       Run only lint cops.
               -x, --fix-layout                 Run only layout cops, with auto-correct on.
               -s, --stdin FILE                 Pipe source from STDIN, using FILE in offense
@@ -233,14 +233,21 @@ def abs(path)
           expect(options.instance_variable_get('@options').keys).not_to include(:parallel)
         end
       end
+    end
 
-      context 'combined with --auto-correct and --fail-fast' do
-        it 'ignores parallel' do
-          msg = '-P/--parallel is being ignored because it is not compatible with -F/--fail-fast'
-          options.parse %w[--parallel --fail-fast --auto-correct]
-          expect($stdout.string).to include(msg)
-          expect(options.instance_variable_get('@options').keys).not_to include(:parallel)
-        end
+    context 'combined with --auto-correct and --fail-fast' do
+      it 'ignores parallel' do
+        msg = '-P/--parallel is being ignored because it is not compatible with -F/--fail-fast'
+        options.parse %w[--parallel --fail-fast --auto-correct]
+        expect($stdout.string).to include(msg)
+        expect(options.instance_variable_get('@options').keys).not_to include(:parallel)
+      end
+    end
+
+    describe '--no-parallel' do
+      it 'disables parallel from file' do
+        results = options.parse %w[--no-parallel]
+        expect(results).to eq([{ parallel: false }, []])
       end
     end