Update auto-gen-config's comment re auto-correct

The auto-gen-config output will say "Cop supports --auto-correct" for
cops which do not support --auto-correct, but which do support
--auto-correct-all. Let's update the output to reflect that. When
someone is working on the todo list, this can be helpful information to
have at hand.

I'll often run something like:

`bin/rubocop --only Style/StringConcatenation -a` and then realize
actually that won't work, and this would save me a few seconds.

lib/rubocop/formatter/disabled_config_formatter.rb

@@ -121,9 +121,15 @@ def output_cop_comments(output_buffer, cfg, cop_name, offense_count)
         output_buffer.puts "# Offense count: #{offense_count}" if show_offense_counts?
 
         cop_class = Cop::Registry.global.find_by_cop_name(cop_name)
-        output_buffer.puts '# Cop supports --auto-correct.' if cop_class&.support_autocorrect?
-
         default_cfg = default_config(cop_name)
+        if cop_class&.support_autocorrect?
+          if default_cfg.nil? || default_cfg['Safe'] || default_cfg['Safe'].nil?
+            output_buffer.puts '# Cop supports --auto-correct.'
+          else
+            output_buffer.puts '# Cop supports --auto-correct-all.'
+          end
+        end
+
         return unless default_cfg
 
         params = cop_config_params(default_cfg, cfg)

spec/rubocop/cli/auto_gen_config_spec.rb

@@ -472,6 +472,41 @@ def fooBar; end
       end
     end
 
+    context 'when cop is not safe to auto-correct' do
+      it 'can generate a todo list, with the appropriate flag' do
+        create_file('example1.rb', <<~RUBY)
+          # frozen_string_literal: true
+
+          users = (user.name + ' ' + user.email) * 5
+          puts users
+        RUBY
+        create_file('.rubocop.yml', <<~YAML)
+          # The following cop supports auto-correction but is not safe
+          Style/StringConcatenation:
+            Enabled: true
+        YAML
+        expect(cli.run(%w[--auto-gen-config])).to eq(0)
+        expect($stderr.string).to eq('')
+        expect(Dir['.*']).to include('.rubocop_todo.yml')
+        todo_contents = File.read('.rubocop_todo.yml').lines[8..-1].join
+        expect(todo_contents).to eq(<<~YAML)
+          # Offense count: 1
+          # Cop supports --auto-correct-all.
+          # Configuration parameters: Mode.
+          Style/StringConcatenation:
+            Exclude:
+              - 'example1.rb'
+        YAML
+        expect(File.read('.rubocop.yml')).to eq(<<~YAML)
+          inherit_from: .rubocop_todo.yml
+
+          # The following cop supports auto-correction but is not safe
+          Style/StringConcatenation:
+            Enabled: true
+        YAML
+      end
+    end
+
     context 'when existing config file has a YAML document start header' do
       it 'inserts `inherit_from` key after hearder' do
         create_file('example1.rb', <<~RUBY)