Suggestion code blocks in messages

Author: sunny

lib/pronto/rubocop/patch_cop.rb

@@ -50,6 +50,16 @@ def team
         @team ||= ::RuboCop::Cop::Team.new(registry, config)
       end
 
+      def autocorrect_team
+        @autocorrect_team ||=
+          ::RuboCop::Cop::Team.new(
+            registry,
+            config,
+            auto_correct: true,
+            stdin: true,
+          )
+      end
+
       def registry
         @registry ||= ::RuboCop::Cop::Registry.new(RuboCop::Cop::Cop.all)
       end
@@ -62,8 +72,34 @@ def processed_source
       def new_message(offence, line)
         path = line.patch.delta.new_file[:path]
         level = level(offence.severity.name)
+        message = message_text(offence)
+
+        Message.new(path, line, level, message, nil, runner.class)
+      end
+
+      def message_text(offence)
+        message = offence.message
+
+        return message unless suggestion_cop_names.include?(offence.cop_name)
+        return message unless corrected
+
+        suggestion = corrected.lines[offence.line - 1]
+        "#{message}\n\n```suggestion\n#{suggestion}```"
+      end
+
+      def corrected
+        @corrected ||= begin
+          autocorrect_team.inspect_file(processed_source)
+          corrector = RuboCop::Cop::Corrector.new(processed_source.buffer)
+          autocorrect_team.cops.each do |cop|
+            corrector.corrections.concat(cop.corrections)
+          end
+          corrector.rewrite unless corrector.corrections.empty?
+        end
+      end
 
-        Message.new(path, line, level, offence.message, nil, runner.class)
+      def suggestion_cop_names
+        @suggestion_cop_names ||= ENV['RUBOCOP_SUGGESTION_COPS'].to_s.split(',')
       end
 
       def level(severity)

spec/pronto/rubocop_spec.rb

@@ -26,6 +26,19 @@ module Pronto
         its(:'first.msg') do
           should =~ /Prefer single-quoted strings/
         end
+
+        context 'with a RUBOCOP_SUGGESTION_COPS environment variable' do
+          before do
+            allow(ENV).to receive(:[]).with('RUBOCOP_CONFIG') { nil }
+            allow(ENV)
+              .to receive(:[]).with('RUBOCOP_SUGGESTION_COPS') { cop_names }
+          end
+          let(:cop_names) { 'Layout/TrailingWhitespace,Style/StringLiterals' }
+
+          it 'adds a block of code with the suggestion' do
+            expect(subject.first.msg).to match(/```suggestion\n  'bar'\n```/)
+          end
+        end
       end
     end
   end