Add progress bar to offense formatter (#5675)

CHANGELOG.md

@@ -32,6 +32,7 @@
 * [#5637](https://github.com/bbatsov/rubocop/issues/5637): Fix error for `Layout/SpaceInsideArrayLiteralBrackets` when contains an array literal as an argument after a heredoc is started. ([@koic][])
 * [#5498](https://github.com/bbatsov/rubocop/issues/5498): Correct IndentHeredoc message for Ruby 2.3 when using `<<~` operator with invalid indentation. ([@hamada14][])
 * [#5610](https://github.com/bbatsov/rubocop/issues/5610): Use `gems.locked` or `Gemfile.lock` to determine the best `TargetRubyVersion` when it is not specified in the config. ([@roberts1000][])
+* Add progress bar to offenses formatter. ([@drewpterry][])
 
 ## 0.53.0 (2018-03-05)
 
@@ -3265,3 +3266,4 @@
 [@anthony-robin]: https://github.com/anthony-robin
 [@YukiJikumaru]: https://github.com/YukiJikumaru
 [@jlfaber]: https://github.com/jlfaber
+[@drewpterry]: https://github.com/drewpterry

lib/rubocop/formatter/offense_count_formatter.rb

@@ -17,10 +17,27 @@ class OffenseCountFormatter < BaseFormatter
       def started(target_files)
         super
         @offense_counts = Hash.new(0)
+
+        return unless output.tty?
+
+        file_phrase = target_files.count == 1 ? 'file' : 'files'
+
+        # 185/407 files |====== 45 ======>                    |  ETA: 00:00:04
+        # %c / %C       |       %w       >         %i         |       %e
+        bar_format = " %c/%C #{file_phrase} |%w>%i| %e "
+
+        @progressbar = ProgressBar.create(
+          output: output,
+          total: target_files.count,
+          format: bar_format,
+          autostart: false
+        )
+        @progressbar.start
       end
 
       def file_finished(_file, offenses)
         offenses.each { |o| @offense_counts[o.cop_name] += 1 }
+        @progressbar.increment if instance_variable_defined?(:@progressbar)
       end
 
       def finished(_inspected_files)

spec/rubocop/formatter/offense_count_formatter_spec.rb

@@ -53,6 +53,7 @@
       end
 
       before do
+        allow(output).to receive(:tty?).and_return(false)
         formatter.started(files)
         finish
       end
@@ -70,5 +71,22 @@
         OUTPUT
       end
     end
+
+    context 'when output tty is true' do
+      let(:offenses) do
+        %w[CopB CopA CopC CopC].map { |c| double('offense', cop_name: c) }
+      end
+
+      before do
+        allow(output).to receive(:tty?).and_return(true)
+        formatter.started(files)
+        finish
+      end
+
+      it 'has a progresbar' do
+        formatter.finished(files)
+        expect(formatter.instance_variable_get(:@progressbar).progress).to eq 1
+      end
+    end
   end
 end