1 files changed, 109 insertions, 0 deletions
diff --git a/rubocop/formatter/graceful_formatter.rb b/rubocop/formatter/graceful_formatter.rb
new file mode 100644
index 00000000000..b5db7c6c192
--- /dev/null
+++ b/rubocop/formatter/graceful_formatter.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require 'rubocop'
+
+module RuboCop
+  module Formatter
+    class GracefulFormatter < ::RuboCop::Formatter::ProgressFormatter
+      CONFIG_DETAILS_KEY = 'Details'
+      CONFIG_DETAILS_VALUE = 'grace period'
+
+      class << self
+        attr_accessor :active_offenses
+      end
+
+      def started(...)
+        super
+
+        self.class.active_offenses = 0
+
+        @silenced_offenses_for_files = {}
+        @config = RuboCop::ConfigStore.new.for_pwd
+      end
+
+      def file_finished(file, offenses)
+        silenced_offenses, active_offenses = offenses.partition { silenced?(_1) }
+
+        @silenced_offenses_for_files[file] = silenced_offenses if silenced_offenses.any?
+
+        super(file, active_offenses)
+      end
+
+      def finished(inspected_files)
+        # See the note below why are using this ivar in the first place.
+        unless defined?(@total_offense_count)
+          raise <<~MESSAGE
+            RuboCop has changed its internals and the instance variable
+            `@total_offense_count` is no longer defined but we were relying on it.
+
+            Please change the implementation.
+
+            See https://github.com/rubocop/rubocop/blob/65a757b0f/lib/rubocop/formatter/simple_text_formatter.rb#L24
+          MESSAGE
+        end
+
+        super
+
+        # Internally, RuboCop has no notion of "silenced offenses". We cannot
+        # override this meaning in a formatter that's why we track what we
+        # consider to be an active offense.
+        # This is needed for `adjusted_exit_status` method below.
+        self.class.active_offenses = @total_offense_count
+
+        report_silenced_offenses(inspected_files)
+      end
+
+      # We consider this run a success without any active offenses.
+      def self.adjusted_exit_status(status)
+        return status unless status == RuboCop::CLI::STATUS_OFFENSES
+        return RuboCop::CLI::STATUS_SUCCESS if active_offenses == 0
+
+        status
+      end
+
+      def self.grace_period?(cop_name, config)
+        details = config[CONFIG_DETAILS_KEY]
+        return false unless details
+        return true if details == CONFIG_DETAILS_VALUE
+
+        warn "#{cop_name}: Unhandled value #{details.inspect} for `Details` key."
+
+        false
+      end
+
+      def self.grace_period_key_value
+        "#{CONFIG_DETAILS_KEY}: #{CONFIG_DETAILS_VALUE}"
+      end
+
+      private
+
+      def silenced?(offense)
+        cop_config = @config.for_cop(offense.cop_name)
+
+        self.class.grace_period?(offense.cop_name, cop_config)
+      end
+
+      def report_silenced_offenses(inspected_files)
+        return if @silenced_offenses_for_files.empty?
+
+        output.puts
+        output.puts 'Silenced offenses:'
+        output.puts
+
+        @silenced_offenses_for_files.each do |file, offenses|
+          report_file(file, offenses)
+        end
+
+        silenced_offense_count = @silenced_offenses_for_files.values.sum(&:size)
+        silenced_text = colorize("#{silenced_offense_count} offenses", :yellow)
+
+        output.puts
+        output.puts "#{inspected_files.size} files inspected, #{silenced_text} silenced"
+      end
+
+      def report_file_as_mark(_offenses)
+        # Skip progress bar. No dots. No C/Ws.
+      end
+    end
+  end
+end