1 files changed, 141 insertions, 0 deletions
diff --git a/rubocop/formatter/todo_formatter.rb b/rubocop/formatter/todo_formatter.rb
new file mode 100644
index 00000000000..14b4242063e
--- /dev/null
+++ b/rubocop/formatter/todo_formatter.rb
@@ -0,0 +1,141 @@
+# frozen_string_literal: true
+
+require 'set'
+require 'rubocop'
+require 'yaml'
+
+require_relative '../todo_dir'
+
+module RuboCop
+  module Formatter
+    # This formatter dumps a YAML configuration file per cop rule
+    # into `.rubocop_todo/**/*.yml` which contains detected offenses.
+    #
+    # For example, this formatter stores offenses for `RSpec/VariableName`
+    # in `.rubocop_todo/rspec/variable_name.yml`.
+    class TodoFormatter < BaseFormatter
+      # Disable a cop which exceeds this limit. This way we ensure that we
+      # don't enable a cop by accident when moving it from
+      # .rubocop_todo.yml to .rubocop_todo/.
+      # We keep the cop disabled if it has been disabled previously explicitly
+      # via `Enabled: false` in .rubocop_todo.yml or .rubocop_todo/.
+      MAX_OFFENSE_COUNT = 15
+
+      class Todo
+        attr_reader :cop_name, :files, :offense_count
+
+        def initialize(cop_name)
+          @cop_name = cop_name
+          @files = Set.new
+          @offense_count = 0
+          @cop_class = RuboCop::Cop::Registry.global.find_by_cop_name(cop_name)
+        end
+
+        def record(file, offense_count)
+          @files << file
+          @offense_count += offense_count
+        end
+
+        def autocorrectable?
+          @cop_class&.support_autocorrect?
+        end
+      end
+
+      def initialize(output, options = {})
+        directory = options.delete(:rubocop_todo_dir) || TodoDir::DEFAULT_TODO_DIR
+        @todos = Hash.new { |hash, cop_name| hash[cop_name] = Todo.new(cop_name) }
+        @todo_dir = TodoDir.new(directory)
+        @config_inspect_todo_dir = load_config_inspect_todo_dir(directory)
+        @config_old_todo_yml = load_config_old_todo_yml(directory)
+        check_multiple_configurations!
+
+        super
+      end
+
+      def file_finished(file, offenses)
+        return if offenses.empty?
+
+        file = relative_path(file)
+
+        offenses.map(&:cop_name).tally.each do |cop_name, offense_count|
+          @todos[cop_name].record(file, offense_count)
+        end
+      end
+
+      def finished(_inspected_files)
+        @todos.values.sort_by(&:cop_name).each do |todo|
+          yaml = to_yaml(todo)
+          path = @todo_dir.write(todo.cop_name, yaml)
+
+          output.puts "Written to #{relative_path(path)}\n"
+        end
+      end
+
+      private
+
+      def relative_path(path)
+        parent = File.expand_path('..', @todo_dir.directory)
+        path.delete_prefix("#{parent}/")
+      end
+
+      def to_yaml(todo)
+        yaml = []
+        yaml << '---'
+        yaml << '# Cop supports --auto-correct.' if todo.autocorrectable?
+        yaml << "#{todo.cop_name}:"
+
+        if previously_disabled?(todo) && offense_count_exceeded?(todo)
+          yaml << "  # Offense count: #{todo.offense_count}"
+          yaml << '  # Temporarily disabled due to too many offenses'
+          yaml << '  Enabled: false'
+        end
+
+        yaml << '  Exclude:'
+
+        files = todo.files.sort.map { |file| "    - '#{file}'" }
+        yaml.concat files
+        yaml << ''
+
+        yaml.join("\n")
+      end
+
+      def offense_count_exceeded?(todo)
+        todo.offense_count > MAX_OFFENSE_COUNT
+      end
+
+      def check_multiple_configurations!
+        cop_names = @config_inspect_todo_dir.keys & @config_old_todo_yml.keys
+        return if cop_names.empty?
+
+        list = cop_names.sort.map { |cop_name| "- #{cop_name}" }.join("\n")
+        raise "Multiple configurations found for cops:\n#{list}\n"
+      end
+
+      def previously_disabled?(todo)
+        cop_name = todo.cop_name
+
+        config = @config_old_todo_yml[cop_name] ||
+          @config_inspect_todo_dir[cop_name] || {}
+        return false if config.empty?
+
+        config['Enabled'] == false
+      end
+
+      def load_config_inspect_todo_dir(directory)
+        @todo_dir.list_inspect.each_with_object({}) do |path, combined|
+          config = YAML.load_file(path)
+          combined.update(config) if Hash === config
+        end
+      end
+
+      # Load YAML configuration from `.rubocop_todo.yml`.
+      # We consider this file already old, obsolete, and to be removed soon.
+      def load_config_old_todo_yml(directory)
+        path = File.expand_path(File.join(directory, '../.rubocop_todo.yml'))
+        config = YAML.load_file(path) if File.exist?(path)
+
+        config || {}
+      end
+    end
+  end
+end