Enhance `rake rubocop:todo:generate` to split TODOs into separate files

Use `rake rubocop:todo:generate` to re-generate all RuboCop TODOs.

Use `rake 'rubocop:todo:generate[Cop/Name,...]'` to re-generate TODOs
for given cop rules.

doc/development/contributing/style_guides.md

@@ -159,25 +159,22 @@ When the number of RuboCop exceptions exceed the default [`exclude-limit` of 15]
 we may want to resolve exceptions over multiple commits. To minimize confusion,
 we should track our progress through the exception list.
 
-When auto-generating the `.rubocop_todo.yml` exception list for a particular Cop,
-and more than 15 files are affected, we should add the exception list to
-a different file in the directory `.rubocop_todo/`. For example, the configuration for the cop
-`Gitlab/NamespacedClass` is in `.rubocop_todo/gitlab/namespaced_class.yml`.
-
-This ensures that our list isn't mistakenly removed by another auto generation of
-the `.rubocop_todo.yml`. This also allows us greater visibility into the exceptions
-which are currently being resolved.
-
-One way to generate the initial list is to run the Rake task `rubocop:todo:generate`:
+The preferred way to [generate the initial list or a list for specific RuboCop rules](../rake_tasks.md#generate-initial-rubocop-todo-list)
+is to run the Rake task `rubocop:todo:generate`:
 
 ```shell
+# Initial list
 bundle exec rake rubocop:todo:generate
+
+# List for specific RuboCop rules
+bundle exec rake 'rubocop:todo:generate[Gitlab/NamespacedClass,Lint/Syntax]'
 ```
 
-You can then move the list from the freshly generated `.rubocop_todo.yml` for the Cop being actively
-resolved and place it in the directory `.rubocop_todo/`. In this scenario, do not commit
-auto-generated changes to the `.rubocop_todo.yml`, as an `exclude limit` that is higher than 15
-makes the `.rubocop_todo.yml` hard to parse.
+This Rake task creates or updates the exception list in `.rubocop_todo/`. For
+example, the configuration for the RuboCop rule `Gitlab/NamespacedClass` is
+located in `.rubocop_todo/gitlab/namespaced_class.yml`.
+
+Make sure to commit any changes in `.rubocop_todo/` after running the Rake task.
 
 ### Reveal existing RuboCop exceptions
 

doc/development/rake_tasks.md

@@ -196,6 +196,16 @@ One way to generate the initial list is to run the Rake task `rubocop:todo:gener
 bundle exec rake rubocop:todo:generate
 ```
 
+To generate TODO list for specific RuboCop rules, pass them comma-seperated as
+argument to the Rake task:
+
+```shell
+bundle exec rake 'rubocop:todo:generate[Gitlab/NamespacedClass,Lint/Syntax]'
+bundle exec rake rubocop:todo:generate\[Gitlab/NamespacedClass,Lint/Syntax\]
+```
+
+Some shells require brackets to be escaped or quoted.
+
 See [Resolving RuboCop exceptions](contributing/style_guides.md#resolving-rubocop-exceptions)
 on how to proceed from here.
 

lib/tasks/rubocop.rake

 # frozen_string_literal: true
+# rubocop:disable Rails/RakeEnvironment
 
 unless Rails.env.production?
   require 'rubocop/rake_task'
@@ -8,18 +9,59 @@ unless Rails.env.production?
   namespace :rubocop do
     namespace :todo do
       desc 'Generate RuboCop todos'
-      task :generate do # rubocop:disable Rails/RakeEnvironment
+      task :generate do |_task, args|
         require 'rubocop'
+        require 'active_support/inflector/inflections'
+        require_relative '../../rubocop/todo_dir'
+        require_relative '../../rubocop/formatter/todo_formatter'
+
+        # Reveal all pending TODOs so RuboCop can pick them up and report
+        # during scan.
+        ENV['REVEAL_RUBOCOP_TODO'] = '1'
+
+        # Save cop configuration like `RSpec/ContextWording` into
+        # `rspec/context_wording.yml` and not into
+        # `r_spec/context_wording.yml`.
+        ActiveSupport::Inflector.inflections(:en) do |inflect|
+          inflect.acronym 'RSpec'
+          inflect.acronym 'GraphQL'
+        end
 
         options = %w[
-          --auto-gen-config
-          --auto-gen-only-exclude
-          --exclude-limit=100000
-          --no-offense-counts
+          --parallel
+          --format RuboCop::Formatter::TodoFormatter
         ]
 
+        # Convert from Rake::TaskArguments into an Array to make `any?` work as
+        # expected.
+        cop_names = args.to_a
+
+        todo_dir = RuboCop::TodoDir.new(RuboCop::TodoDir::DEFAULT_TODO_DIR)
+
+        if cop_names.any?
+          # We are sorting the cop names to benefit from RuboCop cache which
+          # also takes passed parameters into account.
+          list = cop_names.sort.join(',')
+          options.concat ['--only', list]
+
+          cop_names.each { |cop_name| todo_dir.inspect(cop_name) }
+        else
+          todo_dir.inspect_all
+        end
+
+        puts <<~MSG
+          Generating RuboCop TODOs with:
+            rubocop #{options.join(' ')}
+
+          This might take a while...
+        MSG
+
         RuboCop::CLI.new.run(options)
+
+        todo_dir.delete_inspected
       end
     end
   end
 end
+
+# rubocop:enable Rails/RakeEnvironment

rubocop/formatter/todo_formatter.rb

+# 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
+
+      Todo = Struct.new(:cop_name, :files, :offense_count) do
+        def initialize(cop_name)
+          super(cop_name, Set.new, 0)
+
+          @cop_class = RuboCop::Cop::Registry.global.find_by_cop_name(cop_name)
+        end
+
+        def record(file, offense_count)
+          files << file
+          self.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

rubocop/todo_dir.rb

+# frozen_string_literal: true
+
+require 'fileutils'
+require 'active_support/inflector/inflections'
+
+module RuboCop
+  # Helper class to manage file access to RuboCop TODOs in .rubocop_todo directory.
+  class TodoDir
+    DEFAULT_TODO_DIR = File.expand_path('../.rubocop_todo', __dir__)
+
+    # Suffix to indicate TODOs being inspected right now.
+    SUFFIX_INSPECT = '.inspect'
+
+    attr_reader :directory
+
+    def initialize(directory, inflector: ActiveSupport::Inflector)
+      @directory = directory
+      @inflector = inflector
+    end
+
+    def read(cop_name, suffix = nil)
+      read_suffixed(cop_name)
+    end
+
+    def write(cop_name, content)
+      path = path_for(cop_name)
+
+      FileUtils.mkdir_p(File.dirname(path))
+      File.write(path, content)
+
+      path
+    end
+
+    def inspect(cop_name)
+      path = path_for(cop_name)
+
+      if File.exist?(path)
+        FileUtils.mv(path, "#{path}#{SUFFIX_INSPECT}")
+        true
+      else
+        false
+      end
+    end
+
+    def inspect_all
+      pattern = File.join(@directory, '**/*.yml')
+
+      Dir.glob(pattern).count do |path|
+        FileUtils.mv(path, "#{path}#{SUFFIX_INSPECT}")
+      end
+    end
+
+    def list_inspect
+      pattern = File.join(@directory, "**/*.yml.inspect")
+
+      Dir.glob(pattern)
+    end
+
+    def delete_inspected
+      pattern = File.join(@directory, '**/*.yml.inspect')
+
+      Dir.glob(pattern).count do |path|
+        File.delete(path)
+      end
+    end
+
+    private
+
+    def read_suffixed(cop_name, suffix = nil)
+      path = path_for(cop_name, suffix)
+
+      File.read(path) if File.exist?(path)
+    end
+
+    def path_for(cop_name, suffix = nil)
+      todo_path = "#{@inflector.underscore(cop_name)}.yml#{suffix}"
+
+      File.join(@directory, todo_path)
+    end
+  end
+end

spec/rubocop/formatter/todo_formatter_spec.rb

+# frozen_string_literal: true
+# rubocop:disable RSpec/VerifiedDoubles
+
+require 'fast_spec_helper'
+require 'stringio'
+require 'fileutils'
+
+require_relative '../../../rubocop/formatter/todo_formatter'
+require_relative '../../../rubocop/todo_dir'
+
+RSpec.describe RuboCop::Formatter::TodoFormatter do
+  let(:stdout) { StringIO.new }
+  let(:tmp_dir) { Dir.mktmpdir }
+  let(:real_tmp_dir) { File.join(tmp_dir, 'real') }
+  let(:symlink_tmp_dir) { File.join(tmp_dir, 'symlink') }
+  let(:rubocop_todo_dir) { "#{symlink_tmp_dir}/.rubocop_todo" }
+  let(:options) { { rubocop_todo_dir: rubocop_todo_dir } }
+  let(:todo_dir) { RuboCop::TodoDir.new(rubocop_todo_dir) }
+
+  subject(:formatter) { described_class.new(stdout, options) }
+
+  around do |example|
+    FileUtils.mkdir(real_tmp_dir)
+    FileUtils.symlink(real_tmp_dir, symlink_tmp_dir)
+
+    Dir.chdir(symlink_tmp_dir) do
+      example.run
+    end
+  end
+
+  after do
+    FileUtils.remove_entry(tmp_dir)
+  end
+
+  context 'with offenses detected' do
+    let(:offense) { fake_offense('A/Offense') }
+    let(:offense_too_many) { fake_offense('B/TooManyOffenses') }
+    let(:offense_autocorrect) { fake_offense('B/AutoCorrect') }
+
+    before do
+      stub_const("#{described_class}::MAX_OFFENSE_COUNT", 1)
+
+      stub_rubocop_registry(
+        'A/Offense' => { autocorrectable: false },
+        'B/AutoCorrect' => { autocorrectable: true }
+      )
+    end
+
+    def run_formatter
+      formatter.started(%w[a.rb b.rb c.rb d.rb])
+      formatter.file_finished('c.rb', [offense_too_many])
+      formatter.file_finished('a.rb', [offense_too_many, offense, offense_too_many])
+      formatter.file_finished('b.rb', [])
+      formatter.file_finished('d.rb', [offense_autocorrect])
+      formatter.finished(%w[a.rb b.rb c.rb d.rb])
+    end
+
+    it 'outputs its actions' do
+      run_formatter
+
+      expect(stdout.string).to eq(<<~OUTPUT)
+        Written to .rubocop_todo/a/offense.yml
+        Written to .rubocop_todo/b/auto_correct.yml
+        Written to .rubocop_todo/b/too_many_offenses.yml
+      OUTPUT
+    end
+
+    it 'creates YAML files', :aggregate_failures do
+      run_formatter
+
+      expect(rubocop_todo_dir_listing).to contain_exactly(
+        'a/offense.yml', 'b/auto_correct.yml', 'b/too_many_offenses.yml'
+      )
+
+      expect(todo_yml('A/Offense')).to eq(<<~YAML)
+        ---
+        A/Offense:
+          Exclude:
+            - 'a.rb'
+      YAML
+
+      expect(todo_yml('B/AutoCorrect')).to eq(<<~YAML)
+        ---
+        # Cop supports --auto-correct.
+        B/AutoCorrect:
+          Exclude:
+            - 'd.rb'
+      YAML
+
+      expect(todo_yml('B/TooManyOffenses')).to eq(<<~YAML)
+        ---
+        B/TooManyOffenses:
+          Exclude:
+            - 'a.rb'
+            - 'c.rb'
+      YAML
+    end
+
+    context 'when cop previously not explicitly disabled' do
+      before do
+        todo_dir.write('B/TooManyOffenses', <<~YAML)
+          ---
+          B/TooManyOffenses:
+            Exclude:
+              - 'x.rb'
+        YAML
+      end
+
+      it 'does not disable cop' do
+        run_formatter
+
+        expect(todo_yml('B/TooManyOffenses')).to eq(<<~YAML)
+          ---
+          B/TooManyOffenses:
+            Exclude:
+              - 'a.rb'
+              - 'c.rb'
+        YAML
+      end
+    end
+
+    context 'when cop previously explicitly disabled in rubocop_todo/' do
+      before do
+        todo_dir.write('B/TooManyOffenses', <<~YAML)
+          ---
+          B/TooManyOffenses:
+            Enabled: false
+            Exclude:
+              - 'x.rb'
+        YAML
+
+        todo_dir.inspect_all
+      end
+
+      it 'keeps cop disabled' do
+        run_formatter
+
+        expect(todo_yml('B/TooManyOffenses')).to eq(<<~YAML)
+          ---
+          B/TooManyOffenses:
+            # Offense count: 3
+            # Temporarily disabled due to too many offenses
+            Enabled: false
+            Exclude:
+              - 'a.rb'
+              - 'c.rb'
+        YAML
+      end
+    end
+
+    context 'when cop previously explicitly disabled in rubocop_todo.yml' do
+      before do
+        File.write('.rubocop_todo.yml', <<~YAML)
+          ---
+          B/TooManyOffenses:
+            Enabled: false
+            Exclude:
+              - 'x.rb'
+        YAML
+      end
+
+      it 'keeps cop disabled' do
+        run_formatter
+
+        expect(todo_yml('B/TooManyOffenses')).to eq(<<~YAML)
+          ---
+          B/TooManyOffenses:
+            # Offense count: 3
+            # Temporarily disabled due to too many offenses
+            Enabled: false
+            Exclude:
+              - 'a.rb'
+              - 'c.rb'
+        YAML
+      end
+    end
+
+    context 'with cop configuration in both .rubocop_todo/ and .rubocop_todo.yml' do
+      before do
+        todo_dir.write('B/TooManyOffenses', <<~YAML)
+          ---
+          B/TooManyOffenses:
+            Exclude:
+              - 'a.rb'
+        YAML
+
+        todo_dir.write('A/Offense', <<~YAML)
+          ---
+          A/Offense:
+            Exclude:
+              - 'a.rb'
+        YAML
+
+        todo_dir.inspect_all
+
+        File.write('.rubocop_todo.yml', <<~YAML)
+          ---
+          B/TooManyOffenses:
+            Exclude:
+              - 'x.rb'
+          A/Offense:
+            Exclude:
+              - 'y.rb'
+        YAML
+      end
+
+      it 'raises an error' do
+        expect { run_formatter }.to raise_error(RuntimeError, <<~TXT)
+          Multiple configurations found for cops:
+          - A/Offense
+          - B/TooManyOffenses
+        TXT
+      end
+    end
+  end
+
+  context 'without offenses detected' do
+    before do
+      formatter.started(%w[a.rb b.rb])
+      formatter.file_finished('a.rb', [])
+      formatter.file_finished('b.rb', [])
+      formatter.finished(%w[a.rb b.rb])
+    end
+
+    it 'does not output anything' do
+      expect(stdout.string).to eq('')
+    end
+
+    it 'does not write any YAML files' do
+      expect(rubocop_todo_dir_listing).to be_empty
+    end
+  end
+
+  context 'without files to inspect' do
+    before do
+      formatter.started([])
+      formatter.finished([])
+    end
+
+    it 'does not output anything' do
+      expect(stdout.string).to eq('')
+    end
+
+    it 'does not write any YAML files' do
+      expect(rubocop_todo_dir_listing).to be_empty
+    end
+  end
+
+  private
+
+  def rubocop_todo_dir_listing
+    Dir.glob("#{rubocop_todo_dir}/**/*")
+      .select { |path| File.file?(path) }
+      .map { |path| path.delete_prefix("#{rubocop_todo_dir}/") }
+  end
+
+  def todo_yml(cop_name)
+    todo_dir.read(cop_name)
+  end
+
+  def fake_offense(cop_name)
+    double(:offense, cop_name: cop_name)
+  end
+
+  def stub_rubocop_registry(**cops)
+    rubocop_registry = double(:rubocop_registry)
+
+    allow(RuboCop::Cop::Registry).to receive(:global).and_return(rubocop_registry)
+
+    allow(rubocop_registry).to receive(:find_by_cop_name)
+      .with(String).and_return(nil)
+
+    cops.each do |cop_name, attributes|
+      allow(rubocop_registry).to receive(:find_by_cop_name)
+        .with(cop_name).and_return(fake_cop(**attributes))
+    end
+  end
+
+  def fake_cop(autocorrectable:)
+    double(:cop, support_autocorrect?: autocorrectable)
+  end
+end
+
+# rubocop:enable RSpec/VerifiedDoubles

spec/rubocop/todo_dir_spec.rb

+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+require 'fileutils'
+require 'active_support/inflector/inflections'
+
+require_relative '../../rubocop/todo_dir'
+
+RSpec.describe RuboCop::TodoDir do
+  let(:todo_dir) { described_class.new(directory) }
+  let(:directory) { Dir.mktmpdir }
+  let(:cop_name) { 'RSpec/VariableInstance' }
+  let(:cop_name_underscore) { ActiveSupport::Inflector.underscore(cop_name) }
+  let(:yaml_path) { "#{File.join(directory, cop_name_underscore)}.yml" }
+
+  around do |example|
+    Dir.chdir(directory) do
+      example.run
+    end
+  end
+
+  after do
+    FileUtils.remove_entry(directory)
+  end
+
+  describe '#initialize' do
+    context 'when passing inflector' do
+      let(:fake_inflector) { double(:inflector) } # rubocop:disable RSpec/VerifiedDoubles
+      let(:todo_dir) { described_class.new(directory, inflector: fake_inflector) }
+
+      before do
+        allow(fake_inflector).to receive(:underscore)
+          .with(cop_name)
+          .and_return(cop_name_underscore)
+      end
+
+      it 'calls .underscore' do
+        todo_dir.write(cop_name, 'a')
+
+        expect(fake_inflector).to have_received(:underscore)
+      end
+    end
+  end
+
+  describe '#directory' do
+    subject { todo_dir.directory }
+
+    it { is_expected.to eq(directory) }
+  end
+
+  describe '#read' do
+    let(:content) { 'a' }
+
+    subject { todo_dir.read(cop_name) }
+
+    context 'when file exists' do
+      before do
+        todo_dir.write(cop_name, content)
+      end
+
+      it { is_expected.to eq(content) }
+    end
+
+    context 'when file is missing' do
+      it { is_expected.to be_nil }
+    end
+  end
+
+  describe '#write' do
+    let(:content) { 'a' }
+
+    subject { todo_dir.write(cop_name, content) }
+
+    it { is_expected.to eq(yaml_path) }
+
+    it 'writes content to YAML file' do
+      subject
+
+      expect(File.read(yaml_path)).to eq(content)
+    end
+  end
+
+  describe '#inspect' do
+    subject { todo_dir.inspect(cop_name) }
+
+    context 'with existing YAML file' do
+      before do
+        todo_dir.write(cop_name, 'a')
+      end
+
+      it { is_expected.to eq(true) }
+
+      it 'moves YAML file to .inspect' do
+        subject
+
+        expect(File).not_to exist(yaml_path)
+        expect(File).to exist("#{yaml_path}.inspect")
+      end
+    end
+
+    context 'with missing YAML file' do
+      it { is_expected.to eq(false) }
+    end
+  end
+
+  describe '#inspect_all' do
+    subject { todo_dir.inspect_all }
+
+    context 'with YAML files' do
+      before do
+        todo_dir.write(cop_name, 'a')
+        todo_dir.write('Other/Rule', 'a')
+        todo_dir.write('Very/Nested/Rule', 'a')
+      end
+
+      it { is_expected.to eq(3) }
+
+      it 'moves all YAML files to .inspect' do
+        subject
+
+        expect(Dir.glob('**/*.yml')).to be_empty
+        expect(Dir.glob('**/*.yml.inspect').size).to eq(3)
+      end
+    end
+
+    context 'with non-YAML files' do
+      before do
+        File.write('file', 'a')
+        File.write('file.txt', 'a')
+        File.write('file.yaml', 'a') # not .yml
+      end
+
+      it { is_expected.to eq(0) }
+
+      it 'does not move non-YAML files' do
+        subject
+
+        expect(Dir.glob('**/*'))
+          .to contain_exactly('file', 'file.txt', 'file.yaml')
+      end
+    end
+
+    context 'without files' do
+      it { is_expected.to eq(0) }
+    end
+  end
+
+  describe '#list_inspect' do
+    let(:content) { 'a' }
+
+    subject { todo_dir.list_inspect }
+
+    context 'when file exists and is being inspected' do
+      before do
+        todo_dir.write(cop_name, content)
+        todo_dir.inspect_all
+      end
+
+      it do
+        is_expected.to contain_exactly("#{yaml_path}.inspect")
+      end
+    end
+
+    context 'when file exists but not being inspected' do
+      before do
+        todo_dir.write(cop_name, content)
+      end
+
+      it { is_expected.to be_empty }
+    end
+
+    context 'when file is missing' do
+      it { is_expected.to be_empty }
+    end
+  end
+
+  describe '#delete_inspected' do
+    subject { todo_dir.delete_inspected }
+
+    context 'with YAML files' do
+      before do
+        todo_dir.write(cop_name, 'a')
+        todo_dir.write('Other/Rule', 'a')
+        todo_dir.write('Very/Nested/Rule', 'a')
+        todo_dir.inspect_all
+      end
+
+      it { is_expected.to eq(3) }
+
+      it 'deletes all .inspected YAML files' do
+        subject
+
+        expect(Dir.glob('**/*.yml.inspect')).to be_empty
+      end
+    end
+
+    context 'with non-YAML files' do
+      before do
+        File.write('file.inspect', 'a')
+        File.write('file.txt.inspect', 'a')
+        File.write('file.yaml.inspect', 'a') # not .yml
+      end
+
+      it { is_expected.to eq(0) }
+
+      it 'does not delete non-YAML files' do
+        subject
+
+        expect(Dir.glob('**/*')).to contain_exactly(
+          'file.inspect', 'file.txt.inspect', 'file.yaml.inspect')
+      end
+    end
+
+    context 'without files' do
+      it { is_expected.to eq(0) }
+    end
+  end
+end

spec/spec_helper.rb

@@ -458,11 +458,6 @@ RSpec.configure do |config|
     end
   end
 
-  # Allows stdout to be redirected to reduce noise
-  config.before(:each, :silence_stdout) do
-    $stdout = StringIO.new
-  end
-
   # Makes diffs show entire non-truncated values.
   config.before(:each, unlimited_max_formatted_output_length: true) do |_example|
     config.expect_with :rspec do |c|
@@ -475,10 +470,6 @@ RSpec.configure do |config|
     allow_any_instance_of(VersionCheck).to receive(:response).and_return({ "severity" => "success" })
   end
 
-  config.after(:each, :silence_stdout) do
-    $stdout = STDOUT
-  end
-
   config.disable_monkey_patching!
 end
 

spec/support/silence_stdout.rb

+# frozen_string_literal: true
+
+RSpec.configure do |config|
+  # Allows stdout to be redirected to reduce noise
+  config.before(:each, :silence_stdout) do
+    $stdout = StringIO.new
+  end
+
+  config.after(:each, :silence_stdout) do
+    $stdout = STDOUT
+  end
+end

spec/tasks/rubocop_rake_spec.rb

+# frozen_string_literal: true
+# rubocop:disable RSpec/VerifiedDoubles
+
+require 'fast_spec_helper'
+require 'rake'
+require 'fileutils'
+
+require_relative '../support/silence_stdout'
+require_relative '../support/helpers/next_instance_of'
+require_relative '../support/helpers/rake_helpers'
+require_relative '../../rubocop/todo_dir'
+
+RSpec.describe 'rubocop rake tasks', :silence_stdout do
+  include RakeHelpers
+
+  before do
+    stub_const('Rails', double(:rails_env))
+    allow(Rails).to receive(:env).and_return(double(production?: false))
+
+    stub_const('ENV', ENV.to_hash.dup)
+
+    Rake.application.rake_require 'tasks/rubocop'
+  end
+
+  describe 'todo:generate', :aggregate_failures do
+    let(:tmp_dir) { Dir.mktmpdir }
+    let(:rubocop_todo_dir) { File.join(tmp_dir, '.rubocop_todo') }
+    let(:todo_dir) { RuboCop::TodoDir.new(rubocop_todo_dir) }
+
+    around do |example|
+      Dir.chdir(tmp_dir) do
+        with_inflections do
+          example.run
+        end
+      end
+    end
+
+    before do
+      allow(RuboCop::TodoDir).to receive(:new).and_return(todo_dir)
+
+      # This Ruby file will trigger the following 3 offenses.
+      File.write('a.rb', <<~RUBY)
+        a+b
+
+      RUBY
+
+      # Mimic GitLab's .rubocop_todo.yml avoids relying on RuboCop's
+      # default.yml configuration.
+      File.write('.rubocop.yml', <<~YAML)
+        <% unless ENV['REVEAL_RUBOCOP_TODO'] == '1' %>
+          <% Dir.glob('.rubocop_todo/**/*.yml').each do |rubocop_todo_yaml| %>
+        - '<%= rubocop_todo_yaml %>'
+          <% end %>
+        - '.rubocop_todo.yml'
+        <% end %>
+
+        AllCops:
+          NewCops: enable # Avoiding RuboCop warnings
+
+        Layout/SpaceAroundOperators:
+          Enabled: true
+
+        Layout/TrailingEmptyLines:
+          Enabled: true
+
+        Lint/Syntax:
+          Enabled: true
+
+        Style/FrozenStringLiteralComment:
+          Enabled: true
+      YAML
+
+      # Required to verify that we are revealing all TODOs via
+      # ENV['REVEAL_RUBOCOP_TODO'] = '1'.
+      # This file can be removed from specs after we've moved all offenses from
+      # .rubocop_todo.yml to .rubocop_todo/**/*.yml.
+      File.write('.rubocop_todo.yml', <<~YAML)
+        # Too many offenses
+        Layout/SpaceAroundOperators:
+          Enabled: false
+      YAML
+
+      # Previous offense now fixed.
+      todo_dir.write('Lint/Syntax', '')
+    end
+
+    after do
+      FileUtils.remove_entry(tmp_dir)
+    end
+
+    context 'without arguments' do
+      let(:run_task) { run_rake_task('rubocop:todo:generate') }
+
+      it 'generates TODOs for all RuboCop rules' do
+        expect { run_task }.to output(<<~OUTPUT).to_stdout
+          Generating RuboCop TODOs with:
+            rubocop --parallel --format RuboCop::Formatter::TodoFormatter
+
+          This might take a while...
+          Written to .rubocop_todo/layout/space_around_operators.yml
+          Written to .rubocop_todo/layout/trailing_empty_lines.yml
+          Written to .rubocop_todo/style/frozen_string_literal_comment.yml
+        OUTPUT
+
+        expect(rubocop_todo_dir_listing).to contain_exactly(
+          'layout/space_around_operators.yml',
+          'layout/trailing_empty_lines.yml',
+          'style/frozen_string_literal_comment.yml'
+        )
+      end
+
+      it 'sets acronyms for inflections' do
+        run_task
+
+        expect(ActiveSupport::Inflector.inflections.acronyms).to include(
+          'rspec' => 'RSpec',
+          'graphql' => 'GraphQL'
+        )
+      end
+    end
+
+    context 'with cop names as arguments' do
+      let(:run_task) do
+        cop_names = %w[
+          Style/FrozenStringLiteralComment Layout/TrailingEmptyLines
+          Lint/Syntax
+        ]
+
+        run_rake_task('rubocop:todo:generate', cop_names)
+      end
+
+      it 'generates TODOs for given RuboCop cops' do
+        expect { run_task }.to output(<<~OUTPUT).to_stdout
+          Generating RuboCop TODOs with:
+            rubocop --parallel --format RuboCop::Formatter::TodoFormatter --only Layout/TrailingEmptyLines,Lint/Syntax,Style/FrozenStringLiteralComment
+
+          This might take a while...
+          Written to .rubocop_todo/layout/trailing_empty_lines.yml
+          Written to .rubocop_todo/style/frozen_string_literal_comment.yml
+        OUTPUT
+
+        expect(rubocop_todo_dir_listing).to contain_exactly(
+          'layout/trailing_empty_lines.yml',
+          'style/frozen_string_literal_comment.yml'
+        )
+      end
+    end
+
+    private
+
+    def rubocop_todo_dir_listing
+      Dir.glob("#{rubocop_todo_dir}/**/*")
+        .select { |path| File.file?(path) }
+        .map { |path| path.delete_prefix("#{rubocop_todo_dir}/") }
+    end
+
+    def with_inflections
+      original = ActiveSupport::Inflector::Inflections.instance_variable_get(:@__instance__)[:en]
+      ActiveSupport::Inflector::Inflections.instance_variable_set(:@__instance__, en: original.dup)
+
+      yield
+    ensure
+      ActiveSupport::Inflector::Inflections.instance_variable_set(:@__instance__, en: original)
+    end
+  end
+end
+
+# rubocop:enable RSpec/VerifiedDoubles