Add --regenerate-todo option to rebuild the todo file using the pre…

…vious options, or acts as `--auto-gen-config` if there is no valid todo file.

Other options that affect `--auto-gen-config` are accepted, and can be passed in to override values in the previous todo.
eg. `--regenerate-todo --offense-counts` will supercede `--no-offense-counts`.

CHANGELOG.md

@@ -2,10 +2,15 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#8778](https://github.com/rubocop-hq/rubocop/pull/8778): Add command line option `--regenerate-todo`. ([@dvandersluis][])
+
 ### Bug fixes
 
 * [#8774](https://github.com/rubocop-hq/rubocop/issues/8774): Fix a false positive for `Layout/ArrayAlignment` with parallel assignment. ([@dvandersluis][])
 
+
 ## 0.91.1 (2020-09-23)
 
 ### Bug fixes

docs/modules/ROOT/pages/configuration.adoc

@@ -586,7 +586,8 @@ behavior of a cop instead of disabling it completely.
 
 Then you can start removing the entries in the generated
 `.rubocop_todo.yml` file one by one as you work through all the offenses
-in the code.
+in the code. You can also regenerate your `.rubocop_todo.yml` using
+the same options by running `rubocop --regenerate-todo`.
 
 Another way of silencing offense reports, aside from configuration, is
 through source code comments. These can be added manually or

docs/modules/ROOT/pages/usage/basic_usage.adoc

@@ -220,6 +220,9 @@ $ rubocop -h
 | `-r/--require`
 | Require Ruby file (see xref:extensions.adoc#loading-extensions[Loading Extensions]).
 
+| `--regenerate-todo`
+| Regenerate the TODO list using the same options as the last time it was generated with `--auto-gen-config` (generation options can be overridden).
+
 | `--safe`
 | Run only safe cops.
 

lib/rubocop.rb

@@ -628,6 +628,7 @@
 require_relative 'rubocop/cli/command/init_dotfile'
 require_relative 'rubocop/cli/command/show_cops'
 require_relative 'rubocop/cli/command/version'
+require_relative 'rubocop/config_regeneration'
 require_relative 'rubocop/options'
 require_relative 'rubocop/remote_config'
 require_relative 'rubocop/target_ruby'

lib/rubocop/config_regeneration.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+module RuboCop
+  # This class handles collecting the options for regenerating a TODO file.
+  # @api private
+  class ConfigRegeneration
+    AUTO_GENERATED_FILE = RuboCop::CLI::Command::AutoGenerateConfig::AUTO_GENERATED_FILE
+    COMMAND_REGEX = /(?<=`rubocop )(.*?)(?=`)/.freeze
+    DEFAULT_OPTIONS = { auto_gen_config: true }.freeze
+
+    # Get options from the comment in the TODO file, and parse them as options
+    def options
+      # If there's no existing TODO file, generate one
+      return DEFAULT_OPTIONS unless todo_exists?
+
+      match = generation_command.match(COMMAND_REGEX)
+      return DEFAULT_OPTIONS unless match
+
+      options = match[1].split(' ')
+      Options.new.parse(options).first
+    end
+
+    private
+
+    def todo_exists?
+      File.exist?(AUTO_GENERATED_FILE) && !File.empty?(AUTO_GENERATED_FILE)
+    end
+
+    def generation_command
+      File.foreach(AUTO_GENERATED_FILE).take(2).last
+    end
+  end
+end

lib/rubocop/options.rb

@@ -114,6 +114,10 @@ def add_configuration_options(opts)
     def add_auto_gen_options(opts)
       option(opts, '--auto-gen-config')
 
+      option(opts, '--regenerate-todo') do
+        @options.replace(ConfigRegeneration.new.options.merge(@options))
+      end
+
       option(opts, '--exclude-limit COUNT') do
         @validator.validate_exclude_limit_option
       end
@@ -418,6 +422,9 @@ module OptionsHelp
       config:                           'Specify configuration file.',
       auto_gen_config:                  ['Generate a configuration file acting as a',
                                          'TODO list.'],
+      regenerate_todo:                  ['Regenerate the TODO configuration file using',
+                                         'the last configuration. If there is no existing',
+                                         'TODO file, acts like --auto-gen-config.'],
       offense_counts:                   ['Include offense counts in configuration',
                                          'file generated by --auto-gen-config.',
                                          'Default is true.'],

spec/rubocop/config_regeneration_spec.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::ConfigRegeneration, :isolated_environment do
+  include FileHelper
+
+  subject(:config_regeneration) { described_class.new }
+
+  describe '#options' do
+    subject { config_regeneration.options }
+
+    context 'when no todo file exists' do
+      it { is_expected.to eq(auto_gen_config: true) }
+    end
+
+    context 'when there is a blank todo file' do
+      before { create_file('.rubocop_todo.yml', nil) }
+
+      it { is_expected.to eq(auto_gen_config: true) }
+    end
+
+    context 'when the todo file is malformed' do
+      before { create_file('.rubocop_todo.yml', 'todo') }
+
+      it { is_expected.to eq(auto_gen_config: true) }
+    end
+
+    context 'it parses options from the generation comment' do
+      let(:header) do
+        <<~HEADER
+          # This configuration was generated by
+          # `rubocop --auto-gen-config --auto-gen-only-exclude --exclude-limit 100 --no-offense-counts --no-auto-gen-timestamp`
+          # on 2020-06-12 17:42:47 UTC using RuboCop version 0.85.1.
+        HEADER
+      end
+
+      let(:expected_options) do
+        {
+          auto_gen_config: true,
+          auto_gen_only_exclude: true,
+          exclude_limit: '100',
+          offense_counts: false,
+          auto_gen_timestamp: false
+        }
+      end
+
+      before { create_file('.rubocop_todo.yml', header) }
+
+      it { is_expected.to eq(expected_options) }
+    end
+  end
+end

spec/rubocop/options_spec.rb

@@ -52,6 +52,9 @@ def abs(path)
                                                files are present in the directory tree.
                   --auto-gen-config            Generate a configuration file acting as a
                                                TODO list.
+                  --regenerate-todo            Regenerate the TODO configuration file using
+                                               the last configuration. If there is no existing
+                                               TODO file, acts like --auto-gen-config.
                   --exclude-limit COUNT        Used together with --auto-gen-config to
                                                set the limit for how many Exclude
                                                properties to generate. Default is 15.
@@ -370,6 +373,75 @@ def abs(path)
       end
     end
 
+    describe '--regenerate-todo' do
+      subject(:parsed_options) { options.parse(command_line_options).first }
+
+      let(:config_regeneration) do
+        instance_double(RuboCop::ConfigRegeneration, options: todo_options)
+      end
+      let(:todo_options) { { auto_gen_config: true, exclude_limit: '100', offense_counts: false } }
+
+      before do
+        allow(RuboCop::ConfigRegeneration).to receive(:new).and_return(config_regeneration)
+      end
+
+      context 'when no other options are given' do
+        let(:command_line_options) { %w[--regenerate-todo] }
+        let(:expected_options) do
+          {
+            auto_gen_config: true,
+            exclude_limit: '100',
+            offense_counts: false,
+            regenerate_todo: true
+          }
+        end
+
+        it { is_expected.to eq(expected_options) }
+      end
+
+      context 'when todo options are overridden before --regenerate-todo' do
+        let(:command_line_options) { %w[--exclude-limit 50 --regenerate-todo] }
+        let(:expected_options) do
+          {
+            auto_gen_config: true,
+            exclude_limit: '50',
+            offense_counts: false,
+            regenerate_todo: true
+          }
+        end
+
+        it { is_expected.to eq(expected_options) }
+      end
+
+      context 'when todo options are overridden after --regenerate-todo' do
+        let(:command_line_options) { %w[--regenerate-todo --exclude-limit 50] }
+        let(:expected_options) do
+          {
+            auto_gen_config: true,
+            exclude_limit: '50',
+            offense_counts: false,
+            regenerate_todo: true
+          }
+        end
+
+        it { is_expected.to eq(expected_options) }
+      end
+
+      context 'when disabled options are overridden to be enabled' do
+        let(:command_line_options) { %w[--regenerate-todo --offense-counts] }
+        let(:expected_options) do
+          {
+            auto_gen_config: true,
+            exclude_limit: '100',
+            offense_counts: true,
+            regenerate_todo: true
+          }
+        end
+
+        it { is_expected.to eq(expected_options) }
+      end
+    end
+
     describe '-s/--stdin' do
       before do
         $stdin = StringIO.new