Rubocop Setup

.rubocop.yml

require:
  - rubocop-rails

Rails:
  Enabled: true
Metrics/ClassLength:
  Enabled: false
Metrics/AbcSize:
  Enabled: false
Metrics/LineLength:
  Max: 120
  Exclude:
    - spec/**/*
Metrics/MethodLength:
  Enabled: false
Style/Documentation:
  Enabled: false
Metrics/BlockLength:
  Exclude:
    - spec/**/*
AllCops:
  TargetRubyVersion: 2.6.2
  Exclude:
    - 'db/**/*'
    - 'config/**/*'
    - 'bin/*'
    - 'lib/tasks/**/*'
    - 'node_modules/**/*'
    - Guardfile
    - 'node_modules/**/*'

Gemfile

group :development, :test do
  gem 'guard-rake'
  gem 'guard-rspec', require: false
  gem 'guard-rubocop'

  gem 'rubocop-rails'

  gem 'terminal-notifier'
  gem 'terminal-notifier-guard'
end

Guardfile

# frozen_string_literal: true

group :red_green_refactor, halt_on_fail: true do
  guard :rspec, cmd: "bundle exec rspec" do
    # …
  end

  guard :rubocop, all_on_start: false do
    watch(%r{.+\.rb$})
    watch(%r{(?:.+/)?\.rubocop\.yml$}) { |m| File.dirname(m[0]) }
  end
end

# Notification
notification :terminal_notifier, app_name: "AppName ::" if `uname` =~ /Darwin/

Use bundle exec rubocop to check or bundle exec rubocop --safe-auto-correct to fix.