extended rake tasks to run rubocop only on uncommitted files / diff with master or entire project

clean_code.rake

namespace :clean_code do
  # rubcop only available in dev
  if Rails.env.development?
    require 'rubocop/rake_task'
    def diff_files
      cmd = %q( git diff --name-only --diff-filter=ACMRTUXB \
      $(git merge-base HEAD origin/master) \
      | egrep '\.rake$|\.rb$' )
      diff = `#{cmd}`
      diff.split("\n")
    end

    def uncommitted_files
      cmd = "git ls-files -m | xargs ls -1 2>/dev/null | egrep '\.rake$|\.rb$'"
      diff = `#{cmd}`
      diff.split("\n")
    end

    def patterns_for_diff_files
      # should contain at least one file
      patterns = ['lib/tasks/clean_code.rake']
      patterns += diff_files
    end

    def patterns_for_changed_files
      # should contain at least one file
      patterns = ['lib/tasks/clean_code.rake']
      patterns += uncommitted_files
    end

    desc 'Run RuboCop on the entire project'
    RuboCop::RakeTask.new('rubocop') do |task|
      task.fail_on_error = true
    end

    desc 'Run RuboCop on the project based on git diff with master branch'
    RuboCop::RakeTask.new('rubocop_diff') do |task|
      task.patterns = patterns_for_diff_files
      task.fail_on_error = true
    end

    desc 'Run RuboCop on uncommitted files'
    RuboCop::RakeTask.new('rubocop_changed') do |task|
      task.patterns = patterns_for_changed_files
      task.fail_on_error = true
    end

  end
end