Custom Rubocop rules to add

Custom cops to implement

1. Line breaks after guard clauses

    # bad
    return unless condition
    do_stuff
   
    # good
    return unless condition
   
    do_stuff

2. Line breaks around conditional blocks

    # bad
    do_something
    if condition
      do_extra_stuff
    end
    do_something_more
   
    # good
    do_something
   
    if condition
      do_extra_stuff
    end
   
    do_something_more

A good example to get started is probably https://github.com/bbatsov/rubocop/blob/master/lib/rubocop/cop/layout/empty_lines_around_exception_handling_keywords.rb.

---

Also, as discussed with @DouweM, here is a list of potential custom Rubocop cops we'd want to add in the future:

1. Arrays should always use [] instead of any other possible syntax. E.g.: ['foo', 'bar'], %w[foo bar], %i[foo bar] instead of %w(foo bar) or %i{foo bar}...

• Official style-guide rule recommends always using (): https://github.com/bbatsov/ruby-style-guide#percent-literal-braces / https://github.com/bbatsov/ruby-style-guide#percent-w / https://github.com/bbatsov/ruby-style-guide#percent-i

Related to #17478 (closed).