Add RuboCop linting and use frozen_string_literal everywhere

[ur5us]

No description provided.

[ur5us]

@heaven Please let me know if this PR is cramming too many concerns into one issue, especially the RuboCop formatting related ones. I could potentially separate those from the frozen_string_literal changes.

Also, are you planning on cutting a new release by any chance?

[heaven]

Hi @ur5us, I'm a bit concerned about the frozen string literals. As you can see there are 0 tests and I'm not sure what this change can affect. As far as I know, Matz decided not to enable this feature by default in ruby 3.0 and for a good reason. I'd better accept a solution to enable this globally, e.g. via ENV variables than using these magic comments, so that anyone could decide whether they need this feature enabled in their projects or not.

[ur5us]

@heaven Curious, do you have a link? My understanding is that string will be frozen/immutable by default and you’ll need to opt out by adding # frozen_string_literal: false at the top.

The reason I decided to add # frozen_string_literal: true everywhere is because there were a lot of #freeze calls scattered around and only 2 places need a mutable string which you get by using String.new, s. https://www.mikeperham.com/2018/02/28/ruby-optimization-with-one-magic-comment/#notes. But yeah, not having tests is a concern.

[heaven]

I saw this discussion some time ago https://bugs.ruby-lang.org/issues/11473#note-53