rubocop how do you fix Missing magic comment

Question

I have a library of ruby code, and to look for defects I run

$ rubocop

And I get

$ rubocop
Inspecting 153 files
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCWCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCWCCCCCCCWWCCCCC

Offenses:

Gemfile:1:1: C: Missing magic comment # frozen_string_literal: true.
source "https://rubygems.org"

What modifications are required in my Gemfile to make rubocop not complain?

Does this help? Definition: https://idiosyncratic-ruby.com/58-magic-instructions.html, Style guide: https://github.com/bbatsov/ruby-style-guide#magic-comments — Mark Thomas, Oct 31 '17 at 00:28

spickermann · Accepted Answer · 2019-02-17T06:14:24.803

28

Just add

# frozen_string_literal: true

to the first line of each Ruby file. Or run

rubocop -a

to allow Rubocop to fix all offenses automatically that it is able to fix.

Btw. I like Rubocop and use it myself, but I wouldn't call the things it finds defects. I see the list more like suggestions or reasons for a discussion with my co-workers.

edited Feb 17 '19 at 06:14

answered Oct 31 '17 at 07:30

spickermann

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score 12 · Answer 2 · edited Dec 13 '21 at 09:17

12

If you want to be more specific and run rubocop for only # frozen_string_literal: true you can use the --only flag option:

Run only the specified cop(s) and/or cops in the specified departments.

To view those files:

rubocop --only Style/FrozenStringLiteralComment

To autocorrect those specific files use the -A flag (as mentioned in a previous answer):

rubocop --only Style/FrozenStringLiteralComment -A

You can view more information about autocorrect here.

edited Dec 13 '21 at 09:17

Fa11enAngel

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answered Feb 27 '19 at 21:44

jdgray

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Also, to correct the "Add an empty line after magic comments." offenses that running this command will likely produce you can use this: rubocop --only "Style/FrozenStringLiteralComment, Layout/EmptyLineAfterMagicComment" -A – Meursault Aug 29 '20 at 17:28
Hey good call out! Just noticed this in the docs: https://docs.rubocop.org/rubocop/0.89/usage/auto_correct.html – jdgray Aug 31 '20 at 15:05
The letter '-A' must be upper case, as frozen_string_literal is not always safe - or rubocop can not verify wether it is really safe for the file. '-a' is only for safe corrections, see docs linked in answer. – Fa11enAngel Dec 13 '21 at 09:19

score 2 · Answer 3 · answered Oct 31 '17 at 17:32

Try running Rubocop with the -D option:

rubocop -D
Inspecting 1 file
C

Offenses:

spec/rails_helper.rb:1:1: C: Style/FrozenStringLiteralComment: Missing magic comment # frozen_string_literal: true.
require 'spec_helper'
^

Adding -D will cause Rubocop to print the name of the cop that was violated, in this case Style/FrozenStringLiteralComment. You can then search for that cop in the Rubocop documentation:

http://www.rubydoc.info/gems/rubocop/RuboCop/Cop/Style/FrozenStringLiteralComment

This cop is designed to help upgrade to Ruby 3.0. It will add the comment # frozen_string_literal: true to the top of files to enable frozen string literals. Frozen string literals will be default in Ruby 3.0. The comment will be added below a shebang and encoding comment. The frozen string literal comment is only valid in Ruby 2.3+.

score 2 · Answer 4 · answered Nov 18 '19 at 01:53

2

If you want to ignore it, add to your .rubocop.yml

Style/FrozenStringLiteralComment:
  Enabled: false

But may be you want to know what "Magic comment" is, especially if you're using Ruby 2.x

answered Nov 18 '19 at 01:53

Constantin De La Roche

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rubocop how do you fix Missing magic comment

4 Answers4