[ESLint v8] Revert line comment directive support

Tell us about your environment

• ESLint Version: v8.0.0-beta.0
• Node Version: v16.6.0
• npm Version: v7.19.1
• Operating System: MacOS

What parser (default, @babel/eslint-parser, @typescript-eslint/parser, etc.) are you using?

default

Please show your full configuration:

module.exports = {
  rules: {
    'no-unused-vars': 'error',
  }
};

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

// eslint comment that's not actually an eslint comment
// global augmentation can be in any file, and they do not need exports

yarn eslint ./test.js

What did you expect to happen?

No errors

What actually happened? Please copy-paste the actual, raw output from ESLint.

$ /Users/bradzacher/testbed/node_modules/.bin/eslint ./test.js

/Users/bradzacher/testbed/test.js
  1:1   error  Failed to parse JSON from ' comment that's not actually an eslint comment': Unexpected token c in JSON at position 2
  2:11  error  'augmentation' is defined but never used                                                                              no-unused-vars
  2:24  error  'can' is defined but never used                                                                                       no-unused-vars
  2:28  error  'be' is defined but never used                                                                                        no-unused-vars
  2:31  error  'in' is defined but never used                                                                                        no-unused-vars
  2:34  error  'any' is defined but never used                                                                                       no-unused-vars
  2:38  error  'file' is defined but never used                                                                                      no-unused-vars
  2:44  error  'and' is defined but never used                                                                                       no-unused-vars
  2:48  error  'they' is defined but never used                                                                                      no-unused-vars
  2:53  error  'do' is defined but never used                                                                                        no-unused-vars
  2:56  error  'not' is defined but never used                                                                                       no-unused-vars
  2:60  error  'need' is defined but never used                                                                                      no-unused-vars
  2:65  error  'exports' is defined but never used                                                                                   no-unused-vars

✖ 13 problems (13 errors, 0 warnings)

Steps to reproduce this issue:

1. create new folder
2. install eslint v8
3. add a file test.js with the above code
4. add an eslintrc as above
5. run eslint on the file

[aladdin-add]

the change was to improve the DX, but we have to reconsider it if it brings quite a few migrations cost.

just a thought: as the eslint evolves, at some point we may change the eslint directives to be more consistent(eslint-xxx), e.g.

// global(s) => // eslint-global(s)
// export => // eslint-export
// eslint foo => // eslint-rule foo ?
// eslint-enable(-line) => no changes ?
// eslint-env => no changes ?

[nzakas]

I’m fine with reverting. It seems like the cost outweighs the added value. If we want to reintroduce at some point then I agree with @aladdin-add’s point that coming up with an unambiguous format is the right way to go.