Fix: quotes autofix produces syntax error with octal escape sequences

[mdjermanovic]

What is the purpose of this pull request? (put an "X" next to item)

[X] Bug fix

Tell us about your environment

• ESLint Version: 6.2.0
• Node Version: 10.16.0
• npm Version: 6.9.0

What parser (default, Babel-ESLint, etc.) are you using?

default

Please show your full configuration:

Configuration

module.exports = {
  parserOptions: {
    ecmaVersion: 2015,
  },
};

What did you do? Please include the actual source code causing the issue.

/*eslint quotes: ["error", "backtick"]*/

var foo = '\1';

What did you expect to happen?

Given how prefer-template works in similar situations, to report a warning but without the auto-fix.

What actually happened? Please include the actual, raw output from ESLint.

Fixed to:

/*eslint quotes: ["error", "backtick"]*/

var foo = `\1`;

3:12  error  Parsing error: Octal literal in template string

What changes did you make? (Give an overview)

Prevent fix to a template literal if the source string contains an octal escape sequence.

An alternative would be to not report that string at all.

Is there anything you'd like reviewers to focus on?

[platinumazure]

Is there an equivalent escape sequence that is allowed in templates? (Ideally in octal but other radix is good too)

To be clear, I'm not trying to suggest a complicated fix. I'm trying to establish if there is no way for the user to fix the issue (in which case, best not to report at all), or if there is a way they could change the code to get the same value.

[mdjermanovic]

I think there are only 'hex' (\xXX) and 'unicode' (\uXXXX or \u{...}) which is also hex notation, but there is no octal, unlike number literals which have 0oXX....

So, there is a way to manually fix, but the user would be forced to convert octal -> hex. On the other hand octal escapes shouldn't be used anyway, as far as I know it's a legacy feature and is forbidden in strict mode.

Re the auto-fix, it might be not even too complicated, but I guess that rules such as no-octal-escape, no-octal and even no-useless-escape don't have fixer although it wouldn't change behavior, because such literal might be a mistake rather than intention, and it could be better not to silently fix it.

[mysticatea]

LGTM, thank you.

[kaicataldo]

LGTM. Thanks for contributing!

[platinumazure]

LGTM, thanks!

[platinumazure]

Marking as accepted based on this reproduction:

• Before
• After fix (syntax error using autofix code from first example)

[platinumazure]

Thanks for contributing to ESLint!