New: Add no-useless-backreference rule (fixes #12673)

[mdjermanovic]

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

[ X] New rule #12673

Examples of incorrect code for this rule:

/*eslint no-useless-backreference: "error"*/

/^(?:(a)|\1b)$/; // reference to (a) into another alternative

/^(?:(a)|b(?:c|\1))$/; // reference to (a) into another alternative

/^(?:a|b(?:(c)|\1))$/; // reference to (c) into another alternative

/\1(a)/; // forward reference to (a)

RegExp('(a)\\2(b)'); // forward reference to (b)

/(?:a)(b)\2(c)/; // forward reference to (c)

/\k<foo>(?<foo>a)/; // forward reference to (?<foo>a)

/(?<=(a)\1)b/; // backward reference to (a) from within the same lookbehind

/(?<!(a)\1)b/; // backward reference to (a) from within the same lookbehind

new RegExp('(\\1)'); // nested reference to (\1)

/^((a)\1)$/; // nested reference to ((a)\1)

/a(?<foo>(.)b\1)/; // nested reference to (?<foo>(.)b\1)

/a(?!(b)).\1/; // reference to (b) into a negative lookahead

/(?<!(a))b\1/; // reference to (a) into a negative lookbehind

What changes did you make? (Give an overview)

New rule: no-useless-backreference

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

Is the logic correct - are backreferences in these 5 cases which the rule targets always ignored?

[platinumazure]

One small documentation request and one comment in a typo, otherwise this looks fantastic. Love the test coverage. Great work!

[kaicataldo]

LGTM. Really appreciate all the thorough documentation in both the actual docs and the tests.

[platinumazure]

Looks good to me, thanks!

[kaicataldo]

Thanks for contributing!