#11514 New cop to catch unescaped ']' in RegExp

[Andy-Stack]

This pull request adds a new cop that will catch and provide an auto-fix for unescaped closing square bracket meta characters in a regular expression.

[bbatsov]

I wonder if the cop is not way too specific in its current form and shouldn't be expand to account for other similar scenarios.

[Andy-Stack]

Happy to try and expand this. Did you have anything in mind?

[bbatsov]

@owst may have some suggestions. I recall he used to work on some Regexp related checks.

[owst]

@owst may have some suggestions. I recall he used to work on some Regexp related checks.

Yeah, this cop feels closely related to Style/RedundantRegexpEscape.

Having poked about a bit, I think Ruby will warn for an unescaped ] unless it appears as the first character in the pattern (tested with 3.3.0):

$ ruby -e 'p /]/'
/]/
$ ruby -e 'p /]X/'
/]X/
$ ruby -e 'p /X]/'
-e:1: warning: regular expression has ']' without escape: /X]/
/X]/

I agree with @bbatsov - this change feels overly specific at least as-is.

However, perhaps the behaviour in this PR could be achieved by adding a style to the existing cop (perhaps after renaming it?) that allows/requires ] to be escaped even when it is redundant to do so (at the start of the pattern). Similarly, as per #11152 escaping a - is redudant at the start or end of a character class, but I think a similar argument could be made to always require - to be escaped within a character class. There are possibly other cases, too.

As a name to improve on, how about a style name of require_position_dependent to require escapes that are only redundant in certain positions?