Is your feature request related to a problem? Please describe.

Ruby emits a warning for the following:

ruby -c -e '/abc]123/'
-e:1: warning: regular expression has ']' without escape: /abc]123/
Syntax OK

Describe the solution you'd like

It would be nice if Rubocop could catch this statically, as that integrates better into CI.

Describe alternatives you've considered

Tools like Deprecation Toolkit can be configured to catch warnings, but in the case of Deprecation Toolkit, it will only do so while running tests, whereas we encountered a case where the file had already been read by then.