bug#67569: 29.1; ruby-mode syntax highlighting breaks with variable named "index" and "/" operator

[Eli Zaretskii]

> From: Michael Hoy <mjh@mjhoy.com>
> Date: Fri, 01 Dec 2023 09:27:47 -0500
> 
> In the standard ruby-mode, a variable named "index" followed by a "/"
> causes the syntax highlighting to break -- it appears that after the
> slash everything is interpreted as part of a regular expression until
> another "/" appears.
> 
> You can reproduce this fairly easily. using 'emacs -Q', go to the
> scratch buffer and clear it. Run 'M-x ruby-mode'. Enter something like
> the following:
> 
> def foo
>   index = 5
>   x = index / 3
>   puts "#{x}"
> end
> 
> Note that starting after the "/" until the end, syntax highlighting and
> indentation break (everything, in my color scheme, is purple). If you
> add a "/" for instance to the "puts" line, syntax highlighting and
> indentation will be restored after that.
> 
> There is a report here about the bug:
> https://emacs.stackexchange.com/questions/23802/division-sometimes-breaks-syntax-highlighting-in-ruby-mode
> The author says in the comments they used "M-x report-emacs-bug", but I
> couldn't find it (and the comments suggest that it may not have been
> sent correctly). Apologies if this is already reported!

Dmitry, any comments?