Re: Removing no-back-reference restriction from syntax-propertize-rules

[Stefan Monnier]

> -(defun syntax-propertize--shift-groups (re n)
> -  (replace-regexp-in-string
> -   "\\\\(\\?\\([0-9]+\\):"
> -   (lambda (s)
> -     (replace-match
> -      (number-to-string (+ n (string-to-number (match-string 1 s))))
> -      t t s 1))
> -   re t t))
> +(defun syntax-propertize--shift-groups-and-backrefs (re n)
> +  (let ((incr (lambda (s)
> +                (replace-match
> +                 (number-to-string
> +                  (+ n (string-to-number (match-string 1 s))))
> +                 t t s 1))))
> +    (replace-regexp-in-string
> +     "[^\\]\\\\\\([0-9]+\\)" incr
> +     (replace-regexp-in-string "\\\\(\\?\\([0-9]+\\):" incr re t t)
> +     t t)))

I think it's OK, but I think the risk of false positives for `\N` is
sufficiently high (compared to that for `\(?N:`) that I think we need to
be more careful and use `subregexp-context-p`.


        Stefan