bug#72328: [PATCH] Nested backquote in pcase

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: michael_heerdegen@web.de,  thuna.cing@gmail.com,  72328@debbugs.gnu.org
> Date: Fri, 23 Aug 2024 15:11:04 -0400
> 
> >> > Would be good to hear from Stefan
> >> The first step is to declare nested backquotes unsupported and add
> >> a warning when we encounter them.
> > Where and how would you suggest to do that?
> 
> Somethink like...
> 
> 
>         Stefan
> 
> 
> diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
> index fd6b0c8db5c..fe62820f0cb 100644
> --- a/lisp/emacs-lisp/pcase.el
> +++ b/lisp/emacs-lisp/pcase.el
> @@ -1172,7 +1172,10 @@ pcase--expand-\`
>            (upatd (pcase--expand-\` (cdr qpat))))
>        (if (and (eq (car-safe upata) 'quote) (eq (car-safe upatd) 'quote))
>            `'(,(cadr upata) . ,(cadr upatd))
> -        `(and (pred consp)
> +        `(and ,@(when (eq (car qpat) '\`)
> +                  `((guard ,(macroexp-warn-and-return
> +                             "Nested ` are not supported" t nil nil qpat))))
> +              (pred consp)
>                (app car-safe ,upata)
>                (app cdr-safe ,upatd)))))
>     ((or (stringp qpat) (numberp qpat) (symbolp qpat)) `',qpat)

Feel free to install on master, and thanks.