bug#54107: 29.0.50; re-builder signals error when using rx syntax

[Lars Ingebrigtsen <larsi@gnus.org>]

Philipp Stephani <p.stephani2@gmail.com> writes:

> emacs -Q -f toggle-debug-on-error -l re-builder -eval "(customize-set-variable 'reb-re-syntax 'rx)" -f re-builder
>
> This gives an error
>
> Debugger entered--Lisp error: (error "Unknown rx symbol ‘nil’")
>   signal(error ("Unknown rx symbol ‘nil’"))
>   error("Unknown rx symbol `%s'" nil)
>   rx--translate-symbol(nil)
>   rx--translate(nil)
>   rx-to-string(nil)
>   reb-cook-regexp(#("'()" 0 3 (fontified nil)))
>   reb-update-regexp()
>   reb-do-update()
>   reb-initialize-buffer()

The problem is that the initial rx syntax is invalid -- this is caught
elsewhere (and the mode line just says "invalid"), so I've done the same
in startup, which makes the problem go away (in Emacs 29).  But this may
or may not be the best solution here -- perhaps it would be better if
the initial form for rx was valid instead?  

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no