Re: rx and rx-to-string handle (regexp VAR) differently

[Kévin Le Gouguec]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
>> Date: Thu, 08 Jun 2023 23:44:07 +0200
>> 
>> Is there a bug to file here, or have I missed something in the
>> documentation that explains why rx can work with (regexp VAR) but
>> rx-to-string cannot?
>
> FWIW, "Extending Rx" in the ELisp manual says:
>
>    • Definitions are only ever expanded in calls to ‘rx’ or
>      ‘rx-to-string’, not merely by their presence in definition macros.
>
> So I think this ought to be supported, and you should file a bug:
> either the implementation or the documentation should be fixed.

ACK; will do.

I see that the note in rx-to-string's docstring re. only supporting
literal strings for 'regexp' and 'literal' dates from 2019-06-25
"Support (rx (and (regexp EXPR) (literal EXPR))) (Bug#36237)"
(b59ffd2290f):

   (defun rx-to-string (form &optional no-group)
     "Parse and produce code for regular expression FORM.
   FORM is a regular expression in sexp form.
  -NO-GROUP non-nil means don't put shy groups around the result."
  +NO-GROUP non-nil means don't put shy groups around the result.
  +
  +In contrast to the `rx' macro, subforms `literal' and `regexp'
  +will not accept non-string arguments, i.e., (literal STRING)
  +becomes just a more verbose version of STRING."

I might also give that thread a read to see what prompted this
limitation.