bug#70948: 29.3; cperl mode hangs on comments like "#___"

[Harald Jörg]

Eli Zaretskii writes:

> Please note that, barring any unforeseen emergencies, there will be no
> more Emacs 29.x releases.  So I'm not sure the effort of making the
> emacs-29 branch behave better in this matter is justified.

I understand!

My suggested course of action would be like this:

1) Make cperl-mode.el from the master branch work with older Emacsen
   (again).  This needs a one-line fix.

2) Work around the inefficient rx expansion in the master branch.  This
   seems to be another one-line fix in which I replace a rx sequence by
   the expansion it gets in master (explanatory comment omitted here):

     (defconst cperl--basic-identifier-rx
   -    '(sequence (or alpha "_") (* (or word "_")))
   +    '(regex "[_[:alpha:]][_[:word:]]*"))

3) Close the bug report, noting it has already been fixed in master.
   Explain that users can use cperl-mode.el from the repository as a
   drop-in replacement in Emacs 27 or newer if they are affected by the
   bug.

Current "stable" Linux distributions ship with Emacs 28 (Debian
bookworm) or Emacs 29 (Ubuntu Noble Numbat). It won't happen too often,
nevertheless I find it unsettling that Emacs would freeze beyond repair
when opening files with a line of underscores.

On a related note, Perl 5.40 will be released this month.  The new
syntax will be added to cperl-mode.el in the master branch, and Perlers
who want current syntax to be recognized seen to have developed the
habit to pick cperl-mode.el from git.  Such things will run very smooth
once we find a way to publish cperl-mode in ELPA (but keep it in the
Emacs repository, of course).
-- 
Cheers,
haj