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

[Harald Jörg]

tags 70948 confirmed
owner 70948 !
thanks

Patrick Goldmann <patrick.goldmann@gmail.com> writes:

> This was bugging me, so I played around with it a bit more.
>
> It seems this has nothing to do at all with version control etc, but
> with the number of underscores.
>
> I could reproduce it on my private machine with a clean emacs 29.3 install by:
> - C-x C-f foo.pl
> - M-x cperl-mode
> - just keeping underscore pressed

Ok, I can reproduce it:  I see a delay starting after ~20 underscores
and getting quickly worse as more underscores are added.  My first bet
would be some exponential regexp backtracking.

The slowdown does not happen with Emacs built from the repository under
Linux, nor with Emacs 28.2 under Windows.  I need to run more variations
to narrow it down.
--
Cheers,
haj