Re: Why is it so difficult to get a Lisp backtrace?

[Alan Mackenzie]

Hello, Eli.

On Sat, Jun 25, 2022 at 19:51:59 +0300, Eli Zaretskii wrote:
> > Date: Sat, 25 Jun 2022 15:59:52 +0000
> > Cc: emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > Another thing I'd like to be able to do is get a backtrace when
> > there's an error in font-locking during redisplay.  That's a whole
> > order of magnitude difference in complexity.

> The only two ways of having that, AFAIK, are:

>   . emit the backtrace int *Messages*
>   . add the backtrace to delayed-warnings-list

Why can't the backtrace be generated and stored, and only displayed at a
subsequent redisplay (probably the next one)?

> You _cannot_ have a *backtrace* buffer popping up when the error comes
> from some Lisp called by redisplay, because we explicitly disable
> that, and for a good reason.

It would increase the complexity of redisplay, making it fragile, for no
good reason, yes.

-- 
Alan Mackenzie (Nuremberg, Germany).