Re: Random idea: Debugging `quit'

[Helmut Eller]

* Lars Magne Ingebrigtsen [2011-09-11 04:01] writes:

> If something hangs, then I'd really like to know where it hangs.  So I
> always wish that I'd have been running with `debug-on-quit' set.  But
> doing so is really annoying, since `C-g' is a natural thing to do in
> many circumstances.
>
> So wouldn't it be nice if we could say, for instance, `C-u C-g' to get a
> debugging `quit'?  Or perhaps `C-u 6 6 6 C-g', or whatever deemed
> necessary to avoid annoying people...

Yes, that would be nice.

Not so nice, but  kill -SIGUSR2 <emacs-pid>  in shell tells Emacs to
enter the debugger.

Another possibility would be to set debug-on-quit permanently to t
and at the same time set the variable debugger to some function
that is smart enough to look at the queued events:

(require 'cl)
(require 'debug) ; load it now to avoid resetting debugger
(setq debug-on-quit t)
(setq debugger 'my-debug)
(defun my-debug (&rest args)
  (cond ((equal args '(error (quit)))
         (let ((unread-events (loop while (input-pending-p)
                                    collect (read-event nil nil 0.1))))
           (cond ((equal (subseq unread-events -4)
                         '(21 54 54 54)) ;  C-u 6 6 6
                  (debug nil 'my-break))
                 (t
                  (discard-input)
                  (let ((debug-on-quit nil))
                    (signal 'quit nil))))))
        (t
         (apply #'debug args))))

Helmut