Re: Random idea: Debugging `quit'

[Lars Magne Ingebrigtsen <larsi@gnus.org>]

Helmut Eller <eller.helmut@gmail.com> writes:

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

I didn't know that.  That sounds useful.

> 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))))

That works great!  Thanks!  It's now in my .emacs.

I think Emacs 24.2 should have something along these lines switched on
by default.  I think it would make a lot of bug reporting easier, since
it would enable users to get a backtrace on hangs very easily.

-- 
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  bloggy blog http://lars.ingebrigtsen.no/