bug#8789: 23.3; debug backtrace buffer changes window on step-through

[Michael Heerdegen]

martin rudalics <rudalics@gmx.at> writes:

> Could someone (Pete, Michael) check whether the patch fixes the
> original problem?

I tested about 2 hours and encountered many problems.

At first, some general things:

 (1) If the user starts the debugger, do we really want that the
     Backtrace buffer pops up in some other frame only because it was
     displayed there in some window before?

 (2) A problem with this approach: if the Backtrace buffer was already
     visible in several windows, it still hops around, because the
     window `display-buffer-in-window-previously-showing-it' returns is
     not unique.


Now to my tests in detail:

 - When I start debugging with a 3-windowed frame, and this is the first
   time at all that I use the debugger at all, even then, the debugger
   hops around.  This has to do with (1), but I don't know why it hops
   the first time.


But it gets much worse.  Do the following:

 - emacs -Q
 - require 'debug, and load your patch
 - M-x debug-on-entry dired RET
 - C-x d RET
 - hit d three times -> Emacs crashs!

This is reproducible here.  I use GNU Emacs 24.0.93.1
(i486-pc-linux-gnu, GTK+ Version 3.2.3)\n of 2012-02-16 on zelenka,
modified by Debian, btw.


This is all a horror to debug.  Tell me if I can help with something.


Michael