bug#39977: 28.0.50; Unhelpful stack trace

[martin rudalics <rudalics@gmx.at>]

 > So we are talking about :eval in mode-line-format (and similar
 > variables)?

I am but I might be wrong.  Maybe Madhu can tell us where that window
quitting operation is issued.

 > I'm not sure we can detect these actions reliably, as Lisp code can be
 > very complex.  I think we can only handle the consequences of those
 > actions.

We already disallow deleting the last live or visible frame and the last
window on a frame.  So the redisplay code, whenever it runs Lisp in
between, could simply set a boolean that will disallow deleting any
window or frame as well as setting the window configuration and other
dangerous operations that implicitly might kill a window or a buffer.

 > Which is why I proposed to deal with that in SELECTED_FRAME
 > (we could, of course, find some other place where the disastrous
 > results of such code can be detected).

SELECTED_FRAME does not necessarily have to abort.  It could return some
other live frame, maybe selecting it on-the-fly, in the hope that the
configuration stabilizes sooner or later.  But this doesn't help with
the fact that such an :eval can do a lot more nasty things like deleting
windows or killing buffers.

martin