bug#5973: Crash in get_next_display_element

[Juanma Barranquero]

Package: emacs
Version: 24.0.50

> Why do you think it is similar?

Just because get_next_display_element and move_it_in_display_line_to
were involved. Which goes to show how much I know about redisplay :-)

I'm filing a separate bug.

> What am I missing?

My ignorance, of course...

> Yours is with the trunk version, right?

Yes.

> Btw, what were you doing when it crashed?  The backtrace seems to tell
> that Emacs was displaying a message in the echo area (during an Edebug
> session?), and that there were characters in the message area that used
> compositions, is that right?  If so, what was the text of the message?

I was debugging a simple defadvice to narrow-to-region. The "text" of
the message is edebug trying to display END (the argument to n-t-r). I
can reproduce the bug with just this advice:

(defadvice narrow-to-region (before heisenbug activate)
  end)

I instrument it with C-u C-M-x, then C-h N to show NEWS, select a few
lines and C-x n n.

I get a message "Loading c:/emacs/lisp/international/uni-category.el
(source)...done" and then the crash.

> If the crash happens even with normal ASCII characters in the echo
> area, I'd prefer to see a backtrace of that variant.

No, that's the only way I know to trigger it.

    Juanma