More clues on the redisplay bug (Re: Emacs appears to hang)

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Juanma Barranquero <address@hidden> writes:
> On Fri, 19 Jul 2002 12:01:45 +0000 (UTC), "Robert J. Chassell" 
> <address@hidden> wrote:
>
>> Another data point:  no appearance of the bug without ruler-mode:
>
> Er... yes. That's why included M-x ruler-mode in the problem description.
> What I've reported is the simplest way of triggering it that I know.

The bug is not specific to ruler-mode, but I think it's a general
problem that may be related to header lines.  I noticed something
similar in Info:

        emacs -q --no-site-file
                C-h i
                C-v C-v
                M-v M-v
                <Horribly borken display with concatenated lines.>

This is what I see:

        http://caesar.elte.hu/~lorentey/emacs-redisplay-bug.jpg

If I disable the fancy header line, the bug disappears:

        emacs -q --no-site-file --eval '(setq Info-use-header-line nil)'
                C-h i
                C-v C-v
                M-v M-v
                <Normal behaviour.>

All this with today's CVS Emacs, under X.

A few experiments with my previous builds indicate that the bug may be
related to this change:

2002-07-07  Richard M. Stallman  <address@hidden>

        * xdisp.c (make_cursor_line_fully_visible): Don't try short scrolls.
        Instead just return 0 when there is something to be done.
        (try_scrolling): If make_cursor_line_fully_visible returns 0,
        retry scrolling as if cursor were off the bottom.
        (try_cursor_movement): If make_cursor_line_fully_visible returns 0,
        return CURSOR_MOVEMENT_MUST_SCROLL.
        (redisplay_window): If make_cursor_line_fully_visible returns 0,
        go to try_to_scroll.

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