bug#2749: 23.0.91; Visual Line Mode: incorrect line wrapping in corner case

[Stephen Berman]

On Tue, 24 Mar 2009 21:35:02 -0400 Stefan Monnier <monnier@iro.umontreal.ca> 
wrote:

>> This behavior is expected.  The word wrap algorithm treats lines that
>> are too long to wrap using the ordinary line-wrapping rules, and since
>> overflow-newline-into-fringe is disabled in Visual Line mode, the extra
>> empty line is used to show the non-overflowed newline character.
>
>> After the release, I might look into letting word wrap handle
>> overflow-newline-into-fringe behavior.  I suspect, however, that this
>> may lead to confusing results in some circumstances.
>
> BTW: why is overflow-newline-into-fringe ignored when word-wrap is
> non-nil?  What kind of confusing results are you thinking of?

I would like to use a string of length window-width in a display overlay
together with word-wrap and a non-nil wrap-prefix.  Currently this
results in a following empty line with indentation, which is rather
disconcerting.  But after removing `&& (IT)->line_wrap != WORD_WRAP'
from the definition of IT_OVERFLOW_NEWLINE_INTO_FRINGE and rebuilding
Emacs, the empty indented line is gone and I have just what I want.  I
haven't yet seen anything confusing.  So I too would be very interested
to know if there are known or suspected problems with allowing non-nil
overflow-newline-into-fringe with word-wrap.  If it's not clear there
are any, could we allow it and then see if anyone screams bloody murder?

Steve Berman