bug#11199: 24.0.95; killing right-to-left text at eob leads to inconsistent state

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 09 Apr 2012 13:17:33 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 11199@debbugs.gnu.org
> 
> > Date: Mon, 09 Apr 2012 18:48:16 +0900
> > From: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>
> > Cc: Michael Welsh Duggan <md5i@md5i.com>,
> > 	11199@debbugs.gnu.org
> > 
> > >   (gdb) pmtxrows w->current_matrix
> > >   0: edges=(1,78),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   1: edges=(78,141),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   2: edges=(141,191),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   3: edges=(191,192),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   4: edges=(192,199),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   5: edges=(199,237),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   6: edges=(237,305),r2l=0,cont=0,trunc=(0,0),at_zv=0
> > >   7: edges=(305,309),r2l=0,cont=0,trunc=(0,0),at_zv=1
> > (snip)
> > 
> > What is shown by 
> > 
> >   (gdb) p w->current_matrix->rows[6].end.pos
> > 
> > at this stage?  I get
> > 
> >   $7 = {
> >     charpos = 308, 
> >     bytepos = 311
> >   }
> > 
> > and it looks "out of sync" because edges=(237,305) for the 6th row.
> > I hope this is also reproducible at your side.
> 
> It is, thanks!  I now have a lead for my debugging.  Stay tuned.

Does the patch below fixes the problem?  It does not fix the root
cause, but should work around it well enough for the release branch.
I will install a better (but more risky) fix on the trunk.

(There was nothing wrong with the end.pos values above, as long as the
Hebrew text in the next line existed: end.pos gives the position of
the leftmost character on display in that line, which is not
necessarily the first character after the newline.  The problem is
that init_to_row_end should not use row->end at all.)

=== modified file 'src/xdisp.c'
--- src/xdisp.c	2012-03-31 19:30:53 +0000
+++ src/xdisp.c	2012-04-09 10:58:59 +0000
@@ -17137,7 +17137,8 @@ try_window_id (struct window *w)
       if (MATRIX_ROW_ENDS_IN_MIDDLE_OF_CHAR_P (last_unchanged_at_beg_row))
 	GIVE_UP (17);
 
-      if (init_to_row_end (&it, w, last_unchanged_at_beg_row) == 0)
+      if (CHARPOS (last_unchanged_at_beg_row->end.pos) > ZV
+	  || init_to_row_end (&it, w, last_unchanged_at_beg_row) == 0)
 	GIVE_UP (18);
       start_pos = it.current.pos;