Avoid inflooping in redisplay caused by hscrolled R2L lines.

 src/xdisp.c (display_line): Don't assume that the call to
 reseat_at_next_visible_line_start ends up at a character
 immediately following the newline on the previous line.  Avoids
 setting the ends_at_zv_p flag on screen lines that are not at or
 beyond ZV, which causes infloop in redisplay.  For the details, see
 http://lists.gnu.org/archive/html/emacs-devel/2014-08/msg00368.html.

2 files changed, 15 insertions, 3 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 68f6babb991..8c89f693bca 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,12 @@
 2014-08-17  Eli Zaretskii  <eliz@gnu.org>
 
+	* xdisp.c (display_line): Don't assume that the call to
+	reseat_at_next_visible_line_start ends up at a character
+	immediately following the newline on the previous line.  Avoids
+	setting the ends_at_zv_p flag on screen lines that are not at or
+	beyond ZV, which causes infloop in redisplay.  For the details, see
+	http://lists.gnu.org/archive/html/emacs-devel/2014-08/msg00368.html.
+
 	* dispnew.c (buffer_posn_from_coords): Fix mirroring of X
 	coordinate for hscrolled R2L screen lines.  (Bug#18277)
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 776e4d000ee..e60a9d341c6 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -20583,10 +20583,15 @@ display_line (struct it *it)
 	  row->truncated_on_right_p = 1;
 	  it->continuation_lines_width = 0;
 	  reseat_at_next_visible_line_start (it, 0);
-	  if (IT_BYTEPOS (*it) <= BEG_BYTE)
-	    row->ends_at_zv_p = true;
+	  /* We insist below that IT's position be at ZV because in
+	     bidi-reordered lines the character at visible line start
+	     might not be the character that follows the newline in
+	     the logical order.  */
+	  if (IT_BYTEPOS (*it) > BEG_BYTE)
+	    row->ends_at_zv_p =
+	      IT_BYTEPOS (*it) >= ZV_BYTE && FETCH_BYTE (ZV_BYTE - 1) != '\n';
 	  else
-	    row->ends_at_zv_p = FETCH_BYTE (IT_BYTEPOS (*it) - 1) != '\n';
+	    row->ends_at_zv_p = false;
 	  break;
 	}
     }