Fix bug #17244 with line-move-visual when display string covers a lot of text.

 src/xdisp.c (move_it_by_lines): If a large portion of buffer text is
 covered by a display string that ends in a newline, and that cases
 going back by DVPOS lines to hit the search limit, lift the limit
 and go back until DVPOS is reached.
 src/indent.c (Fvertical_motion): Handle correctly the case when the
 display string is preceded by an empty line.

3 files changed, 42 insertions, 2 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 22f25bef6f3..cb17738d139 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,13 @@
+2014-04-12  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (move_it_by_lines): If a large portion of buffer text is
+        covered by a display string that ends in a newline, and that cases
+        going back by DVPOS lines to hit the search limit, lift the limit
+        and go back until DVPOS is reached.  (Bug#17244)
+
+        * indent.c (Fvertical_motion): Handle correctly the case when the
+        display string is preceded by an empty line.
+
 2014-04-11  Eli Zaretskii  <eliz@gnu.org>
 
         * w32.c (sys_umask) <WRITE_USER>: Remove redundant constant, and
diff --git a/src/indent.c b/src/indent.c
index 683d44841b9..dc862518924 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -2051,8 +2051,15 @@ whether or not it is currently displayed in some window.  */)
            string, move_it_to will overshoot it, while vertical-motion
            wants to put the cursor _before_ the display string.  So in
            that case, we move to buffer position before the display
-           string, and avoid overshooting.  */
-        move_it_to (&it, disp_string_at_start_p ? PT - 1 : PT,
+           string, and avoid overshooting.  But if the position before
+           the display string is a newline, we don't do this, because
+           otherwise we will end up in a screen line that is one too
+           far back.  */
+        move_it_to (&it,
+                    (!disp_string_at_start_p
+                     || FETCH_BYTE (IT_BYTEPOS (it)) == '\n')
+                    ? PT
+                    : PT - 1,
                     -1, -1, -1, MOVE_TO_POS);
 
       /* IT may move too far if truncate-lines is on and PT lies
diff --git a/src/xdisp.c b/src/xdisp.c
index 53bd46328f2..eb3a6df1fc5 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -9511,6 +9511,7 @@ move_it_by_lines (struct it *it, ptrdiff_t dvpos)
       ptrdiff_t start_charpos, i;
       int nchars_per_row
         = (it->last_visible_x - it->first_visible_x) / FRAME_COLUMN_WIDTH (it->f);
+      bool hit_pos_limit = false;
       ptrdiff_t pos_limit;
 
       /* Start at the beginning of the screen line containing IT's
@@ -9527,8 +9528,11 @@ move_it_by_lines (struct it *it, ptrdiff_t dvpos)
         pos_limit = BEGV;
       else
         pos_limit = max (start_charpos + dvpos * nchars_per_row, BEGV);
+
       for (i = -dvpos; i > 0 && IT_CHARPOS (*it) > pos_limit; --i)
         back_to_previous_visible_line_start (it);
+      if (i > 0 && IT_CHARPOS (*it) <= pos_limit)
+        hit_pos_limit = true;
       reseat (it, it->current.pos, 1);
 
       /* Move further back if we end up in a string or an image.  */
@@ -9572,6 +9576,25 @@ move_it_by_lines (struct it *it, ptrdiff_t dvpos)
           else
             bidi_unshelve_cache (it2data, 1);
         }
+      else if (hit_pos_limit && pos_limit > BEGV
+               && dvpos < 0 && it2.vpos < -dvpos)
+        {
+          /* If we hit the limit, but still didn't make it far enough
+             back, that means there's a display string with a newline
+             covering a large chunk of text, and that caused
+             back_to_previous_visible_line_start try to go too far.
+             Punish those who commit such atrocities by going back
+             until we've reached DVPOS, after lifting the limit, which
+             could make it slow for very long lines.  "If it hurts,
+             don't do that!"  */
+          dvpos += it2.vpos;
+          RESTORE_IT (it, it, it2data);
+          for (i = -dvpos; i > 0; --i)
+            {
+              back_to_previous_visible_line_start (it);
+              it->vpos--;
+            }
+        }
       else
         RESTORE_IT (it, it, it2data);
     }