Fix bug #17969 with vertical-motion through continuation lines with TABs.

 src/xdisp.c (move_it_to): Adjust calculation of line_start_x to what
 x_produce_glyphs does when it generates a stretch glyph that
 represents a TAB.

2 files changed, 25 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 89621bd54ec..d2f1999b546 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2014-07-08  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (move_it_to): Adjust calculation of line_start_x to what
+        x_produce_glyphs does when it generates a stretch glyph that
+        represents a TAB.  (Bug#17969)
+
 2014-07-05  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (pos_visible_p): If CHARPOS is at beginning of window,
diff --git a/src/xdisp.c b/src/xdisp.c
index 28752a42cb9..61d1fa24c68 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -9250,6 +9250,25 @@ move_it_to (struct it *it, ptrdiff_t to_charpos, int to_x, int to_y, int to_vpos
                 {
                   line_start_x = it->current_x + it->pixel_width
                     - it->last_visible_x;
+                  if (FRAME_WINDOW_P (it->f))
+                    {
+                      struct face *face = FACE_FROM_ID (it->f, it->face_id);
+                      struct font *face_font = face->font;
+
+                      /* When display_line produces a continued line
+                         that ends in a TAB, it skips a tab stop that
+                         is closer than the font's space character
+                         width (see x_produce_glyphs where it produces
+                         the stretch glyph which represents a TAB).
+                         We need to reproduce the same logic here.  */
+                      eassert (face_font);
+                      if (face_font)
+                        {
+                          if (line_start_x < face_font->space_width)
+                            line_start_x
+                              += it->tab_width * face_font->space_width;
+                        }
+                    }
                   set_iterator_to_next (it, 0);
                 }
             }