Fix bug #17047 with cursor motion when invisible text starts a line.

 src/xdisp.c (redisplay_window): If all previous attempts to find the
 cursor row failed, try a few alternatives before falling back to
 the top-most row of the window.  Use row_containing_pos.

2 files changed, 48 insertions, 4 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index e8ae781bf4d..a9a0ebbe4a1 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2014-03-23  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (redisplay_window): If all previous attempts to find the
+        cursor row failed, try a few alternatives before falling back to
+        the top-most row of the window.  (Bug#17047)
+
 2014-03-22  Daniel Colascione  <dancol@dancol.org>
 
         * process.c (conv_sockaddr_to_lisp): When extracting the string
diff --git a/src/xdisp.c b/src/xdisp.c
index 6f39324d2f0..53bd46328f2 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -16400,12 +16400,50 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
   /* Consider the following case: Window starts at BEGV, there is
      invisible, intangible text at BEGV, so that display starts at
      some point START > BEGV.  It can happen that we are called with
-     PT somewhere between BEGV and START.  Try to handle that case.  */
+     PT somewhere between BEGV and START.  Try to handle that case,
+     and similar ones.  */
   if (w->cursor.vpos < 0)
     {
-      struct glyph_row *row = w->current_matrix->rows;
-      if (row->mode_line_p)
-        ++row;
+      /* First, try locating the proper glyph row for PT.  */
+      struct glyph_row *row =
+        row_containing_pos (w, PT, w->current_matrix->rows, NULL, 0);
+
+      /* Sometimes point is at the beginning of invisible text that is
+         before the 1st character displayed in the row.  In that case,
+         row_containing_pos fails to find the row, because no glyphs
+         with appropriate buffer positions are present in the row.
+         Therefore, we next try to find the row which shows the 1st
+         position after the invisible text.  */
+      if (!row)
+        {
+          Lisp_Object val =
+            get_char_property_and_overlay (make_number (PT), Qinvisible,
+                                           Qnil, NULL);
+
+          if (TEXT_PROP_MEANS_INVISIBLE (val))
+            {
+              ptrdiff_t alt_pos;
+              Lisp_Object invis_end =
+                Fnext_single_char_property_change (make_number (PT), Qinvisible,
+                                                   Qnil, Qnil);
+
+              if (NATNUMP (invis_end))
+                alt_pos = XFASTINT (invis_end);
+              else
+                alt_pos = ZV;
+              row = row_containing_pos (w, alt_pos, w->current_matrix->rows,
+                                        NULL, 0);
+            }
+        }
+      /* Finally, fall back on the first row of the window after the
+         header line (if any).  This is slightly better than not
+         displaying the cursor at all.  */
+      if (!row)
+        {
+          row = w->current_matrix->rows;
+          if (row->mode_line_p)
+            ++row;
+        }
       set_cursor_from_row (w, row, w->current_matrix, 0, 0, 0, 0);
     }