Fix bug #7952 with vertical motion in Grep buffers.

 src/window.c (window_scroll_line_based): Use a marker instead of
 simple variables to record original value of point.

2 files changed, 17 insertions, 6 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index bb660036c17..f029daa684d 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,8 @@
 2011-04-29  Eli Zaretskii  <eliz@gnu.org>
 
+        * window.c (window_scroll_line_based): Use a marker instead of
+        simple variables to record original value of point.  (Bug#7952)
+
         * doprnt.c (doprnt): Fix the case where a multibyte sequence
         produced by %s or %c overflows available buffer space.  (Bug#8545)
 
diff --git a/src/window.c b/src/window.c
index b56ed84bc61..4dbee41c5f4 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5076,7 +5076,12 @@ static void
 window_scroll_line_based (Lisp_Object window, int n, int whole, int noerror)
 {
   register struct window *w = XWINDOW (window);
-  register EMACS_INT opoint = PT, opoint_byte = PT_BYTE;
+  /* Fvertical_motion enters redisplay, which can trigger
+     fontification, which in turn can modify buffer text (e.g., if the
+     fontification functions replace escape sequences with faces, as
+     in `grep-mode-font-lock-keywords').  So we use a marker to record
+     the old point position, to prevent crashes in SET_PT_BOTH.  */
+  Lisp_Object opoint_marker = Fpoint_marker ();
   register EMACS_INT pos, pos_byte;
   register int ht = window_internal_height (w);
   register Lisp_Object tem;
@@ -5126,7 +5131,8 @@ window_scroll_line_based (Lisp_Object window, int n, int whole, int noerror)
   pos = PT;
   pos_byte = PT_BYTE;
   bolp = Fbolp ();
-  SET_PT_BOTH (opoint, opoint_byte);
+  SET_PT_BOTH (marker_position (opoint_marker),
+               marker_byte_position (opoint_marker));
 
   if (lose)
     {
@@ -5177,8 +5183,9 @@ window_scroll_line_based (Lisp_Object window, int n, int whole, int noerror)
           else
             top_margin = pos;
 
-          if (top_margin <= opoint)
-            SET_PT_BOTH (opoint, opoint_byte);
+          if (top_margin <= marker_position (opoint_marker))
+            SET_PT_BOTH (marker_position (opoint_marker),
+                         marker_byte_position (opoint_marker));
           else if (!NILP (Vscroll_preserve_screen_position))
             {
               SET_PT_BOTH (pos, pos_byte);
@@ -5200,8 +5207,9 @@ window_scroll_line_based (Lisp_Object window, int n, int whole, int noerror)
           else
             bottom_margin = PT + 1;
 
-          if (bottom_margin > opoint)
-            SET_PT_BOTH (opoint, opoint_byte);
+          if (bottom_margin > marker_position (opoint_marker))
+            SET_PT_BOTH (marker_position (opoint_marker),
+                         marker_byte_position (opoint_marker));
           else
             {
               if (!NILP (Vscroll_preserve_screen_position))