2 files changed, 16 insertions, 4 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b1f13e62b40..4b1281c17e6 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2013-05-29  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * fileio.c (Finsert_file_contents): Preserve undo info when reverting
+        a buffer (bug#8447).
+
 2013-05-27  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (pos_visible_p): When CHARPOS is displayed frrom a
@@ -25,8 +30,8 @@
         (struct MonitorInfo): New struct.
         (free_monitors, make_monitor_attribute_list): Declare.
 
-        * frame.c (Qgeometry, Qworkarea, Qmm_size, Qframes, Qsource): New
-        Lisp_Object:s.
+        * frame.c (Qgeometry, Qworkarea, Qmm_size, Qframes, Qsource):
+        New Lisp_Object:s.
         (free_monitors, make_monitor_attribute_list): New functions.
         (syms_of_frame): DEFSYM Qgeometry, Qworkarea, Qmm_size, Qframes,
         Qsource.
diff --git a/src/fileio.c b/src/fileio.c
index f20721251e6..e2b1007fb0b 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3506,6 +3506,11 @@ by calling `format-decode', which see.  */)
   bool set_coding_system = 0;
   Lisp_Object coding_system;
   bool read_quit = 0;
+  /* If the undo log only contains the insertion, there's no point
+     keeping it.  It's typically when we first fill a file-buffer.  */
+  bool empty_undo_list_p
+    = (!NILP (visit) && NILP (BVAR (current_buffer, undo_list))
+       && BEG == Z);
   Lisp_Object old_Vdeactivate_mark = Vdeactivate_mark;
   bool we_locked_file = 0;
   bool deferred_remove_unwind_protect = 0;
@@ -4108,6 +4113,7 @@ by calling `format-decode', which see.  */)
         {
           del_range_byte (same_at_start, same_at_end, 0);
           temp = GPT;
+          eassert (same_at_start == GPT_BYTE);
           same_at_start = GPT_BYTE;
         }
       else
@@ -4120,6 +4126,7 @@ by calling `format-decode', which see.  */)
         = buf_bytepos_to_charpos (XBUFFER (conversion_buffer),
                                   same_at_start - BEGV_BYTE
                                   + BUF_BEG_BYTE (XBUFFER (conversion_buffer)));
+      eassert (same_at_start_charpos == temp - (BEGV - BEG));
       inserted_chars
         = (buf_bytepos_to_charpos (XBUFFER (conversion_buffer),
                                    same_at_start + inserted - BEGV_BYTE
@@ -4404,7 +4411,7 @@ by calling `format-decode', which see.  */)
 
   if (!NILP (visit))
     {
-      if (!EQ (BVAR (current_buffer, undo_list), Qt) && !nochange)
+      if (empty_undo_list_p)
         bset_undo_list (current_buffer, Qnil);
 
       if (NILP (handler))
@@ -4546,7 +4553,7 @@ by calling `format-decode', which see.  */)
           p = XCDR (p);
         }
 
-      if (NILP (visit))
+      if (!empty_undo_list_p)
         {
           bset_undo_list (current_buffer, old_undo);
           if (CONSP (old_undo) && inserted != old_inserted)