1 files changed, 41 insertions, 11 deletions

diff --git a/src/buffer.c b/src/buffer.c
index dc6bcd8f6d3..6a11569c85a 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -146,6 +146,9 @@ Lisp_Object Vinhibit_read_only;
 Lisp_Object Vkill_buffer_query_functions;
 Lisp_Object Qkill_buffer_query_functions;
 
+/* Hook run before changing a major mode.  */
+Lisp_Object Vchange_major_mode_hook, Qchange_major_mode_hook;
+
 /* List of functions to call before changing an unmodified buffer.  */
 Lisp_Object Vfirst_change_hook;
 
@@ -1711,9 +1714,18 @@ the window-buffer correspondences.  */)
   char *err;
 
   if (EQ (buffer, Fwindow_buffer (selected_window)))
-    /* Basically a NOP.  Avoid signalling an error if the selected window
-       is dedicated, or a minibuffer, ...  */
-    return Fset_buffer (buffer);
+    {
+      /* Basically a NOP.  Avoid signalling an error in the case where
+         the selected window is dedicated, or a minibuffer.  */
+
+      /* But do put this buffer at the front of the buffer list,
+         unless that has been inhibited.  Note that even if
+         BUFFER is at the front of the main buffer-list already,
+         we still want to move it to the front of the frame's buffer list.  */
+      if (NILP (norecord))
+        record_buffer (buffer);
+      return Fset_buffer (buffer);
+    }
 
   err = no_switch_window (selected_window);
   if (err) error (err);
@@ -2142,10 +2154,11 @@ current buffer is cleared.  */)
 {
   struct Lisp_Marker *tail, *markers;
   struct buffer *other;
-  int undo_enabled_p = !EQ (current_buffer->undo_list, Qt);
   int begv, zv;
   int narrowed = (BEG != BEGV || Z != ZV);
   int modified_p = !NILP (Fbuffer_modified_p (Qnil));
+  Lisp_Object old_undo = current_buffer->undo_list;
+  struct gcpro gcpro1;
 
   if (current_buffer->base_buffer)
     error ("Cannot do `set-buffer-multibyte' on an indirect buffer");
@@ -2154,10 +2167,11 @@ current buffer is cleared.  */)
   if (NILP (flag) == NILP (current_buffer->enable_multibyte_characters))
     return flag;
 
-  /* It would be better to update the list,
-     but this is good enough for now.  */
-  if (undo_enabled_p)
-    current_buffer->undo_list = Qt;
+  GCPRO1 (old_undo);
+
+  /* Don't record these buffer changes.  We will put a special undo entry
+     instead.  */
+  current_buffer->undo_list = Qt;
 
   /* If the cached position is for this buffer, clear it out.  */
   clear_charpos_cache (current_buffer);
@@ -2357,8 +2371,17 @@ current buffer is cleared.  */)
       set_intervals_multibyte (1);
     }
 
-  if (undo_enabled_p)
-    current_buffer->undo_list = Qnil;
+  if (!EQ (old_undo, Qt))
+    {
+      /* Represent all the above changes by a special undo entry.  */
+      extern Lisp_Object Qapply;
+      current_buffer->undo_list = Fcons (list3 (Qapply,
+                                                intern ("set-buffer-multibyte"),
+                                                NILP (flag) ? Qt : Qnil),
+                                         old_undo);
+    }
+
+  UNGCPRO;
 
   /* Changing the multibyteness of a buffer means that all windows
      showing that buffer must be updated thoroughly.  */
@@ -2416,7 +2439,7 @@ the normal hook `change-major-mode-hook'.  */)
   Lisp_Object oalist;
 
   if (!NILP (Vrun_hooks))
-    call1 (Vrun_hooks, intern ("change-major-mode-hook"));
+    call1 (Vrun_hooks, Qchange_major_mode_hook);
   oalist = current_buffer->local_var_alist;
 
   /* Make sure none of the bindings in oalist
@@ -6028,6 +6051,13 @@ t means to use hollow box cursor.  See `cursor-type' for other values.  */);
                doc: /* List of functions called with no args to query before killing a buffer.  */);
   Vkill_buffer_query_functions = Qnil;
 
+  DEFVAR_LISP ("change-major-mode-hook", &Vchange_major_mode_hook,
+               doc: /* Normal hook run before changing the major mode of a buffer.
+The function `kill-all-local-variables' runs this before doing anything else.  */);
+  Vchange_major_mode_hook = Qnil;
+  Qchange_major_mode_hook = intern ("change-major-mode-hook");
+  staticpro (&Qchange_major_mode_hook);
+
   defsubr (&Sbuffer_live_p);
   defsubr (&Sbuffer_list);
   defsubr (&Sget_buffer);