From f87a68b369018158bbddabbec049a7d4e2df52ee Mon Sep 17 00:00:00 2001
From: "Richard M. Stallman" <rms@gnu.org>
Date: Sat, 12 Jun 1993 18:10:20 +0000
Subject: [PATCH] (syms_of_undo): Set up Qinhibit_read_only. (Fprimitive_undo):
 Sometimes bind inhibit-read-only to t.

---
 src/undo.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/undo.c b/src/undo.c
index 18bfc3a3b2b..1c399fb873f 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -26,6 +26,8 @@ and this notice must be preserved on all copies.  */
 /* Last buffer for which undo information was recorded.  */
 Lisp_Object last_undo_buffer;
 
+Lisp_Object Qinhibit_read_only;
+
 /* Record an insertion that just happened or is about to happen,
    for LENGTH characters at position BEG.
    (It is possible to record an insertion before or after the fact
@@ -286,6 +288,7 @@ Return what remains of the list.")
   (count, list)
      Lisp_Object count, list;
 {
+  int count = specpdl_ptr - specpdl;
   register int arg = XINT (count);
 #if 0  /* This is a good feature, but would make undo-start
 	  unable to do what is expected.  */
@@ -298,6 +301,10 @@ Return what remains of the list.")
     list = Fcdr (list);
 #endif
 
+  /* Don't let read-only properties interfere with undo.  */
+  if (NILP (current_buffer->read_only))
+    specbind (Qinhibit_read_only, Qt);
+
   while (arg > 0)
     {
       while (1)
@@ -401,11 +408,14 @@ Return what remains of the list.")
       arg--;
     }
 
-  return list;
+  return unbind_to (count, list);
 }
 
 syms_of_undo ()
 {
+  Qinhibit_read_only = intern ("inhibit-read-only");
+  staticpro (&Qinhibit_read_only);
+
   defsubr (&Sprimitive_undo);
   defsubr (&Sundo_boundary);
 }