bug#33492: 27.0.50; desktop-locals-to-save won't consider buffer-undo-list as local

[Glenn Morris <rgm@gnu.org>]

Glenn Morris wrote:

> This issue (buffer-local-variables does not include buffer-undo-list)
> is present since Emacs 24.3, due to 36429c8, which moved undo_list to
> the end of struct buffer.

The following works, but I don't know if it is the best solution.

--- i/src/buffer.c
+++ w/src/buffer.c
@@ -1266,6 +1266,20 @@ buffer_lisp_local_variables (struct buffer *buf, bool clone)
   return result;
 }
 
+Lisp_Object
+buffer_local_variables_1 (struct buffer *buf, int offset)
+{
+  int idx = PER_BUFFER_IDX (offset);
+  if ((idx == -1 || PER_BUFFER_VALUE_P (buf, idx))
+      && SYMBOLP (PER_BUFFER_SYMBOL (offset)))
+    {
+      Lisp_Object sym = PER_BUFFER_SYMBOL (offset);
+      Lisp_Object val = per_buffer_value (buf, offset);
+      return EQ (val, Qunbound) ? sym : Fcons (sym, val);
+    }
+  return Qnil;
+}
+
 DEFUN ("buffer-local-variables", Fbuffer_local_variables,
        Sbuffer_local_variables, 0, 1, 0,
        doc: /* Return an alist of variables that are buffer-local in BUFFER.
@@ -1277,6 +1291,7 @@ No argument or nil as argument means use current buffer as BUFFER.  */)
 {
   struct buffer *buf = decode_buffer (buffer);
   Lisp_Object result = buffer_lisp_local_variables (buf, 0);
+  Lisp_Object tem;
 
   /* Add on all the variables stored in special slots.  */
   {
@@ -1284,18 +1299,16 @@ No argument or nil as argument means use current buffer as BUFFER.  */)
 
     FOR_EACH_PER_BUFFER_OBJECT_AT (offset)
       {
-	idx = PER_BUFFER_IDX (offset);
-	if ((idx == -1 || PER_BUFFER_VALUE_P (buf, idx))
-	    && SYMBOLP (PER_BUFFER_SYMBOL (offset)))
-	  {
-	    Lisp_Object sym = PER_BUFFER_SYMBOL (offset);
-	    Lisp_Object val = per_buffer_value (buf, offset);
-	    result = Fcons (EQ (val, Qunbound) ? sym : Fcons (sym, val),
-			    result);
-	  }
+        tem = buffer_local_variables_1 (buf, offset);
+        if (!NILP (tem))
+          result = Fcons (tem, result);
       }
   }
 
+  tem = buffer_local_variables_1 (buf, PER_BUFFER_VAR_OFFSET (undo_list));
+  if (!NILP (tem))
+    result = Fcons (tem, result);
+
   return result;
 }