(mark_buffer): Mark the undo_list slot specially;

don't mark a marker just cause it is in this list.
(Fgarbage_collect): Discard from all undo-lists
all elements that adjust markers that were not marked.

diff --git a/src/alloc.c b/src/alloc.c
index 47fa6820102e3529ad01259a627690ff19bc2b3d..be4c82d0a1e97e8e843f56a282c29d412d8820d0 100644 (file)
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1816,6 +1816,46 @@ Garbage collection happens automatically if you cons more than\n\
     }  
   mark_kboards ();
 
+  /* Look thru every buffer's undo list
+     for elements that update markers that were not marked,
+     and delete them.  */
+  {
+    register struct buffer *nextb = all_buffers;
+
+    while (nextb)
+      {
+       /* If a buffer's undo list is Qt, that means that undo is
+          turned off in that buffer.  Calling truncate_undo_list on
+          Qt tends to return NULL, which effectively turns undo back on.
+          So don't call truncate_undo_list if undo_list is Qt.  */
+       if (! EQ (nextb->undo_list, Qt))
+         {
+           Lisp_Object tail, prev;
+           tail = nextb->undo_list;
+           prev = Qnil;
+           while (CONSP (tail))
+             {
+               if (GC_CONSP (XCONS (tail)->car)
+                   && GC_MARKERP (XCONS (XCONS (tail)->car)->car)
+                   && ! XMARKBIT (XMARKER (XCONS (XCONS (tail)->car)->car)->chain))
+                 {
+                   if (NILP (prev))
+                     nextb->undo_list = tail = XCONS (tail)->cdr;
+                   else
+                     tail = XCONS (prev)->cdr = XCONS (tail)->cdr;
+                 }
+               else
+                 {
+                   prev = tail;
+                   tail = XCONS (tail)->cdr;
+                 }
+             }
+         }
+
+       nextb = nextb->next;
+      }
+  }
+
   gc_sweep ();
 
   /* Clear the mark bits that we set in certain root slots.  */
@@ -2228,6 +2268,39 @@ mark_buffer (buf)
 
   MARK_INTERVAL_TREE (BUF_INTERVALS (buffer));
 
+  if (CONSP (buffer->undo_list))
+    {
+      Lisp_Object tail;
+      tail = buffer->undo_list;
+
+      while (CONSP (tail))
+       {
+         register struct Lisp_Cons *ptr = XCONS (tail);
+
+         if (XMARKBIT (ptr->car))
+           break;
+         XMARK (ptr->car);
+         if (GC_CONSP (ptr->car)
+             && ! XMARKBIT (XCONS (ptr->car)->car)
+             && GC_MARKERP (XCONS (ptr->car)->car))
+           {
+             XMARK (XCONS (ptr->car)->car);
+             mark_object (&XCONS (ptr->car)->cdr);
+           }
+         else
+           mark_object (&ptr->car);
+
+         if (CONSP (ptr->cdr))
+           tail = ptr->cdr;
+         else
+           break;
+       }
+
+      mark_object (&XCONS (tail)->cdr);
+    }
+  else
+    mark_object (&buffer->undo_list);
+
 #if 0
   mark_object (buffer->syntax_table);