Index: buffer.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/buffer.c,v
retrieving revision 1.480
diff -u -r1.480 buffer.c
--- buffer.c	27 May 2005 11:01:38 -0000	1.480
+++ buffer.c	27 May 2005 17:06:47 -0000
@@ -178,6 +178,12 @@
 Lisp_Object Qinsert_in_front_hooks;
 Lisp_Object Qinsert_behind_hooks;
 
+#define OVERLAY_EVAPORATE_TESTING
+#ifdef OVERLAY_EVAPORATE_TESTING
+Lisp_Object Qnever_set;
+static Lisp_Object evaporate_overlay P_ ((Lisp_Object));
+#endif
+
 static void alloc_buffer_text P_ ((struct buffer *, size_t));
 static void free_buffer_text P_ ((struct buffer *b));
 static struct Lisp_Overlay * copy_overlays P_ ((struct buffer *, struct Lisp_Overlay *));
@@ -3602,6 +3608,11 @@
   XOVERLAY (overlay)->plist = Qnil;
   XOVERLAY (overlay)->next = NULL;
 
+#ifdef OVERLAY_EVAPORATE_TESTING
+  XOVERLAY (overlay)->plist
+    = Fcons (Qevaporate, Fcons (Qnever_set, XOVERLAY (overlay)->plist));
+#endif
+
   /* Put the new overlay on the wrong list.  */
   end = OVERLAY_END (overlay);
   if (OVERLAY_POSITION (end) < b->overlay_center)
@@ -3656,6 +3667,24 @@
 
 Lisp_Object Fdelete_overlay ();
 
+#ifdef OVERLAY_EVAPORATE_TESTING
+static Lisp_Object
+evaporate_overlay (overlay)
+     Lisp_Object overlay;
+{
+  if (EQ (Qnever_set, Foverlay_get (overlay, Qevaporate)))
+    {
+	Lisp_Object args[3];
+	args[0] = build_string("WARNING: Evaporating %S %S");
+	args[1] = overlay;
+	args[2] = Foverlay_properties(overlay);
+	Fmessage(3,args);
+    }
+
+  return Fdelete_overlay (overlay);
+}
+#endif
+
 static struct Lisp_Overlay *
 unchain_overlay (list, overlay)
      struct Lisp_Overlay *list, *overlay;
@@ -3704,7 +3733,13 @@
   CHECK_NUMBER_COERCE_MARKER (end);
 
   if (XINT (beg) == XINT (end) && ! NILP (Foverlay_get (overlay, Qevaporate)))
-    return Fdelete_overlay (overlay);
+    return
+#ifndef OVERLAY_EVAPORATE_TESTING
+      Fdelete_overlay
+#else
+      evaporate_overlay
+#endif
+      (overlay);
 
   if (XINT (beg) > XINT (end))
     {
@@ -4088,7 +4123,13 @@
       if (EQ (prop, Qevaporate) && ! NILP (value)
 	  && (OVERLAY_POSITION (OVERLAY_START (overlay))
 	      == OVERLAY_POSITION (OVERLAY_END (overlay))))
-	Fdelete_overlay (overlay);
+#ifndef OVERLAY_EVAPORATE_TESTING
+	Fdelete_overlay
+#else
+        evaporate_overlay
+#endif
+          (overlay);
+
     }
   return value;
 }
@@ -4330,7 +4371,12 @@
 	  hit_list = Fcons (overlay, hit_list);
       }
   for (; CONSP (hit_list); hit_list = XCDR (hit_list))
-    Fdelete_overlay (XCAR (hit_list));
+#ifndef OVERLAY_EVAPORATE_TESTING
+    Fdelete_overlay
+#else
+    evaporate_overlay
+#endif
+      (XCAR (hit_list));
 }
 
 /* Somebody has tried to store a value with an unacceptable type
@@ -5207,6 +5253,10 @@
   staticpro (&Qoverlayp);
   Qevaporate = intern ("evaporate");
   staticpro (&Qevaporate);
+#ifdef OVERLAY_EVAPORATE_TESTING
+  Qnever_set = intern ("never-set");
+  staticpro (&Qnever_set);
+#endif
   Qmodification_hooks = intern ("modification-hooks");
   staticpro (&Qmodification_hooks);
   Qinsert_in_front_hooks = intern ("insert-in-front-hooks");