no-nonsense debug information about tail calls

lbaselib.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lbaselib.c,v 1.122 2003/02/24 16:50:41 roberto Exp roberto $
+** $Id: lbaselib.c,v 1.123 2003/02/24 16:54:20 roberto Exp roberto $
 ** Basic library
 ** See Copyright Notice in lua.h
 */
@@ -123,6 +123,9 @@ static void getfunc (lua_State *L) {
     if (lua_getstack(L, level, &ar) == 0)
       luaL_argerror(L, 1, "invalid level");
     lua_getinfo(L, "f", &ar);
+    if (lua_isnil(L, -1))
+      luaL_error(L, "cannot get/set environment (tail call at level %d)",
+                    level);
   }
 }