function prepares vararg only if it really uses them (chunks

are always declared vararg but seldom uses them)

ldo.c

@@ -1,5 +1,5 @@
 /*
-** $Id: ldo.c,v 2.142 2015/10/28 12:06:45 roberto Exp roberto $
+** $Id: ldo.c,v 2.143 2015/10/28 12:25:36 roberto Exp roberto $
 ** Stack and Call structure of Lua
 ** See Copyright Notice in lua.h
 */
@@ -357,7 +357,7 @@ int luaD_precall (lua_State *L, StkId func, int nresults) {
       checkstackp(L, p->maxstacksize, func);
       for (; n < p->numparams; n++)
         setnilvalue(L->top++);  /* complete missing arguments */
-      if (!p->is_vararg)
+      if (p->is_vararg != 1)  /* do not use vararg? */
         base = func + 1;
       else {
         ptrdiff_t funcr = savestack(L, func);

lobject.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.h,v 2.113 2015/09/08 16:54:52 roberto Exp roberto $
+** $Id: lobject.h,v 2.114 2015/09/17 15:51:05 roberto Exp roberto $
 ** Type definitions for Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -407,7 +407,7 @@ typedef struct LocVar {
 typedef struct Proto {
   CommonHeader;
   lu_byte numparams;  /* number of fixed parameters */
-  lu_byte is_vararg;
+  lu_byte is_vararg;  /* 2: declared vararg; 1: uses vararg */
   lu_byte maxstacksize;  /* number of registers needed by this function */
   int sizeupvalues;  /* size of 'upvalues' */
   int sizek;  /* size of 'k' */

lparser.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lparser.c,v 2.146 2014/11/27 18:41:43 roberto Exp roberto $
+** $Id: lparser.c,v 2.147 2014/12/27 20:31:43 roberto Exp roberto $
 ** Lua Parser
 ** See Copyright Notice in lua.h
 */
@@ -760,7 +760,7 @@ static void parlist (LexState *ls) {
         }
         case TK_DOTS: {  /* param -> '...' */
           luaX_next(ls);
-          f->is_vararg = 1;
+          f->is_vararg = 2;  /* declared vararg */
           break;
         }
         default: luaX_syntaxerror(ls, "<name> or '...' expected");
@@ -956,6 +956,7 @@ static void simpleexp (LexState *ls, expdesc *v) {
       FuncState *fs = ls->fs;
       check_condition(ls, fs->f->is_vararg,
                       "cannot use '...' outside a vararg function");
+      fs->f->is_vararg = 1;  /* function actually uses vararg */
       init_exp(v, VVARARG, luaK_codeABC(fs, OP_VARARG, 0, 1, 0));
       break;
     }
@@ -1610,7 +1611,7 @@ static void mainfunc (LexState *ls, FuncState *fs) {
   BlockCnt bl;
   expdesc v;
   open_func(ls, fs, &bl);
-  fs->f->is_vararg = 1;  /* main function is always vararg */
+  fs->f->is_vararg = 2;  /* main function is always declared vararg */
   init_exp(&v, VLOCAL, 0);  /* create and... */
   newupvalue(fs, ls->envn, &v);  /* ...set environment upvalue */
   luaX_next(ls);  /* read first token */