Small corrections when setting 'L->top'

- OP_NEWTABLE can use 'ra + 1' to set top (instead of ci->top);
- OP_CLOSE doesn't need to set top ('Protect' already does that);
- OP_TFORCALL must use 'ProtectNT', to preserve the top already set.
  (That was a small bug, because iterators could be called with
   extra parameters besides the state and the control variable.)
- Comments and an extra test for the bug in previous item.

lapi.h

@@ -11,12 +11,22 @@
 #include "llimits.h"
 #include "lstate.h"
 
+
+/* Increments 'L->top', checking for stack overflows */
 #define api_incr_top(L)   {L->top++; api_check(L, L->top <= L->ci->top, \
 				"stack overflow");}
 
+
+/*
+** If a call returns too many multiple returns, the callee may not have
+** stack space to accomodate all results. In this case, this macro
+** increases its stack space ('L->ci->top').
+*/
 #define adjustresults(L,nres) \
     { if ((nres) <= LUA_MULTRET && L->ci->top < L->top) L->ci->top = L->top; }
 
+
+/* Ensure the stack has at least 'n' elements */
 #define api_checknelems(L,n)	api_check(L, (n) < (L->top - L->ci->func), \
 				  "not enough elements in the stack")
 

lparser.c

@@ -694,9 +694,10 @@ static Proto *addprototype (LexState *ls) {
 
 /*
 ** codes instruction to create new closure in parent function.
-** The OP_CLOSURE instruction must use the last available register,
+** The OP_CLOSURE instruction uses the last available register,
 ** so that, if it invokes the GC, the GC knows which registers
 ** are in use at that time.
+
 */
 static void codeclosure (LexState *ls, expdesc *v) {
   FuncState *fs = ls->fs->prev;

lvm.c

@@ -1258,7 +1258,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         if (TESTARG_k(i))
           c += GETARG_Ax(*pc) * (MAXARG_C + 1);
         pc++;  /* skip extra argument */
-        L->top = ci->top;  /* correct top in case of GC */
+        L->top = ra + 1;  /* correct top in case of emergency GC */
         t = luaH_new(L);  /* memory allocation */
         sethvalue2s(L, ra, t);
         if (b != 0 || c != 0)
@@ -1478,7 +1478,6 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         vmbreak;
       }
       vmcase(OP_CLOSE) {
-        L->top = ra + 1;  /* everything is free after this slot */
         Protect(luaF_close(L, ra, LUA_OK));
         vmbreak;
       }
@@ -1755,7 +1754,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         /* push function, state, and control variable */
         memcpy(ra + 4, ra, 3 * sizeof(*ra));
         L->top = ra + 4 + 3;
-        Protect(luaD_call(L, ra + 4, GETARG_C(i)));  /* do the call */
+        ProtectNT(luaD_call(L, ra + 4, GETARG_C(i)));  /* do the call */
         updatestack(ci);  /* stack may have changed */
         i = *(pc++);  /* go to next instruction */
         lua_assert(GET_OPCODE(i) == OP_TFORLOOP && ra == RA(i));
@@ -1776,7 +1775,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         if (n == 0)
           n = cast_int(L->top - ra) - 1;  /* get up to the top */
         else
-          L->top = ci->top;  /* correct top in case of GC */
+          L->top = ci->top;  /* correct top in case of emergency GC */
         last += n;
         if (TESTARG_k(i)) {
           last += GETARG_Ax(*pc) * (MAXARG_C + 1);

testes/nextvar.lua

@@ -671,7 +671,8 @@ collectgarbage()
 
 local function f (n, p)
   local t = {}; for i=1,p do t[i] = i*10 end
-  return function (_,n)
+  return function (_, n, ...)
+           assert(select("#", ...) == 0)  -- no extra arguments
            if n > 0 then
              n = n-1
              return n, table.unpack(t)