Expose number of expected C call results from Lua

Author: sbx320

src/lapi.c

@@ -1134,3 +1134,9 @@ LUA_API void lua_addtotalbytes(lua_State *L, int n)
     global_State *g = G(L);
     g->totalbytes += n;
 }
+
+// MTA addition to access expected results
+LUA_API int lua_ncallresult(lua_State *L)
+{
+    return L->nexpectedresults;
+}

src/ldo.c

@@ -335,6 +335,8 @@ int luaD_precall (lua_State *L, StkId func, int nresults) {
         allowed = pPreCallHook ( *curr_func(L)->c.f, L );
     if ( allowed )
     {
+        // MTA Specific: Store number of expected results for lua_ncallresult
+        L->nexpectedresults = nresults;
         n = (*curr_func(L)->c.f)(L);  /* do the actual call */
         // MTA Specific
         if ( pPostCallHook )

src/lstate.h

@@ -124,6 +124,8 @@ struct lua_State {
   GCObject *gclist;
   struct lua_longjmp *errorJmp;  /* current error recover point */
   ptrdiff_t errfunc;  /* current error handling function (stack index) */
+  int nexpectedresults; /* MTA specific: Number of expected results from a C call. Only valid inside a function call. 
+						   May no longer be valid if any further Lua calls were made (e.g. via lua_pcall) */
 };
 
 

src/lua.h

@@ -220,7 +220,13 @@ LUA_API int   (lua_load) (lua_State *L, lua_Reader reader, void *dt,
                                         const char *chunkname);
 
 LUA_API int (lua_dump) (lua_State *L, lua_Writer writer, void *data);
-
+// MTA specific: Returns the number of expected results in a C call.
+// Note that this will no longer be reliable if 
+// It will also not be reliable in case of incorrectly called functions
+// e.g. 
+//   local a, b = tostring(3) 
+// will return 2, despite tostring only returning one number
+LUA_API int (lua_ncallresult) (lua_State* L);
 
 /*
 ** coroutine functions