BUG: GC can collect a long string still in use during parser

llex.c

@@ -1,5 +1,5 @@
 /*
-** $Id: llex.c,v 2.63 2013/03/16 21:10:18 roberto Exp $
+** $Id: llex.c,v 2.63.1.1 2013/04/12 18:48:47 roberto Exp roberto $
 ** Lexical Analyzer
 ** See Copyright Notice in lua.h
 */
@@ -133,6 +133,9 @@ TString *luaX_newstring (LexState *ls, const char *str, size_t l) {
     setbvalue(o, 1);  /* t[string] = true */
     luaC_checkGC(L);
   }
+  else {  /* string already present */
+    ts = rawtsvalue(keyfromval(o));  /* re-use value previously stored */
+  }
   L->top--;  /* remove string from stack */
   return ts;
 }

ltable.h

@@ -1,5 +1,5 @@
 /*
-** $Id: ltable.h,v 2.16 2011/08/17 20:26:47 roberto Exp $
+** $Id: ltable.h,v 2.16.1.1 2013/04/12 18:48:47 roberto Exp roberto $
 ** Lua tables (hash)
 ** See Copyright Notice in lua.h
 */
@@ -17,6 +17,10 @@
 
 #define invalidateTMcache(t)	((t)->flags = 0)
 
+/* returns the key, given the value of a table entry */
+#define keyfromval(v) \
+  (gkey(cast(Node *, cast(char *, (v)) - offsetof(Node, i_val))))
+
 
 LUAI_FUNC const TValue *luaH_getint (Table *t, int key);
 LUAI_FUNC void luaH_setint (lua_State *L, Table *t, int key, TValue *value);