Re: duplicated user destructor for lookahead

[Paul Eggert]

"Joel E. Denny" <address@hidden> writes
in <http://lists.gnu.org/archive/html/bison-patches/2005-08/msg00035.html>:

> I added a bool yytoken_shifted alongside yytoken.  It tracks whether the
> parser has shifted yytoken onto any stack yet.  Like yytoken, it is a
> local variable in yyparse().  There's also a yytoken_shiftedp like
> yytokenp in yyGLRStack.  The parser does not call the user destructor for
> the lookahead if yytoken_shifted.

Thanks for the test case and for the proposed patch.  But even with
the patch, if the token is shifted onto two stacks before memory is
exhausted, won't its associated value be freed twice?  (Sorry, I don't
quite follow the logic.)

Let's put it another way.  Here's a bogus patch that I just tried; can
you please explain a little why it's bogus?

--- glr.c.~1.120.~      2005-09-11 22:28:02.000000000 -0700
+++ glr.c       2005-09-14 15:59:48.000000000 -0700
@@ -1806,6 +1806,7 @@ yyprocessOneStack (yyGLRStack* yystack, 
            {
              YYDPRINTF ((stderr, "On stack %lu, ", (unsigned long int) yyk));
              YY_SYMBOL_PRINT ("shifting", *yytokenp, yylvalp, yyllocp);
+             *yytokenp = YYEMPTY;
              yyglrShift (yystack, yyk, yyaction, yyposn+1,
                          *yylvalp, yyllocp);
              YYDPRINTF ((stderr, "Stack %lu now in state #%d\n",