Date: Tue, 25 Jul 2000 04:43:57 -0700 (PDT) From: bertho@j.auh.dk To: freebsd-gnats-submit@FreeBSD.org Subject: misc/20172: byacc 1.9 fails to generate $default transitions for non-terminals Message-ID: <20000725114357.EAAFF37BCD5@hub.freebsd.org>
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>Number: 20172
>Category: misc
>Synopsis: byacc 1.9 fails to generate $default transitions for non-terminals
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jul 25 04:50:08 PDT 2000
>Closed-Date:
>Last-Modified:
>Originator: Bertho
>Release: N/A
>Organization:
Aarhus University Hospital
>Environment:
N/A
>Description:
Transitions on declared, but unused tokens are not included into
state transitions. You normally would get $default transitions,
but byacc insists on specifying all tokens. This leads to wrong
results because a syntax-error is generated on a perfectly legal
input.
Version of byacc:
yysccsid[] = \"@(#)yaccpar 1.9 (Berkeley) 02/21/93\";"
The bug was also sent to the maintainer as mentioned in the source's
README file. However, it is promised in that file that no rapid response
is to be expected.
>How-To-Repeat:
Try this source, once without the tNL rule, and once with. A syntax
error is generated if the rule is not implemented. When the rule is
there, then the proper result is printed.
To compile (use attached source below):
$ byacc byacc-bug.y
$ gcc -o byacc-bug y.tab.c
$ ./byacc-bug
---- file byacc-bug.y ----
%{
#include <stdio.h>
#include <stdlib.h>
%}
%token tTOK tNUM tNL
%left '+'
%%
lines : line
| lines line
;
line : tTOK xpr ',' xpr {
if(yychar == tNL)
printf("Success: Got tNL\n");
}
/* Declare NON-terminal as used */
/* | tNL */
;
xpr : xpr '+' xpr
| tNUM
;
%%
int yylex(void)
{
static int tok[] = {tTOK, tNUM, ',', tNUM, tNL, 0};
static int idx = 0;
#define NTOK (sizeof(tok)/sizeof(tok[0]))
if(idx < NTOK)
return tok[idx++];
return 0;
}
void yyerror(char *s)
{
printf("yyerror: %s\n", s);
exit(1);
}
int main(void)
{
return yyparse();
}
>Fix:
You have to define a rule that captures all non-terminal tokens (i.e. all
tokens in %token, %left and %right declarations that are otherwise
unused). This can be tricky if such a rule has grammatical side-effects.
A real fix requires a patch in byacc (but I am not familiar with its
internals). OTOH, GNU bison does not suffer from this bug and can
be used as an alternative.
>Release-Note:
>Audit-Trail:
>Unformatted:
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