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Fix handling of yychar manipulation in user semantic actions.

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The problem was that yacc.c didn't always update the yychar
translation afterwards.  However, other skeletons appear to be
fine.  glr.c appears to already translate yychar before every
use.  lalr1.cc does not define yychar and does not document its
replacement, yyla, for users.  It does provide yyclearin, but
that does not manipulate yyla and thus requires no translation
update.  In lalr1.java, yychar is out of scope during semantic
actions.
* NEWS (2.5): Document.
* data/yacc.c (YYBACKUP): Don't bother translating yychar into
yytoken here.
(yyparse, yypush_parse): Instead, translate before every use of
yytoken, and add comments explaining this approach.
* tests/actions.at (Destroying lookahead assigned by semantic
action): New test group checking that translation happens before
lookahead destructor calls at parser return.  Previously,
incorrect destructors were called.
* tests/conflicts.at (parse.error=verbose and consistent
errors): New test group checking that translation happens at
syntax error detection before the associated verbose error
message and the associated lookahead destructor calls.  While
the destructor call is fixed by this patch, the verbose error
message is currently incorrect due to another bug (see
comments in test group), so this is an expected failure for now.
This commit is contained in:
Joel E. Denny
2009-12-20 02:22:53 -05:00
parent 4395a9ff4f
commit df222dfaf4
7 changed files with 612 additions and 344 deletions
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25
data/yacc.c
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@@ -630,7 +630,6 @@ do \
{ \
yychar = (Token); \
yylval = (Value); \
yytoken = YYTRANSLATE (yychar); \
YYPOPSTACK (1); \
goto yybackup; \
} \
@@ -1429,6 +1428,17 @@ yyreduce:
]b4_user_actions[
default: break;
}
/* User semantic actions sometimes alter yychar, and that requires
that yytoken be updated with the new translation. We take the
approach of translating immediately before every use of yytoken.
One alternative is translating here after every semantic action,
but that translation would be missed if the semantic action invokes
YYABORT, YYACCEPT, or YYERROR immediately after altering yychar or
if it invokes YYBACKUP. In the case of YYABORT or YYACCEPT, an
incorrect destructor might then be invoked immediately. In the
case of YYERROR or YYBACKUP, subsequent parser actions might lead
to an incorrect destructor call or verbose syntax error message
before the lookahead is translated. */
YY_SYMBOL_PRINT ("-> $$ =", yyr1[yyn], &yyval, &yyloc);
YYPOPSTACK (yylen);
@@ -1457,6 +1467,10 @@ yyreduce:
| yyerrlab -- here on detecting error |
`------------------------------------*/
yyerrlab:
/* Make sure we have latest lookahead translation. See comments at
user semantic actions for why this is necessary. */
yytoken = YYTRANSLATE (yychar);
/* If not already recovering from an error, report this error. */
if (!yyerrstatus)
{
@@ -1609,8 +1623,13 @@ yyexhaustedlab:
yyreturn:
if (yychar != YYEMPTY)
yydestruct ("Cleanup: discarding lookahead",
yytoken, &yylval]b4_locations_if([, &yylloc])[]b4_user_args[);
{
/* Make sure we have latest lookahead translation. See comments at
user semantic actions for why this is necessary. */
yytoken = YYTRANSLATE (yychar);
yydestruct ("Cleanup: discarding lookahead",
yytoken, &yylval]b4_locations_if([, &yylloc])[]b4_user_args[);
}
/* Do not reclaim the symbols of the rule which action triggered
this YYABORT or YYACCEPT. */
YYPOPSTACK (yylen);