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[Bug] dangerous lookahead check may fail [sf#38] #40
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- changed the title
[-]dangerous lookahead check may fail[/-][+][Bug] dangerous lookahead check may fail [sf#38][/+]on Feb 15, 2015 - added this to the milestone
on Feb 15, 2015 Commented by lsf37 on 2001-05-04 21:16 UTC
Logged In: YES
user_id=93534it is not clear yet wether this bug will be fixed soon
Updated by lsf37 on 2001-09-27 13:05 UTC
- status: open --> open-later
Commented by lsf37 on 2004-11-07 06:05 UTC
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user_id=93534Updated by lsf37 on 2004-11-07 06:05 UTC
- priority: 7 --> 2
Commented by lsf37 on 2004-11-07 06:08 UTC
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user_id=93534The warning is now safe (version 1.4.1), but very crude (reports
way too many cases as unsafe).Commented by lsf37 on 2007-11-25 11:53 UTC
Logged In: YES
user_id=93534
Originator: YESfixed in svn revision 299.
Updated by lsf37 on 2007-11-25 11:53 UTC
- status: open-later --> open-fixed
Updated by lsf37 on 2008-05-27 11:46 UTC
- status: open-fixed --> closed
- modified the milestone:
on Feb 17, 2015
Reported by lsf37 on 2001-05-04 21:15 UTC
for some lookahead expressions JFlex will fail to print a warning that they are dangerous (r1 / r2 is
dangerous if any postfix of r1 matches a prefix r2).
Example:
.+ "a" / "b" .+ { action }
will not produce a warning/error message, but the postfix .+"a" of r1 matches a prefix of r2 (the
whole lookahead).
These lookahead expressions might match some inputs incorrectly. It is guaranteed that the rule
gets chosen if there is a match for the expression r1r2 (concatenation of r1 and r2), and it is
guaranteed that yytext() matches r1. It is not guaranteed that there is an instance of r2 after
yytext() (because too few lookahead characters were put back into the input).
Workaround: check manually if your lookahead expressions are dangerous.
(reported by Robert Hubley)