From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Gierth <andrew@tao11.riddles.org.uk>
Cc: pgsql-hackers@postgresql.org
Subject: Re: A really subtle lexer bug
Date: Thu, 23 Aug 2018 10:55:15 -0400
Message-ID: <18470.1535036115@sss.pgh.pa.us> (raw)
In-Reply-To: <87ftz90yma.fsf@news-spur.riddles.org.uk>
References: <87va851ppl.fsf@news-spur.riddles.org.uk>
<87ftz90yma.fsf@news-spur.riddles.org.uk>
Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
> "Andrew" == Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
> Andrew> I guess the fix is to extend the existing special case code
> Andrew> that checks for one character left after removing trailing [+-]
> Andrew> and also check for the two-character ops "<>" ">=" "<=" "=>"
> Andrew> "!=".
> Patch attached.
> This fixes two bugs: first the mis-lexing of two-char ops as mentioned
> originally; second, the O(N^3) lexing time of strings of - or +
> characters is reduced to O(N^2) (in practice it's better than O(N^2)
> once N gets large because the bison stack gets blown out, ending the
> loop early).
Looks reasonable offhand (didn't test). A couple of thoughts:
* Some regression tests exercising these code paths might be a good thing.
* There should likely be a comment near where EQUALS_GREATER and
friends are defined, pointing out that if we add any more multi-character
operators with special precedences, this code has to be taught about them.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, andrew@tao11.riddles.org.uk
Subject: Re: A really subtle lexer bug
In-Reply-To: <18470.1535036115@sss.pgh.pa.us>
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