Horton

Re: A really subtle lexer bug

Andrew Gierth <andrew@tao11.riddles.org.uk>

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From: Andrew Gierth <andrew@tao11.riddles.org.uk>
To: pgsql-hackers@postgresql.org
Date: 2018-08-20T16:58:49Z
Lists: pgsql-hackers

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>>>>> "Andrew" == Andrew Gierth <andrew@tao11.riddles.org.uk> writes:

 Andrew> select f(a =>-1);  -- ERROR:  column "a" does not exist

 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).

-- 
Andrew (irc:RhodiumToad)

Commits

  1. Fix lexing of standard multi-character operators in edge cases.