Re: LPEG bug?

[Daurnimator <quae@...>]

On 5 June 2015 at 00:15, Roberto Ierusalimschy <roberto@inf.puc-rio.br> wrote:
>> Today I was working on an lpeg pattern, and ran into this oddity,
>> which I believe to be a bug.
>> I've condensed it down as far as I could, if I remove any more the bug
>> seems to disappear.
>>
>> The following script throws in the assert.
>> If you uncomment either of the alternate `path_abempty` definitions, it works.
>>
>> local lpeg = require "lpeg"
>> local P = lpeg.P
>> local HEXDIG = lpeg.R("09","af", "AF")
>> local pct_encoded = P"%" * lpeg.C ( HEXDIG * HEXDIG ) / function (hex_num)
>> return string.char(tonumber(hex_num, 16))
>> end
>> local pchar         = lpeg.R("az","AZ") + pct_encoded
>> local path_abempty  = ( P"/" * pchar^0 )^0
>> -- local path_abempty  = ( P"/" * pchar^0 )^0 * ( P"/" * pchar^0 )^0
>> -- local path_abempty  = ( P"/" * pchar^0 )^0 * function() return true end
>> local path_rootless = pchar^1 * path_abempty
>> local path_absolute = P"/" * path_rootless^-1
>>
>> assert(lpeg.Cs ( path_absolute ):match "/var/log/messages" ==
>> "/var/log/messages")
>
> The problem can be reduced to the following example:
>
>    local re = require're'
>    local p = re.compile[[ { ('ab' ('c' 'ef'?)*)? } ]]
>    s = "abcefccefc"
>    print(s, p:match(s))  --> abcefccefc abcefc
>
> (An optional at the end of a repetition at the end of an
> optional...) The bug is caused by a wrong optimization; the following
> patch (in lpcode.c) should fix it:
>
> @@ -759,7 +759,7 @@
>        /* L1: test (fail(p1)) -> L2; <p>; jmp L1; L2: */
>        int jmp;
>        int test = codetestset(compst, &st, 0);
> -      codegen(compst, tree, opt, test, fullset);
> +      codegen(compst, tree, 0, test, fullset);  /* ?????? */
>        jmp = addoffsetinst(compst, IJmp);
>        jumptohere(compst, test);
>        jumptothere(compst, jmp, test);
>
> (I think there is a similar bug in repetitions, line 678, but I have to
> recheck that.)
>
> -- Roberto


Hi Roberto,

Have you had a chance to follow up this and the outstanding LPEG bugs?
  - http://lua-users.org/lists/lua-l/2015-05/msg00483.html
  - http://lua-users.org/lists/lua-l/2015-05/msg00410.html