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Re: [perl #129897] Unexpected behavior with a regular expression

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October 17, 2016 21:40
Re: [perl #129897] Unexpected behavior with a regular expression
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On 17 October 2016 at 18:37, demerphq <> wrote:
> On 17 October 2016 at 04:50, Zefram <> wrote:
>> Jorma Laaksonen wrote:
>>>Any hint if I'm doing something wrong or not doing something I should
>> No, that's all supported usage.  You're quite right about the behaviour
>> being erroneous.
> Agreed.
> It seems to be a bug about unwinding .*? although it also interacts
> with TRIE code in ways I dont entirely understand. (Making the code
> not produce a TRIE fixes the bug, but on the other hand, so does
> removing the .*?)
> Nevertheless I can fix the bug (while possibly introducing new bugs)
> with the code in yves/fix_129897
> c09f087940c61f3b6e57e7cf5e5b7a4faa683420
> I would prefer that Dave have a look into this, as I dont entirely
> understand why my patch fixes things for this case, but that in most
> other cases it is not needed.
> The key point is that when we fail a .*? match we should unwind and
> reset any buffers we matched after our current point. But STAR and
> PLUS do not initialize the proper member fields so that we can do this
> unwinding properly.
> I have to admit that this bug is quite surprising. I would have
> thought that if we have a bug like this that we fail our regex tests
> completely, but apparently not.
> Of course, it may have to do with the fact that the form of this bug
> is incredibly horrible. Having an unanchored .* at the beginning of a
> pattern is a good way to make your regex quadratic on failure. (We may
> trigger an optimisation that automagically adds the anchor, and we may
> not....)
> So it may simply be that most times we dont trigger this bug, but I
> admit its not obvious to me why not.

Cause my analysis was wrong... Dave, forget it, nothing you need to poke into.

Put simply, the "short-circuit" logic in the TRIE code should not
trigger when there is a jump table.

I have a patch ready, but i am having issues talking to the master
repo right now.


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