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Re: Backporting ac3afc4b35 (regcomp.c: make \K+ and \K* illegal.)

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Dan Book
February 11, 2020 00:02
Re: Backporting ac3afc4b35 (regcomp.c: make \K+ and \K* illegal.)
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On Mon, Feb 10, 2020 at 6:43 PM <> wrote:

> Karl Williamson <> wrote:
> :I can't think of any legitimate purposes for quantifying any zero-length
> :assertion.
> :
> :Using the general form of expressing them, I don't see a difference
> :between any of {0,1} {0,2} {0,3} ... {0, infinity}.  They are all
> :no-ops, except possibly for side effects in code blocks, as Grinnz
> :pointed out on IRC.
> :
> :Nor do I see any difference between {1,1} {1,2} ... {2,2} {2,3} ...
> :in programs that aren't in error.
> :
> :So why can't we optimize all such constructs to their minimal forms.
> :That would make \K+ optimize to effectively \K{1,1}, and the infinite
> :loop would go away, and non-broken programs wouldn't be affected.  This
> :could be done for 5.30.2, I think
> :
> :We could make it fatal in blead.
> :
> :And optimizing all quantifiers of zero width assertions away or to {0,1}
> :in blead would prevent things like this from happening anywhere.
> If we can optimize them to a non-looping form for 5.30.2, that seems
> like a fine solution - there sees no reason thereafter to make if fatal
> in blead.

The reason to make them fatal in blead is because they are nonsensical, and
so this user error should be pointed out loudly.


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