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

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February 10, 2020 23:43
Re: Backporting ac3afc4b35 (regcomp.c: make \K+ and \K* illegal.)
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Karl Williamson <> wrote:
:I can't think of any legitimate purposes for quantifying any zero-length 
: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.


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