[pcre-dev] [Bug 2211] New: Possible bug in pcredemo when che…

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A: pcre-dev
Assumpte: [pcre-dev] [Bug 2211] New: Possible bug in pcredemo when checking for an empty match with patterns involving \K in lookarounds
https://bugs.exim.org/show_bug.cgi?id=2211

            Bug ID: 2211
           Summary: Possible bug in pcredemo when checking for an empty
                    match with patterns involving \K in lookarounds
           Product: PCRE
           Version: N/A
          Hardware: x86
                OS: Windows
            Status: NEW
          Severity: bug
          Priority: medium
         Component: Documentation
          Assignee: ph10@???
          Reporter: tattarakis@???
                CC: pcre-dev@???


Hi Philip!

It appears that mIRC, regex101, and even PHP are mishandling global matches
with patterns involving \K in lookarounds, and I believe I've traced the
problem to the following bit of code in pcredemo:

[code]

/* If the previous match was for an empty string, we are finished if we are
at the end of the subject. Otherwise, arrange to run another match at the
same point to see if a non-empty match can be found. */

if (ovector[0] == ovector[1])

[/code]

Because the user can distort ovector[0] by using \K in lookarounds such as
"(?<=\K.)" and "(?=.\K)", I believe some cases of empty matches are going
undetected.

I think the solution would be to instead compare ovector[1] to the initial
start_offset value, which cannot be altered.

Thank you as always!

- John

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