https://bugs.exim.org/show_bug.cgi?id=2326
Bug ID: 2326
Summary: Inconsistent results with backreference setting in
negative lookarounds used as conditions
Product: PCRE
Version: 8.42
Hardware: x86
OS: Windows
Status: NEW
Severity: bug
Priority: medium
Component: Code
Assignee: ph10@???
Reporter: tattarakis@???
CC: pcre-dev@???
Another bug I came across recently..
The docs state that backreferences are set in negative lookaheads only when
used as the condition in a conditional subpattern, which does indeed seem
logical. However, I'm not observing that happening consistently, and can only
force the behaviour in certain circumstances:
re: "^(?(?!(a))|a){1}"
str: "abc"
The above does not set \1.
re: "^(?(?!(a))|a){2}"
str: "abc"
This sets \1. It is not until the conditional subpattern takes a "yes" route
that the backreference becomes set.
And some odd behaviour: introducing an empty lookahead to the above prevents \1
from being set:
re: "^(?(?!(a))|(?=)a){2}"
str: "abc"
Difficult come, easy go :P
Once again, sorry if PCRE2 targets this issue.
Best,
John Tattarakis
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