I use a closed-source scripting language using PCRE inside wrapper
functions.
I observe a parasitic empty match for every DEFINE special condition.
I'd like to report the issue but before doing so I find it preferable
to make a more precise diagnosis.
How do we differentiate between an unused capturing group and a
pseudo-match resulting from a DEFINE?
For instance and in Perl format, the following patterns give me the
same result on input 'bbb' even when the DEFINE is not actually used:
/(a)? (b+)/x
/(?(DEFINE) (?<head> xyz)) (b+)/x
In both cases I get:
'' (an empty capture)
'bbb'
In the latter case I would expect only one captured group:
'bbb'
This is of course what I get when I remove definition of head.
So I'd like to point out how to prevent the bug in this particular
implementation, in order to simplify dev job. I suspect it has to do
with how ovector entries are interpreted but from the PCRE docs it
seems both empty group and DEFINE return (-1, -1) well, provided I read
the docs correctly.
Thank you for an outstanding product and support!
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