The test in question passes now.
< bartolin> bisectable6: say "ab" ~~ rx:P5/^(a(??{"(?!)"})|(a)(?{1}))b/ &&
$1 # RT 125027
< bisectable6> bartolin, Bisecting by exit code (old=2015.12 new=5929887).
Old exit code: 1
<+synopsebot> RT#125027 [new]:
https://rt.perl.org/Ticket/Display.html?id=125027 [REGEX] Roast rakudo
skip/todo test:./S05-modifier/perl5_9.t line:35 reason: 'Quantifier quantifies
nothing'
< bisectable6> bartolin, bisect log:
https://gist.github.com/996a9c0aeea60fd1061784bc71ceefbd
< bisectable6> bartolin, (2017-09-03)
https://github.com/rakudo/rakudo/commit/4c25df745cb98e2cad3b75b53f4fb39a36449371
I'm closing this ticket as 'resolved'.