From @masak

<masak> r​: say [] ... []
<p6eval> rakudo c1bfbb​: OUTPUT«(timeout)»
<masak> <TimToady> why is rakudo not smartmatching the [] and stopping
immediately?
* masak submits rakudobug
<masak> n​: say [] ... []
<p6eval> niecza v19-15-g051783d​: OUTPUT«␤»
<moritz> wait
<moritz> it doesn't even generate list elements
<moritz> it's in sink context
<moritz> so it must loop in the detection stage somewhere
<masak> ...still a bug...
<moritz> yes

From @usev6

This works now and there is a passing test in S03-sequence/basic.t

$ perl6 -e 'say [] ... []'

$ perl6 -e 'say ([] ... []).perl'
([],)

I'm closing this ticket as 'resolved'.

@usev6 - Status changed from 'new' to 'resolved'