In 9.2 the number does not completely disappear : if you select the line you see it is white (in fact background color) on pale blue outline.
In addition, not all lines disappear ; in a func like this (Quinn, that should tell you something) :
func combinations<Elements, Element>(
ofLength length: Int,
elements: Elements
) -> AnySequence<[Element]> where Elements : Collection, Elements.Element == Element {
if length == 0 {
return AnySequence(CollectionOfOne([]))
}
let prefixes = combinations(ofLength: length - 1, elements: elements)
return AnySequence(prefixes.lazy.flatMap { (prefix) in
elements.lazy.map { (element) in
// Uncomment this to check that everything is happening lazily.
// print("tick")
return prefix + [element]
}
})
}
lines 6, 8, 9, 10 13 only disappear ; but first level lines still have their line numbers visible