> set k1 := {error("k1")}
> session save
> reload
-> k1

> set k2 <<= k1 map identity
> session save
> reload
-> k2
$ must-mirror build.sbt build.check.1

> set k1 := {}
> session save
> reload
> k1
> k2
$ must-mirror build.sbt build.check.2

> set k1 <<= k1 map {_ => error("k1")}
> set k2 := {}
> session save
> reload
-> k1
> k2
$ must-mirror build.sbt build.check.3