Partial unification unconditional; deprecate -Xexperimental #6309
Sounds like @eed3si9n's "Restligeist macro" idea: https://twitter.com/eed3si9n/status/770584274819055617
We have those in sbt 1 for the old sbt 0.9-0.12 operators: https://github.com/sbt/sbt/blob/v1.1.1/main-settings/src/main/scala/sbt/std/TaskMacro.scala#L129-L130.
Partial unification is now enabled unless -Xsource:2.12 is specified. The -Ypartial-unification flag has been removed and the -Xexperimental option, which is now redundant, has been deprecated.