I wonder if -Xsource:3 would have agreed.

I wonder if -Xsource:3 would have agreed.

I did not try that. Not sure how.

I identified them using TASTy MiMa.

I see -Xsource:3 does infer the overridden types, but for bincompat the explicit narrow types are required, presumably.

Also because sys.process package object extends a trait, I learned you can't @nowarn a package object, it must be a object package, at least in Scala 2.

I did not include the explicit types for scala.collection.[im]mutable.BitSet.bitSetFactory from the original PR as TASTy MiMa complains for scala.collection.mutable.BitSet.bitSetFactory. This could be a false positive. I'll update those when I am sure they are correct.

There's a similar case at scala/scala-xml#655

Currently, -Xsource:3 changes the way the compiler operates, but there are no warnigns emitted in either case. If someone wants to clean up their codebase and find all definitions that change under this condition, what can they do? Use MiMa?

I think a warning for this case under -Xsource:3 would be good. @som-snytt wdyt?

➜ sandbox s

scala> trait A { def f: Object }; object B extends A { def f = "" }; B.f
val res0: String = ""


➜ sandbox s -Xsource:3

scala> trait A { def f: Object }; object B extends A { def f = "" }; B.f
val res0: Object = ""

@lrytz I'm about to try your other suggestion to make -Xsource:3 migrations only warnings (for the quill explicit types issue), and I will include warning when inferred override changes.

Resoved a conflict in JavaCollectionWrappers.scala.