@uncheckedVariance stripped from case class's copy default getter(s)

[dwijnand]

Compiler version

3.0.0-RC3

Minimized code

import scala.annotation.unchecked.uncheckedVariance

final case class Outlet[T](out: T)
final case class SourceShape[+T](val out: Outlet[T @uncheckedVariance])

Output

-- Error: test.scala:4:29 ------------------------------------------------------
4 |final case class SourceShape[+T](val out: Outlet[T @uncheckedVariance])
  |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |covariant type T occurs in invariant position in type [T] => Outlet[T] of method copy$default$1
1 error found

Expectation

I expect it to compile like it does for Scala 2 (2.13.5).

Notes

I believe this doesn't happen in Scala 2 with scala/scala@fb38e47, which was addressing scala/bug#2382. Did that get removed with #9909? More recently #11704 also touched this, but that shipped in 3.0.0-RC2 and I originally saw this in 3.0.0-RC1. Either way, it looks like this is accidentally breaking compilation.

Btw, this comes from cross-compiling Akka Streams to Scala 3. Potentially this can be worked around by making un-casing the case classes, hand-writing all the boilerplate. For non-copy methods you can try overloading, though that becomes difficult when you have other default arguments (which is the case in Akka Streams)...

[smarter]

I believe this doesn't happen in Scala 2 with scala/scala@fb38e47, which was addressing scala/bug#2382.

That change in Scala 2 is unsound in general, cf 5b46ac2

Did that get removed with #9909?

Looks like that's what you're hitting here yeah, we strip @uncheckedVariance from the inferred types but it turns out we need it for the default getter inferred type.