An opaque type should not be covariant when the underlying type is invariant

Compiler version

3.1.0

Minimized code

opaque type CovariantArray[+A] = Array[A]

object CovariantArray:
  def crash() =
    val stringArray: CovariantArray[String] = Array("foo", "bar")
    val anyArray: CovariantArray[Any] = stringArray
    anyArray(0) = 42
    stringArray(0).length

CovariantArray.crash()

Output

java.lang.ArrayStoreException: java.lang.Integer
	at Playground$CovariantArray$.crash(main.scala:9)
	at Playground$.<clinit>(main.scala:12)
	... 13 more

Expectation

Should not compile

[dwijnand]

OK I thought one would need to put the annotation on the wildcard (which doesn’t seem to be possible BTW - is this a bug?)

I don’t see a bug, putting it after (Array[_ <: A @scala.annotation.unchecked.uncheckedVariance]) still annotates the type argument, not its upper bound.

[prolativ]

I thought of something like

type CovariantArray[+A] = Array[_ @scala.annotation.unchecked.uncheckedVariance <: A]