`Array[A[Int]]` where `A[_]` is an abstract type member causes ClassCastException at runtime

[albertpchen]

Compiler version

3.6.3

Minimized code

trait Foo:
  type A[T]
  var arr: Array[A[Int]] = null

class Bar() extends Foo:
  type A[T] = Int

object Main:
  def main(args: Array[String]) =
    val bar = new Bar()
    bar.arr = Array.ofDim[Int](1)
    bar.arr(0) = 123

Output

Exception in thread "main" java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [I ([Ljava.lang.Object; and [I are in module java.base of loader 'bootstrap')

Expectation

It should run without crashing

[som-snytt]

Same behavior at current 3.7.1-RC1-bin-SNAPSHOT-nonbootstrapped-git-d519790

"Fixed in Scala 2"

[albertpchen]

In case anyone else is running into this issue, I was able to work around this by adding a type bound

trait Foo:
  type Dummy
  type A[T] <: Dummy
  var arr: Array[A[Int]] = null

class Bar() extends Foo:
  type Dummy = Any
  type A[T] = Int

object Main:
  def main(args: Array[String]) =
    val bar = new Bar()
    bar.arr = Array.ofDim[Int](1)
    bar.arr(0) = 123