Java Generic Signature for nested refinements imprecise

[retronym]

object Test {
  def main(args: Array[String]) {
    println(classOf[Foo[_]].getTypeParameters.apply(0).getBounds)
  }
}

class C1 { def c1 = 0 }
trait T1 { def t1: Int }
trait T2 { def t2: Int }
class Foo[T <: (C1 with T1) with T2]// Note the parentheses

Prints: class C1, interface T2

Could we include T1 in the signature, too?

Discovered during porting of our implementation to dotty: scala/scala3#3234 (comment)

Fix is probably as simple as adding a recursive case to:

  private def hiBounds(bounds: TypeBounds): List[Type] = bounds.hi.dealiasWiden match {
    case RefinedType(parents, _) => parents map (_.dealiasWiden)
    case tp                      => tp :: Nil
  }

(Or using the existing flattening in RefinedType.normalize)

We need to be careful when changing this that we maintain the invariant that the erased type conforms to the generic type.