Cyclic reference involving type X

[marcus-nl]

Using dotty M3 and also the current master branch.

Minimized code

trait SomeTrait

trait CollBase[A <: SomeTrait, +CC[A2 <: SomeTrait]] {
  val companion: CollCompanion[CC]
}

trait Coll[A <: SomeTrait] extends CollBase[A, Coll]

trait CollCompanion[+CC[A <: SomeTrait]]

(Simplified from Graph for Scala's GraphCompanion, GraphBase, EdgeLike, etc)

Output

-- [E046] Cyclic Error: tests/pos/cyclic-type-var.scala:70:29 ------------------
70 |trait CollCompanion[+CC[A <: SomeTrait]]
   |                             ^
   |                             Cyclic reference involving type CC

longer explanation available when compiling with `-explain`
-- [E046] Cyclic Error: tests/pos/cyclic-type-var.scala:70:19 ------------------
70 |trait CollCompanion[+CC[A <: SomeTrait]]
   |                   ^
   |                   Cyclic reference involving method <init>

Expectation

A similar case without the restriction A <: SomeTrait does work:

trait CollBase[A, +CC[_]] {
  val companion: CollCompanion[CC]
}

trait Coll[A] extends CollBase[A, Coll]

trait CollCompanion[+CC[_]]

I don't understand why the restriction would cause a cyclic reference. Seems like a bug to me?