A ?->{cap} B is not a synonym behaviorally of A ?=> B

[markehammons]

Compiler version

3.4.0

Minimized code

trait Ptr[A]
@capability trait Scope:
  def allocate(size: Int): Ptr[Unit]^{this}


object Scope: 
  def confined[A](fn: Scope ?->{cap} A): A = 
    val scope = new Scope:
      def allocate(size: Int) = new Ptr[Unit] {}

    fn(scope)

Output

Scala 3.4.0 treats A ?->{cap} B as if it were a regular function rather than a context function, including downstream when you use it. using parameters are not picked up (like in the above example), and context is missing without a pattern bound context like so:

val s = Scope.confined{ case given Scope =>
  val s2 = summon[Scope]
  Scope.confined{ case given Scope =>
    s2.allocate(5)
  }
  5
}

Expectation

I expected the pure version of a context function with specificied captures to work like the impure version A ?=> B.