Cannot define `consume def` in templates with `caps.ExclusiveMutablity` in the parents

[hamzaremmal]

Compiler version

3bea2f3

Minimized code

import scala.language.experimental.captureChecking
import scala.language.experimental.separationChecking

trait Foo extends caps.ExclusiveCapability:
  consume def sink: Unit = ()

Output

-- Error: test.scala:7:14 ------------------------------------------------------
7 |  consume def sink: Unit = ()
  |              ^
  |Update method sink must be declared in a class extending the `Mutable` trait.

Expectation

I understand that consume implies update in a Mutable context but it would be nice to be able to define consume def in an ExclusiveCapability context too (by definition of what an ExclusiveCapability is). As a workaround, one could do the following:

import scala.language.experimental.captureChecking
import scala.language.experimental.separationChecking

trait Foo extends caps.ExclusiveCapability
object Foo:
  extension (consume self: Foo)
    def sink: Unit = ()

def Test =
  val x: Foo^ = new Foo {}
  x.sink
  x.sink // error as expected