Type members are not checked for overriding during CC

[noti0na1]

Compiler version

3.6.4-RC1-bin-20241125-0afabd6-NIGHTLY, the main branch

Minimized code

import language.experimental.modularity
import caps.*

class IO
class File

trait Abstract(tracked val io: IO^):
  type C >: CapSet <: CapSet^{io}
  def f(file: File^{C^}): Unit

class Concrete1(io: IO^) extends Abstract(io):
  type C = CapSet
  def f(file: File) = ()

class Concrete2(io1: IO^, io2: IO^) extends Abstract(io1):
  // Overriden member: type C >: CapSet <: CapSet^{io1}
  type C = CapSet^{io2} // should be error, since CapSet^{io2} !<:< CapSet^{io1}
  def f(file: File^{io2}) = ()

Output

Compiled without any error

Expectation

Should report error overriding type C in Concrete2

[noti0na1]

However, if we encode the capture set into a type parameter, the same program can be checked correctly with #22000:

import language.experimental.modularity
import caps.*

class IO
class File

trait Abstract[X^]:
  type C >: CapSet <: X
  def f(file: File^{C^}): Unit

class Concrete1(io: IO^) extends Abstract[CapSet^{io}]:
  type C = CapSet
  def f(file: File) = ()

class Concrete2(io1: IO^, io2: IO^) extends Abstract[CapSet^{io1}]:
  type C = CapSet^{io2} // error
  def f(file: File^{io2}) = ()

-- [E164] Declaration Error: Stest.scala:1718:7 --------------------------------
1718 |  type C = CapSet^{io2} // error
     |       ^
     |error overriding type C in trait Abstract with bounds >: caps.CapSet <: caps.CapSet^{Concrete2.this.io1};
     |  type C, which equals caps.CapSet^{Concrete2.this.io2} has incompatible type
     |
     | longer explanation available when compiling with `-explain`
1 error found

[noti0na1]

Maybe related to !compatTypes(memberTp(upwardsSelf), otherTp(upwardsSelf))) in checkAllOverrides during cc phase? The upwardsSelf gives wrong types.