Using language.experimental.subCases interferes with pattern match exhaustivity checking

[ppurang]

Compiler version

Scala CLI version: 1.12.2
Scala version (default): 3.8.1

Minimized code

//> using scala 3.8.1
//> using options -deprecation -feature -Wunused:all -Werror

import language.experimental.subCases

case class NotFound(id: String)
enum AcceptError:
  case IsCancelled(id: String)
  case Denial
case object CatastrophicError
type Error = NotFound | AcceptError | CatastrophicError.type

import AcceptError.*

def errorToString : Error => String =
  case NotFound(id) => s"NotFound: $id"
  case CatastrophicError => s"It is all doom"
  case ae if ae match    //this shouldn't trigger non-exhaustive warning ..
      case Denial => s"In Denial"
      case IsCancelled(id) => s"IsCancelled: $id"

@main def start =
  val e = Denial
  println(errorToString(e))

Output

> scala-cli run -w sub-cases.scala

Compiling project (Scala 3.8.1, JVM (21))
[error] ./sub-cases.scala:17:3
[error] match may not be exhaustive.
[error] 
[error] It would fail on pattern case: AcceptError.IsCancelled(_), Denial
[error]   case NotFound(id) => s"NotFound: $id"
[error]   ^
Error compiling project (Scala 3.8.1, JVM (21))
In Denial
Program exited with return code 0.
Watching sources, press Ctrl+C to exit, or press Enter to re-run.

Expectation

Expect it to be exhaustive i.e. equivalent to compiler's behaviour when encountering this:

def errorToString : Error => String =
  case NotFound(id) => s"NotFound: $id"
  case CatastrophicError => s"It is all doom"
  case Denial => s"In Denial"
  case IsCancelled(id) => s"IsCancelled: $id"

Another bothersome thing: Compiler spits out the warning as an error but the code is still run. Note the lines in the output:

Error compiling project (Scala 3.8.1, JVM (21))
In Denial
Program exited with return code 0.