Type pattern doesn’t narrow type

[julienrf]

(tested with 0.23.0-RC1 only, maybe it has already been fixed upstream?)

Minimized code

sealed trait Foo
case object Qux extends Foo

def problem(foo: Foo): Qux.type = foo match {
  case qux: Qux.type => qux
}

https://scastie.scala-lang.org/yJbmLhdYTNivTXwKg4E1wQ

Output

[error] -- [E007] Type Mismatch Error: 
[error]    |        case qux: Qux.type => qux
[error]    |                              ^^^
[error]    |               Found:    (qux : Foo)
[error]    |               Required: Qux.type

Expectation

qux should have type Qux.type instead of Foo.

[julienrf]

It seems to be already fixed by #8710 (https://scastie.scala-lang.org/PDYvElVnQ8uSAGgygSmiNw)