incorrect union type exhaustive match warning with ClassTag

[bohonghuang]

Compiler version

3.0.0-RC1

Minimized code

import scala.reflect.ClassTag

type A
given ClassTag[A] = ???
var a: A|Null = null
a match { //WARNING: match may not be exhaustive. It would fail on pattern case: _: A
  case null =>
  case a: A =>
}

[nicolasstucki]

same issue with type test

def test[A](a: A|Null)(using scala.reflect.TypeTest[A|Null,A]) =
  a match { //WARNING: match may not be exhaustive. It would fail on pattern case: _: A
    case null =>
    case a: A =>
  }

[nicolasstucki]

These are special cases as we know that ClassTag and TypeTest their spec guarantees that they will match all A.

[liufengyun]

We will be able to do this with #11186 , the concrete test case: f18ad26