Wrong warning on matching union types

[scf37]

Compiler version

3.2.2

Minimized code

sealed trait Unset

def foo(v: Unset|Option[Int]): Unit = v match
  case v: Unset => ()
  case v: Option[Int] => ()

Output

the type test for Option[Int] cannot be checked at runtime

Expectation

No warning. Unset is sealed trait and therefore this match should be exhaustive. For example, v: String|Option[Int] compiles without warning.

[SethTisue]

Agree this is a bug, and significant enough that I hope to see it get attention. This is fairly basic stuff, and as the report above shows, there are some forms of it that do already work.

And it came up on Discord today, so that's a second user who hit it.

I see there was an attempt to fix it which is now abandoned. I also see @dwijnand was interested enough to comment on the PR. Dale, not sure your remaining level of interest.

[liufengyun]

Also encountered this one. It's a little annoying. Working on a fix.