Catch case with alias of union type catches types not in union

[eejbyfeldt]

Compiler version

3.3.7. 3.7.3, 3.8.0-RC1-bin-20251106-b6d9a6d-NIGHTLY

Minimized code

object test {
  class E1 extends Exception
  class E2 extends Exception

  type E1or2 = E1 | E2

  def main(args: Array[String]): Unit = {
    try throw new Exception {}
    catch
      case e: E1or2 => assert(e.isInstanceOf[E1or2])
      case _ => ()
  }
}

Output

$ scala-cli run -S 3.nightly catch_union.scala 
Compiling project (Scala 3.8.0-RC1-bin-20251106-b6d9a6d-NIGHTLY, JVM (21))
Compiled project (Scala 3.8.0-RC1-bin-20251106-b6d9a6d-NIGHTLY, JVM (21))
Exception in thread "main" java.lang.AssertionError: assertion failed
        at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:13)
	at test$.main(catch_union.scala:9)
	at test.main(catch_union.scala)

Expectation

The code should run without issues since. The case e: E1orE2 should only match E1 | E2 and inlineing the alias E1orE2 does have this correct behavior.