Inconsistent Behaviour in Union and Intersection Types with compiler crashes

[mikearnaldi]

Compiler version

3.0.0

Minimized code

Minimal repros:

1. https://github.com/Matechs-Garage/scala-3-zio/blob/scala-bug-union/src/main/scala/Main.scala
2. https://github.com/Matechs-Garage/scala-3-zio/blob/scala-bug-has/src/main/scala/Main.scala

Output

1. crashes with https://github.com/Matechs-Garage/scala-3-zio/blob/scala-bug-union/error.log, some unions have duplicates as per comments in code.

2. main type is inferred as IO[Nothing, Nothing, Unit] meaning the compiler has inferred X to be Nothing in Has[Math] & X => Has[Math] & Has[Console]

Expectation

1. shouldn't crash and union types should not show duplicates

2. removing Has from the code like in https://github.com/Matechs-Garage/scala-3-zio/blob/scala-ok-intersection/src/main/scala/Main.scala correctly infer X to Console in Math & X => Math & Console

---

The master branch contains a "kind of working" variant of the expected behavior worked around by playing with the parameter variance (even though it shouldn't be needed given & and |)

[smarter]

Is 2. the same issue as #12077 ?

[smarter]

Minimized 1. (which I'll take this issue to be about, if there are other issues they need to be opened separately):

trait IO[E] {
  def map[B](f: Any => B): IO[E] = ???
  def flatMap[C](f: Any => IO[C]): IO[E | C] = ???
}

class Test {
  def test: Unit = {
    val a: IO[Nothing] = ???

    val d = a.flatMap(y => a.flatMap(z => a.map(_ => z)))
  }
}

[smarter]

This is likely an instance of #8900

[mikearnaldi]

Is 2. the same issue as #12077 ?

It seem related I can't say if it is 100% the same but it appears so