Spurious unreachable case warning

[Bersier]

Compiler version

3.2.0

Minimized code

sealed trait Nat
case class Zero() extends Nat
case class Succ[N <: Nat](n: N) extends Nat

def foo(n: Nat): Int = n match
  case Zero() => 0
  case Succ(Zero()) => 1
  case _ => 2 // warning for this line

foo(Succ(Succ(Zero()))) // evaluates to 2

Compiler warning

Unreachable case except for null (if this is intentional, consider writing case null => instead).

Expectation

No warning

[strelec]

I has a similar issue in #15661

[tusharmath]

Facing similar issue here - https://github.com/zio/zio-schema/actions/runs/3226341119/jobs/5279743723

[tusharmath]

I am still facing this issue in 3.2.1 Has the fix not been released yet?

[KacperFKorban]

The fix will be released in 3.2.2. It is currently included in 3.2.2-RC1 pre-release.

[tusharmath]

I tried again on 3.2.2-RC1 and am observing the same error.

[KacperFKorban]

@tusharmath Which snippet are you running? The one from the issue description works correctly in 3.2.2-RC1 for me.

[tusharmath]

I think in my case it's a valid warning :D

[tusharmath]

Actually this is still failing with 3.2.2-RC1
https://github.com/zio/zio-schema/actions/runs/3497863080/jobs/5857488661#step:5:126

[KacperFKorban]

@tusharmath If you think that the warning in zio-schema is wrong, then could you create a new issue for it? (this would mean that it is caused by a different bug)

[tusharmath]

Created a small repro — #16379