Pattern Match Exhaustiveness Check Misses a Case

[CyrilFMoser]

Compiler version

3.4.1

Minimized code

sealed trait T_A[B]
sealed trait T_B[C]
case class CC_B[C]() extends T_A[T_B[C]]
case class CC_C[B, C](c: T_A[B], d: T_B[C]) extends T_B[C]
case class CC_E[C]() extends T_B[C]

val v_a: T_B[Int] = CC_C(null, CC_E())
val v_b: Int = v_a match {
  case CC_C(_, CC_C(_, _)) => 0
  case CC_E()              => 5
}

Output

Crashes

Expectation

Should give a warning at compile time that the pattern match is not exhaustive.

[Gedochao]

Crashes

I wasn't able to reproduce the crash.
Assuming this to just be a reporting issue.

[Gedochao]

Ah, right. There's no crash, but the code fails by throwing an exception at runtime when run as a script.

// repro-script.sc
sealed trait T_A[B]
sealed trait T_B[C]
case class CC_B[C]() extends T_A[T_B[C]]
case class CC_C[B, C](c: T_A[B], d: T_B[C]) extends T_B[C]
case class CC_E[C]() extends T_B[C]

val v_a: T_B[Int] = CC_C(null, CC_E())
val v_b: Int = v_a match {
  case CC_C(_, CC_C(_, _)) => 0
  case CC_E()              => 5
}

scala-cli run repro-script.sc
Compiling project (Scala 3.4.2, JVM (17))
Compiled project (Scala 3.4.2, JVM (17))
Exception in thread "main" scala.MatchError: CC_C(null,CC_E()) (of class repro$minusscript$_$CC_C)
        at repro$minusscript$_.<init>(repro-script.sc:10)
        at repro$minusscript_sc$.script$lzyINIT1(repro-script.sc:25)
        at repro$minusscript_sc$.script(repro-script.sc:25)
        at repro$minusscript_sc$.main(repro-script.sc:29)
        at repro$minusscript_sc.main(repro-script.sc)

[Gedochao]

Very similar issues which were reported together with this, potentially duplicates:

• Pattern Match Exhaustiveness Check Misses a Case #20128
• Pattern Match Exhaustiveness Check Misses a Case #20129
• Pattern Match Exhaustiveness Check Misses a Case #20131
• Pattern Match Exhaustiveness Check Misses a Case #20132